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156
SPIRITS. 157
In experiments in which pure amyl alcohol was added to spirit
with a view of testing the process, the organic acid obtained had the
characteristic odor of valeric acid and a combining weight closely ap-
proximating to 102.
Of course, the so-called estimation of amyl alcohol in spirits is in
reality the estimation, in terms of amyl alcohol, of such higher alco-
hols and other bodies as may be extracted by chloroform or carbon
tetrachloride, and converted into volatile organic acids on oxidation,
but it is noticeable that the higher alcohols other than amyl alcohol
will give products which do not materially affect the results. Thus
isobutyl alcohol on oxidation yields isobutyric acid, which body un-
dergoes further change into acetic and carbonic acids. But the acetic
acid formed will neutralise just the same amount of alkali as the
isobutyric acid would have done.
Dr. James Bell has modified Marquardt's process by using potassium
permanganate in place of dichromate, and continuing the oxidation
for a very long period. The change appears a very objectionable one.
Potassium permanganate is very liable to contain traces of per-
chlorate, which, being isomorphous, cannot be removed by any process
of recrystallisation. On distillation with acid such impure perman-
ganate yields distinct traces of perchloric acid (or other oxide of
chlorine), which when boiled with barium carbonate yields a soluble
salt, the acid in which has nearly the same combining weight as valeric
acid (HG1O 4 == 100'5 ; HC 5 H 9 O 2 = 102). Even pure permanganate
appears to act on chloroform far more readily than dichromate does,
and on subsequently distilling the liquid a distillate is obtained having
a yellow color and a strong chlorous odor.
Besides the various modifications of the oxidation process of esti-
mating higher alcohols in spirits, certain physical methods have been
suggested. The capillary method of Trauber, as modified by Els-
worthy (Jour. Chem. Soc., liii. 102), has not been found suitable. The
Roese-Herzfeld method, depending on the increase in the volume of
chloroform when shaken with the spirit reduced to a constant strength,
appeared more promising ; but the absolute necessity of adjusting the
strength of spirit accurately within the limits of 29'96 and 30*04 per
cent, of absolute alcohol is a serious bar to the use of the process,
which in the end gives rather an estimation of the total oily bodies
present than of the higher alcohols, and fails even with these when
the proportion is as low as commonly occurs in practice. More en-
couraging results have been secured by using carbon tetrachloride
instead of chloroform, while the employment of brine for dilution ren-
158 SPIRITS.
ders the strength of the spirit immaterial within wide limits ; but the
process thus modified has not yet been perfected.
The presence of ethers or furfural will invalidate the determination
of amyl alcohol by oxidation, as these bodies are extracted both by
chloroform and carbon tetrachloride, and on oxidation will yield
organic acids. Thus ethyl acetate will yield two equivalents of acetic
acid, and will falsify the amyl alcohol result to an extent equal to
double its own weight.
The ethers of spirits can be determined (in terms of a typical com-
pound such as ethyl acetate) by a process apparently originating with
Berthelot, and applied by Dupre" to the ethers of wine. It is substan-
tially the same as was subsequently used by Koettstorfer for the exam-
ination of butter and other fats, and is based on the amount of alkali
required for the saponification of the ether; but in the examination of
spirits the difficulty occurs that bodies of the type of aldehyde and
furfural are present, and these also react with alkali. Aldehyde
reacts with alkali with formation of aldehyde-resin and production of
a formate and acetate, but the reaction does not appear to have been
examined in its quantitative relationships, or to correspond to any
simple formula. Furfural, however, has been found by Dr. A. Cole-
fax to react with alkali almost strictly according to the following
equation :
2C 4 H 3 OCOH -f KHO == C 4 H 3 OCOOK -j- C 4 H 3 OCH 2 OH
Furfural. Pyromucate. Furfuryl alcohol.
It is probable that a determination of furfural might be based on
this reaction. Fortunately, the error introduced into the determina-
tion of the ethers by the presence of aldehyde and furfural can be ob-
viated by means recently described by E. Mohler, who has found that
on digestion with a solution of aniline in syrupy phosphoric acid the
aldehyde and furfural are converted into non-volatile compounds,
while the ethers can be distilled off unchanged.
The procedure is as follows : The distillation is conducted as indi-
cated on page 154, but only one-half of the mixed distillate is reserved
for titration with T ^ alkali. The other half is treated with 1 c.c. of
aniline and 1 c.c. of phosphoric acid solution of T442 sp. gr., boiled
under a reflux condenser for at least two hours, then distilled to small
bulk, and the distillate heated with / 7 soda, exactly as was done with
the other half of the original distillate. The difference between the
amount of alkali which has reacted with the two portions represents
that which has reacted with the furfural and aldehyde, and when only
the former is present 0'0192grm. corresponds to 1 c.c. of ^ alkali.
SPIRITS. 159
The presence of furfural in spirits can be detected, and the propor-
tion roughly guessed at, by the reaction of the sample with a solution
of aniline in glacial acetic acid. Ten drops of aniline should be dis-
solved in 2 c.c. of glacial acetic acid, and the mixture added to 10 c.c.
of the spirit to be tested. A red coloration is produced, which in-
creases in intensity on standing. The reaction is peculiar to fur-
fural and extremely delicate, one part per million giving a distinct
coloration.
Aldehyde may be detected in spirits by Gayon's reagent consisting
of 30 c.c. of a solution of magenta (rosaniline hydrochloride) in 1,000
parts of water ; 20 c.c. of sodium acid sulphite solution (of 1*31 sp.
gr.) ; 3 c.c. of sulphuric acid ; and 200 c.c. of water. 4 c.c. of this
mixture should be added to 10 c.c. of the spirit to be tested, when a
crimson coloration is produced, increasing in intensity on standing.
According to Mohler, no satisfactory colorimetric determination can
be based on this reaction, but the following proportions of aldehydes
can be detected: Acetic and oenanthic aldehydes, O'Ol grm. per
litre ; valeric aldehyde, 0'02 ; propionic and isobutyric, 0'05 ; normal
butyric aldehyde, furfural, and acetone, 0*5 grm. per litre. Alco-
hols and ethers give no coloration with the rosaniline reagent, but it is
difficult to meet with commercial alcohol so pure as to give a wholly
negative reaction. It has been stated by Borntrager that the reagent
is untrustworthy, as it merely indicates the presence of an oxidising
agent ; but this is evidently not the case, as the proportion of sulphite
present is many times the amount requisite to prevent any oxidising
action of the aldehyde (see under aldehydes).
At present there exists no satisfactory means of determining alde-
hyde in the minute quantities in which it exists in spirits. Its be-
havior with alkalies to produce aldehyde-resin and the accompanying
odor is the most characteristic reaction.
Acetal is a body having the constitution of a diethyl-aldehydate. It
has an agreeable odor, and is produced by the prolonged contact of
aldehyde with alcohol, and hence has been recognised as a constituent
of old wine and matured spirits. We have not been able to recognise
its presence with certainty in the moderate quantities of spirits we have
worked on. Acetal is unaffected by alkalies if air be excluded, but
on treatment with dilute acid is at once split up into alcohol and alde-
hyde. Its most characteristic reaction is the formation of a colorless
liquid with caustic soda and iodine solution, which yields a dense pre-
cipitate of iodoform when acidified. This reaction does not occur in
very dilute solutions of acetal. Acetal is extracted by chloroform and
160
LIQUORS AND CORDIALS.
carbon tetrachloride from its solution in dilute alcohol, and hence will
affect the determination of theamyl alcohol if not previously removed,
which may be done by first heating the spirit with an acid, and
subsequently distilling with alkali.
Various methods of stating the results of analysis of spirituous
liquids have been adopted. The statement in " parts per 100 of absolute
alcohol " has certain merits ; but in practice is less convenient than
"parts per 100 of proof spirit." "Grams per 100 c.c." and
" grams per litre " have the advantage of ready calculation, but state-
ments so made are apt to be misleading if the strength of the spirit is
not also borne in mind. The statement in " grains per proof-gallon "
has the advantage of defining the strength of the spirit, and avoids
the long decimals necessary in other forms of statement.
Results of Analyses of Samples of "Grog" (the Spirit-
uous Liquid obtained by Steaming Old Whisky Casks)
and Whisky.
Grog from a
cask in which
the finest pot-
still whisky
had been kept
18 years.
First fraction
obtained on
distilling a
sample of
grog.
Last fraction
obtained on
distilling a
sample of
grog.
Com-
mercial
Scotch
whisky.
Com-
mercial
Irish
whisky.
Specific gravity, . . .
0-9735
0-8260
0-9040
0-8416
0-9408
Proof spirit (per cent.
by measure), . .
39-68
161-86
112-41
81-17
81-64
Absolute alcohol (per
cent, by weight), .
18-46
88-76
56-32
39-05
39-30
Secondary constit-
uents expressed in
grains per imperial
gallon :
Free acid in terms
of acetic acid, .
21'2
0-5
7'5
10-2
6-8
Ethers in terms of
acetic ethers, .
46-5
519-0
76-7
46-5
23-1
Higher alcohols in
terms of amyl
alcohol, . . .
291-0
803-4
89-6
78-8
Aldehyde, . . . .,
Strong
Marked
None
Distinct
Trace
trace
amount
trace
Furfural, ....
Strong
None
Marked
Trace
Distinct
trace
amount
trace
Liqueurs or Cordials. Under these names is included a number
of special and proprietary drinks consisting of grain spirit heavily
sweetened and flavored. They are sometimes brightly colored ; indigo,
LIQUORS AND CORDIALS.
161
cochineal, turmeric, and gamboge being among the least objectionable
agents employed, while aniline dyes, picric acid, and salts of copper
are occasionally used. Sweetened gin is, strictly speaking, a cordial
rather than a true spirit. Among the most popular liqueurs may be
mentioned absinthe, cura9oa, maraschino, and noyeau. Robur, or
" tea-spirit," which had a short-lived popularity due to extensive
advertising, consisted of grain spirit, strongly sweetened and mixed
with infusion of tea-leaves. Cherry- brandy, orange-bitters, and simi-
lar drinks are also of the nature of cordials. These preparations do
not require detailed description.
ABSINTHE is a liqueur containing a somewhat variable proportion
of real alcohol, and several units of volatile oils, those of cinnamon,
cloves, peppermint, anise, and angelica being frequently employed.
Its characteristic constituent, however, is the oil of wormwood (Arte-
misia absinthium), to which the alleged deleterious properties of
absinthe are probably attributable. In consequence of the presence
of essential oils, absinthe becomes milky on addition of water. Some
varieties of absinthe contain little or no sugar. The following table
shows the amounts of alcohol and essential oils contained in four dif-
ferent brands of absinthe. The figures are due to Adrian, and are
expressed in terms of a glass of 30 c.c. of the liqueur :
Absolute
alcohol.
Oil of
wormwood.
Total essential
oils.
Ordinary absinthe, ....
"Demi-fine" ,, ....
"Fine" ....
Swiss ,, ....
14-3 c.c.
15-0
20-4
24-2
'005 grm.
010
010
010
'030 grm.
046
085
085
A. Wynter Blyth states the average composition of the absinthe
consumed in London (where its use is on the increase) to be
alcohol, 50*00; oil of wormwood, 0'33 ; other essential oils, 2'52;
sugar, 1'50; chlorophyll, traces; and water, 45'65 per cent.
Absinthe nearly always has a faintly acid reaction, which is proba-
bly due to acetic acid. It usually amounts to 1*5 gms. of acetic acid
per litre. The green color of absinthe ought to be due to chlorophyll,
introduced from spinach, nettles, or parsley. A mixture of sulphate
of indigo with picric acid or turmeric is not unfrequently employed,
and salts of copper have also been used. Copper can be readily
detected by diluting the liqueur and adding potassium ferrocyanide
which will occasion a brown color. The vegetable coloring matters
11
162 TINCTURES.
are, perhaps best detected by their absorption-spectra. Picric acid
may be recognised by diluting the liqueur with weak sulphuric acid,
and shaking with ether, which will acquire a yellow color and will
dye silk yellow. Sulphuric acid and antimony compounds are stated
by Gardun to have been added to absinthe.
The alcohol contained in absinthe may be determined by the ordi-
nary process of distillation, the proportion of essential oils being insuf-
ficient to affect the density materially. For the determination of the
essential oils, Baudrimont recommends that the distilled liquid should
be diluted with twice its measure of water to cause the oils to separate,
and then shaken with carbon disulphide. This being removed from
the bottom by a tap, and allowed to evaporate spontaneously, leaves
the essential oils.
NOYEAU has a flavor which is sometimes due to hydrogen cyanide,
and in other cases to oil of bitter-almonds, or to nitrobenzene (see
Kirschwasser, page 141).
Tinctures. In medicine, various alcohol solutions are employed,
their permanency rendering them very convenient. These solutions
are called " tinctures " or " spirits." In some cases they are directed
to be prepared with " Rectified Spirit, B.P." (sp. gr. "835 = 84 per
cent, by weight of absolute alcohol). The tinctures and spirits of
chloroform, ether, aconite, ferric chloride, ferric acetate, iodine, myrrh,
nux vomica, camphor, ginger, &c., are made in this way. On the
other hand, " Proof Spirit, B.P." (sp. gr. '920) is directed to be used
in making the tinctures of orange-peel, belladonna, cantharides, cate-
chu, digitalis, ergot, opium, rhubarb, squills, &c.
There are in most cases good reasons for the choice of the above
strengths of spirit, as experience shows them to be the best adapted
for the solution of the active principles of the respective drugs.
As, in the preparation of the above tinctures, proof spirit is some-
times substituted for rectified spirit, and a mixture of equal measures
of rectified spirit and water for proof spirit, it is sometimes required
to ascertain the strength of the alcohol which has been employed.
Mere distillation is sufficient to separate the alcohol from the tinct-
ures of aconite, arnica, belladonna, calumba, capsicum, catechu, jalap,
nux vomica, opium, quinine, &c. ; and the same is true of the tinct-
ures of iodine, ferric acetate, &c., if they be first treated with soda in
slight excess. On the other hand, the tinctures of benzoin, myrrh,
ginger, camphor, rhubarb, &c., give distillates contaminated with
essential oils or similar volatile matters in quantity sufficient to affect
seriously the determination of the alcohol by the density. The same
TINCTURES. 163
is true of the "aromatic spirit of ammonia" and tinctures prepared
with it, with the additional objection that the distillate will contain
ammonia, unless the alkaline reaction of the spirit be previously care-
fully neutralised by hydrochloric acid.
Spirits of chloroform, nitrous ether, and ether will of course yield
distillates requiring special examination, or they can be examined
directly. In the other tinctures to which the distillation process is
not directly applicable, the alcohol may be determined in the follow-
ing manner : 50 c.c. are taken and made up to 350 c.c. by addition of
water. This usually causes a precipitation of the volatile oils or resin-
ous matters, owing to their insolubility in water or very dilute alcohol.
The liquid cannot be directly filtered, owing to the fine state of divi-
sion in which the precipitate exists, but it may be clarified by adding
a few drops of a strong solution of calcium chloride, followed by some
sodium phosphate. The resultant precipitate of calcium phosphate
entangles the oily and resinous matters. The liquid is now made up
to 400 c.c., filtered through a dry filter, and 250 of the filtrate dis-
tilled at a low temperature, the distillate made up to 250 c.c. by addi-
tion of water, and its density observed. If the foregoing instructions
be adhered to, the percentage of proof spirit corresponding to the
density of the distillate, multiplied by 8, will be the percentage by
volume of proof spirit contained in the tincture. The percentage of
absolute alcohol by weight corresponding to this amount will be the
percentage of alcohol contained in the spirit of the tincture.
This is the most convenient mode of expressing the alcoholic
strength of tinctures, as it gives a figure which should approximate
to the percentage by weight of absolute alcohol in the spirit used for
making the tincture. Close accordance is not to be expected, for
many of the drugs used contain water, and in other cases they sensibly
increase the volume of the liquid. 1 In deciding on the strength of the
alcohol employed in making the tincture, the nature of the other
ingredients should be carefully considered, and, when possible, a simi-
lar tincture should be made up with alcohol of known strength, and
analysed in a similar manner to the sample. 2
1 Spirit of camphor has a volume equal to the sum of the measures of the camphor and
alcohol used in preparing it.
2 A good example of the mode of examining a tincture is afforded by the " compound
tincture of camphor," B.P., a remedy largely employed by the medical profession, and
commonly known to the public by the obsolete name of " Paregoric Elixir." This prepa-
ration consists of a solution of 40 grains each of opium and benzoic acid, 30 of camphor,
and half a fluid drachm of oil of anise, dissolved in proof spirit, and diluted with the
same to one pint. The spirit being the most costly ingredient, there is a strong induce-
164 TINCTURES.
If from any cause, such as the appearance or smell of the distillate,
there be doubt as to the freedom of the alcohol from matters liable to
affect its gravity, the distillate may be examined by Monell's colori-
metric method (see page 101).
Occasionally tinctures are fraudulently prepared with methylated
spirit. The substitution may be detected by the methods described
on page 79 et seq.
DEPOSITS FROM TINCTURES. Many tinctures have a tendency to
give deposits on keeping, and it is evidently important to know
whether the active principles of the tinctures have a tendency to pass
into the deposited matter. The subject has been investigated by
R. A. Cripps (Pharm. Jour. [3] xiv. 483), whose results may be epit-
omised as follows :
The deposits from the tinctures of calumba, cardamoms, gentian,
ipecacuanha, and lobelia were free from the active principles of the
drugs. The deposit from tincture of rhubarb contained a small pro-
portion of chrysophanic acid, but was not tested for cathartic acid.
Tincture of cinchona gives a deposit containing a notable but variable
proportion of alkaloids, and the deposit from the compound tincture
is of the same character, in addition to containing cochineal. Tincture
of quinine is made by dissolving sulphate of quinine in tincture of
orange-peel, and gives a deposit containing much calcium sulphate.
ment to the vendor to reduce its amount, a practice which necessitates the omission of a
portion of some of the other ingredients. On diluting genuine compound tincture of
camphor the major part of the oil of anise is precipitated, and if the diluted liquid be
then treated with calcium chloride and excess of sodium phosphate, filtered, rendered
distinctly alkaline, and distilled, the alcohol is obtained in a state of approximate purity.
The small quantity of camphor present in the original tincture passes over with the spirit,
and modifies the density of the product to a slight extent; the difference is unimportant.
In the case of compound tincture of camphor, the treatment with calcium chloride is not
strictly necessary, as the proportion of oil of anise is very small, but carbonate of sodium
should be added to fix the benzoic acid. The " extract " from the distillation should be con-
centrated to a small bulk, and strong hydrochloric acid added in excess. This should
cause a precipitation of benzoic acid, and on shaking the liquid with ether, separating
the upper layer, and evaporating off the ether by a current of dry air, the benzoic acid is
obtained in a state of approximate purity and in a state fit for weighing. After weigh-
ing it may be moistened with ferric chloride, which will produce a deep red color if the
original preparation contained opium. Sometimes the benzoic acid is wholly omitted
from the compound tincture of camphor. The same remark applies to the oil of anise,
more than traces of which cannot be present if the tincture remains clear when diluted
with three or four times its measure of water. The proportion of opium present in com-
pound tincture of camphor can be judged of by the depth of red color produced when the
sample (previously diluted with water or proof spirit) is treated with ferric chloride. By
comparing the tint obtained with that given by a similar tincture of known quality, a
fair criterion of the proportion of opium may be obtained.
AMYL ALCOHOL. 165
On exposure to a low temperature, however, crystals of quinine
sulphate are apt to form. The bydrochloride or hydrobromide
of quinine would yield a tincture preferable to that made from the
sulphate.
AMYL ALCOHOL.
Amyl Hydrate. Potato-spirit. C 5 H r2 O = C5 ^ n j O.
Several amyl alcohols are known, differing somewhat in their
physical and chemical properties. Normal amyl alcohol boils at 137
C. Iso-amyl alcohol boils at 128 to 132 C., and has a density of
8148 at 14 C. This is the variety of amyl hydrate produced by
fermentation, and therefore present in fusel oil, and all subsequent
statements respecting amyl alcohol have reference to the iso-variety. 1
The preparation of amyl alcohol from fusel oil is described on page
169.
Pure amyl alcohol is a colorless liquid of strong peculiar odor
and acrid burning taste. Dropped on paper it produces an oily mark
which disappears slowly.
One part of pure amyl alcohol dissolves in 39 parts of water at
15*5 C., forming a liquid of '998 specific gravity. One part of water
dissolves in 11 '6 parts of amyl alcohol, forming a clear liquid of *835
specific gravity.
Amyl alcohol is miscible in all proportions with ethyl alcohol,
ether, chloroform, carbon disulphide, benzene, petroleum ether, and
fixed and volatile oils; and is itself a solvent for sulphur, phosphorus,
iodine, camphor, and many alkaloids and resins.
Amyl alcohol dissolves in all proportions in glacial acetic acid
diluted with an equal bulk of water, and may thus be separated from
neutral amyl ethers (e.g., acetate, valerate, and pelargonate) which are
not soluble in acetic acid.
Commercial amyl alcohol is liable to contain traces of an alka-
loidal body which may be removed by agitation with dilute acid, but
the presence of which renders the liquid unfit for use as a solvent for
alkaloids, &c., in toxicological investigations.
Amyl alcohol is very injurious. A few drops will produce all the
intoxicating effects of a large quantity of ethyl alcohol, with giddi-
1 Further information respecting the alcohols of fusel oil will be found on page 167.
166 AMYL ALCOHOL.
ness, nausea, and other unpleasant symptoms. 1 In larger doses it
proves fatal. To its presence in new whisky the injurious effects of
that spirit are attributable. On keeping the spirit, most of the amyl
alcohol becomes more or less oxidised or converted into comparatively
harmless ethers, and the injurious effects are less evident (see note on
p. 153).
DETECTION OF AMYL ALCOHOL.
When amyl alcohol warmed with 1 to 2 times its volume of strong
sulphuric acid, amyl-sulphuric acid, C 5 H U ,HSO 4 , is formed, with pro-
duction of a red color. Amyl-sulphuric acid is viscid, soluble in
water and alcohol, and decomposed by distillation. In presence of
sugar and other fixed substances this test is very fallacious, but if
applied to a product of distillation, especially if boiling between 120
and 135 C., the production of even a faint red color is strong pre-
presumptive evidence of the presence of amyl alcohol.
When amyl alcohol is heated with an acetate, and strong sulphuric
acid, amyl acetate is formed, which when perfectly pure has the odor
of the jargonelle pear. In presence of -g^-th part of ethyl alcohol, the
product smells of the bergamot pear.
When amyl alcohol is heated with an oxidising agent, e.g., sul-
phuric acid and potassium dichromate, an apple-like odor of valeric
aldehyde, C 5 H 10 O, is first produced, followed by the strong and pecu-
liar smell of valeric acid, C 5 H 10 O 2 . In presence of much ethyl alco-
hol, the smell of the resultant acetic acid quite overpowers that of the
valeric acid.
THE DETERMINATION OF AMYL ALCOHOL may be approximately
effected by oxidising it to Valeric acid by dilute chromic acid mixture
as described under "compound ethers." In the absence of other
acid-yielding substances, the valeric acid may be determined by titra-
tion, but otherwise the method described in the section on the " Homo-
logues of Acetic Acid " must be resorted to.
The determination of amyl alcohol in spirituous liquids is based on
the above principles.
1 According to the experiments of Rabuteau, amyl alcohol produces intoxicating
effects of a similar kind to those due to ethyl alcohol, but 15 times as intense. (The
effects of butyl alcohol were only 5 times as intense.) The researches of other observers
have shown that the physiological effect of the alcohols increases with the number of
carbon atoms. Brockhaus has personally investigated the effects of propyl, butyl,
and amyl alcohols on the system. He found the disagreeable symptoms to increase
with the molecular weight of the alcohols, and amyl alcohol itself proved to be a very
violent poison. He concluded that the impurities of potato-brandy had a much more
active influence on the human organism than was exerted by ethyl alcohol.
FUSEL OIL. 167
THE SEPARATION OF AMYL ALCOHOL from moderate quantities of
ethyl alcohol is fully described under fusel oil (see page 169). From
butyl alcohol and valeric aldehyde (boiling at 93 C.), amyl
alcohol may be approximately separated by fractional distillation
(see page 169). From neutral amyl ethers, amyl alcohol may be
separated by agitation with glacial acetic acid diluted with an equal
bulk of water a mixture in which the ethers are insoluble.
Fusel Oil.
In the alcoholic fermentation of potatoes, corn, and the marc of
grapes, there are always formed, and especially when the fermenta-
tion is conducted in an alkaline, or but slightly acid, liquid, in addi-
tion to common alcohol, various oily bodies of higher boiling points
than alcohol, and which are, therefore, found in the last portions of
the distillate obtained in the process of rectification. These liquids
consist chiefly of alcohols of the series C n H 2n+2 O, and together consti-
tute " fusel " or " fousel oil."
Potato fusel oil sometimes consists almost entirely of ethyl and
amyl alcohols, 1 the latter forming the larger proportion. Fusel oil
from other sources often contains propylic, butylic, and hexylic alco-
hols, and various aldehydes and ethers are frequently present.
The researches of Pasteur, Le Bel, and Ley have proved that the
amyl alcohol of fusel oil really consists of a mixture of two iso-
primary amyl alcohols of nearly identical boiling points and specific
gravities. One of these (iso-butyl carbinol) is optically inactive, but
the other presents the unique property (for an alcohol) of rotating the
plane of a polarised ray of light to the left. On oxidation they are
acted on with very different facilities, but both furnish valeric alde-
hydes, which on further oxidation are converted into valeric acids.
The acid derived from the optically active alcohol is also optically
1 The following proportions of various alcohols, &c., were obtained by Rabuteau
(Compt. Rend., Ixxxvii. 501) from 1 litre of potato fusel oil :
Iso-propyl alcohol, 150 c.c.
Propyl alcohol, 30 ,,
. Iso-butyl alcohol, 50
Normal butyl alcohol, 65
Methyl-propyl carbinol, 60
Iso-amyl alcohol, 275
Products boiling above 132 and retaining amyl alcohol, 170
Water, 125
Ethyl alcohol, aldehyde, and ethyl acetate, 75
Trimethyl -carbinol also appears to have been present. No mention is made of the
presence of amyl ethers.
168
FUSEL OIL.
active, but dextro-rotatory, and it forms a gummy barium salt, that
from the inactive acid being crystalline. The quinine salts exhibit
the same difference.
The following table shows the formula, densities, and boiling points
of the various alcohols which occur, or are supposed to occur, in fusel
oil:
.
Density
Boiling
Point
C 2 H 6
Ethyl Alcohol, CH 3 .CH 2 .OH,
.7938
78-4
(Methyl-carbinol.)
C 3 H 8
Propyl alco- -|
hols
1. Normal Propyl Alcohol, CH 3 .CH 2 .CH 2 .OH,
(Ethyl-carbinol.)
2. Iso- or secondary Propyl Alcohol, (CH 3 )o : CH.OH, . . .
8066
787
97-4
82-8
(Dimethvl-carbinoU
1. a-Normal-primaryi Butyl Alcohol, CH 3 .CH 2 .CH 2 .CH 2 .OH
813
117-0
(Propyl-carbinol. >
Butyl alco-
hols
1. 0-Iso-primary Butyl Alcohol, (CH^ 2 : CH.CHo.OH, . . .
(Iso-propyl-carbinol.)
2. Tertiaryi Butyl Alcohol, (CH 3 ) 3 : C.OH,
799
melts at
108-4
82-5
(Trimet hyl-carbinol. )
Lo
1. a-Normal-primary Amyl Alcohol, CH 3 .CHo.CHo.CHo.CH 2 .
820
137
OH, (Butyl-carbinol.)
C 5 H 12
Pentyl alco-
1. /3-Iso-priniary Amyl Alcohol, (CH 3 ) 2 : CH.CH 2 .CH 2 .OH,
(Isobuty 1-carbinol. )
814
131
hols
1. y-Iso-primary Amyl Alcohol, CH 3 ) . PT r PT r nTT
(Secondary Butyl carbinol.) C 2 H 5 | ' CH.CHo.OH, . .
813
128
2. Methyl-propyl carbinol, J^ | : CH.OH,
816
120
C 6 H 14
C 7 H 16
Iso-primary Hexyl Alcohol, ?CH 3 ) 2 : CH.CHo.CHo.CHo.OH,
Iso-primary Heptyl Alcohol, (CH 3 )o: CH.CH^CHoICHoTCH.,.
148-154
OH, ." .". . "
155-160
1 The classification of alcohols as primary, secondary, and tertiary is based on their sup-
posed constitution. In the primary alcohols the hydroxyl group is always connected
with the group CH 2 . ; thus, CH 2 .OH. In the secondary alcohols it is linked to CH., and
in tne tertiary alcohols to C. . The boiling points of the primary are higher than those of
the secondary, and these again boil at a higher temperature than the corresponding
tertiary alcohols. On oxidation by chromic acid mixture the primary alcohols
yield aldehydes containing the same number of carbon atoms, and these by further oxi-
dation are converted into acids of the acetic series containing the same number of carbon
atoms as the original alcohols ; the secondary alcohols yield ketones containing the same
number of carbon atoms, but which on further oxidation furnish acids of the acetic series
containing fewer carbon atoms than the original alcohols; and, lastly, the tertiary alcohols
do not under any circumstances yield acids containing the same number of carbon atoms.
The following method enables alcohols of different series to be more readily recognised.
The alcohol is heated with hydriodic acid, and thus converted into the corresponding
iodide. This is dried and added to an equal weight of dry argentic nitrite, previously
mixed with its own volume of dry sand. The flask is heated over a small flame, and
when action is over the mixture is distilled into a test-tube, where it is shaken with three
times its measure of strong potash solution containing some potassium nitrite. Dilute
sulphuric acid is then added drop by drop till the reaction is acid. If a primary alcohol
has been operated on, the liquid will assume an intense red color ; if a secondary, it
becomes dark blue ; while the product from a tertiary alcohol remains colorless. The test
succeeds with as little as half a grm.'of the alcoholic iodide.
FUSEL OIL. 169
Amyl alcohol may be separated from fusel oil in a state of approxi-
mate purity, by agitating the liquid with strong brine, separating and
distilling the oily layer, and collecting separately the portion which
passes over between 125 and 140 C. The fraction which passes
over between 105 and 120 C. consists almost entirely of iso-butyl
alcohol.
The amyl alcohol obtained in the above manner may be further puri-
fied by agitating it with hot milk of lime, drying with chloride of cal-
cium, rectifying, and collecting separately the portion which distils
between 128 and 132 C.
For the mode of separating arayl alcohol from the neutral ethers
and aldehydes of fusel oil, see page 167.
Fusel oil may be imported into England free of duty if it contain
less than 15 per cent, of proof spirit. It is tested by the Excise by
shaking it with an equal volume of water to remove the spirit, and
then ascertaining the amount of alcohol contained in the aqueous
liquid by taking its specific gravity. The test gives erroneous results,
as fusel oil is a mixture of various alcohols, of which only amylic is
approximately insoluble in water. As an improvement on this test,
G. L. Ulex (Neues Jahrb. der Pharm., xxxix. 333) recommends the
following, based on the low temperature at which ethyl alcohol distils :
100 c.c. of the sample are heated in a retort till 5 c.c. have passed
over; the distillate is shaken with an equal volume of a saturated
solution of common salt, and the mixture allowed to stand. If the
fusel oil which separates amounts to one-half of the distillate or more,
the sample is sure to contain less than 15 per cent, of spirit, and is
free from any fraudulent admixture with the same. If less fusel oil,
or none at all, separate, the presence of 15 per cent, of the spirit may
be safely assumed. In the latter case, the quantity of the adulterant
may be determined by shaking a known measure of the sample with
an equal bulk of a saturated solution of common salt (in which propyl
and butyl alcohols are much less soluble than in water), allowing the
aqueous liquid to settle out, distilling it, and estimating the contained
alcohol by noting the volume and density of the distillate.
The author has proved the accuracy of another method of approxi-
mately separating amyl from ethyl alcohol, which is to agitate the
sample in a graduated tube with an equal volume of benzene or petro-
leum spirit, subsequently adding sufficient water to cause the benzene
to separate. The increase in the volume of the benzene indicates with
approximate accuracy the amount of amyl alcohol in tjfo sample
under examination. ^^*\^ \ B R A A?~^
0* THK
UNIVERSITY
170 FUSEL OIL.
Detection of Amyl Alcohol in Spirituous Liquids.
Amyl alcohol occurs to a greater or less extent in many varieties
of commercial alcohol, especially those obtained by the fermentation
of grain or potatoes. To its presence in recently manufactured whisky
the deleterious effects of the raw spirit are attributable. On keeping,
the amyl alcohol is more or less destroyed by oxidation and conver-
sion into comparatively harmless ethers (see note, p. 153).
The actual proportion of amyl alcohol present in different varieties
of whisky is very uncertain, but few accurate experiments having been
made. According to Dupre, a sample of Scotch whisky contained
0'19 of amyl alcohol for 100 of ethyl alcohol. A sample of " Cape
Smoke" contained 0'24, and of "Common Samshoe" 0*18 of amyl
alcohol per 100 of ethyl alcohol.
The alleged adulteration of whisky with fusel oil is probably based
on an error, though it is quite possible that it has occurred in excep-
tional cases. The natural variation in the proportion of amyl
alcohol contained in spirit is very considerable, being materially
affected by the mode of distillation, in addition to the causes previ-
ously mentioned.
Of the many methods of detecting amyl alcohol in spirituous liquids,
comparatively few have any value. The following have all been tried
by the author, and verified to the extent stated :
A useful rough test is to pour the sample of spirit on filter paper
contained in a plate or flat basin, allowing it to evaporate spontane-
ously, or by the application of a very gentle heat. In the last por-
tions the smell of fusel oil is often distinctly recognisable, especially if
the liquid be warmed. A sample of gin to which ^innr ^ am yl & l co '
hoi had been added was found by the author to respond to this test.
Another useful indication is afforded by dissolving 1 grm. of caustic
potash in 150 c.c. of the spirit, evaporating the liquid slowly down to
15 c.c., and then mixing it with an equal measure (15 c.c.) of dilute
sulphuric acid, when the liquid will exhale an odor which is often
characteristic of the origin of the spirit, and indicative of its source
in raw grain, malt, potatoes, rye, arrack, &c. The odor produced is
often very disgusting.
A valuable means of concentrating the fusel oil is to distil off the
greater part of the alcohol at as low a temperature as possible. In the
residual liquid, especially while it is warm, the fusel oil may often be
detected by the smell. The residual liquid is mixed with an equal
measure of ether, and then well shaken. If the ethereal layer do not
FUSEL OIL. 171
separate spontaneously, an equal measure of water should be added.
The ethereal layer is separated, and allowed to evaporate spontane-
ously. In the residue, amyl alcohol may be recognised by its smell
and chemical characters. Petroleum ether may be advantageously
substituted for the ether, as, owing to its slight solubility in alcohol, it
may often be applied to the original liquid.
By pouring the mixed liquid through a wet filter, the author found
he could get rid of the ordinary alcohol and water, while the amyl
alcohol was retained by the ether, which rapidly evaporated and left
the fusel oil in a state readily recognisable by the smell. The amyl
alcohol in a gin, to which -^TOTT h ft d been purposely added, was readily
recognised by the author in this manner. If desired the residue can
be further examined by one of the following tests :
L. Marquardt dilutes 40 c.c. of the spirit with sufficient water to
bring the density to about '980, and then agitates the liquid with 15
c.c. of pure chloroform. The chloroform is allowed to settle, sepa-
rated, and, after shaking with an equal measure of water, is allowed
to evaporate spontaneously. The residue is treated with a little water
and one or two drops of sulphuric acid, and sufficient solution of
potassium permanganate is then added to cause the mixture to remain
red after standing for 24 hours in a closed tube. Shortly after adding
the permanganate, the smell of valeric aldehyde will be observed,
but after standing only the odor of valeric acid is distinguishable.
This can be recognised even when the original residue is almost
odorless, and the smell is not masked by the presence of essential oils,
&c.
Many samples of alcohol containing fusel oil to the extent of 0*1
per cent, respond to the following test, which depends on the existence
of furfural in the sample : 10 c.c. of the spirit are mixed with
10 drops of colorless aniline, and 2 or 3 drops of sulphuric acid,
when a fine red color will be produced. The test is still more delicate
if the residue of a chloroform or ether extraction of the spirit be used
for the experiment.
THE DETERMINATION OF FUSEL OIL IN SPIRITS cannot be effected
very accurately, as it is present in very small proportion and is not a
definite substance, being a variable mixture of amyl, butyl, and
other alcohols, various amyl ethers, &c. Most methods aiming at
the actual estimation of the fusel oil are based on the determination
of the amyl alcohol, which is its leading constituent.
The following process, due to L. Marquardt (Ber. Chem. Ges., xv.
1661, and Jour. Soe. Chem. Ind., i, 331, 377), is based on the extrac-
172 FUSEL OIL.
tion of the amyl alcohol by chloroform, its oxidation to valeric acid,
the conversion of the latter into barium valerate, and the estimation
of the barium thus combined : 150 grm. of the sample are diluted
with water to a density of about '980 and agitated with 50 c.c. of
pure chloroform l for a quarter of an hour. The aqueous layer is
separated and shaken with another 50 c.c. of chloroform, and subse-
quently treated a third time. The 150 c.c. of chloroform, containing
in solution the amyl alcohol of the spirit, is then washed thoroughly
by repeated shaking with water to remove ethyl alcohol, and treated
in a strong flask or bottle with 2 grm. of sulphuric acid and a solu-
tion of 5 grm. of potassium bichromate in 30 c.c. of water. The
flask is then closed and kept at a temperature of 85 C., with frequent
agitation, for six hours. The liquid is then distilled till all but 20 c.c.
have passed over, when 80 c.c. of water is added to the residue and
the distillation repeated till only 5 c.c. remains in the flask. The dis-
tillates are digested for half an hour with barium carbonate, in a flask
furnished with an inverted condenser, after which the chloroform is
distilled off and the aqueous liquid evaporated to a volume of 5 c.c.
The solution is then filtered from the excess of barium carbonate, and
the filtrate evaporated to dryness at 100. The residue ("A") is
weighed, dissolved in water, and the solution diluted to 100 c.c. 50
c.c. measure is acidulated with nitric acid and precipitated by silver
nitrate, the resultant chloride of silver being collected, weighed, and
calculated into its equivalent of chlorine (143'5 of AgCl = 35'5 of
Cl). The remaining 50 c.c. is precipitated with dilute sulphuric acid,
the barium sulphate being collected and weighed. The weight found
is calculated into its equivalent of barium (233 of BaSO 4 = 137 of
Ba). The sum of the weights of the barium and chlorine found, sub-
tracted from that of the residue A, gives the weight of the valeric
radicle contained therein, and this multiplied by the factor 0'871
gives the weight of amyl alcohol in the 150 grm. of spirit em-
ployed for the operation. The errors produced by the presence of
substances in the fusel oil other than amyl alcohol tend to compen-
sate each other, and hence the results are very fairly accurate. Mar-
1 Chloroform prepared from chloral is to be preferred, as the ordinary kind, though it
may not color sulphuric acid, is apt to contain impurities which yield valeric acid and other
volatile fatty acids by oxidation. For its purification, 220 c.c. are heated in a well-
closed bottle with 3 grm. of potassium dichromate, 1'4 grm. of sulphuric acid, and
a small quantity of water. The mixture is kept at 85 C. for six hours and frequently
shaken. The chloroform is then distilled off, and shaken with water and barium carbon-
ate. The mixture is heated for half an hour in a flask fitted with an inverted condenser,
when the chloroform is again distilled.
FUSEL OIL. 173
quardt obtained 1*02 grra. of fusel oil for 1000 grm. of spirit, against
1-00 grin, added.
When the proportion of fusel oil is considerable, the amount may
be approximately ascertained by distilling 500 or 1000 c.c. of the
spirit to 135 C. in a flask furnished with a fractionating tube (see
page 32). When the thermometer rises to 98 the receiver is changed,
and the portion distilling between that temperature and 110 collected
separately and again fractionally distilled. The last portion so ob-
tained is added to the part of the first distillate coming over between
110 and 135 C. These united distillates are set aside ; after the
first hour or two, if no aqueous layer separates at the bottom, ith of
the volume of water is added, and the whole agitated. After twelve
hours, the aqueous layer is separated with a pipette and the residual
fusel oil measured or weighed. This process aims at the direct deter-
mination of the fusel oil as such, instead of the estimation of any
leading constituent. Probably the method might be advantageously
modified by agitating the fusel oil distillate in a graduated tube with
an equal volume of benzene or petroleum spirit, and estimating the
amount of fusel oil from the increase in the bulk of the upper layer.
Determination of Fusel Oil, A. 0. A. C. The apparatus recommended for this
determination is Brom well's modification of Roese's fusel-oil apparatus. It con-
sists of a pear-shaped bulb, holding about 200 c.c., stoppered at the upper end
and sealed at the lower to a graduated stem about 4 mm. in internal diameter.
To the lower end of this graduated stem is sealed a bulb of 20 c.c. capacity, the
lower end of which bears a stopcock tube. The apparatus is graduated to 0*02
c.c., from 20 c.c. to 22 '5 c.c.
The reagents required are fusel-free alcohol that has been prepared by frac-
tional distillation over caustic soda or caustic potash, and diluted to exactly 30
per cent, by volume (sp. gr. 0'96541), chloroform freed from water and redis-
tilled, and sulphuric acid (sp. gr. 1'2857 at 15'6).
Distill slowly 200 c.c. of the sample under examination till about 175 c.c.
have passed over, allow the distilling flask to cool, add 25 c.c. of water, and
distill again till the total distillate measures 200 c.c. Dilute the distillate to
exactly 30 per cent, by volume (sp. gr. 0'96541 at 15'6).
The following is an accurate method for diluting any given alcohol solution
to a weaker solution of definite percentage : Designate the volume percentage of
the stronger alcohol by V, and that of the weaker alcohol by v. Mix v volumes
of the stronger alcohol with water to make V volumes of the product. Allow
the mixture to stand till full contraction has taken place, and till it has reached
the temperature of the original alcohol and water, and make up any deficiency
in the V volumes with water.
Prepare a water-bath, the contents of which are kept at exactly 15, and
place in it the apparatus (covering the end of the tube with a rubber cap to pre-
vent wetting the inside of the tube), and the vessel containing the 30 per cent.
174 FUSEL OIL.
fusel-free alcohol, chloroform, sulphuric acid, and the distillate diluted to 30 per
cent, by volume. When the solutions have all attained the temperature of 15,
fill the apparatus to the 20 c.c. mark with the chloroform, drawing it through
the lower tube by means of suction, add 100 c.c. of the 30 per cent, fusel-free
alcohol and 1 c.c. of the sulphuric acid, invert the apparatus, and shake vigor-
ously for two or three minutes, interrupting once or twice to open the stopcock
for the purpose of equalizing -pressure. Allow the apparatus to stand ten or
fifteen minutes in water that is kept at the temperature of 15, turning occa-
sionally to hasten the separation of the reagents, and note the volume of the
chloroform. After thoroughly cleansing and drying the apparatus, repeat this
operation, using the diluted distillate from the sample under examination, in
place of the fusel-free alcohol. The increase in the chloroform volume with the
sample under examination over that with the fusel-free alcohol is due to fusel
oil, and this difference (expressed in cubic centimetres), multiplied by the factor
0*663, gives the volume of fusel oil in 100 c.c., which is equal to the percentage
of fusel oil by volume in the 30 per cent, distillate. This must be calculated to
the percentage of fusel oil by volume in the original liquor.
Determination of Aldehydes, A. 0. A. C. Eighty c.c. of a saturated solution
of sodium acid sulphite are mixed with a solution of 0' 12 grm. of fuchsin in about
800 c.c. of water, 12 c.c. of sulphuric acid added, the solution thoroughly mixed,
and diluted with water to 1 litre. A portion of the sample is diluted with
water or strengthened with aldehyde-free alcohol until it contains 50 per
cent, of alcohol by volume, and 25 c.c. of this solution are treated with 10
c.c. of the reagent, and allowed to stand twenty minutes. At the same
time 25 c.c. of a solution of 0'05 grm. of acetic aldehyde in 1000 c.c.
of 50 per cent, alcohol are treated in the same manner and allowed to
stand the same length of time. The relative intensity of the colors of the two
solutions is then determined by means of a colorimeter, and from the figure thus
obtained the weight of aldehyde is estimated as acetic aldehyde, and cal-
culated to percentage of the original liquor.
A. Stutzer and R. Maul (abs. Analyst, 1896, 213) describe a process for the
estimation of fusel oil in rectified spirit, which requires greater care than in
brandy, based on the observation of Stutzer and Reitman {Analyst, 1890, 189,
203) that fusel oil may be concentrated by fractional distillation, distilling only
in the last small fraction.
One litre of rectified spirit is left in contact with 100 grm. of dry potash in
a large flask for several hours. It is then distilled over a brine -bath until
three-fourths have passed over. The flask is then cooled, 250 c.c. of water
added, and 100 c.c. distilled over a paraffin-bath. This distillate is added to
the last alcoholic distillate, the mixture diluted to 500 c.c., the specific gravity
accurately determined at 15 C. , and the liquid brought to 30 per cent, by
volume of alcohol.
For the shaking, an apparatus similar to that of Windisch, graduated in
0'02 c.c. and allowing of a reading of O'Ol c.c. , is used. Each apparatus should be
standardised with pure spirit of 30 per cent, by volume, which may be obtained
by distilling the best commercial rectified spirit made alkaline with potash,
FUSEL OIL. 175
rejecting the first 20 per cent, and the last 60 per cent., using the intermediate
fraction.
In making an estimation chloroform is first introduced, so that the lower
meniscus at 20 C. corresponds to the lowest mark ; 250 c.c. at 15 C. of the
alcohol, brought to 30 per cent, by volume, are then introduced, and 2*5 c.c. of
sulphuric acid of specific gravity 1*286 added. The stoppered apparatus is then
well shaken (about 150 times), and finally placed in a cylinder of water main-
tained at 20 C. After about one hour the liquids will have separated, and the
increase in volume of the chloroform due to fusel oil can be read off.
Following are some examples :
Difference.
C.C. C.C.
With pure alcohol, 20'59
,, O'Ol per cent, amyl alcohol, 20 '63 0*04
,i O'lO 21-03 0-44
0-20 21-48 0-89
Hence a difference in volume of O'l c.c. corresponds to 0*022472 per cent, of
amyl alcohol in 30 per cent, spirit, orO'075 per cent, in 100 per cent, spirit; and
thus, by concentrating the amyl alcohol, as described above, O'OOS per cent, by
volume in 100 per cent, spirit can be accurately determined. L.
An examination into the accuracy of the usual methods for estimating fusel
oil was made in 1895, under the auspices of the A. O. A. C. A fusel oil having
the following composition :
Amyl alcohols, 43'67
Butyl alcohols, 10'96
Propyl alcohols, 18*25
was added to pure alcohol, to the extent of 0153 per cent., and samples of this
were sent to various analysts. The results reported varied from 0'136 to 1*044
by Dupr6's method ; from 0*139 to 0"601 by Marquardt's method, and from
0*0265 to 0-660 by the Roese-Hertsfeld method. The amount actually added was
0*153, but allowing for the difference of methods of calculation employed by the
various analysts, the amounts found should have been as follows : By Dupre's
method 0*187, by Marquardt's method 0*156, and by the Roese-Hertsfeld method
0*179.
It will be seen, therefore, by these results, obtained under the best practical
method of testing an analytic process, that the estimation of fusel oil cannot
be conducted with the accuracy that was formerly supposed.
Dupre's method is condemned by several of the reporting analysts as tedious
and unreliable. (Proc. of the 12th Ann. Conv. A. O. A. C., p. 99.) See also
Analyst, 1896, p. 213. L.
NEUTRAL ALCOHOLIC DERIVATIVES.
Among the neutral derivatives of the alcohols are included a num-
ber of important bodies, of which chloroform, ether, compound ethers,
and aldehyde are prominent examples.
As a rule, the neutral derivatives of the alcohols are volatile ethe-
real liquids, but important exceptions exist to this generalisation.
The bodies of this division employed in commerce are of too varied a
nature to admit of general description. The more important of them
are fully discussed under special sections devoted to them.
ETHER.
Ethyl Ether. Ethyl Oxide.
French Ether. German Aether.
[CH 3
O.C 2 H 5 .
When used as a proper name the term " ether " always signifies
ethyl ether. When employed generically the word ether has a far
wider signification.
Ether can be obtained by a variation of reactions, but is always
manufactured in practice by distilling alcohol with strong sulphuric
acid. 1 The reaction consists first in the production of ethyl-sulphuric
acid (sulphovinic acid) C 2 H 5 HSO 4 , and this product at a higher tem-
perature (130 C.) acts on a second molecule of alcohol with forma-
tion of ether.
1. C 2 H 5 HO + H 2 S0 4 = C 2 H 5 HSO 4 -f- H 2 O ; and
2. C 2 H 5 HS0 4 -f C 2 H 5 HO = (C 2 H 5 ) 2 O -f H 2 SO 4 .
It is thus evident that sulphuric acid is reproduced. Theoretically,
therefore, a limited quantity of sulphuric acid is capable of convert-
1 In reference to this mode of preparation, ether was formerly called " sulphuric
ether."
176
ETHER. 177
ing a much larger quantity of alcohol into ether. Advantage is taken
of this fact in practice, but the formation of secondary products ulti-
mately puts a stop to the process. The first distillate contains (besides
ether) alcohol, water, sulphurous and acetic acids, oil of wine, &c.
By addition of water the alcohol may be eliminated, the ether forming
a separate layer on the surface. The acids and water may be got rid
of by agitation with potassium carbonate, and the ether obtained pure
by redistillation. 1
Ether is a highly volatile, colorless, limpid liquid, of penetrating
agreeable odor, and pungent sweetish taste. When pure, it boils at
35 C., and has a density according to Mendelejeff of 0'7195 at 15
C., or 07364 at C. It solidifies at 129 C. to a white crystal-
line mass, which liquifies at 117-4 C.
Ether is sparingly soluble in water, and still less so in glycerin, the
solutions having a neutral reaction. With alcohol, chloroform, ben-
zene, petroleum spirit, fixed and volatile oils, ether is miscible in all
proportions.
Ether dissolves resins, fats ; many alkaloids ; phosphorus, bromine,
and iodine ; ferric, mercuric and auric chlorides ; and mercuric (but
not mercurous) iodide.
In the air, ether oxidises very slowly to acetic acid. Both the liquid
and vapor are very combustible, burning with a white luminous
flame.
Commercial Ether.
Commercial ether frequently contains water (1 part of water dis-
solves in 35 of ether), and very considerable quantities of alcohol.
" Ether " B.P., is described as having a specific gravity of 0*735,
and containing not less than 92 per cent, by volume of real ether.
The " Ether " of the German Pharmacopeia has a specific gravity
of 0-724 to 0-728, and boils at 34 to 36 C.
The " Ether " of the French Codex has a density of 0'720 to 0'725
at 15 C.
The " Ether " of the United States Pharmacopeia has a density of
i In the arrangement employed by Dr. Squibb, the vapors of ether and unchanged
alcohol are first washed by a solution of caustic potash maintained at a temperature above
the boiling point of alcohol, the latter liquid is then condensed in a worm kept at a
suitable temperature, and runs back into the still, while the ether vapor retaining about
4 per cent, of alcohol is condensed in a well-cooled arrangement. 360 Ibs. of concentrated
sulphuric acid suffice to etherify 120 barrels of clean spirit, and then has to be changed
chiefly because the impurities of the spirit render the mixture dark and tarry and liable
to froth in the still (Ephemeris, ii. 590).
12
178
ETHER.
about 0'750, and consists of 74 per cent, of real ether, and 26 per
cent, of alcohol containing a little water. " jiEther fortior," U.S.P.,
is stated to have a density not exceeding 0*725 at 15 C., and to boil
at 37 C.
[The current U.S. Pharmacopeia describes only "^Ether, a liquid composed of
about 96 per cent, by weight of absolute ethyl oxide, and about 4 per cent, of
alcoh61 containing a little water. Sp. gr. 0.725 to 0.728 at 15 C. ; 0.714 to
0.717 at 25 C."-L.]
From these characters it is evident that the presence of water or
alcohol in ether tends to raise the boiling point and increase the
density of the liquid.
The following table by Dr. Squibb (Ephemeris, ii. 598) shows the
density of various mixtures of ether of '71890 specific gravity with
alcohol of -82016 specific gravity (= 90'94% by weight of absolute
alcohol) ; the densities of both liquids being taken at 60 F. (== 15'5
C.), and compared with water at the same temperature taken as
unity :
Percentage of
Ether by
Weight.
Specific
Gravity.
Percentage of
Ether by
Weight.
Specific
Gravity.
Percentage of
Ether by
Weight.
Specific
Gravity.
99
72021
89
73298
79
74495
98
72152
88
73428
78
74612
97
72284
87
73547
77
74729
96
72416
86
73666
76
74846
95
72541
85
73785
75
74975
94
72666
84
73904
74
75104
93
72792
83
74022
73
75233
92
72918
82
74141
72
75362
91
73043
81
74260
71
75492
90
73168
80
74378
70
75623
Absolute ether forms a clear mixture with any proportion of oil of
copaiba. If it contain alcohol or water it forms an emulsion when
shaken with a considerable proportion of the oil. Anhydrous ether
also forms a perfectly clear mixture with an equal bulk of carbon
disulphide ; but if the smallest quantity of water be present the mix-
ture is milky.
Gallotanuic acid (tannin) is not affected by perfectly anhydrous
ether, but it deliquesces to a syrup if a small proportion of alcohol or
water be present.
The most delicate test for the presence of alcohol in ether is that of
Lieben, founded on the formation of iodoform by alcohol but not by
ETHER. 179
ether. The method of applying the test is described on page 90.
Very careful purification is necessary to obtain ether which does not
respond to this test, and mere keeping in presence of moisture gener-
ates traces of alcohol sufficient to produce the reaction.
Several chemists have pointed out that crystallised fuchsine (acetate
of rosaniline 1 ) is insoluble in pure anhydrous ether or chloroform, but
that it imparts more or less color to these liquids when alcohol or water
is present.
When the sample is well agitated with dry chloride of calcium to
remove alcohol and water, it loses the power of dissolving fuchsine,
becoming tinged only very faintly when shaken with the dye.
To employ the above facts for the determination of small quantities
of alcohol in ether, the author operates in the following manner
(Analyst, ii. 97) : A minute quantity of powdered fuchsine is placed
in a narrow test-tube, 10 c.c. of the ether added, the tube corked, and
the whole agitated. If the ether be pure and anhydrous, the color-
ation of the liquid will be almost nil. If the coloration be consid-
erable, 10 c.c. of ether which has been treated with chloride of calcium
is placed in another tube of the same bore as the first, adding fuchsine
as before, -^th c.c. of alcohol is then added to it from a finely-divided
burette, and the whole is shaken. If this quantity of alcohol be insuf-
ficient to produce a coloration of the liquid equal to that of the sample
to be tested, a further addition of alcohol must be made until the
liquids have the same depth of color. The tint is best observed by
holding the two tubes side by side in front of a window and looking
through them transversely. The use of a piece of wet filter-paper
behind them facilitates the observation. It is well to permit the
alcohol to drop right into the ether, and not allow it to run down the
sides of the tube, as in the latter case it will dissolve any adherent
particles of fuchsine, forming a solution which will be precipitated on
mixing with the ether. For a similar reason it is not convenient to
dilute the sample with pure ether, so as to reduce the color to that of
a standard tint. In practice, each O'l c.c. of alcohol added from the
burette may be considered as indicating 1 per cent, of impurity in the
sample. Of course this assumption is not strictly correct, but the
error introduced is insignificant when the percentage of alcohol is
small. The method is very suitable for small proportions of alcohol,
but becomes difficult to apply when the latter exceeds 5 per cent, of
the sample, owing to the intensity of the color. The results are within
4 per cent, of the truth. Occasionally the tints of the two liquids are
1 Aniline hydrochloride is not suitable for this test.
180 ETHER.
not readily comparable, but on placing the tubes for a few minutes in
cold water, this difficulty is overcome. It has been pointed out by
E. R. Squibb, that the fuchsine test fails to detect a proportion of
alcohol below 0'2 per cent. ; but allows the recognition of very minute
traces of water in ether.
Ether free from alcohol is soluble in eleven times its measure of
water. Agitation with water extracts any alcohol it may contain, and
thus diminishes the volume of the ether. The method appears very
unpromising in presence of much alcohol, but with certain precau-
tions, it is possessed of considerable accuracy. The following are the
details of the procedure the author has found preferable (Analyst, ii.
98) : A small quantity of fuchsine is placed in a separator or Mohr's
burette, which is then filled with water and a small proportion of
ether, and the whole agitated. By this means a colored etherised
water is obtained, in which ether is quite insoluble, while alcohol
readily dissolves. 10 c.c. measure of the etherised water is run into a
glass tube holding about 25 c.c., and having divisions of ^ c.e., 10
c.c. of the sample of ether are next added, the tube corked, and the
whole well shaken. On the ether rising to the surface, its volume can
be easily read off. Any reduction in its volume is due to admixture
of alcohol. Thus each 01 c.c. lost represents 1 per cent, of alcohol.
If the proportion of alcohol in the sample does not exceed 20 per
cent., the ether will be colorless, and the result of the experiment will
be correct ; but if the proportion of alcohol be much above 20 per
cent., the layer of ether will be colored, and the result below the
truth. The absence of color, therefore, in the ethereal layer, indicates
the accuracy of the experiment. If the ether be colored, an accurate
result can still be obtained by adding 5 c.c. of anhydrous ether, and
again agitating. It is better, however, to dilute a fresh portion of the
sample with an equal bulk of pure ether, and use the diluted sample
instead of the original. By proceeding in this manner the proportion
of alcohol in mixtures of that liquid with ether can be ascertained
within 1 or 2 per cent, with great facility. The process has been veri-
fied up to 60 per cent, of alcohol.
In all cases the proportion of alcohol must be deduced from the
reduction in the volume of the ether, and not from the increase in
that of the aqueous liquid. Care must be taken to prevent any vola-
tilisation of the ether.
The above method of agitation with etherised water is far more
rapid and generally preferable to the shaking with glycerin sometimes
recommended.
ESTERS. 1 81
The presence of more objectionable impurities in ether is indicated
when at least 10 c.c. of the sample is allowed to evaporate spontane-
ously on filter-paper contained in a flat dish, and the odor of the
" tailings " is carefully observed.
Some specimens of commercial ether liberate iodine from potassium
iodide, a reaction which is not improbably due to the presence of
traces of ethyl nitrite.
Methylic Ether. (CH 3 ) 2 O. When methyl alcohol is heated
with sulphuric acid it yields methylic ether, which is a gas condensible
only at a very low temperature, and the solution of which in ordinary
ether possesses remarkable anaesthetic properties. Owing to the
extreme volatility of methylic ether, ether made from methylated
spirit would be practically pure ethylic ether, were it not for the
presence in it of other constituents of wood spirit. Ether prepared
from methylated spirit is known as " methylated ether."
"SPIRIT OF ETHER," B.P., is a solution of about 28 parts of real
ether in 72 of rectified spirit. The corresponding preparations of the
German and United States Pharmacopeias contain respectively 23?
and 22 per cent, of ether.
COMPOUND ETHERS (ESTERS).
This terra is applied to the products obtained when acids react on
alcohols with elimination of water, as in the cases represented by the
following formulae :
H j Q (C 2 H 5 ) j Q _ (C 2 H 5 ) ) Q E
(C 2 H 3 0)j C H | C -(C 2 H 3 0)} e E
Acetic acid. Ethyl alcohol. Acetate of ethyl.
H;'
Succinic acid. Glycol. Ethylene succinate.
3HC1 + ( 3 H 3 5) "' } B = (C 3 H 5 )'"C1 3 + ^ 3 1 O s .
Hydrochloric Glycerin. Trichloride
acid. of glycyl.
Ethers can be produced in various ways, but the following general
methods may be specially mentioned :
1. By the action of the concentrated acid upon the anhydrous or con-
centrated alcohol containing the radicle of which an ether is desired.
2. By distilling the alcohol with strong sulphuric acid and a salt of
the acid the radicle of which is to be introduced into the ether.
3. By dissolving the acid in the alcohol and passing hydrochloric
acid gas into the liquid.
182
ESTERS.
4. By reaction between the iodide of the alcohol radicle the ether
of which is required and the silver salt of the acid.
In many respects the ethers may be regarded as true salts of the
alcohol radicles, but they rarely react directly with the ordinary tests
for the contained acid radicles.
As a class, the ethers are mostly volatile solids or liquids having
little solubility in water, but miscible in all proportions with alcohol
and ether. They are frequently split up into the corresponding acids
and alcohols by distillation with water (and especially by high-pressure
steam), and yield the alcohol and an alkaline salt when treated with
caustic alkali.
The following is a tabular list of the chief ethers of monatomic
alcohol-radicles of which practical application is made : l
Name.
Formula.
Boil-
ing
Point
Specific
Gravity.
Other Characters and Applications.
at
0C.
at 15
to 18
C.
Methyl acetate, . .
CH 3 ,C.,H 3 Oo
56-3 ! -867
Readily soluble in water ; present in
wood naphtha.
salicylate,
CH 3 ,C 7 H 5 3
222-
1-18
See vol. ii.
,, chloride, .
CH 3 ,C1
-23'
[
Gaseous at ordinary temperatures ;
used for refrigerating and for pro-
ducing methyl-aniline dyes.
,, iodide, . .
CH 3 ,I
42-5
2-23
Turns brown in the light. " Aniline
dyes.
Ethyl formate, . .
C,H 5 ,CH0 2
54-4
945
919
Odor of peach-kernels; used for
flavoring arrack and rum.
,, acetate, . .
C^AH-A
74-3
. .
908
Fragrant odor ; solvent of morphia ;
butyrate, .
C 2 H 5 ,C 4 H 7 O. 2
120-
902
Odor of pine-apples ; used in fruit-
essences. "Rum-essence" is ob-
tained by distilling saponified but-
ter with sulphuric acid aud alcohol
,, valerate, .
,, pelargonate,
C 2 H 5 ,C 5 H 9 2
C 2 H 5 ,C 9 H 17 2
134-
228'
866
863
Odor of valerian.
Odor of French Brandy ; used for
^
flavoring factitious wines.
,, benzoate, .
,, nitrite, . .
CoH 5 ,C 7 H 5 2
Co"H 5 ,N0 2
m-
18-
1-051
947
Fragrant odor.
Odor of apples ; used in medicine ;
see page 191 et seq.
,, nitrate, . .
,, chloride, .
C 2 H 5 ,N0 3
C 2 H 5 ,C1
86-3
12-5
1-132
921
Sweet ; hot vapor is explosive.
Burns with smoky green-edged
flame, producing HC1.
,, bromide, .
C 2 H 5 ,Br
40-7
1-473
1-419
Burns with difficulty, giving fine
green flame without smoke, and
giving off bromine.
iodide, . .
CoH 5 ,I
71-6
1-975 '1-931
Turns brown in the light, liberating
iodine. Organic research, and
aniline dyes.
Amyl acetate, . .
,, butyrate, . .
C 5 H n ,C 2 H 3 2
C 5 H n ,C 4 H 7 0.,
137'
176-
884
876
852
Odor of jargonelle pears.
Fragrant odor.
,, valerate, . .
C 5 H n) C 5 H 9 2
188'
. .
864
Odor of apples; used as a fruit-
essence.
nitrite, . .
C 5 H n ,N0 2
99-
902
877
Used in medicine.
chloride, . .
C 5 H U ,C1
101-
886
874
Burns with luminous green flame
producing HC1.
,, iodide, . . .
C 5 H n ,I
147-
1-468
Faint odor; turns brown in light.
1 In addition to the above, the salts of ethyl-sulphuric and ethyl-disulphocarbonic acids
are employed, and are described in separate sub-sections on page 189 et seq.
ESTERS. 183
From the above table it will be seen that the ethers of monatomic
alcohol radicles form a very extensive and interesting series of bodies,
some of them, as the nitrites of ethyl and arayl, and the acetate of
ethyl, being employed in medicine, some in perfumery, others in the
manufacture of coal-tar dyes, and many others are used for compound-
ing artificial fruit-essences. The more important, and such as some-
times require chemical examination, are described in detail in sepa-
rate paragraphs. They may generally be assayed and analysed
by methods similar to those employed for examining ethyl acetate.
Sperm oil, spermaceti, and the waxes have also the constitution of
ethers of monatomic alcohol radicles, but will be more conveniently
considered in the division on " Fixed Oils and Fats."
The ethers of diatomic alcohol radicles have received few practical
applications, and do not require special description.
The ordinary natural fixed oils and fats may be regarded as ethers,
of the triatomie alcohol-radicle containing glycyl, C 3 H 5 '". By treat-
ment with alkalies or high-pressure steam they yield glycyl alcohol
(glycerin) and stearic, oleic, or other " fatty acid."
The detailed consideration of the fixed oils and fats may be conve-
niently deferred, as they form a true natural group, and do not pre-
sent close physical analogies to the salts of monatomic alcohols, to
which the term " ether " was originally, and with greater propriety,
applied.
A general process for the analysis of compound ethers is based on
their reaction with alcoholic potash or soda, which decomposes them
with production of alcohol and formation of a salt of the alkali-
metal, as in the following example :
(C 2 H 5 )C 4 H 7 O 2 + KHO = KC,H 7 O 2 + (C 2 H 5 )HO.
Ethyl butyrate. Potassium Potassium Ethyl alcohol,
hydroxide. butyrate.
The following are the details of the process, which is practically
identical with that of Koettstorfer for the examination of fats :
A volume of 50 c.c. (measured with the greatest attainable accu-
racy) of a solution containing about 60 grm. of caustic potash in
1 litre of pure rectified spirit is introduced into a strong bottle hold-
ing about 100 c.c. 1 A quantity of the ether, weighing from 4 to 6
grm., is then added in such a manner as to avoid loss. The ether
may be contained in a small glass bulb, or a known weight of the
ether dissolved in pure alcohol may be added. The bottle is then
1 The spirit should be previously distilled with addition of caustic potash .
184 ESTERS.
closed with an india-rubber stopper which is to be firmly secured by
wire, and is next exposed to a temperature of about 100 C. for half
an hour, after which it is allowed to cool, opened, a few drops of
pheuol-phthalein solution added, and the liquid at once titrated with
standard sulphuric or hydrochloric acid. A blank experiment is then
made by heating 50 c.c. of the alcoholic potash alone for half an hour,
and titrating with acid as before. The difference between the measure
of standard acid required in the blank experiment, and that in which
the ether was present, gives the measure of acid corresponding to the
alkali neutralised by the ether. Each cubic centimetre of normal
acid thus employed represents 0*0561 grm. of KHO, or, in other
words, each 1 c.c. of difference between the measure of the acid origi-
nally employed, and that used in the blank experiment represents one
equivalent in milligrammes of the ether present. 1
The foregoing method of decomposing ethers with alcoholic alka-
line solutions often furnishes valuable evidence of the purity of the
substances examined. Thus an elementary combustion would scarcely
detect 10 per cent, of ethyl alcohol in ethyl acetate, or of ainyl alco-
hol in amyl acetate, but the above process would indicate the impurity
with certainty.
After decomposing the compound ether with alkali as above de-
scribed, and titrating the products with standard acid, a further
knowledge of the ether may be obtained in the following manner :
The free alcohol is got rid of by distilling or evaporating the slightly
alkaline liquid. The residue is treated with an amount of sulphuric
acid fully sufficient to doubly neutralise the alkali originally added
(i.e., to effect the reaction KHO -f H 2 SO 4 = KHSO 4 + H 2 O), and the
liquid is distilled. The acid of the ether will be liberated, and, if
volatile without decomposition, will pass more or less perfectly into the
distillate, where it may be further examined, converted into a barium
salt, &c. 2
*As an example : Suppose that 45 c.c. of normal acid were employed in the blank
experiment, and that 8 c.c. were required after saponification of the ether. The difference
of 37 c.c. represents the measure of normal alkali employed for the decomposition of the
ether. As each centimeter of this contains 56'1 m.grm., or one equivalent in milli-
grammes of KHO, it follows that the weight of ether employed contained a number of
milligrammes equal to 37 times its equivalent. Supposing the weight of ether employed
was 4'810 gim., then its equivalent would be 4 |f = 130. Of course, the equivalent
thus found is identical with the molecular weight, one-half of the molecular weight, or
one-third of the molecular weight, according to the constitution of the ether.
Conversely, if the equivalent of the ether were known to be 130, the weight of it
present in the quantity of the sample taken would be 130 X 37 = 4810 m.grm.
2 It must be remembered, however, that if hydrochloric acid were used in the original
ESTERS. 185
The foregoing method may be conveniently employed for the deter-
mination of chloroform and chloral hydrate when in alcoholic solu-
tion, the reactions being :
a. With chloroform : 4KHO + CHC1 3 = KCHO 2 + 3KC1 + H 2 O.
b. With chloral hydrate : 5KHO + C 2 HC1 3 O,H 2 O = 2KCH0 2 +
3KC1 + 2H 2 O.
The first reaction requires 4 equivalents, and the latter 5, of alkali.
Hence, each c.c. of difference in the amounts of normal sulphuric acid
required will represent 29*9 m.grm. of chloroform or 33*1 of chloral
hydrate.
A. Dupre has applied the above process to the determination of the
fixed and volatile ethers of wine. 250 c.c. of the wine are distilled
down to about 50, and the distillate made up to 250 c.c. In 100 c.c.
of this, the free volatile acid is determined by standard alkali, and
another 100 c.c. is digested with a known excess of decinormal alco-
holic soda. The extent to which this is neutralised over and above
that due to the free acid represents the volatile ethers, which are best
expressed in terms of acetic ether. To determine the fixed ethers
(assumed to be ethyl tartrate), 250 c.c. measure of the wine is evapor-
ated on a water-bath to about 40 c.c. 1 The residue is distilled with
excess of caustic alkali, a little tannin being added to prevent froth-
ing. The distillate contains the alcohol produced by the decomposi-
tion of the tartaric ether. It is rendered slightly acid with sulphuric
acid, and again distilled, 20 c.c. being driven over. The alcohol in
these 20 c.c. may be determined by the density, or preferably by the
oxidation-method described on page 102.
A useful general method of examining compound ethers was de-
vised by Chapman and Smith (Jour. Chem. Soc., xix. 477). It is
based on the fact that organic bodies whe.n oxidised in a sealed tube
by a mixture of sulphuric acid and acid chromate of potassium, yield
proximate products of oxidation closely related to the radicles con-
tained in them. Special applications of this process are given on pages
81,90,102,171, Ac.
Shortly, the process consists in heating a known weight of the sub-
stance in a sealed tube for some hours with an aqueous solution of
bichromate of potassium, containing from 3 to 8 per cent, of the salt,'
titration more or less of it will appear in the distillate, unless excess of silver sulphate be
added to the contents of the retort before distillation. Standard sulphuric may be
substituted for the hydrochloric acid.
1 With wine containing much sugar the residual liquid should be diluted, and the
evaporation repeated.
186
ESTERS.
Ethyl alcohol, .
C 2 H 6 + 2
Amyl alcohol,
C 5 H 12 + 2
Ethyl acetate,
C 2 H 5 ,C 2 H 3 2 + 2
Amyl acetate,
C 5 H n ,C 2 H 3 2 + 2
Amyl valerate, .
C 5 H U ,C 5 H 9 2 + 2
Amyl nitrite,
C 5 H U ,N0 2 + 3
Ethyl nitrate, .
C 2 H 5 ,N0 3 + 2
Ethyl iodide,
2C 2 H 5 I + O 5
Isopropyl iodide,
2CH 2 (C 2 H 5 )I + O n
Ethyl-amine,
C 2 H 5 ,H 2 N + 2
Ethyl-amyl-amine,
C 2 H 5 ,C 5 H n ,HN + (
Ethyl benzoate, .
C 2 H 5 ,C 7 H 5 2 + 2
and 5 parts by weight of concentrated sulphuric acid to every 4 of
the bichromate. The following reactions were verified by the authors
of the method as occurring with very considerable accuracy :
= HC 2 H 3 O 2 + H 2 O.
= HC 5 H 9 O 2 + H 2 O.
= 2HC 2 H 3 O 2 .
= HC 2 H 3 2 + HC 5 H 9 2 .
= 2HC 5 H 9 2 .
= HC 5 H 9 O 2 + HNO 3 .
= HC 2 H 3 O 2 + HNO 3 .
= 2HC 2 H 3 2 + H 2 + I 2 .
= 2HC 2 H 3 2 + 2C0 2 + 3H 2 + I 2 .
= HC 2 H 3 O 2 + NH S .
t = HC 2 H 3 O 2 + HC 5 H 9 O 2 + NH 3 .
HC 2 H 3 2 + HC 7 H 5 2 .
Compounds containing methyl yield formic acid by oxidation, but
the greater part of this is further oxidised to carbonic acid and water.
Messrs. Chapman and Smith (Jour. Chem. Soc., xx. 173) further
showed that the process was capable of being used for investigating
the structure of isomeric bodies. This is exemplified in the equation
representing the oxidation of isopropyl iodide.
The foregoing methods of examining ethers are of such general
application, that, with the aid of the table on page 182, most of the
ethers in common use may be readily identified, and even quantita-
tively determined. The assay of commercial ethers may usually be
conducted as described in the following section on " Ethyl Acetate."
A few, however, owing to their special properties or great individual
importance, will be considered in separate sections.
Ethyl Acetate. Acetic Ether.
French Ether acetique. German Essigather.
fH
C 4 H A = C 2 H 5 ,C 2 H 3 O 2 = ?** | O = C J j|
LCO.O(C 2 H 5 ).
Acetate of ethyl is best prepared by distilling dried sodium acetate
with alcohol and'sulphuric acid x ; (C 2 H 5 )HO + NaC 2 H 3 O 2 -f- H 2 SO 4
= NaHS0 4 + (C 2 H 5 )C 2 H 3 O 2 + H 2 O.
The product of the distillation is best purified from alcohol by agi-
1 The best method of operating has been fully detailed in a paper by W. Inglis Clark
(Pharm. Jour., [3] xiii. 777), who has also placed on record much other valuable infor-
mation on acetic ether.
ESTERS. 187
tation with a saturated solution of calcium chloride, and subsequently
dehydrated by contact for some days at the ordinary temperature
with recently ignited potassium carbonate, or distillation over dried
acetate of sodium. The use of solid calcium chloride for dehydra-
tion causes considerable loss from the formation of a compound with
the ethyl acetate, decomposed on addition of water.
Ethyl acetate occurs in many wines and in wine-vinegar. It is
produced spontaneously in several pharmaceutical preparations, nota-
bly in the tincture of ferric acetate. It possesses considerable solvent
powers, and is especially employed for extracting morphine and tan-
nins from aqueous liquids.
Pure ethyl acetate is a colorless liquid, of very fragrant, agreeable
odor. When pure it has a density of about 0'908 at 15 C., and boils
at 73*5 to 74'3 C. Ethyl acetate is miscible in all proportions with
alcohol, ether, and chloroform, but is only sparingly soluble in water,
requiring 8 measures at 0, or 9 at 15 C. for its solution. The solu-
bility of water in acetic ether is 1 measure in 26 at 0, and 1 in 24 at
15 C. In a saturated solution of calcium chloride, ethyl acetate is
but very slightly soluble, requiring 47 measures at 15 C. and almost
as large a proportion at 0.
COMMERCIAL, ACETIC ETHER is often impure. In a series of eight
samples representing the products of most of the leading makers,
"W. Inglis Clark found proportions of real ethyl acetate ranging from
90-14 to 30-6 per cent. ; the alcohol from 7'2 to 48'0 per cent.; the
free acetic acid from a trace up to 7*0 per cent. ; while the " water,
ether, &c." (estimated by difference) ranged from T5 to 29'6 per cent.
For the analysis of commercial acetic ether, the following process
gives satisfactory results :
Dissolve 5 c.c. in proof spirit, 1 add a few drops of phenol phthalein,
and titrate the free acetic acid by decinormal caustic soda. Each 1 c.c.
of decinormal soda neutralised represents 0'006 grm. of CaH^ in
the 5 c.c. of sample used.
Add to another quantity of 5 c.c. of the sample the same measure
of decinormal soda which has been employed in the titration, and then
saponify the neutralised liquid by alcoholic potash as described on p.
183. Each 1 c.c. of normal alkali neutralised by the sample repre-
sents 0'088 grm. of ethyl acetate in the quantity of the sample used ; or
0'046 of alcohol regenerated from the ether.
i The spirit should be first freed from traces of free acid by adding a few drops of
phenol-phthale'in, and then dropping in dilute alkali till a faint pink tint remains after
shaking.
188 ESTERS.
Treat 20 c.c. of the sample with 20 c.c. of water and about 12 grm.
of solid caustic potash in a flask furnished with an inverted condenser.
After digesting for some time at the ordinary temperature, heat the
flask to 100 C. for about two hours, add 20 c.c. of water, and distil
over exactly 50 c.c. Ascertain the alcohol in the distillate by calcu-
lation from its density, divide the weight so found by 4, and subtract
from the dividend the amount of alcohol derived from the saponifi-
cation of the ether, as ascertained in the manner already described.
The difference is the actual alcohol present in 5 c.c. of the sample.
By subtracting the sum of the acetic acid, ethyl acetate, and alcohol
found as above from the weight of 5 c.c. of the sample, the amount of
" water, ether, &c." may be ascertained.
A very simple and approximately accurate method of ascertaining
the proportion of real ethyl acetate present in commercial acetic ether
consists in agitating 10 c.c. of the sample, in a graduated tube, with an
equal measure of a saturated solution of chloride of calcium. The
volume of the layer which rises to the surface is the quantity of ethyl
acetate in the measure of the sample examined. The results are fairly
accurate, if the water and alcohol of the sample do not together
much exceed 20 per cent, by measure, but with larger proportions the
volume of ether which separates is sometimes notably below the real
amount of ethyl acetate present. The error may be avoided in some
measure by adding to the sample twice its measure of acetic ether
which has been previously treated with calcium chloride solution. 20
c.c. of the fortified sample should then be shaken with 20 c.c. of cal-
cium chloride, when the diminution in the volume of the ethereal
layer will represent the measure of impurities in - 2 ^- = 6'67 c.c. of the
sample.
The foregoing method of operating is due to W. Inglis Clark.
The employment of water previously saturated with washed acetic
ether, and colored with fuchsine does not give satisfactory results. The
German and the United States Pharmacopeias require that when acetic
ether is shaken with an equal volume of water, the water shall not be
augmented more than ^ of its original volume.
The specific gravity of ethyl acetate is not a satisfactory indication
of its purity, as it dissolves alcohol, ether, and chloroform in all pro-
portions, and may be diluted with spirit of approximately the same
density as the pure substance.
Acetic ether should not contain more than a trace of free acid, and
should be entirely volatile without residue, nor be blackened by strong
sulphuric acid.
ESTERS. 189
Ethyl-Sulphates. M',C 2 H 5 SO 4 = C ^ 5 1 SO 4 .
The ethyl-sulphates or " sulphovinates " are the salts of ethyl-
sulphuric acid, which body has the composition of an ethyl-hydrogen
sulphate, but possesses decided acid properties, and forms a well-defined
series of salts. Hence it might with equal propriety be considered
among the acid derivatives of the alcohols.
Ethyl-sulphuric acid is produced by the reaction of alcohol on strong
sulphuric acid, thus : C 2 H 5 ,HO + H 2 SO 4 = C 2 H 5 ,HSO 4 -f H 2 O. The
change is much facilitated by keeping the liquid at a temperature of
100 C. for 24 hours. The less water there is present, the more perfect
the change ; but the reaction is always far from complete. If the tem-
perature be raised much above 100 C., ordinary ether is produced,
and, at higher temperatures still, ethylene and other products are
formed.
From the crude ethyl-sulphuric acid, obtained as above, barium
ethyl-sulphate may be prepared by neutralising the product with car-
bonate of barium, filtering off" the insoluble barium sulphate, and
evaporating the filtrate to crystallisation. The calcium salt may be
obtained in similar manner, and the lead salt by employing litharge
instead of barium carbonate.
SODIUM ETHYL-SULPHATE, NaC 2 H 5 SO 4 -f- H 2 O, may be obtained by
decomposing one of the above salts with sodium carbonate, or by
adding powdered carbonate of sodium and alcohol, or alcoholic solu-
tion of caustic soda, to the crude acid, filtering from the insoluble
sodium sulphate, and evaporating the filtrate to crystallisation.
Sodium ethyl-sulphate (sodium sulphovinate) is a white crystal-
line salt of faint ethereal odor, and cooling, sweetish, somewhat
aromatic taste, very deliquescent, soluble in 0'7 parts of cold water^
and also soluble in alcohol, with which it is capable of forming a
crystalline compound. Sodium ethyl-sulphate is insoluble in ether.
It has been employed in medicine as a saline purgative. At 86 C.
sodium ethyl-sulphate melts and becomes anhydrous; at 120 C. it
decomposes, evolving alcohol vapor, and leaving acid sulphate of
sodium. It also decomposes spontaneously at ordinary temperatures,
especially when in solution, with formation of sodium sulphate. The
presence of a little free alkali prevents this change. The commercial
salt is liable to contain barium, calcium, lead, arsenic, sulphates, &c.
It is not unfrequently contaminated with foreign organic matter.
When pure it does not char on ignition. It has been adulterated by
1 90 ESTERS.
admixture with sulphate of sodium, and has been replaced by acetate
of barium. The last dangerous substitution would at once be detected
by adding dilute sulphuric acid to the aqueous solution.
The characters of the ethyl-sulphates are sufficiently indicated by
the above description of the sodium salt. They are soluble in water.
When heated with dilute sulphuric acid they evolve alcohol, and with
strong sulphuric acid, ether. With sulphuric acid and an acetate they
give a fragrant odor of acetic ether. The same result is obtained by
simply heating together an acetate and sulphovinate.
ETHYL-SULPHURIC ACID, HC 2 H 5 SO 4 , may be obtained in a state of
purity by decomposing the barium salt by an equivalent amount of
dilute sulphuric acid, or a solution of lead ethyl-sulphate by
hydrogen sulphide. On concentrating the filtered liquid, the
acid is obtained as a limpid, oily, very sour, unstable liquid of 1*31
sp. gr. It is miscible with water and alcohol in all proportions, but
it is insoluble in ether.
Ethyl Disulpho-Carbonates ; Xanthates.
C 2 H
M'C 3 H 5 S 2 O = CO"
M'
The xanthates are the salts of xanthic acid, which, though having
the composition of an ether, possesses decided acid properties. Hence,
it ought strictly to be considered among the acid derivatives of the
alcohols.
When boiling absolute alcohol is saturated with pure caustic potash,
and carbon disulphide added gradually till it ceases to be dissolved, or
the liquid becomes neutral, potassium xanthate is formed according to
the equation : C 2 H 5 HO + KHO -f CS 2 = KC 2 H 5 COS 2 + H 2 0.
On cooling, the potassium xanthate crystallises in slender color-
less prisms, which must be pressed between blotting paper and dried
in a vacuum. Potassium xanthate is readily soluble in water and
alcohol, but insoluble in ether. On exposure to air it suffers gradual
decomposition.
On adding dilute sulphuric or hydrochloric acid to potassium
xanthate, xanthic acid, HC 3 H 5 S 2 O, is liberated as a colorless, heavy,
oily liquid, of peculiar and powerful odor and astringent bitter taste.
It is very combustible. Xanthic acid reddens litmus, and ultimately
bleaches it. At a very slight rise of temperature it undergoes decom-
position into alcohol and carbon disulphide. Owing to this property
the xanthates have been successfully used as a remedy for the phylloxera,
ESTERS. 191
which attacks the vine, and is equally efficacious against the ravages
of other noxious insects. The xanthate is mixed with earth, either
alone or together with superphosphate, when it gradually undergoes
decomposition with formation of carbon disulphide. Xanthic acid
possesses powerful antiseptic properties. Sodium xanthate is employed
to effect the reduction of ortho-nitrophenylpropiolic acid to indigo-blue.
When warmed with nitric acid, xanthic acid and xanthates evolve an
odor of ethyl nitrite. On distillation, the xanthates are decomposed
with formation of CO. 2 ,CS 2 ,H 2 S, and a peculiar sulphuretted oil, while a
metallic sulphide and carbon remain behind.
The most characteristic reaction of xanthic acid, and the one from
which it derived its name, is that produced with salts of copper. On
adding cupric sulphate to a neutral solution of a xanthate a brownish
precipitate of cupric xanthate is first formed, which quickly changes
to bright yellow flocks of cuprous xanthate. This substance is
insoluble in water and in dilute acids, but is decomposed by strong
acids. It is slightly soluble in alcohol, and rather more so in carbon
disulphide, and is said to be insoluble in ammonia. It is not sensibly
attacked by sulphuretted hydrogen, but is instantly decomposed by
a soluble sulphide. The formation of cuprous xanthate has been
employed for detecting carbon disulphide in coal-gas, the gas being
passed through alcoholic potash, the excess of alkali neutralised by
carbonic or tartaric acid, the insoluble salt removed by filtration, and
the liquid treated with sulphate of copper.
The formation of cuprous xanthate has also been proposed by E. A.
Grete (Jour. Chem. Soc., xxx. 551) as a means of determining copper
and caustic alkali, and has been applied by B. Nickels to the deter-
mination of carbon disulphide in commercial benzols. The method of
the latter chemist is essentially an estimation of xanthate by a stand-
ard solution of copper.
Xanthates may also be estimated by titration with a standard solu-
tion of iodine (C. Vincent, Ann. Chem. Phys., [5] xxii. 544), or by
oxidation with permanganate, and precipitation of the resultant
sulphate by barium chloride (H. L. Greville, Jour. Soc. Chem,
Ind. t ii. 490).
Ethyl Nitrite. Nitrous ether. C 2 H 5 NO 2 = ^ 5 j O. This sub-
stance has been known in an impure state for a long time. It may be
obtained by passing the red vapors of nitrogen trioxide (evolved by
acting on starch by nitric acid) into alcohol ; by distilling nitrite of
potassium or sodium with alcohol and sulphuric acid ; or by the direct
192 ESTERS.
action of nitric acid on alcohol. In the last case the nitric acid is
reduced by a portion of the alcohol, and the nitrous acid so formed
acts on the remainder to form ethyl nitrite. A considerable quantity
of aldehyde results from the oxidation of the alcohol, so that the ether
obtained by this process is largely contaminated. This reaction may
be avoided in great measure by adding metallic copper to the contents
of the retort.
Pure ethyl nitrite is a nearly colorless liquid, of very fragrant
odor. It is soluble in all proportions in alcohol, but requires forty-
eight parts of water for solution. It boils at 18 C., and has a density
of '947 at 15'5 C. (60 F.). It is liable to decompose on keeping,
especially in presence of water. It gives many of the ordinary
reactions of the nitrites. Thus, when mixed with a little dilute sul-
phuric acid, and poured on a strong aqueous solution of ferrous
sulphate, it develops a dark brown color ; when dissolved in alcohol,
and treated with a few drops of dilute sulphuric or acetic acid, it
liberates iodine from potassium iodide, and therefore the mixture
produces the well-known blue color on addition of starch.
Spirit of Nitrous Ether.
French. Ether azoteux alcoolise". German. Versiisster
Salpetergeist.
"Spirit of Nitrous Ether" l (Spiritus cetheris nitrosi, B.P.) is the
present official name of a preparation consisting essentially of a solu-
tion of impure ethyl nitrite in rectified spirit. Spirit of nitrous ether
is the modern representative of the old "Sweet Spirit of Nitre"
(Spiritus nitri dulcis, P.L. 1745) which was prepared by distilling
together rectified spirit and nitric acid. In the London Pharmacopoeia
of 1787, it is called Spiritus cetheris nitrosi, which name was modified
in the London Pharmacopoeia of 1809 to Spiritus cetheris nitrici. The
essential nature of the product was clearly recognised in 1809, a
1 The literature of spirit of nitrous ether is somewhat extensive. The following is a list
of references to it in comparatively recent volumes of the Pharmaceutical Journal :
B. H. Paul, [3] vii. 1071.
F. W. Kiinmington, [3] viii. 341, 362,
377; x. 41, 220.
J. Williams, [3] viii. 441, 453.
W. Smeeton, [3] x. 21.
A. Dupre", [3] x. 93.
J. Muter, [3] x. 94.
W. Pollard, [3] x. 100.
J. F. Eykman, [3] xiii. 63.
W. H. Symons, [3] xiv. 281.
U. S. and German Preparations, [3] xiv.
101.
D. J. Leech, [3] xiv. 322.
A. C. Abraham, [3] xiv. 390, 876, 915.
P. MacEwan, [3] xiv. 817, 826, 896, 936.
D. B. Dott, [3] xiv. 819, 826, 895; xv.
200, 492, 592.
T. S. Dymond, [3] xv. 101.
ESTERS. 193
translation of the London Pharmacopoeia of that date containing a
note referring to the brown coloration with ferrous sulphate, and to
the difficulty attending the separate preparation of " nitric ether."
The name "spirit of nitric ether" was retained in subsequent London
Pharmacopoeias, including the last, published in 1851. The nearly
contemporary Dublin Pharmacopoeia described it as Spiritus cethereus
nitrosus, and directed that it should be made by dissolving previously
prepared ethyl nitrite in rectified spirit. While the name of the
preparation of the London Pharmacopoeia of 1851 clearly indicated
the intention that the product should contain ethyl nitrite or nitrate as
an essential constituent, the process of manufacture prescribed led in
practice to the production of an article of exceedingly variable char-
acter. The reaction was of a very complex nature, and, even in
experienced hands, the product sometimes contained only a compara-
tively small proportion of nitrous ether, while the amount of aldehyde
formed by the oxidation of the alcohol was considerable. In the
British Pharmacopoeia of 1867, the name of the preparation was
changed to " spirit of nitrous ether." The method of preparation was
also modified, an addition of metallic copper being directed to be made
to the contents of the retort, whereby the nitric acid is largely con-
verted into nitrous acid, which then acts on the alcohol with forma-
tion of ethyl nitrite. The use of copper prevents, in great measure,
the formation of aldehyde, and gives a distillate richer in nitrous ether
than that obtained by the old process. 1
The characters of " spirit of nitrous ether " are thus described in the
British Pharmacopoeia of 1867 : " Transparent and nearly colorless,
1 A large majority of respectable Pharmacists, when asked for " sweet spirit of nitre,"
recognise the "spirit of nitrous ether, B.P." as the modern and official representative of
that preparation, and supply their customers with it accordingly. Some firms still manu
facture an article of the nature of the "spirit of nitric ether, L.P.," and sell it under
the name of "sweet spirit of nitre," and an article of a density of '900 appears on the
price-lists of certain wholesale houses. Such a practice is highly objectionable, as a
preparation of such a density will either be destitute of nitrous ether when made, or will
very shortly become so. Sweet spirit of nitre prepared by the process of the London
Pharmacopoeia of 1851 has a pleasanter taste than the B.P. article, which may account
for the alleged preference of the public for the former. It is, however, asserted that many
medical practitioners prefer the L.P. preparation, which, if true, is not improbably due
to their being asked whether they wish to be served with " the 845 or the 850 article,"
and erroneously assuming that the higher figure indicates a greater strength (combined
with the advantage of a lower price).
In Cooley's Cyclopsedia of Practical Receipts (sixth edition, 1880, page 1545) it is
stated that much of the spirit used for making sweet spirit of nitre of *850 specific gravity
is a waste product from the manufacture of fulminating mercury, and as such frequently
contains no inconsiderable quantity of hydrocyanic acid.
13
194 ESTERS.
with a very slight tinge of yellow, mobile, inflammable, of a peculiar
penetrating apple-like odor, and sweetish, cooling, sharp taste. Spe-
cific gravity, 0'845. It effervesces feebly, or not at all, when shaken
with a little bicarbonate of soda. When agitated with solution of sul-
phate of iron and a few drops of sulphuric acid, it becomes a deep
olive-brown or black. If it be agitated with twice its volume of satu-
rated solution of chloride of calcium in a closed tube, 2 per cent, of its
original volume will separate in the form of nitrous ether, and rise to
the surface of the mixture." In later reprints of the British Pharma-
copoeia of 1867, the words " an ethereal layer " are substituted for
" nitrous ether " in the last sentence.
The spirit of nitrous ether of the German Pharmacopeia has a
density of 0'840 to 0'850, while the U.S. preparation has a density of
0'823 to 0-825, and is described as containing between 4 and 5 per
cent, of ethyl nitrite.
Spirit of nitrous ether is a liquid of very complex composition.
Besides the ethyl nitrite, alcohol, and water which may be regarded as
its normal constituents, it usually contains aldehyde, and probably
paraldehyde and ethyl acetate and nitrate. After keeping, sensible
quantities of free nitrous and acetic acids are developed, and other
changes occur. In addition to the foregoing constituents, the occur-
rence of which is generally admitted, according to Eykman (Pharm.
Jour., [3] xiii. 63) spirit of nitrous ether is also liable to contain ethyl
oxide (ether); ethyl formate and oxalate; cyanogen compounds;
glyoxal ; glyoxalic, oxalic, malic, and saccharic acids ; &C. 1
The composition of spirit of nitrous ether varies very considerably,
and but few analyses have been made showing the proportions even of
the principal components (other than ethyl nitrite), and in these cases
the determinations have not been made by unexceptionable methods.
The following analyses by F. M. Rimmington 2 are the most complete
hitherto published :
1 To this formidable list, the author suggests the addition, as a possible constituent, of
nitro-ethane (C 2 H 5 N0 2 = CHs.HaC.NOa), a body isomeric with ethyl nitrite, but having a
density of 1-058 and boiling at 111 to 113 C.
Although the ethyl nitrite is the most characteristic constituent of spirit of nitrous
ether, and all the processes of preparation and tests of quality aim at obtaining a product
containing it in quantity, it is supposed by some that the nitrite of ethyl is not the only
constituent of value in spirit of nitrous ether. There appears to be little foundation for
this view. There are even those who contend that nitrous ether is not an essential con-
stituent of the L.P. preparation, on the ground that it may be so made as to be nearly
destitute of nitrous or nitric compounds. Such a product appears to bear the same relation
to a well-made preparation that diseased milk does to the milk from a healthy cow.
2 Pharm. Jour., [3] x. 41. In these analyses the ethyl nitrite is probably considerably
ESTERS.
195
Ethyl
Nitrite.
Nitrous
Acid.
Acetic
Acid.
Alde-
hyde.
Alcohol.
Water.
1. Agreeing with B.P. tests, .
1-69
0-59
0-47
119
88-10
7-96
2.
1-72
0'56
0-50
1'19
88-10
7-93
3. Commercial u Best, " . . .
0'75
0-29
016
0-75
87-50
10-55
4.
0-17
0-27
0-03
0-21
85-20
14-12
5. ,, ,, ...
o-io
0-69
0-18
0"26
82-60
16-17
6. ,, ., ...
0-07
0:68
0-16
(TOO
83-60
15-49
The following analyses are by P. MacEwan. 1 Being all made by
the same method, they are interesting as showing the increase in the
proportion of aldehyde and free acids by keeping, but some of the
figures have probably more a relative than an absolute value :
Ethyl Nitrite.
Nitrous Acid.
Acetic Acid.
Aldehyde.
1. B.P. Spirit, old sample, . .
0-87
0-47
1-20
0-80
2. B.P. One week old, . . .
3-54
0-22
0-21
0-85
Two weeks old, . . .
0-26
0-25
0-95
Three weeks old, . .
3-14
0-27
0-35
,
3. B.F. Two days old
2-01
.
.
0-80
Four days old, . . .
0-24
0-22
1-14
Seven days old, . . .
1-24
0-32
0-25
2-00
4. B.P. One month old, . . .
1-93
0-24
0-41
1-67
5. L.P. Spirit, four months old,
3-53
0-16
0-29
1-50
6 - ii n
1-64
0-35
0-49
1-43
' ?1 ? ? 7
0-22
0-19
0-25
0-20
The tendency of spirit of nitrous ether and kindred preparations to
undergo gradual deterioration with destruction of the nitrous ether is
a point of great practical importance. The exact conditions which
facilitate or retard the change are not thoroughly understood, but it is
established beyond doubt that tne presence of excess of water greatly
favors the destruction of the nitrous ether. Hence adulteration of
understated, at least in the case of the first two samples. In making the analysis, the
nitrites were reduced by a copper-zinc couple, and the resultant ammonia distilled off and
titrated with standard acid. The free acids were determined by evaporating 10 c.c. with
potassium carbonate, and separating the acetate and nitrite in the residue by means of
alcohol (making an allowance of 0-021 grm. for KN(>2 dissolved in 10 c.c. of alcohol). The
aldehyde was determined by treating the sample with 10 c.c. of hydrogen peroxide, and
noting the increase in the acidity. The alcohol was deduced from the density of the
sample, and the water estimated by difference.
1 Pharm. Jour., [3] xiv. 817. In these analyses, Eykman's method (measurement of
nitric oxide, page 200), was employed for estimating the ethyl nitrite. The free acids were
ascertained by titrating in succession with methyl-orange and phenol-phthalei'n as indica-
tors, and the aldehyde was estimated by Thresh's coloritnetric method.
196 ESTERS.
sweet spirit of nitre, &c., with water, a practice which is very common,
not only dilutes the preparation, but greatly enhances the tendency of
the nitrous ether to undergo decomposition. The author proved, by
direct experiment, that a sample of spirit of nitrous ether kept per-
fectly well for very many months when undiluted, but the same sample
when mixed with one-third of its measure of water contained no nitrous
ether whatever after an interval of four months. In these experiments
the samples were kept in well-closed bottles, but of course imperfect
closing of the bottle, or exposure to light or to excessive temperature,
will be certain to cause loss of so volatile a substance as is the nitrite
of ethyl. 1 On the other hand, a solution of pure nitrous ether in
absolute alcohol was found by the author to contain a considerable
1 The presence of water, even in moderate proportion, greatly increasing the tendency
to change, and the ordinary' spirit of nitrous ether being of uncertain strength and com-
position, Mr John Williams has proposed to substitute for it a solution of pure ethyl
nitrite in nine or nineteen times its weight of absolute alcohol. Such a preparation
appears to be remarkably permanent, and if rectified spirit were substituted for the
absolute alcohol the solution would still be very stable, but unfortunately these preparations
are not found to have the flavor of ordinary spirit of nitrous ether, though the difference
may have been largely due to greater concentration of the solution. Similarly, Mr
Williams experimented with aldehyde, the flavor of which was highly objectionable, and
with a mixture of aldehyde and ethyl nitrite dissolved in alcohol, and has recently
suggested that sweet spirit of nitre may contain the polymer of aldehyde known as
paraldehyde, which it closely resembles in flavor. Paraldehyde, however, is more sedative
in effect than diuretic, like sweet spirit of nitre, so that the strong probability is that the
therapeutic value of the preparation really lies in the ethyl nitrite, and possibly in the
nitrous acid or other nitrous compounds which may be present. This view is strongly
endorsed by Professor Matthew Hay, who writes " With regard to the sweet spirit of
nitre my opinion is that its most active ingredient ought to be the nitrite of ethyl. The
nitrite is very active even in very small quantity, and I believe that if a preparation
could be obtained containing a constant proportion of nitrite of ethyl, it would be a great
gain to practical pharmacy and to therapeutists^. The unreliability of the common forms
of it has, I believe, led largely in recent years to its disuse. Murrell states that nitro-
glycerine is powerfully diuretic, and I have shown thatnitro-glycerine is decomposed into
nitrite in blood, hence its physiological action hence diuresis." The subject has been
further investigated by Dr D. J. Leech (Practitioner, October 1883), who writes to the
author : " I cannot agree with the contention of the drug trade that the medicinal value
of the drug is not connected with the nitrous ether it contains." " After trying the
effects of the various individual substances which spirit of nitrous ether contains, I
can come to no other conclusion than that the nitrous ether is the chief, if not the only,
active ingredient." "We have carefully analysed in our pharmaceutical laboratory
(Owens College, Manchester) samples of spirit of nitrous ether prepared in various ways,
and although we found traces of many other products, such as nitric ether, aldehyde,
paraldehyde, &c., still of none of these is there sufficient to act medicinally."
Professor J. Attfield, again, has expressed his views in the following words (Pharm.
Jour., [3] viii. 454) : " He did not disparage the use of so ancient and excellent a medi-
cine when properly prepared. At the same time it was well known that many medical
ESTERS. 197
proportion of ethyl nitrite, and mere traces of free acid, after being
kept for fully seven years.
ANALYSIS OF SPIRIT OF NITROUS ETHER.
The assay of spirit of nitrous ether is somewhat difficult, on account
of the complex character of the preparation.' 1 Of the B.P. tests
(page 193) the density, behavior with sodium bicarbonate, and reaction
with ferrous sulphate in presence of free acid are serviceable ; but the
test with solution of calcium chloride is worthless and absolutely mis-
leading.
The following methods are the most satisfactory of the many which
have been devised for the examination of commercial spirit of nitrous
ether :
Water can be estimated with sufficient accuracy by taking the
density of the sample. The B.P. spirit has a density of O845, but a
slightly higher density may be tolerated. If, however, the specific
gravity of the sample exceed 0'853, the presence of an excessive pro-
portion of water may be considered proved. Commercial samples of
sweet spirit of nitre are sometimes adulterated so largely with water
as to bring the density to 0'910 or even higher, 2 an inferior spirit of
0'900 sp. gr. being sold wholesale. A density of 0*845 corresponds,
according to the alcohol tables on page 93 et seq., to a content of 81*7
men had considered that sweet spirit of nitre was altogether valueless. The reason was,
doubtless, that some samples of the article sent into pharmacy for the use of medical
practitioners had been little else than spirit of wine." " He himself was under the
impression that the active principle of sweet spirit of nitre was the nitrite of ethyl, and
he was led to that conclusion mainly by the researches of Dr. Richardson, who had
experimented largely upon the nitrites."
i The original edition of the British Pharmacopoeia of 1867 stated that spirit of nitrous
ether, on agitation with twice its measure of a saturated solution of calcium chloride,
yielded " 2 per cent, of its original volume in the form of nitrous ether," but Dr Redwood
has since deprecated this statement (Pharm. Jour., [3] viii. 377, 455), and, on his recom-
mendation, the reprints of the British Pharmacopoeia of 1867 state that 2 per cent, of
"an ethereal layer" will rise, which according to Dr Redwood represents 10 per cent, of
ether in the original liquid. But it has been found that the ethereal layer is by no means
pure nitrite of ethyl, containing as it does a proportion of that body variously estimated,
but admittedly not exceeding 50 per cent. Besides the uncertainty due to this cause, no
ethereal layer whatever can be obtained from samples slightly poorer in ethyl nitrite than
the newly made B.P. spirit, so that the test is worthless even as a rough means of
assaying commercial spirit of nitrous ether. It may be applied to samples giving no
indication in their original condition, by saturating 100 c.c. of the liquid with dry calcium
chloride, distilling off 20 c.c. at a gentle heat, and treating the distillate with twice its
measure of a saturated solution of calcium chloride.
2 The author recently examined a sample having a density of - 940, which was very
naturally devoid of nitrous ether.
198 ESTERS.
per cent, by weight of absolute alcohol, or 152'4 per cent, by volume
of proof spirit. The extent to which- a sample has been diluted with
water may be found by multiplying the percentage of proof spirit (as
found by the table) by the factor -656 (= Jjy^), when the product
will be the percentage by volume of spirit of nitrous ether of B.P.
density contained in the sample. To find the percentage by measure
of spirit of '850 density originally present, the percentage of proof
spirit in the sample should be multiplied by '673 (==TyW) g
The nitrous ether, though denser than alcohol, is present in too
small a proportion to affect sensibly the estimation of water from the
density. The addition of water to sweet spirit of nitre is a highly rep-
rehensible practice, for it not only reduces the immediate strength and
medicinal value of the preparation, but also renders it far more liable
to change, owing to the tendency of ethyl nitrite to undergo decompo-
sition in presence of water.
Free Acid will be indicated by the reaction with litmus paper, and
by the effervescence occasioned on adding bicarbonate of sodium to the
sample. The presence of notable proportions of free acid renders
spirit of nitrous ether incompatible with potassium iodide, from which
it liberates iodine. 1 The proportion of acid may be ascertained by
titration with standard alkali, but, as some samples of sweet spirit of
nitre contain both free acetic and free nitrous acid, it is sometimes of
interest to determine them separately, which is done by P. MacEwan
in the following manner: 10 c.c. measure of the sample is placed in
a flask in which a drop of phenol-phthalein solution has been previ-
ously put, and two or three drops of methyl-orange solution are next
added. A porcelain slab, spotted with drops of methyl-orange solu-
tion, is arranged in readiness. A semi-normal solution of caustic soda
( = 20 grm. NaHO per litre) is then rapidly added to the contents of
the flask, and as soon as the red color begins to' fade, a drop of the
liquid is removed by a glass rod and brought in contact with a spot
of the methyl-orange on the plate. If the spot assume a pink tint,
the nitrous acid is not quite neutralised, in which case the addition of
the alkali solution is continued, until, on re-testing, a spot of methyl-
orange is rendered only faintly pink. The volume of standard alkali
1 A sample of spirit of nitrous ether, which gave no perceptible effervescence with
sodium bicarbonate, liberated a considerable amount of iodine from potassium iodide.
After being agitated with sodium bicarbonate and left in contact with the salt for twenty-
four hours, a notable quantity of iodine was still liberated and nitric oxide gas evolved ;
but when neutral sodium carbonate was employed instead of the acid carbonate, mere
traces of iodine and gas were liberated on addition of potassium iodide.
ESTERS. 199
used is then noted, and the titration continued until the pink tint pro-
duced by the phenol-phthalein denotes alkalinity. Each c.c. of semi-
normal alkali first used represents 0'0235 grm. of nitrous acid (HNO 2 ),
while each c.c. of the additional alkali requisite to produce the phenol-
phthalein reaction corresponds to*0300 grm. of acetic acid (HC 2 H 3 O 2 ).
The process is approximate only.
Aldehyde will be indicated by the brown coloration produced on
heating the sample with caustic potash. A sample free from an exces-
sive proportion of aldehyde, when treated at the ordinary temperature
with half its volume of a dilute solution of caustic potash, assumes a
yellow color, which gradually deepens but does not become brown in
twelve hours.
For the determination of aldehyde, F. Rimmington treats the sample
with hydrogen peroxide, and ascertains by titration the amount of
(acetic) acid over that previously present. A preferable method is to
treat 5 or 10 c.c. of the spirit by Thresh's colorimetric method, as
described under aldehyde.
The proportion of aldehyde present in preparations made by the old
processes is much larger than in the " spirit of nitrous ether, B.P."
Ethyl Chloride and other chlorinated bodies may be detected by
igniting a little of the sample in a porcelain basin, and holding a
beaker moistened with nitrate of silver solution over the flame. If
chloride of silver be formed, the sample may be evaporated with pure
caustic soda and the chloride in the residue determined.
Ethyl Nitrite may be detected by the brown coloration produced by
adding ferrous sulphate to an acidulated solution of the sample of
spirit. Of various ways of making the test, the author has found the
following mode of operating to be the most delicate and reliable : 10
c.c. of the spirit is mixed with 5 c.c. of a strong aqueous solution of
ferrous sulphate. Pure, concentrated sulphuric acid should next be
poured down the side of the test-tube in such a manner as to form a
distinct stratum under the spirituous mixture. A brown zone will
thereupon be produced at the junction of the two layers, the intensity
of which is an indication of the strength of the sample in nitrous ether.
With good samples, the coloration is increased and extended by caus-
ing the layers to become partially mixed, but with inferior specimens
the brown color is more or less destroyed by such treatment. 1
1 Some samples of spirit of nitrous ether give a brown coloration with the ferrous solu-
tion alone, a reaction which might be attributed to free nitrous acid. A sample which
had been thoroughly agitated with neutral sodium carbonate gave no immediate reaction
with ferrous sulphate solution, but in the course of a few minutes a strong brown color was
developed.
200 ESTERS.
W. H. Symons proposes to obtain rough quantitative results by dis-
solving 1 part of ferrous sulphate in 5 of dilute sulphuric acid, and
adding to 10 c.c. of this solution 1 c.c. of the sample to be tested.
The coloration produced is compared with that yielded by a standard
specimen or a solution of a nitrite.
The process of J. F. Eykman for assaying spirit of nitrous ether is
practically a quantitative application of the iron reaction, but, instead
of relying on the depth of the brown coloration, the nitric oxide gas
evolved is collected and measured. Eykman's process has given excel-
lent results in the hands of P. MacEwan and F. S. Dymond. 1 Their
reports have been confirmed in the main by an extensive experience
of its capabilities in the writer's own laboratory, where the accuracy
of the process has been fully verified when a known quantity of pure
sodium nitrite is employed. With solutions of ethyl nitrite several
sources of error exist, which tend to cause the method to give results
somewhat below the truth. The following is the mode of operating
the author has found preferable, and it must be strictly followed to
ensure results having the nearest approach to accuracy :
To a small, round-bottomed, tubulated flask (A, fig. 11) is adapted a
well-fitting rubber stopper, through which passes a narrow glass tube
B, which extends nearly to the bottom of the flask, the end being
drawn out to a point and turned up, so as to prevent any gas from
entering. 2 Outside the flask the tube is bent over and connected by
an india-rubber joint with a narrow vertical tube C, the lower end of
which is drawn out to a point and arranged to reach nearly to the
bottom of a conical glass D. The side-tube E of the flask is connected
by a few inches of india-rubber F with the stopper of a Lunge's nitro-
meter G. The nitrometer is filled with solution of soda of about 1*10
specific gravity, which should be previously freed from dissolved oxy-
gen by agitating it with a little ferrous sulphate, and allowing the
precipitated oxide of iron to subside. A solution of ferrous sulphate
is prepared by dissolving 100 grm. of the powdered crystallised salt
in 500 c.c. of water, and adding 0*5 c.c. of strong sulphuric acid. A
dilute sulphuric acid is prepared by diluting one volume of the strong
acid (free from nitrous compounds) with three measures of water.
In commencing an experiment, about 30 c.c. of the iron solution
should be poured into the flask, and the india-rubber cork well wetted
1 D. B. Dott has confirmed the general accuracy of the process, and has fouml the
results very constant, even when the conditions of the experiment are varied.
8 The side-tube of the flask should be situated only just below the rubber-stopper, and
not strictly as represented in the figure.
ESTERS.
201
and adjusted firmly in the neck. The flask is then connected with the
nitrometer, the tap of the latter being closed and a small quantity of
soda solution being contained in the cup. The tube C is immersed in
the solution of iron contained in the glass D, and the screw-clip at H
is open. The flask is then warmed to expel some of the air through
C, when the source of heat is removed, and about 30 c.c. of iron solu-
tion is allowed to enter the flask, when the clip at H is firmly closed.
The contents of the flask are then heated to boiling, and when the
india-rubber at F shows signs of internal pressure, the tap G is opened,
and the air from the flask allowed to bubble out through the soda con-
tained in the cup of the nitrometer. When the air is thoroughly
expelled the tap G is closed, the source of heat is removed, and the
H
FIG. 11.
contents of the flask allowed to become quite cool. From 5 to 10 c.c.
of the sample (according to its strength) is then placed in the conical
glass, and diluted with 10 to 20 c.c. of water containing 1 or 2 grm.
of common salt. The clip F is then cautiously opened, and the vacuous
liquid allowed to flow into the flask until the orifice of the tube C is
only just covered. A little iron solution is then poured into the conical
glass together with 5 c.c. of the dilute sulphuric acid, and this in its
turn allowed to enter the flask. This is repeated until the liquid in
the glass and tube is no longer colored brown, care being taken not to
allow any air to pass into the flask. The clip at H is then perma-
nently closed and the contents of the flask heated to boiling. As soon
as the india-rubber connection with the nitrometer shows signs of pres-
202 ESTERS.
sure, the tap G is turned so as to open communication between the
flask and the graduated tube of the nitrometer K, when the nitric
oxide gas produced by the reaction passes into K and is there collected.
The process is stopped as soon as the contents of the flask are no longer
brown, the tap G being closed and the clip at H simultaneously
opened, when the liquid in the flask is forced back into A and the
apparatus is in order for another experiment. 1 After standing half an
hour to acquire the temperature of the air, the volume of gas in the
nitrometer is observed, care being previously taken to adjust the level
of the liquid in K with that in the open limb L. After reading off
the volume of gas it is allowed to escape into the cup, when the nitrom-
eter is ready to receive the gas evolved in another experiment.
The following is the reaction occurring in the foregoing process :
2C 2 H 5 NO 2 + 2FeS0 4 -j- H 2 SO 4 = Fe 2 (SO 4 ) 3 + 2C 2 H 6 O + 2NO.
Thus, 75 parts by weight of ethyl nitrite evolve 30 of nitric oxide gas.
From the volume of nitric oxide obtained, the percentage of ethyl
nitrite in the sample employed can be calculated by the following
formula, in which v represents the number of cubic centimetres of
gas obtained ; p, the barometric pressure in millimetres; e, the tension
of aqueous vapor at the temperature at which the gas is measured ;
d, the density of the sample (water = 1) ; n, the number of c.c. em-
ployed ; and t the temperature in centigrade degrees:
ENO 2 == v X P ~ e X 0-1207.
d X n 273 + t
When strictly accurate results are not required, the corrections for
1 Although the manipulation involved in the process is difficult to describe, it is very
simple in practice, and when everything is ready the whole operation does not occupy
more than fifteen minutes. Care must be taken to open and close the tap and clip at the
right moment, and to avoid the introduction of any air by leakage or faulty manipulation.
In the original apparatus employed by Eykman the gas is collected in a graduated tube
arranged over a glass basin containing soda solution, but the use of a nitrometer furnished
with a three-way tap is a decided improvement, in the opinion of the author, though
many operators may prefer to adhere to the original arrangement. According to Eyk-
inan's original instructions the sample is to be mixed with the acid and ferrous sulphate
solution before introducing it into the flask, but this procedure seems liable to occasion
loss of gas from strong samples. If the liquid in the flask be not tolerably cool when the
solution of the ether is allowed to enter, some of the ethyl nitrite may be volatilised unde-
composed. The instruction to add some sodium chloride is not in accordance with the
practice of Eykman, but it adds materially to the accuracy of the process, in the experi-
ence of the writer. It is important to conclude the operation as soon as the contents of
the flask no longer have a brown color, and the steam has driven the nitric oxide into the
nitrometer-tube. In the case of strong samples the measure of reagents employed should
be increased.
ESTERS. 203
pressure, temperature, and tension of aqueous vapor may be omitted,
and the calculation much simplified. Thus, if the volume of 0*030
grm. of nitric oxide (representing 0*075 grm. of C 2 H 3 NO 2 ) under the
ordinary conditions of pressure and temperature be taken at 23*55
c.c., then
volume of gas in c.c. X 0'3184
= percentage by weight of C 2 H 5 NO 2 .
measure of sample in c.c. X density of sample
Eykman's process has a tendency to give results with ethyl nitrite
sensibly below the truth, partly, no doubt, from incomplete reaction,
but also owing to the solubility of nitric oxide in aqueous liquids.
The loss from the latter cause is reduced to a minimum if a nitrom-
eter be employed as recommended, instead of the gas being caused
to bubble up through a solution of soda. Probably still closer results
might be obtained by saturating the soda solution with common salt.
Instead of reducing the ethyl nitrite by means of ferrous sulphate,
a solution of potassium iodide may be employed for the purpose. In
this case the reaction takes place at the ordinary temperature, and the
manipulation is greatly simplified. A nitrometer should be filled with
strong brine. 5 c.c. of the sample to be tested should then be placed
in the cup of the nitrometer, and allowed to enter through the tap,
taking care that no air gets in at the same time. 5 c.c. of a strong
solution of potassium iodide is next allowed to enter, and this is fol-
lowed by about 5 c.c. of dilute sulphuric acid. Effervescence imme-
diately ensues, and if the tube be vigorously agitated at intervals, the
reaction is complete in five to ten minutes, when the level of the liquid
in the two limbs of the nitrometer is adjusted, and the volume of nitric
oxide gas read off.
If the volume of gas evolved be small, another 5 c.c. of the sample
should be let into the nitrometer, and the agitation repeated. The
calculation is the same as in Eykman's process, the reaction being
(C 2 H 5 )N0 2 + KI + H 2 SO 4 = (C 2 H 5 )OH + KHSO 4 + 1 + NO. 1 With
most specimens of sweet spirit of nitre, a considerable amount of nitric
oxide is produced (and iodine liberated) before adding the acid, the re-
1 The method described in the test has not been published up to the time of going to
press. It suggested itself to the author as an improvement on the process of D. B. Dott
(see page 204). It has been proved to give very good results with pure sodium nitrite
(prepared from silver nitrite) employed in known amount. The results with spirit of
nitrous ether are somewhat higher than those given by Eykman's method, the difference
being least when sodium chloride is employed in the latter process and time given for the
ferrous solution to react thoroughly on the solution of ethyl nitrite. The results by the
iodide method are almost certainly more accurate than those by Eykman's process.
204
ESTERS.
action probably depending on the presence of free acid in the sample
(see footnote on page 198j. The results obtained in the nitrometer are
remarkably constant, and the method furnishes a very easy means of
assaying sweet spirit of nitre with considerable accuracy. 1
Volume of
NO from 5 c.c.
Weight of
NO from 5 c.c.
C 2 H 5 N0 2
per cent.
1. 25# Solution in Absolute Alcohol (two
months old)
c.c.
29'0 (fromO'5c c.)
milligrammes.
923-6
22-02
2. Spt. Nitrous Ether B.P. (two months
old)
39-4
50'4
2-98
3. Spt. Nitrous Ether, B.P. (age un-
known),
27'0
34'6
2'03
4. "Spt. JEther Nit. -850" (new), ....
5. "Sp. ^Ether Nit. Dulc. -900" (new), .
14-7
22-0
18-8
28-2
1-10
1-56
No. 1 was prepared by Mr. J. Williams by dissolving 1 part by weight of carefully purified
ethyl nitrite in 3 parts by weight of absolute alcohol. The density was 0'8387.
D. B. Dott (Pharm. Jour., [3] xv. 492) has proposed to determine
ethyl nitrite by treating the liquid with an acidulated solution of
potassium iodide, and ascertaining the iodine set free by titration with
a standard solution of sodium thiosulphate. If the treatment with
potassium iodide be effected in an open basin in presence of air,
the amount of nitrite found is liable to be seriously in error, but if air
be excluded Dott's method gives fair approximate results, somewhat
in excess of the truth. The process can be advantageously employed
on the solution which has already been decomposed with potassium
iodide in the nitrometer. The nitric oxide is allowed to escape into
the air, and the brown liquid is washed into a basin and at once titrated
with decinorrnal thiosulphate. 1 c.c. of this solution '(containing 15*8
grm. of Na 2 S 2 O 3 per litre) will react with the iodine liberated by *0075
grm. of ethyl nitrite. 2
1 The process has the advantage of great ease and rapidity, and actually measures the
nitrous compounds present in the sample, instead of leaving their proportion to be inferred
from a more or less complex reaction, such as the reduction of permanganate, &e. The
following results were obtained by the author from five typical samples. No correction
was made for pressure or solubility, the figures representing the actual volumes of gas
measured at about 15 C.
2 The results obtained in this manner show a constant difference of about 0'005 grm.
of nitric oxide above that corresponding to the volume of gas liberated in the nitrometer,
the true amount doubtless lying between the two. The difference is most probably due to
a small amount of nitric oxide remaining dissolved in the aqueous liquid, which causes the
volume of gas to be slightly low, and becoming oxidised to nitrous acid during the subse-
quent titration liberates a small additional amount of iodine. This source of error
becomes very serious if the bulk of the nitric oxide be not previously removed as is done
in the nitrometer. Thus, if an attempt be made to determine ethyl nitrite by adding the
sample of spirit to an acidulated solution of potassium iodide contained in an open basin,
and immediately titrating with standard thiosulphate, the first result is too low, owing to
ESTERS. 205
A useful approximate estimation of the nitrous compounds in spirit
of nitrous ether may be made by comparing the depth of the color
developed on adding an acidulated solution of potassium iodide to a
known measure of the sample with that of a standard solution of iodine
in potassium iodide. Five or ten drops of the sample should be placed
in a narrow test-tube, a little water added, and then one or two drops
of olive oil, to prevent access of air. An acidulated solution of potas-
sium iodide is then added, and, after five or ten minutes, the color of the
liquid is compared with a standard solution of iodine in the usual way.
Various other methods of assaying spirit of nitrous ether have been
devised, having for their principle the determination of the real nitrite
present. Some of these processes ignore the presence of aldehyde, and
others are unsatisfactory for other reasons. Certain of them give fair
results in the case of samples of good quality, but are most erratic in
their indications when employed for the assay of inferior specimens,
and especially those prepared by the London Pharmacopoeia process.
Muter's process is interesting from the fact that it has been recently
employed in the Inland Revenue Laboratory for estimating the nitrous
ether contained in commercial sweet spirit of nitre, all the oxidisable
matters indicated by the reduction of the permanganate being calcu-
lated to their equivalent of ethyl nitrite and reported as " nitrous
ether." l The following are the details of the process as described by
Muter in his original paper (Analyst, iv. 125), where he distinctly points
out that the results include the reduction due to aldehyde and other
oxidisable bodies which may be present, while he has since given the
preference to the more recent and accurate method of Eykman. 10
c.c. of the sample should be digested with 2 grm. of potassium hydrate
and 10 c.c. of alcohol in a small strong flask, closed by a cork through
which passes a bent delivery-tube dipping under the surface of mer-
cury, so that a slight pressure may be maintained on heating the flask.
the nitrous ether requiring a sensible time for its decomposition. In a few minutes this
error is more than compensated by the additional amount of iodine set free by the nitrous
acid produced by the action of the air on the nitric oxide formed in the primary reaction,
and this liberation of iodine goes on so rapidly that the stirring necessary to mix the
standard solution with the liquid in the basin causes the liquid again to acquire a yellow
tinge, which rapidly deepens. If the liquid in the basin be allowed to stand for some
time exposed to the air before titrating, the iodine set free often amounts to fully twice
the quantity primarily liberated by reaction with the ethyl nitrite present.
i In this connection it may be noted that a sample of " sweet spirit of nitre," which was
found on independent examination by four different chemists to give but faint indications
of ethyl nitrite or other nitrous compounds by the ferrous sulphate color-test, was, on
reference b'eing made to the chemists at Somerset House, certified to contain 1 '3 per cent,
of nitrous ether.
206 ESTERS.
After digestion for about an hour, with frequent agitation, water is
added, and the contents of the flask evaporated in a basin till the
smell of alcohol is no longer perceptible. The residual liquid is ren-
dered just neutral with sulphuric acid, and filtered into a flask con-
taining 75 c.c. of decinorrnal permanganate (3'162 grm. KMnO 4 per
litre) previously diluted to 200 c.c. with water and acidulated with 20 c.c.
of dilute sulphuric acid (1 in 3). The flask is corked and allowed to
stand for half an hour, when excess of a saturated solution of potas-
sium iodide is added, and the liberated iodine titrated with decinormal
thiosulphate. The volume of this solution required, deducted from
75, gives the number of c.c. of permanganate decolorised by 10 c.c. of
the sample. 1 c.c. of decinormal permanganate oxidises 0'00375 grm.
of ethyl nitrite.
By this process, Muter found oxidisable matters equivalent to 2*85
to 3*05 per cent, by weight of ethyl nitrite in samples of spirit of
nitrous ether answering strictly to the B.P. tests. With such prepara-
tions the method is probably capable of yielding useful comparative
results, but in specimens containing much aldehyde, as the preparation
of the London Pharmacopoeia of 1851, the indications are completely
worthless, and should on no account be expressed in terms of nitrous
ether.
The official process of the United States Pharmacopeia for the
estimation of nitrous ether is also based on oxidation, the volume of
permanganate said to be decolorised by a spirit of proper strength
corresponding to the presence of fully 4 per cent, of nominal ethyl
nitrite in the American preparation. 1
1 S. P. Sharpies of Boston, Mass., has communicated to the author a modification of the
U. S. Pharmacopeia process by which an assay of spirit of nitrous ether can be made in
about an hour. He does not claim that the process accurately determines the ethyl nitrite,
but that it gives constant results with the same sample, which some other of the published
methods do not. 10 grm. of the sample are treated with 50 grm. of strong alcoholic
potash, and the mixture boiled vigorously for half an hour in a flask furnished with an
inverted condenser well supplied with cold water. The contents of the flask are then
poured into a porcelain capsule and diluted with 50 .c.c. of water, and the liquid kept on
the water-bath until the alcohol has evaporated. The solution is then acidified with dilute
sulphuric acid, and titrated with decinormal permanganate, the end of the reaction being
reached when the color produced by 1 c.c. persists for a minute. Professor Sharpies states
that during the winter of 1883-4 he was unable to meet with any spirit of nitrous ether
which answered the requirements of the U.S. Pharmacopeia, the average of the apparent
ethyl nitrite being not much over 2 per cent. He states that in America there are sold
various so-called " concentrated ethers," which are said to contain 90 per cent, and
upwards of real ethyl nitrite, but a very small proportion of these distilled at the boiling
point of real nitrous ether, and the best of them did not contain more than 60 per cent, of
ethyl nitrite, while some contained less than 20 per cent.
ESTERS. 207
The current revision of the United States Pharmacopeia, official since Janu-
ary, 1894, prescribes the following tests for spirit of nitrous ether :
If a test-tube be half filled with the spirit and put into a water-bath heated
to 65 C. (149 F.) until it has acquired this temperature, the spirit should boil
distinctly upon the addition of a few small pieces of broken glass.
If 10 c.c. of the spirit be mixed with 10 c.c. of potassium hydroxide of 3 per
cent, strength, the mixture will assume a yellow color which should not turn
decidedly brown within twelve hours (limit of aldehyde).
If 5 c.c. of recently prepared spirit of nitrous ether be introduced into a
nitrometer and followed first by 10 c.c. of normal potassium iodide and then by
10 c.c. of normal sulphuric acid, the volume of nitrogen dioxide generated at
the ordinary in-door temperature (about 25 C. or 77 F.) should not be less than
55 c.c. (corresponding to about 4 per cent, of pure ethyl nitrite). L.
Eykman's and the permanganate processes of assaying spirit of
nitrous ether estimate the total nitrites present, and fail to distinguish
the ethyl nitrite from the free nitrous acid. As the latter has probably
the same therapeutic value as the former, this distinction is rarely
important. It may be made, when necessary, by multiplying the
free nitrous acid found by titration by 1-6 (= Jy) and subtracting the
product from the weight of total nitrites calculated as ethyl nitrite.
The difference is the true amount of ethyl nitrite. If preferred, the
correction may be made by adding some potassium or sodium bicar-
bonate to a definite quantity of the sample, evaporating to dryness at
100 C., dissolving the residue in water, and estimating the nitrite
from the nitric oxide evolved. By deducting the amount thus found,
which represents that originally present as free nitrous acid, from the
total, the real nitrous ether may be estimated.
The proportion of ethyl nitrite in spirit of nitrous ether B.P., as
deduced from the total nitrites, should not fall below 2J per cent, in a
fresh and well-made preparation. In some cases, and especially after
keeping, it may fall as low as 2 per cent., but this may be regarded as
the minimum limit in a reasonably good preparation. Spirit prepared
by the officially obsolete process of the London Pharmacopoeia (1851)
contains less nitrous ether than the B.P. preparation, and " sweet spirit
of nitre " is frequently met with in commerce containing little or no
nitrous ether. This is sometimes due to want of care in the distilla-
tion, or to the employment of too weak an alcohol, but it is more fre-
quently consequent upon adulteration of the manufactured article by
addition of water, with consequent decomposition of the nitrous
ether.
Methylated Spirit is said to be occasionally employed for the prepara-
tion of sweet spirit of nitre. The substitution may be detected by agi-
208 ESTERS.
tating 30 c.c. of the sample with 3 or 4 grm. of ignited potassium
carbonate, treating 15 c.c. of the decanted dehydrated spirit in a small
flask with 10 grm. of anhydrous calcium chloride, attaching a con-
denser, and heating the flask in boiling water till about 5 c.c. has
passed over or scarcely any further distillate can be obtained. The
operation proceeds slowly, but requires little attention and should be
carried out thoroughly. The contents of the flask are next treated
with 5 c.c. of water, and another 2 c.c. distilled. This second distil-
late is then oxidised by bichromate of potassium and sulphuric acid as
described on page 81, and the product tested with silver nitrate. If
the sample were free from methyl alcohol, the solution darkens, and
often assumes transiently a purple tinge, but continues quite translu-
cent ; and the test-tube, after being rinsed out and filled with water,
appears clean or nearly so. But if the sample contains only 1 per
cent, of methylic alcohol (=10 to 20 per cent, of methylated spirit),
the liquid turns first brown, then almost black and opaque, and a film
of silver, which is brown by transmitted light, is deposited on the tube.
When the sample is methylated to the extent of 3 or 4 per cent, the
film is sufficiently thick to form a brilliant mirror. To ensure accuracy
the observations should be made by daylight.
Ethyl Chloride. Hydrochloric ether. "Sweet spirit of salt."
C 2 H 5 C1.
Ethyl chloride is a fragrant, exceedingly volatile liquid, boiling at
12*2 C., and burning when ignited with a smoky green-edged flame,
producing fumes of hydrochloric acid. It is sparingly soluble in water,
but readily so in alcohol, neither solution giving any precipitate with
nitrate of silver. Its solution in an equal volume of alcohol is some-
times employed in medicine. The ether is prepared by distilling alco-
hol, sulphuric acid, and common salt together, or by passing dry
hydrochloric acid gas into absolute alcohol ; by adding chloride of
zinc to the alcohol, the whole of the latter may be converted into ethyl
chloride (Jour. Chem. Soc., xxvii. 636).
The last product is a crystalline substance identical with that pro-
duced by the action of chlorine on Dutch liquid. In the chlorination
of ethyl chloride the /S-series of isomers are obtained, and these are also
produced on a considerable scale in the manufacture of chloral. A
very variable mixture of the middle members of the series is an article
of commerce under the name of Liquor ancestheticus. Another similar
mixture, containing the less chlorinated bodies, is the jEiher ancesthct-
icus Aranii, boiling between 64 and 100 C. The JEther ancestheticus
ESTERS.
209
Wiggers contains the more highly chlorinated products, and boils
between 100 and 140 C.
By the continued action of chlorine on ethyl chloride, a series of
substitution-products may be obtained, in which the hydrogen is more
or less completely replaced by chlorine. Some of these products are
identical with, and others merely isomeric with, similar bodies
obtained by other reactions. The following is a list of the products in
question :
Empirical
Formula.
Name.
Constitutional
Formula.
Boiling
Point.
C.
Specific
Gravity.
C 2 H 5 C1
CsH^lo
Ethyl chloride ; chlorethane,
f Ethylene Chloride ; a-Dichlorethane, . .
1 (Dutch liquid.)
(.Ethylidene Chloride; /3-Dichlorethane, .
( a-Trichlorethane
CHg.CHoCl
CH 2 C1.CH 2 C1
CHo.CHClo
CHC1 CHClo
12-2
84
60
115
0-921 at
1-256 at 12
1-1 74 at 17
1-422 at 17
CoHgClg
{ /3-Trichlorethane, . .
CHg.CCl,
75 '
1-372 at
CoHfCl 4
f a-Tetrachlorethane,
{ j3-Tetrachlorethane,
CHClo.CHCl 2
CHoCl.CClg
147
127-5
1-614 at
1-530 at 17
CHCk
Pentachlorethane, . .
CHC1 2 CC1 3
158
1-71 at
c;a 6
Hexachlorethane ; Carbon trichloride, .
CC1 3 .CC1 3
182
2-00
ETHYLIDENE CHLORIDE, CHLORINATED ETHYL CHLORIDE, or
/2-DiCHLOR-ETHANE, C 2 H 4 C1 2 = CH 3 .CHC1 2 , is now prepared in a pure
state by the action of chlorine on ethyl chloride, or by distilling alde-
hyde with phosphorus pentachloride. Ethylidene chloride possesses
valuable anaesthetic properties, appearing to occupy a position inter-
mediate between chloroform and ether, being safer than chloroform,
while a smaller quantity is required than of ether (Brit. Med. Jour.,
Dec. 18, 1880). It produces ansesthesia in dogs and rabbits in three
or four minutes, but there is no sign of failure of the heart's action.
In this respect it differs from chloroform and methylene dichloride,
both of which diminish the action of the heart. The isomer of chlor-
inated ethyl chloride, the dichloride of ethylene or Dutch liquid, pro-
duces severe convulsions when its vapor is inhaled. 1 Ethylidene
chloride is distinguished by its negative reaction with potassium,
whereas Dutch liquid is violently acted on, forming a porous mass and
evolving hydrogen and chlor-ethylene, C 2 H 3 C1, the latter being a gas
of alliaceous odor. The same gas is produced when Dutch liquid is
heated with alcoholic potash, while ethylidene chloride is unaffected
by the same reagent. The boiling point and density also distinguish
Dutch liquid from its isomer. From chloroform, ethylidene chloride
1 A similar difference is observable between the action of butyl chloride and that of its
isomer iso-butyl chloride.
14
210 ESTERS.
is distinguished by its density, boiling point, and negative reaction
with Hofmanu's test.
METHYL-CHLOROFORM or ^-TRICHLORETHANE, CH 3 .CC1 3 , and its
isomer CH 2 C1.CHC1 2 , appear likely to prove valuable as anaesthetics
(Brit. Med. Jour., Nov. 13, 1880).
Ethyl Bromide. 1 Hydrobromic ether. Brora-ethane. C 2 H 5 Br.
This ether has recently been employed in medicine as a substitute,
in certain cases, for chloroform. It boils at 40'7 C., and has a density
of 1*419. It burns with difficulty, giving a bright green but smokeless
flame, and forming fumes of hydrochloric acid. The boiling point and
smokeless flame distinguish it from ethyl chloride.
Ethyl bromide is liable to contain an admixture of ordinary ether,
which reduces the specific gravity. Some samples are contaminated
with an acrid impurity, of extremely unpleasant alliaceous odor, and
less volatile than pure ethyl bromide. Such specimens are unfit for
medicinal use.
Amyl Acetate. Pentyl acetate.
C 7 H U 2 = C 5 H n ,C 2 H 3 2 = ? O.
Amyl acetate is prepared by distilling amyl alcohol with an acetate
and sulphuric acid. When pure, it is a colorless liquid having an
exceedingly fragrant odor. It is insoluble in water, but soluble in all
proportions in ether, amyl alcohol, and ordinary alcohol. The last
solution constitutes the essence of jargonelle pear of commerce. Amyl
acetate boils at 137 C., and has a density of '8763 at 15 C.
Amyl acetate has recently been proposed as a suitable liquid to burn
in a standard lamp for photometric purposes.
Amyl acetate may be determined by the general method on page
183. From alcohol it may be separated by agitating the liquid with
an equal measure of saturated solution of chloride of calcium, which
dissolves the alcohol only.
Any admixture of amyl alcohol may be separated and determined
approximately by treating the sample in a graduated tube with a mix-
ture of equal volumes of glacial acetic acid and water.
This dissolves amyl alcohol, but leaves the amyl acetate insoluble
(together with any amyl valerate or pelargonate which may be
present). By first separating the ethyl alcohol by salt water, or petro-
1 On the preparation and characters of ethyl bromide, see Pharm. Jour., [3] x. 9, 962 ;
xi. 3.
ESTERS. 211
leum spirit, as described on page 169, this method may be applied
to the essence of jargonelle pear.
Amyl Nitrite. C 5 H U N0 2 = ^^3] } O.
Amyl nitrite is prepared by processes similar to those employed for
obtaining ethyl nitrite, amyl alcohol being substituted for spirit of
wine. To obtain a product fit for medicinal use, the amyl alcohol
should be carefully purified, and have a boiling point of 129 to 132
O. By passing nitrous acid gas (best prepared by the reaction of nitric
acid on arsenious oxide) into this alcohol, a very pure nitrite is obtained.
After washing the product with water and solution of carbonate of
sodium, the oily liquid is rectified, the fraction passing over between
90 and 100 C. being retained. By carefully refractionating the
distillate with a dephlegmator (page 32) a very pure product may
be obtained, but it must be again washed with sodium carbonate to
separate traces of acid produced by decomposition of the ether during
redistillation. 1
Pure amyl nitrite has a density of 0'877, and is said to boil con-
stantly at about 96 C., though on this point there are conflicting
statements (see Pharm. Jour., [3] ix. 899, and x. 231). It has a
yellowish color, penetrating apple-like odor, pungent aromatic taste,
and produces a very powerful effect on the system when its vapor is
inhaled. It burns, when ignited, with a fawn-colored smoky flame.
Amyl nitrite is insoluble in water, but soluble in alcohol in all pro-
portions. It also dissolves in amyl and methyl alcohols, in glacial
acetic acid, and is miscible in all proportions with ether, chloroform,
carbon disulphide, benzene, petroleum spirit, and oils.
In contact with the air, and apparently more readily under the
influence of light, amyl nitrite develops an acid reaction owing to
partial decomposition. Probably tljis change occurs more readily in
presence of moisture.
Concentrated sulphuric acid attacks amyl nitrite with great energy,
red fumes being evolved, and a black, foul-smelling liquid formed.
Occasionally the mixture inflames.
A characteristic test for amyl nitrite is the formation of potassium
valerate when the liquid is dropped on fusing caustic potash. When
1 Amyl nitrite is said to give an orange-yellow vapor, but this phenomenon is due to the
liberation of nitrogen oxides. These are commonly assumed to be produced by decom-
position of the amyl nitrite, but E. T. Chapman states their production to be due to the
ready solubility of nitric oxide in amyl nitrite and its evolution on heating.
212
ESTERS.
gently warmed with excess of an aqueous solution of caustic potash,
potassium nitrite is formed, and a stratum of amyl alcohol floats on
the surface of the liquid. The change occurs more readily by using
alcoholic potash and subsequently adding water to cause the separation
of the amyl alcohol. On removing the aqueous liquid, acidulating it
with acetic acid, and adding potassium iodide, the nitrite will occasion
an abundant liberation of iodine.
When amyl nitrite is distilled slowly with methyl alcohol it is
completely decomposed, with formation of amyl alcohol and methyl
nitrite. Ethyl alcohol causes a less complete change, but it is evident
that a spirituous solution of amyl nitrite would be liable to undergo
decomposition.
COMMERCIAL AMYL NITRITE.
The amyl nitrite commonly met with is sometimes far from pure,
being liable to contain ethyl and amyl alcohols, amyl nitrate, butyl
and hexyl nitrites, nitropentane, valeric aldehyde, water, and other
impurities. If the amyl nitrite be prepared in the manner directed
on page 211, most of these bodies will be present in but very in-
significant proportion, but the contrary is the case if impure fusel
oil be substituted for carefully purified amyl alcohol, or if the latter
be converted by treatment with nitric acid instead of nitrous acid, as
is done by some manufacturers. 1
The following table shows the composition, densities, and boiling
points of the more important bodies likely to be present in impure
commercial nitrite of amyl :
Name.
Formula.
Specific Gravity.
Boiling Point C.
Nitropentane,
Amyl nitrite
C 5 H H (N0 2 )
C 6 H U O NO
877
'902 at C
150-160
96
C 5 H 1 f.O.NO 2
I'OOO at 7
148
Amyl alcohol
C-H,, O.H
814 at 15
128-131
Valeric aldehyde,
C 4 H 9 .CO.H
8057 at 17
92 '5
From these data it is evident that any valeric aldehyde in the crude
product will not be likely to be removed by fractional distillation,
though the other impurities can be more or less perfectly eliminated
by such treatment. Any admixture of valeric aldehyde or amyl
1 The use of nitric acid is certain to result in the formation of much valeric aldehyde
and more or less amyl nitrate, and the boiling point of the former of these bodies pre-
cludes the possibility of subsequently separating it by fractionating the crude product.
ESTERS. 213
alcohol will tend to reduce the specific gravity of the preparation,
while amyl nitrate acts in a contrary manner. As, however, the last
body has a comparatively high boiling point, a very instructive exami-
nation of commercial amyl nitrite can be made by distilling the sam-
ple with a dephlegmator, and noting the volumes, densities, and odors
of the fractions collected at different temperatures. A fairly pure
article, when fractionally distilled in this manner, will yield fully 80
per cent, of its original measure between 90 and 100 C., and should
leave no very considerable residue at the latter temperature. Some
specimens have been found to boil at temperatures ranging from 70
to 180, and occasionally to leave a residue at 220 C. 1 As a rule,
incomplete distillation at 100 is due chiefly to the. presence of amyl
alcohol, some of which may apparently be formed by partial
decomposition of the nitrite during distillation. Hence commercial
amyl nitrite of good quality may leave a residue of 5 to 10 per cent,
at 100.
A further examination of the nature of the 90 to 100 fraction
might be made by gently heating it for some time with methyl alcohol
in a flask furnished with an inverted condenser. On subsequent dis-
tillation, the fraction passing over between 90 and 100 will consist
mainly of the valeric aldehyde of the original sample, the amyl nitrite
having been converted into amyl alcohol and the very volatile methyl
nitrite.
Nitropentane, C 5 H n NO 2 , a body isomeric with amyl nitrite, appears
to be present in most commercial specimens of the latter, and some-
times in notable quantity. It may be detected by subjecting the
fraction distilling between 140 and 170 C. to the action of nascent
hydrogen, when amylamine, C 5 H n NH 2 , will be formed, and may be
recognised by the alkaline character of the distillate obtained on
boiling with caustic potash. Nitropentane may also be detected by
1 The data given in the text respecting the results of fractionating commercial amyl
nitrite are based chiefly on the observations of D. B. Dott and W. H. Greene (Pharm.
Jour., [3] ix. 172, 899 ; x. 231), but they are wholly at variance with the experience of
E. R. Squibb (Ephemeris, ii. 707 ; and Pharm. Jour., [3] xv. 485), who has fractionated
three typical specimens of American amyl nitrite. The purest of these samples gave
only 19-2 per cent, by measure of distillate at 95 C., and 45-6 at 100, a total of 90'2 per
cent, distillating below 128. The distillation was conducted in an ordinary retort with
the bulb of the thermometer immersed in the liquid, whereas in the experiments of Dott
and Greene, a flask with a dephlegmating tube was used. These differences in the mode
of manipulation would materially affect the proportions of the distillate obtained at a
particular temperature, but Squibb's results still point to the presence of much besides
amyl nitrite in the samples examined by him.
214 ESTERS.
dissolving the 140 to 170 fraction in solution of caustic potash,
adding a little sodium nitrite, and then dilute sulphuric acid very
cautiously, when a blood-red coloration will be produced, which disap-
pears when the solution becomes acid. The pentyl-nitrolic acid
produced may be extracted by agitation with ether. Probably the
test might be applied by warming the original sample with alcoholic
potash and cautiously adding dilute sulphuric acid.
Amyl Nitrate, C 5 H n NO 3 , if present, will be contained in the last
fractions obtained on distilling a sample of amyl nitrite. There is no
simple direct test for its presence, and D. B. Dott states that he has
failed to detect it in cases where he made a special search for it.
Valeric Aldehyde, C 5 H 10 O, may be detected by treating the sample
with three measures of a mixture in equal parts of strong ammonia and
absolute alcohol, then adding a few drops of silver nitrate solution
and warming gently, when a dark brown coloration will be produced
if valeric aldehyde be present.
Butyl and Hexyl Compounds may be detected by saponifying the
sample with caustic potash and examining the amyl alcohol layer for
butyl and hexyl alcohols by distillation, &c., as indicated on page 169.
Free Add may be detected and determined as in spirit of nitrous
ether after dissolving the sample in rectified spirit. The United
States and German Pharmacopeias agree that the free acid in 10 c.c.
of amyl nitrite should be wholly neutralised by agitation with 2 c.c.
of a mixture of 1 measure of ammonia of *950 sp. gr. and 9 parts of
water.
Hydroyen Cyanide, occasionally present as a by-product, may be
recognised by largely diluting the sample with alcohol and adding silver
nitrate, when white curdy silver cyanide will be precipitated.
The real Amyl Nitrite present in a commercial sample might probably
be determined by saponifying the sample with alcoholic potash and
treating the product by Eykman's or Dott's process (pages 200, 204)
Water increases the specific gravity of the preparation, and renders
it turbid when cooled to the melting point of ice. The presence of
water increases the tendency to decomposition.
Artificial Fruit Essences. The natural bouquets and flavors of
fruits have been found to depend, in many instances, on the presence
of small quantities of compound ethers, and these bodies are now pre-
pared on a very extensive scale for the imitation of the natural flavors.
The following is a list of the natural odors and flavors of fruits, &c.,
which can be almost exactly simulated by unmixed products of arti-
ficial origin :
ESTERS.
215
Natural Odor or Flavor.
Simple Artificial Body.
Bitter almond'; Peach.
Jargonelle Pear.
Apple.
Quince.
Pine-apple.
Melon.
Greengage.
Mulberry.
Gaultheria procumbens.
Spirea ulmaria.
Nitrobenzene ; Beuzoic'aldehyde.
Amyl acetate.
Amyl valerate.
Ethyl pelargonate.
Ethyl butyrate.
Ethyl sebate.
Ethyl 03iianthylate.
Ethyl suberate.
Methyl salicylate.
Salicylic aldehyde.
The following table, compiled from the recipes of J. H. Maisch,
shows the composition of various artificial fruit-essences and flavors
employed in practice. The numbers given indicate the number of
measures of the ethers, &c., to be added to each 100 measures of rectified
spirit. The chloroform and aldehyde can be omitted in most cases
without serious detriment to the flavor. To make the essences of
orange and lemon, 10 parts of the respective essential oils must be
employed in addition to the ingredients given in the table. In cases
in which acids are employed, the figures refer to volumes of a cold
saturated solution of the acid in alcohol of '830 specific gravity :
i
\
|j
j
JL
1
a
&
!H
^
|
8
f;
1
"3
a
c3
&
3S
2l
3
Q.
?
f
p
i
A
6
^
d5
-
<1
A
O
Chloroform
1
9
1
j
9
1
Aldehyde
1
?
1
1
9
B
2
Methyl salicylate
^
1
Ethyl nitrite
i
i
1
1
formate, . .
1
i
l
2
1
5
1
acetate, . .
5
B
B
1
5
5
6
S
5
10
butyrate,
5
4
5
1
...
...
..
2
io
5
1
10
5
5
5
pelargonate
j
1
10
1
1
1
5
1
sebate, . .
10
1
1
Amyl alcohol, .
...
...
...
...
..
2
2
...
..
j
2
10
butyrate
10
9
^
1
10
Tartaric acid
5
5
5
1
1
10
Oxalic acid
1
1
1
3
1
Benzoic acid
1
1
Glycerin,
3
3
2
4
10
4
2
3
8
4
B
10
5
Peach oil (ben-j
4
5
zoic aldehyde), J '
The color of strawberry and raspberry essences is communicated by
aniline-red mixed with a little caramel.
216 ALDEHYDES.
The true strength and flavoring powers of fruit-essences are best ascer-
tained by noting their taste and odor after copious dilution with water.
For examination of the ethers, the sample should be treated with dry
calcium chloride, which will unite with the alcohol, and the ethers
may generally be distilled off.
ALDEHYDES.
The aldehydes are a series of compounds intermediate in composition
between the alcohols and their corresponding acids. Those correspond-
ing to the monatomic alcohols of the ethyl series may be expressed by
the general formula
Aldehydes result from the treatment of the corresponding alcohols
by oxidising agents of moderate power, such as dilute nitric acid or
dilute chromic acid mixture used cautiously. They are also formed by
distilling a mixture of the sodium or calcium salt of the correspond-
ing acid with the similar compound of the acid next lowest in the
series, thus :
NaC 2 H 3 2 + NaCHO 2 = C 2 H 4 O + Na 2 CO 3
Sodium acetate. Sodium Acetaldehyde. Sodium
formate. carbonate.
Aldehydes may also be obtained by the action of nascent hydrogen
on the chlorides of the corresponding acid radicles, and by various
other reactions.
When pure, the aldehydes may apparently be preserved without
change, but the presence of mere traces of impurity (e.g., mineral
acids), tends to cause their gradual conversion into polymers or con-
densation-products, in the latter case one or more molecules of water
being simultaneously eliminated.
By oxidation, the aldehydes are very readily converted into the
corresponding acids. Hence, they are powerful reducing agents, pre-
cipitating metallic silver from the ammonio-nitrate, decolorising per-
manganate, &c.
By the action of nascent hydrogen (sodium amalgam), the aldehydes
are reduced to the corresponding alcohols, but the fixation of hydrogen
is often attended with condensation, and consequent co- formation of a
higher diatomic alcohol.
When heated with solutions of caustic alkalies, the aldehydes are
mostly converted into resinous bodies which are probably condensation-
ALDEHYDES. 217
products. By fusion with caustic potash, aldehydes are converted into
the potassium salts of the corresponding acids, hydrogen being simul-
taneously evolved ; in some cases this acts on another portion of the
aldehyde and converts it into the corresponding alcohol; thus:
2C 7 H 6 O + KHO = KC 7 H 5 O 2 + C 7 H 8 O
Benzoic Potassium Benzylic
aldehyde. benzoate. alcohol.
Many of the aldehydes form compounds with water, hydrochloric
acid, &c., but the products are very unstable.
The aldehydes readily combine with ammonia, the products first
formed often undergoing molecular condensation more or less rapidly.
The ammonia-compounds of the aldehydes of the acetic series are not
liable to this change, and are stable crystalline bodies which liberate
the original aldehyde on treatment with dilute sulphuric acid.
A reaction peculiar to the aldehydes and allied bodies (ketones),
and common to all members of the class, is the property of forming
stable crystalline compounds with the acid sulphites of the alkali-
metals. The sodium compound is readily obtained on treating the
aldehyde or its aqueous solution with excess of a saturated cold solu-
tion of acid sulphite of sodium, when the compound separates in crys-
tals which are soluble in water or alcohol, but insoluble in a strong
solution of acid sulphite of sodium. From this compound the alde-
hyde may be regenerated by treatment with dilute sulphuric acid (or
sodium carbonate), or sometimes by simply warming the aqueous
solution. Aldehydes of the acetic series (as also chloral) reduce hot
Fehling's solution, but aldehydes of the aromatic series do not.
All bodies of the aldehyde class give a violet coloration with an acid
solution of rosaniline previously mixed with sufficient sodium sulphite
almost to decolorise it. 1
A mere trace of most bodies of the aldehyde class produces a fine
scarlet color with a solution of phenol in excess of sulphuric acid, the
color changing to a dark red on warming the mixture.
1 Examined as described in the text, acetaldehyde, paraldehyde, and propionaldehyde
give an intense red-violet coloration. Chloral gives at once a fine color, but chloral hy-
drate gives no reaction. Acrolein and butyl chloral produce a violet color on shaking.
Furfural and benzaldehyde give the color more readily. Salicylic and cuminic aldehydes
react well after some agitation. Cinnamic aldehyde and furfur-acrole'fn give at first an
intense yellow color, soon changing to violet-red. Acetone readily reacts on shaking, but
acetophenone and benzophenone have no action. Methyl and ethyl alcohols give a faint
violet color on shaking, propylic and isopropylic alcohols a scarcely perceptible reaction,
while with their higher homologues, and phenols, glycols, quinine, sugars, and formic
acid, no color whatever is obtained.
218 ALDEHYDES.
A delicate test for aldehydes is the violet-red color they give with
diazobenzene-sulphonic acid in presence of free alkali (Ber., xvi. 657).
1 part of freshly- prepared diazobenzene-sulphonic acid is dissolved in
60 parts of cold water rendered alkaline by caustic soda. To this
solution is added the liquid to be tested (previously mixed with dilute
solution of caustic soda) together with a little sodium amalgam. If an
aldehyde be present, an intense violet-red coloration is produced, either
immediately or within 20 minutes. The color is destroyed by long
exposure to the air, and is changed by the addition of an acid.
The reaction is readily yielded by a solution containing 1 part in
3000 of benzoic aldehyde (oil of bitter almonds), and has been obtained
with acetic, valeric, and oenanthic aldehydes, as also with furfural
and glyoxal. Chloral and benzoin do not give the reaction. Acetone
and ethyl aceto-acetate give a red color, but without the violet
tint characteristic of an aldehyde. The reaction is not produced
by phenol, resorcinol, or pyrocatechol (if care be taken to have excess
of alkali present), but is given by glucose. It is said to be more deli-
cate than that with rosaniline reduced with sulphurous acid ; but the
reaction is more especially suitable for the detection of aldehydes which
are permanent in alkaline solutions.
E. Fischer recommends the employment of phenylhydrazine hydro-
chloride as a reagent for detecting bodies of the aldehyde class (Ber.,
xvii. 573 ; Jour. Soc. Chem. Ind., iii. 330).
Acrolem, Valeral, Furfural and the Essential oils of bitter almonds,
cinnamon, cloves, cumin, and meadow-sweet have the constitution and
characters of aldehydes. All these form crystalline compounds with
acid sulphites.
Acetone and Aeetal are bodies allied to the aldehydes, and Chloral
is a trichloraldehyde.
Formic Aldehyde. Formaldehyde. Methaldehyde. CH 2 O.
This body is produced by the limited oxidation of methyl alcohol.
Its formation is probably the first stage towards the production of
carbohydrates, &c., in plants, by the deoxidation of carbonic acid.
Formic aldehyde presents a general resemblance to ordinary or acetic
aldehyde, but it is polymerised with extreme readiness. It is gaseous
at the ordinary temperature, and hitherto has not been obtained pure,
though its polymer paraformaldehyde, C 3 H 6 O 3 , is a white insoluble
body, subliming at the temperature of boiling water, and suffering de-
polymerisation at a higher temperature, or when heated to 140 with
excess of water in a sealed tube.
ALDEHYDES. 219
Formaldehyde may be determined by treatment with excess of
standard ammonia, which converts it into hexamethylene-amine,
thus : 6CH 2 O -f 4NH 3 = (CH 2 ) 6 N 4 -f 6H 9 O. The excess of ammonia
may be titrated with standard acid, or the resultant hexamethylene-
amine may be weighed. When heated on the water-bath for several
days with caustic soda, formaldehyde yields sodium formate and methyl
alcohol, and the reaction may be employed quantitatively.
Formaldehyde has acquired great importance within the last few years on
account of its employment as a disinfectant and food preservative. The litera-
ture concerning it is very large and the most important part relates to the detec-
tion of the substance in food, especially milk. It is principally sold as a 40
per cent, solution in water, under the name "formalin." Formaldehyde forms
compounds with many albuminous and gelatinous substances, often rendering
them very insoluble. A few drops of formalin added to a solution of gelatin,
cause the liquid to set to a mass which cannot be melted when held in a flame.
The compounds obtained in this manner retain to some extent the properties of
formaldehyde and have been recommended for antiseptic surgical dressings.
When solutions of formaldehyde are boiled, a considerable portion of the sub-
stance passes over with the steam, but if the distillate be transferred to a dish
on the steam-bath and evaporated, much of the formaldehyde will remain as a
white solid the polymeric modification.
Formaldehyde seems to supply one of the desiderata in sanitary work,
namely, a disinfectant for large enclosed spaces ; it is thought that it may re-
place sulphur dioxide. In this use it is produced economically by burning
commercial methyl alcohol in a special form of lamp. The solid polymer is also
used by heating it strongly, by which it is converted into vapor.
The amount of formaldehyde present in a commercial solution of fair purity
may be determined by the specific gravity. W. A. Davis (J. 8. C. /., 1897, 502)
has revised the determination of specific gravity, the earlier figures being no
longer reliable because applicable to the impure solutions formerly sold.
The following are a few of the data given by him :
Specific Gravity Percentage of Formaldehyde,
at 15-6 C. By Weight. By Volume.
10025 1-0 I'O
10125 5-0 5-0
10250 10-0 10*25
10380 15-0 15-6
10530 20-0 21-1
10670 25-0 26-7
10830 30-0 32-5
11040 35-0 38-6
11250 40-0 45-0
Numerous reactions are known for its detection in fairly pure solution. A few
of these only need be given :
Schiff's reagent is a delicate test for formaldehyde, especially adapted for its
detection in milk. Allen gives the following method for its preparation : Forty
c.c. of a five per cent, solution of magenta (fuchsin) are mixed with 250 c.c. of
water, 10 c.c. of sodium acid sulphite solution of 1*375 sp. gr., and then 10 c.c.
of pure sulphuric acid. The mixture is allowed to stand for some time, when
220 ALDEHYDES.
it will become colorless. A red color resembling that caused by formaldehyde
may be obtained by blowing air through the reagent, by contact with aerated
water, or even by warming.
Trillat (Compt. Rend., cxvi., 1891) has proposed the following test for formal-
dehyde : The solution containing the formaldehyde is mixed with dimethyl-
aniline, acidified with sulphuric acid and agitated. The liquid is heated for
half an hour on the water-bath, made alkaline, and boiled until the odor of
dimethylaniline has disappeared. It is then filtered and the filter-paper moist-
ened with acetic acid. If some powdered lead dioxide be then sprinkled over
the paper, a blue color will be produced if formaldehyde was present. This
blue color, which is not very stable, is due to the formation of tetramethyl-
diamido-diphenylmethane. Another test is based upon the fact that when a
solution of formaldehyde is mixed with a 0'3 per cent, solution of aniline, a
white precipitate is produced. This white precipitate, anhydro-formaldehyde-
aniline, may be weighed, and the amount of formaldehyde originally present
deduced. The following equation represents the reaction :
C 6 H 5 NH 2 + CH 2 = CH 2 : N.C 6 H 5 + H 2 O
Aniline. Formaldehyde. Anhydro-formaldehyde-aniline.
Acetaldehyde also gives a precipitate. This test must be performed in the
cold, as the precipitate is soluble in hot water, reappearing on cooling. The
precipitate with acetaldehyde is more soluble than that given by formaldehyde.
Trillat states that, owing to the formation of condensation products, formalde-
hyde cannot always be detected in preserved foods after lapse of some time.
Richmond and Bosely have confirmed this, but state that they can always detect
it in milk by this process, if the sample has not curdled.
Lebbin (abst. J. S. C. /., 1898, 74) gives the following :
Boil a few c.c. of the liquid to be tested with 0*05 grm. of resorcinol, to
which half or an equal volume of a 50 per cent, solution of sodium hydroxide
is added. If formaldehyde is present, the yellow solution changes to a fine red
color. Analogous compounds showing the usual reactions characteristic of
aldehydes fail to give this coloration. The reaction is said to be sufficiently
delicate to detect one part of formaldehyde in ten million parts of water.
Hehner has shown that when a solution of formaldehyde is mixed with
sulphuric acid containing a minute amount of ferric chloride, a blue color is
produced. This is a very delicate reaction.
If to an aqueous solution of formaldehyde one drop of a dilute aqueous
solution of phenol be added, and the mixture be poured upon some strong
sulphuric acid in a test-tube, a bright crimson zone appears at the point of
contact of the two liquids. The reaction must be carried out as described. A
trace only of phenol must be used, and it must be first mixed with the
solution to be tested before adding to the sulphuric acid.
Several quantitative methods of determining formaldehyde have been recently
published. The following are described by G. Romijn (abst. Analyst, 1897, 221) :
lodiometric Method. Ten c.c. of the aldehyde solution are mixed with 25 c.c.
of decinormal iodine solution, and sodium hydroxide solution added, drop by
drop, until the liquid becomes clear yellow. After ten minutes hydrochloric
acid is added to liberate the uncombined iodine, which is then titrated with
ALDEHYDES. 221
decinormal sodium thiosulphate solution. Two atoms of iodine are equiva-
lent to one molecule of formaldehyde. This method is suitable for the accurate
determination of formaldehyde alone, but does not give good results in the
presence of other aldehydes and ketoues.
Potassium Cyanide Method. This is based upon the fact that formaldehyde
combines with potassium cyanide. The addition-product reduces silver nitrate
in the cold, but if the silver nitrate be acidified with nitric acid before the
addition of the aldehyde mixture, no precipitate results if the aldehyde in the
latter be in excess. If, on the other hand, the cyanide is in excess, one
molecule of potassium cyanide is left in combination with one molecule of the
formaldehyde, while the excess precipitates silver cyanide from the silver
nitrate solution.
Ten c.c. of decinormal silver nitrate solution, acidified with nitric acid, are
mixed with 10 c.c. of potassium cyanide solution (prepared by dissolving 3'1
grrn. of the 96 per cent, salt in 500 c.c. of water), the whole diluted to
500 c.c., filtered, and 25 c.c. of the filtrate titrated by Volhard's method.
The difference between this blank result and that obtained by titrating the
filtrate after the addition of the aldehyde solution gives the amount of deci-
normal sulphocyanate corresponding to the silver not precipitated by the excess
of potassium cyanide. From this the amount of formaldehyde can be calculated.
Results by this method are said to be correct, even in the presence of acetalde-
hyde, if titrated immediately after shaking.
The determination of formaldehyde, in the small quantities in which it is
employed for preserving milk, is attended with great difficulty, and cannot, at
present, be effected with accuracy. The preliminary isolation of the preserva-
tive by distilling the milk is open to objection, but the experiments recorded by
Leonard and Smith (Analyst, 1897, p. 5) show that rough indications of the
amount of formaldehyde present can be obtained in this manner if certain
precautions be taken. From their experiments they conclude that (1) The
distillate from fresh milk exerts no appreciable reducing action on alkaline
permanganate, but milk three or four days old yields a distillate having marked
reducing properties. (2) The separation of formaldehyde from milk is facili-
tated by acidulating the liquid with sulphuric acid and blowing live steam
through it. Under these conditions the first 20 c.c. of distillate from 100 c.c. of
milk will contain about one-third and the first 40 c.c. about one-half of the
total amount of formaldehyde present. (3) The fact that the distillate from
milk does not contain the whole of the formaldehyde present is to a great extent
explained by the behavior of solutions of formaldehyde on distillation, and is
only partly due to any specific action of the preservative on the constituents of
milk.
The amount of formaldehyde contained in the distillate from milk and other
very dilute solutions may be ascertained by determining its reducing power on
permanganate, silver ammonio-nitrate, and similar reagents ; but in view of the
fact that the amount of formaldehyde which is found in the distillate may bear
no definite relation to that originally added to the milk, the determination has
little practical value.
O. Hehner (Analyst, xxi. 94) suggests that the phenol-sulphonic acid test
described by him for the detection of formaldehyde might be used as a means of
222 ALDEHYDES.
determining the strength of dilute formalin solutions. The precipitate obtained
is very insoluble, and so might easily be washed and weighed if required.
R. Orchard (Analyst, xxii. 4) has applied the reaction of formaldehyde with
ammoniacal silver nitrate to its quantitative determination in the following
manner : A convenient measure of formaldehyde solution is mixed with 25 c.c.
of decinormal silver nitrate solution and 10 c.c. of ammonium hydroxide solu-
tion (1 : 50). The mixed solutions are boiled together in a conical flask over a
reflux condenser for about four hours- The precipitate, after being washed and
dried, is ignited and weighed as metallic silver. The residual silver nitrate in
the filtrate may also be determined as a check upon the other result. Since one
molecule of formaldehyde reacts with one molecule of silver oxide, the weight
of the silver precipitated, multiplied by the factor 01389, gives the weight of
formaldehyde ; also, 1 c.c. of deciuormal silver nitrate corresponds to 0*0015 grm.
of formaldehyde. L.
Acetic Aldehyde. Acetaldehyde. Ethylidene Oxide.
This is the body from which the class of aldehydes derived their
name, and when the word aldehyde is used as a proper name without
qualification, ordinary or acetic aldehyde is always understood.
In constitution, aldehyde is intermediate between ethyl alcohol and
acetic acid ; thus
Ethyl alcohol, C 2 H 6 O = C 2 CH 3 CH 2 OH.
Aldehyde, C 2 H 4 O = C 2 CH 3 COH.
Acetic acid, C 2 H 4 O 2 = C 2 CH 3 COOH.
Aldehyde results from the destructive distillation of various organic
compounds, and from the limited oxidation of alcohol by dilute
chromic acid, nitric acid, air in presence of platinum black, &c. In
practice, aldehyde is prepared by distilling together alcohol, sulphuric
acid, and manganese dioxide, but it may be obtained in various other
ways.
Acetic aldehyde is a mobile, colorless liquid, having a pungent,
suffocating odor. In pure samples, the disagreeable odor is much less
marked than in the crude substance. Its density is "790, and it boils
at 22 C. It does not redden litmus, either when absolute or when in
solution ; but turns acid on exposure to air, from oxidation to acetic
acid, which change occurs with great facility.
Acetic aldehyde is miscible in all proportions with water, alcohol,
ALDEHYDES. 223
and ether. It is insoluble in a saturated solution of calcium chloride,
but this fact is not of service for the quantitative separation of alde-
hyde from alcohol. A better method of separation is to treat the
liquid with dry calcium chloride, which forms a compound with the
alcohol, when the aldehyde may be distilled off by the heat of a
water-bath.
When kept in closed vessels, aldehyde often becomes converted into
liquid or solid polymeric modifications, especially in presence of traces
of mineral acid or certain other impurities. The alcoholic solution of
aldehyde is tolerably permanent. Oxidising agents convert aldehyde
into acetic acid. Dehydrating agents, such as phosphoric anhydride
and concentrated sulphuric acid, when heated with aldehyde turn it
thick and black ; but aldehyde may be distilled from sulphuric acid
diluted with an equal weight of water.
Aldehyde is a powerful reducing agent. It separates metallic silver
from the ammonio-nitrate, when gently warmed, acetate being
formed in the liquid. The reaction is rendered more delicate by the
addition of caustic alkali. A suitable mixture may be prepared by
mixing equal measures of 10 per cent, aqueous solutions of silver
nitrate and caustic soda, and then adding ammonia drop by drop till
the oxide of silver is dissolved. 1 This reagent yields an immediate
mirror with a liquid containing 1 per cent, of aldehyde, and in half a
minute with a solution containing 1 in 1000, while 1 part of aldehyde
in 10,000 of water yields a yellow-brown mirror in five minutes. The
solution to be tested should be previously distilled, as several varieties
of sugar slowly reduce the reagent.
Aldehyde gives a copious precipitate of red cuprous oxide when
heated with Fehling's solution. Neither this reaction nor that with
silver solution appears to be applicable for its quantitative determina-
tion.
When in alcoholic or aqueous solution, aldehyde is conveniently
detected by its reaction on heating with caustic alkali. When thus
treated, the liquid becomes yellow and turbid, and a reddish-brown
resinous mass rises to the surface, the liquid emitting a highly dis-
agreeable odor. The solution contains a formate and acetate of alkali
metal. This formation of the aldehyde-resin is the most character-
istic reaction of aldehyde, and has been utilised by J. C. Thresh
(Pharm. Jour., [3] ix. 409), for its approximate determination. To
effect this, 1 part of pure aldehyde should be diluted with 200
i The reagent should be freshly prepared, as it is liable to decompose with deposition of
fulminating silver.
224 ALDEHYDES.
measures of water, 30 measures of a syrupy solution of caustic soda
added, and the whole heated and kept at the boiling point for a few
seconds. It is then allowed to cool, and after two hours is diluted
with 200 measures of warm methylated spirit (free from aldehyde),
and then made up to 500 measures by addition of water. This solu-
tion is quite clear, and of a reddish-yellow color. As it quickly alters,
it is desirable to make a solution of bichromate of potassium of the
same tint, and employ that instead of the original liquid. To deter-
mine aldehyde, the liquid containing it, suitably diluted and previously
distilled if necessary, is treated in exactly the same manner as the pure
aldehyde, and the color of the liquid obtained compared with the
standard, and the darker diluted with water till the tints are identical.
The comparison is affected in much the same manner as in Nessler's
method of determining ammonia.
A characteristic property of aldehyde, but common to all bodies of
the class, is the formation of white crystalline compounds with the
acid sulphites of the alkali metals. Thus : C 2 H 3 OH + NaHSO 3 =
Na(C 2 H 3 )SO 3 -f H 2 O. These compounds are more or less soluble in
alcohol and water, but insoluble in strong solutions of the acid sul-
phites. Hence, by adding excess of acid sodium sulphite to an
aqueous solution of aldehyde, the latter substance may be entirely
separated as sodium ethylidene sulphite, and can be obtained in a free
state by distillation with a dilute mineral acid or an alkaline car-
bonate.
Aldehyde also combines with ammonia, forming a crystalline sub-
stance of the formula C 2 H 4 O,NH 3 , or CH 3 .CH(NH 2 ).OH (amido-
ethyl alcohol), insoluble in ether and decomposed on distillation
with moderately dilute sulphuric acid.
PARALDEHYDE. C 6 H 12 O 3 . This solid polymeride of acetaldehyde is
produced by adding a minute quantity of hydrochloric or sulphurous
acid to ordinary aldehyde. Also, on adding a drop of concentrated
sulphuric acid to aldehyde violent ebullition occurs, much aldehyde is
volatilised, and the residue consists of paraldehyde. Zinc chloride acts
similarly, but calcium chloride and potassium acetate do not. The
paraldehyde may be purified from unchanged aldehyde by cooling the
liquid below 0, when the crystals which separate are pressed between
folds of blotting paper and distilled.
Paraldehyde is a colorless liquid, solidifying at 10 C. and boiling
at 124. The density is 0'998 at 15. It has a pleasant ethereal odor,
is soluble in 8? measures of cold water, and in all proportions of
alcohol and ether. It may be distilled alone without change, but if a
CHLORAL. 225
small proportion of ziuc chloride or sulphuric or hydrochloric acid be
present the operation reconverts it into ordinary aldehyde.
Paraldehyde is employed in medicine as a substitute for chloral,
over which it presents some advantages, but has a persistent and acrid
after taste. Some commercial specimens are very impure.
METALDEHYDE, #C 2 H 4 O, is another polyraeride produced simul-
taneously with paraldehyde (see page 224). It is insoluble in water,
and almost insoluble in alcohol or ether, but dissolves somewhat in
acetaldehyde. Its best solvents are hot chloroform and benzene. At
ordinary temperatures the crystals are permanent in the air. It is re-
converted more or less completely into ordinary aldehyde by repeated
distillation, or by heating in a sealed tube to 110 or 115, and readily
by distillation with a little dilute sulphuric acid. Permanganate,
chromic acid mixture, and ammonia are without effect on metaldehyde,
but chlorine at once converts it into ordinary chloral. With a hot
strong solution of caustic potash or soda metaldehyde very slowly
yields aldehyde- resin, the reaction being probably preceded by a
formation of ordinary aldehyde.
ACETAL, C 6 H U O 2 , has the constitution of a di-oxyethyl-acetalde-
hyde: CH 3 .CH(OC 2 H 5 ) 2 . It is produced by the action of aldehyde
on alcohol, and hence is a constituent of crude spirit and of the
" feints " obtained in the rectification of alcohol. When pure, acetal
is a liquid of pleasant taste and odor, boiling at about 105 C. and
having a density of '821 at 22 C. By oxidising agents it is con-
verted into acetic acid and aldehyde, and when heated with acetic
acid, it yields ethyl acetate and aldehyde. If a dilute aqueous solu-
tion be treated with caustic soda and iodine a clear colorless liquid is
formed, which yields a dense precipitate of iodoform when acidified.
From alcohol, acetal may be separated by distillation over dry
chloride of calcium, and from aldehyde and ethyl acetate by heating
the liquid with strong solution of potash.
Dimethyl- acetal occurs in crude wood spirit in proportions varying
from 1 to 2 per cent.
CHLORAL.
Trichloraldehyde. C 2 HC1 3 O = CC1 3 .CO.H.
Chloral is obtained in practice by the prolonged action of dry
chlorine on absolute alcohol. When the liquid possesses a density of
1'400 it is distilled with an equal weight of strong sulphuric acid, the
fractions passing over below 94 being kept separate, and the process
15
226 CHLORAL.
stopped when the temperature rises to 100 C. The distillate is
neutralised with chalk and again distilled. The reactions which occur
in the manufacture of chloral are very complicated, and various
secondary products are formed. 1
Anhydrous chloral is a thin colorless oily liquid, of a density of
1-544 at 0, or 1'502 at 18 C. It boils at 94'4 and distils unaltered.
It is soluble in ether or chloroform without change.
When kept for some time, or when left in contact with moderately
concentrated sulphuric acid, chloral is converted into an insoluble
polymeric modification called metachloral, C 6 H 3 CI 9 O3, which is insol-
uble in cold and but sparingly soluble in boiling water, and insoluble
in alcohol or ether even when boiling. When perfectly pure, anhydrous
chloral does not become polymerised, and the change is also said to be
prevented by addition of a little chloroform. When heated to 180
metachloral distils with reversion to liquid chloral. By the action of
alkalies chloral yields chloroform and a formate, thus :
CC1 3 .COH -{- KOH = KCHO 2 + CHC1 3 .
1 The action of chlorine on absolute alcohol results in the formation of aldehyde and
acetal, thus : C 2 H 6 + 1 2 = C 2 H 4 + 2HC1; and C 2 H 4 + 2C 2 H 6 = C 2 H 4 (C 2 H 5 0) 2 +
H 2 0. By the continued action of chlorine, that element replaces three atoms of hydrogen,
farming trichlor-acetal, C 2 HC1 3 (C 2 H 5 0) 2 , which may be regarded as a compound of chloral
with ether, C 2 HC1 3 0,(C 2 H 5 ) 2 0. By reaction with the generated hydrochloric acid this
yields chloral alcoholate, C 2 HC1 3 0,C 2 H 6 0, and ethyl chloride, C 3 H 5 C1. Most of the latter
reacts with the alcohol present to form ether, which is converted by fresh chlorine step by
step into mono-, di-, tri-, and tetra-chlorinated ether.
During the subsequent distillation with concentrated sulphuric acid, the tetra-chlorin-
ated ether and the chloral alcoholate split up into chloral and ethyl-sulphuric acid, as
follows :
C 2 H 5 .O.C 2 HC1 4 + H 2 S0 4 = HC1 + C 2 HC1 3 + (C 8 H 6 )HS04
and C 2 HC1 3 0,C 2 H 5 HO + H 2 S0 4 = II 2 + C 2 HC1 3 + (C 2 H 6 )IIS0 4 .
The ethyl-sulphuric acid reacts with hydrochloric acid to form sulphuric acid and ethyl
chloride, (C 2 H 6 )HS0 4 + HC1 = H 2 S0 4 + (C 8 H 6 )C1.
By the continued action of chlorine on tetra-chlorinated ether, a penta-chlorinated
ether (C 2 H 5 .O.C 2 C1 5 ) is produced. This body has a density of T65, and does not yield
chloral when treated with sulphuric acid. Hence, in practice, the current of chlorine gas
is interrupted when the liquid has reached a density of 1*40.
By reacting on the ethyl chloride formed in the process, chlorine produces a whole
series of chlorinated substitution-products.
By the chlorination of two associated molecules of aldehyde, a substance called butyl-
chloral is formed, having the formula C^IsClaO. It is distinguished from ordinary
chloral by its boiling point and the melting point of its hydrate, as well as by the mode
of its decomposition by alkalies.
The occurrence of many or all of the above reactions sufficiently accounts for the
variety of the impurities sometimes contained in commercial chloral hydrate and chloro-
form. The distinction between the different chlorinated oils, and their recognition in
chloroform, chloral, &c., can at present be effected but very imperfectly.
OP TM
UNIYEBSITY
CHLORAL.
If an aqueous solution of chloral be heated to 50 C. with zinc, and
very dilute acid gradually added, aldehyde and paraaldehyde are
formed and may be distilled off. C 2 HC1 3 O -f H 6 = 3HC1 +*C 2 H 4 O.
When chloral is mixed with an equivalent quantity of absolute
alcohol it is converted into
Chloral Alcoholate. C 4 H 7 C1 3 O 2 = C 2 HC1 3 O,C 2 H 6 O.
This substance forms white crystals, which melt at 46 C. It boils
at 11 3 '5 C. (see page 228). These properties, amongst others, distin-
guish it from
Chloral Hydrate. Trichlor-ethylidene glycol. C 2 H 3 CJ 3 O 2 =
C.,HCI 3 O,H 2 = CCJ 3 .CH(OH) 2 .
This important substance results from the mixture of equivalent
quantities of anhydrous chloral and water. The mixture becomes
heated and solidifies to a mass of crystals of the hydrate. Chloral
hydrate is soluble in H times its weight of water. It is also soluble in
alcohol, ether, benzene, petroleum spirit, and carbon disulphide. When
crystallised from the last solution it boils at 97'5 C.
When mixed with an equal weight of camphor or carbolic acid
chloral hydrate rapidly liquefies. The liquid smells of both its con-
stituents, and does not precipitate nitrate of silver.
Chloral hydrate is soluble with difficulty in cold chloroform, requiring
four times its weight, a fact which distinguishes it from the alcoholate,
which is readily soluble in chloroform. The distinction of chloral
hydrate from chloral alcoholate is important, as the latter is said to
have been substituted for the former. The alcoholate contains a smaller
percentage of chloral than the hydrate, and its physiological effect
appears to be different.
Chloral hydrate and alcoholate should be completely volatile. Their
aqueous solutions should be perfectly neutral to litmus.
An aqueous solution of chloral hydrate gives no reaction with silver
nitrate in the cold, but when the liquid is heated to boiling, and a few
drops of ammonia added, a metallic mirror is readily produced. If
kept some time, chloral hydrate contains a trace of hydrochloric acid,
and the solution in water then gives a cloud with nitrate of silver ; the
production of a distinct precipitate indicates serious impurity.
When the water of hydration is in excess, chloral hydrate is deli-
quescent, and in warm weather even melts. Hence it is now generally
made slightly deficient in hydration. If more than a shade short of
being fully hydrated the product has a tendency to become acid, and
ultimately partially insoluble from formation of metachloral.
228
CHLORAL.
In the following table are given other useful distinctions between
chloral alcoholate and chloral hydrate :
Chloral Alcoholate.
Chloral Hydrate.
1. Melting point.
2. Boiling point.
3. Density of the fused sub-
stance at 66 C.
46 C.
113-5 C.
1-344
48-49 C.
97-5 C.
1-57
4. Sp. gr. of the aqueous solu-
tion at 15-5 C.
5 per cent.
10
15
20
1T07
1-028
1-050
1-071
1-019
1-040
1-062
1-085
5. Gently heated with nitric
acid of 1'2 sp. gr.
6. Shaken with an equal vol-
ume of strong sulphuric
acid.
Violently attacked.
Brown coloration. 1
Scarcely acted on.
No visible change. l
7. Warmed with two volumes
of water.
Melts without com-
plete solution, and
on cooling con-
geals below the
surface.
Readily dissolved.
8. Heated on platinum foil.
9. With alkali and iodine.
Inflames readily.
Gives iodoform.
Scarcely burns.
Gives no iodoform.
The solidifying point of melted chloral hydrate is an indication of
some value. The sample should be placed in a small test-tube, fused,
and the tube immersed in water at about 55 C. A thermometer is
placed in the chloral, and the temperature at which the liquid becomes
opalescent noted. The best chloral hydrate solidifies at about 48 to
49 C., and the best practically adjusted specimens within half a degree
of 50 C. A low freezing point indicates excess of water, and such
specimens are liable to deliquesce. Small granular crystals and sac-
charoid masses are purer than large crystals or needles.
The boiling point of chloral hydrate is also of service as a test of
purity. The sample should be placed in a test-tube with some broken
glass. With a pure sample, rapid boiling will commence at 97 C., and
the temperature will not vary very much till fully one-half has been
volatilised. Chloral hydrate appears, however, to undergo slow decom-
position at its boiling point, so that the first portions of the distillate
are under-hydrated, and the last over-hydrated. The boiling point
consequently undergoes a gradual rise. The best commercial speci-
mens, i.e., those slightly under-hydrated, begin to boil throughout the
* Other impurities besides the alcoholate cause a darkening with sulphuric acid.
CHLORAL. 229
liquid at about 96'5 C. The under-hydrated portion boils off in a
few seconds, and the boiling point rises to 97 C., and finally to 97'5
or 98 C., by the time half the liquid has boiled off. A boiling point
above 98 C. indicates an over-hydrated and deliquescent sample. If
the boiling fairly commences below 95 C., the sample is too much
under-hydrated, and is liable to decompose on keeping.
DETECTION AND DETERMINATION OF CHLORAL.
The detection and determination of chloral have acquired considerable
importance of recent years on account of the not infrequent employment o/ the
substance for drugging liquor to facilitate the commission of robbery or rape.
L.
Valuable as chloral hydrate is as a sedative and hypnotic, fatal
poisoning by it is not uncommon. In such cases it may be detected by
the same means as chloroform (page 233), into which it appears to be
converted in the system.
Solutions of chloral reduce Fehling's solution on heating. The
reaction may be employed to detect traces of chloral if other reducing
substances be absent, and might probably be made quantitative.
Traces of chloral may be detected by Hofmann's delicate test for
chloroform (see page 233) ; also, by boiling the liquid and passing
the vapor through a red-hot tube, when hydrochloric acid will be
formed, and hence the condensed water will precipitate silver nitrate.
For the determination of real chloral in commercial samples of the
hydrate advantage may be taken of its reaction with alkalies, which
results in the separation of chloroform and the production of an alka-
line formate :
C 2 HC1 3 0,H 2 -f NaHO = NaCHO 2 + H 2 O + CHC1 3 .
K. Miiller places 25 grm. of the sample in a finely-graduated
tube, and then adds a strong solution of caustic potash, in quantity
rather more than sufficient for the above reaction. A large excess of
alkali must be avoided. The tube must be kept well cooled, as the
action is very violent at first. Afterwards, the tube may be closed
and the mixture shaken. After resting an hour or two the liquid
becomes clear, and separates into two layers. The lower layer is
chloroform, and, after being brought to a temperature of 17 C., the
volume may be read off. Its density is 1/491, and hence the measure
of chloroform in c.c., multiplied by 1/84, gives the grm. of anhy-
drous chloral in the quantity of the sample employed. If the factor
2'064 be substituted, the product will be the weight of chloral hydrate
present. Miiller obtained by this process an average of 71*6 per cent.
230 CHLORAL.
of chloroform from pure chloral hydrate, against 72'2 per cent, as
required by theory.
C. H. Wood (Pharm. Jour. [3] i. 703) distils the sample of chloral
hydrate with milk of lime. 10 grm. weight of the sample is dissolved
in 50 c.c. of water contained in a small flask, and 4 grm. of slaked
lime is added. A cork with a tube bent twice at right angles is
adapted to the flask, the outer end of the tube being somewhat drawn
out and immersed in a small quantity of water, contained in a narrow
graduated glass tube surrounded with cold water. A gentle heat is
applied to the flask, and the chloroform slowly distilled over. After
a few minutes the heat is gradually increased, so as to keep the mixture
boiling, the operation being continued till 10 c.c. measure has passed
over. Nothing remains but to bring the chloroform to the proper
temperature and read off the volume. The addition of a few drops of
potash solution destroys the meniscus of the chloroform, and enables
the operator to observe the measure accurately. The process does not
occupy more than a quarter of an hour. Too much lime occasions
frothing, but an excess appears to have no decomposing action on the
chloroform. Lieben's iodoform test for alcoholate is readily applied
to the aqueous portion of the distillate. The writer has found this
plan convenient and fairly accurate. A correction may advantageously
be made for the slight solubility of chloroform. This is about 0*3 c.c.
for every 100 c.c. of aqueous liquid.
A very simple and accurate modification of the above process for
assaying chloral hydrate has been suggested by M. Meyer, and has
given the writer very satisfactory results. It has the advantage of
being applicable to very moderate quantities of material. 1 or 2
grm. of the sample should be dissolved in water, and any free acid
which may be present removed by shaking the liquid with chalk or
barium carbonate and subsequently filtering. The filtrate is then
treated with a moderate excess of normal caustic soda, and titrated
back with acid in the usual way, litmus being used as an indicator.
Each c.c. of normal alkali neutralised by the sample corresponds to
1475 grm. of real chloral (C,HC1 3 O), or '1655 grm. of chloral hydrate.
Other processes of assaying chloral hydrate have been based on its
decomposition by ammonia and on its conversion into anhydrous
chloral by sulphuric acid, but they are more liable to error, and are
in no way superior to the methods already described.
TRICHLOR-ACETIC ACID, HC 2 C1 3 O 2 , is a product of the action of
oxidising agents on chloral. When equivalent quantities of chloral
hydrate and potassium permanganate are cautiously mixed in coucen-
CHLORAL. 231
trated solution, potassium trichlor-acetate is formed, and may be
obtained in white silky crystals by filtering and evaporating the liquid.
By the action of alkalies, trichlor-acetic acid yields chloroform and a
carbonate, and responds to all other tests for chloral dependent on its
conversion into chloroform.
Butyric Chloral. Butyl Chloral. Butyric trichlor-aldehyde.
Erroneously, Croton chloral. C 4 H 6 CI 3 O = C 3 H 4 C1 3 .COH. When
chlorine is passed into aldehyde, this substance is formed in addition
to ordinary chloral. It bears the same relation to butyl alcohol and
butyric acid that ordinary chloral bears to ethyl alcohol and acetic
acid.
Butyl chloral was at first called croton chloral, the hydrogen being
under-estimated, which led to the supposition that it was the trichlorin-
ated aldehyde of crotonic acid, C 4 H 6 O 2 , the fourth member of the
acrylic or oleic acid series.
Butyric chloral is a dense oily liquid of peculiar odor, boiling at
about 163 C. When treated with a considerable excess of warm
water it dissolves, and on cooling deposits
Butyric or Butyl Chloral Hydrate. C 4 H 5 C1 3 O,H 2 O.
This substance farms white silvery crystalline scales melting at 78
C., and having a sweetish melon flavor. The specific gravity is 1/695,
that of solid chloral hydrate being 1/818. Butyric chloral hydrate is
but little soluble in cold water, but more so in hot. Its solubility is
increased by addition of glycerin. It is very soluble in alcohol and
ether, but insoluble, or nearly so, in chloroform. This last property
may be employed to separate it approximately from ordinary chloral
hydrate. It differs also from the latter body in its melting and boiling
point. The two bodies may also be separated by distillation, ordinary
chloral hydrate passing over a little below 100, while butyric chloral
hydrate is decomposed into water, which distils at about 100, and
anhydrous butyric chloral boiling at about 163 C.
When acted on by alkalies, butyric chloral hydrate is at first
decomposed with production of a formate and propylic chloroform,
C 3 H 5 CI 3 , but this again splits up with formation of a chloride of alkali-
metal and allylene dichloride, C 3 H 4 C1 2 . It is to the production of
the last substance that the curious and valuable medicinal effects of
butyl chloral are chiefly due.
BICHLORIDE OF ALLYLENE is very unstable, being gradually
decomposed, even at ordinary temperatures, and acquiring an acid
reaction and disagreeable odor. The proneness to change, so marked
"232 CHLOROFORM.
in some samples of commercial chloroform, and the readiness with
which the latter decomposes and becomes acid, are properties not
improbably due to the presence of dichloride of allylene. Its presence
is probably due to the existence of aldehyde in the crude alcohol used
for the preparation of the chloroform. By the action of chlorine the
aldehyde is converted into butyl chloral, and this, by subsequent con-
tact with the chalk used for neutralisation, gives dichloride of allylene.
CHLOROFORM.
Trichloro-methane. Methenyl trichloride. CHC1 3 .
Chloroform is generally manufactured by distilling dilute alcohol
with calcium Hypochlorite and hydrate (bleaching powder and slaked
lime). A complicated reaction ensues, 1 and the product requires
careful purification for the removal of secondary products. Chloro-
form is also prepared by distilling chloral hydrate with dilute alkali,
when the following reaction occurs :
C 2 HC1 3 0,H 2 -f NaHO = NaCHO 2 + H 2 O -f CHC1 3 .
Chloral hydrate. Sodium formate. Chloroform.
The product is purified by treatment with strong sulphuric acid or
an alkaline solution of potassium permanganate.
It is extremely probable that the dangerous and fatal effects occa-
sionally attending the administration of chloroform are due to impuri-
ties in the commercial article. Hence, the careful preparation and
thorough purification of chloroform are of great importance.
Chloroform is a colorless limpid liquid, of peculiar odor, and sweet
but somewhat burning taste. The anaesthetic effects produced by
inhaling its vapor are well known. Pure chloroform is not com-
bustible, but when mixed with alcohol it burns with a smoky flame
edged with green.
The density is 1'500 at 15 C. and the boiling point 60'8. Accord-
ing to Thorpe, the reduced and corrected boiling point of chloroform
is 61'2, and the density at C. 1*5266, compared with water at the
same temperature.
i The production of chloroform by the action of bleaching powder on alcohol may be rep-
resented by the equation : 4C 2 H 6 + 1 6CaCl 2 = 2CHC1 3 -f- 3Ca(CH0 2 ) 2 + 13CaCl 2 -f 8H 2 0.
Recent researches, however, have shown that the reactions which occur in practice are
far more complicated (see note on page 226). It is probably on this account that pure
methyl alcohol yields no chloroform on treatment with chlorine and an alkali. Acetone,
on the other hand, may be substituted for alcohol in the preparation of chloroform.
CHLOROFORM. 233
Chloroform is almost insoluble in water ('44 grm. in 100 c.c.), to
which, however, it imparts a sweet taste. It is miscible in all propor-
tions with absolute alcohol, ether, benzene, and petroleum spirit. It is
soluble to a limited extent in aqueous alcohol.
Chloroform possesses remarkable solvent properties, dissolving many
organic bases, fats, wax, resins, camphor, india-rubber, gutta-percha,
pitch, iodine, bromine, and phosphorus.
DETECTION AND DETERMINATION OF CHLOROFORM.
As a rule, the detection of chloroform itself is less important than
the recognition and estimation of other substances in presence of
chloroform.
A very delicate method for the detection of chloroform in presence
of large quantities of alcohol has been described by A. W. Hofmann.
All that is necessary is to add some alcoholic soda and a little aniline
to the liquid to be tested. Either immediately or on gently warming
the mixture, a strong and peculiar smell will be observed, due to the
formation of beuzo-isonitrile (phenyl isocyanide), C 7 H 5 N. Bromoform
and iodoform give the same reaction, as also do chloral, trichlor-acetic
acid, and all other bodies which yield either of the above products by
treatment with alkalies. On the other hand, ethylidene chloride,
GYH^Cla, gives no isonitrile under the same conditions. The test is so
delicate that one part of chloroform dissolved in 5000 parts of alcohol
may be detected with certainty by means of it.
The reduction of Fehling's alkaline copper solution is also a good
and delicate test for chloroform, with which it reacts thus: CHC1 3 -f
5KHO + 2CuO = Cu 2 O -f- K 2 CO 3 + 3KC1 -f 3H 2 O.
When the solution is heated, the formation of the yellow-red cuprous
oxide occurs very promptly. The reaction might probably be used for
the determination of chloroform in the absence of other reducing
agents, especially if the test were applied to a liquid obtained by dis-
tillation. Chlor-ethylidene and alcohol do not interfere with the test.
When chloroform vapor mixed with hydrogen is passed through a
red-hot tube, it is decomposed with production of hydrochloric acid.
This fact may be employed for the detection and estimation of chloro-
form. The sample should be boiled in a small flask through which a
current of hydrogen is allowed to pass. The mixed hydrogen and
chloroform vapor are then caused to traverse a short length of heated
combustion tube containing platinum wire-gauze.
The products of the reaction are collected in a bulb-tube containing
water, and the hydrochloric acid produced is titrated with standard
234 CHLOROFORM.
alkali, or precipitated with nitrate of silver. 109'5 parts of hydro-
chloric acid, or 430*5 of chloride of silver, represent 119*5 of chloro-
form. Berthelot points out that the reaction with silver is apt to be
vitiated by the presence of acetylene and hydrocyanic acid, and
recommends that the aqueous solution of the gases should be well
boiled before adding silver nitrate.
This process is especially useful for the determination of small
quantities of chloroform contained in other non-chlorinated liquids.
It may be employed for the detection and estimation of chloroform in
blood. When its detection only is required, a current of air may be
substituted for the hydrogen. There is no occasion to heat the blood.
Vitali suggests that the mixture of hydrogen with chloroform vapor
obtained as in the last reaction should be submitted to Hofmann's
isonitrile reaction (test a), or passed through a freshly prepared
mixture of thymol and solid caustic potassa, when if chloroform be
present the mixture will be colored a fine reddish-violet.
When chloroform is added to a solution of a- or /J-naphthol in
strong caustic potash, and the liquid is heated to about 50 C., a fine
Prussian blue color is developed, changing in contact with the air to
blue-green, green, green-brown, and finally brown.
Chloral and chloral hydrate resemble chloroform in their behavior
with naphthol.
Commercial Chloroform.
Many specimens of commercial chloroform undergo more or less
change on keeping. According to Personne, samples liable to altera-
tion always contain chloro-carbonic ether, C 2 H 5 CO 2 C1. The change
has also been attributed to the presence of dichloride of allylene. At
any rate, certain specimens of chloroform, originally of good quality,
on keeping become impregnated with hydrochloric, hypochlorous, and
formic acids. J. Regnauld has found that carbon oxychloride, COC! 2 ,
was readily produced by the action of ozonised air on chloroform, and
considers the accidental presence of this body in chloroform very
common. He has also found that very carefully prepared chloroform
can be kept unchanged if exposed to air or light simply, but that the
combined action of air and light rapidly affects the purity of the
preparation. The change is entirely prevented by the addition of 0*1
per cent, of alcohol, which is said to be more efficacious than a larger
proportion.
In addition to the impurities resultant from decomposition by keep-
ing, commercial chloroform may contain alcohol, aldehyde, and various
CHLOROFORM. 235
chlorinated oils. These last are very injurious and even poisonous,
and are detected and eliminated with considerable difficulty. Other
products may be present if the alcohol employed for the manufacture
of the chloroform contained methyl or amyl compounds. Methylic
alcohol is generally supposed to be capable of forming chloroform,
but, from experiments on the perfectly pufe substance, this notion
seems to have been disproved. Alcohol and aldehyde are sometimes
added to chloroform in very considerable proportions. The adultera-
tion of chloroform with ether and acetic ether has also been practised.
Free chlorine and hypochlorous and hydrochloric acids in chloroform
may be recognised by shaking the sample with a solution of nitrate of
silver, which in presence of either of the above impurities will produce
a white precipitate, whereas chloroform itself gives no reaction with
silver nitrate, either in aqueous or alcoholic solution. If the precipitate
blacken on heating the presence of aldehyde or formic acid is indicated.
Free chlorine and hypochlorous acid are distinguished from hydro-
chloric acid by their power of bleaching instead of merely reddening
litmus, and by liberating iodine from a solution of pure iodide of po-
tassium when the sample is shaken with it. The liberated iodine
colors the chloroform reddish-violet.
Dichloride of Ethylene, C 2 H 4 C1 2 , may be detected in chloroform by
drying the sample by agitation with dry carbonate of potassium, and
then adding metallic potassium. This does not act on pure chloroform,
but in presence of the above impurity it produces chlor-ethylene,
C 2 H 3 C1, a gas of an alliaceous odor. It is very doubtful whether the
substance in chloroform of the formula C 2 H 4 C1 2 is always dichloride of
ethylene. It is probably more frequently the isomer ethylidene chlo-
ride, CH 3 .CHC1 2 .
The presence of ethyl chloride, C 2 H 5 C1, in chloroform is best recog-
nised by distilling the sample with water in a water-bath. The first
portions of the distillate will have a distinct smell of the foreign body.
" METHYLATED CHLOROFORM" is chloroform prepared from wood
spirit, or methylated spirit. It is a mistake to suppose that methylated
chloroform has received an actual addition of wood spirit, but such
chloroform is liable to be much less pure than that obtained solely
from ethylic alcohol. Chloroform prepared from methylated spirit is
more difficult to purify than that made from pure alcohol, but a product
is now manufactured from the former source which appears to be equal
in all respects to the dearer article.
Imperfectly purified methylated chloroform is specifically lighter
than the pure substance, has an empyreumatic odor, and produces
236 CHLOROFORM.
disagreeable sensations when inhaled. In some cases such chloroform
seems actually poisonous, and produces general and rapid prostration.
Such impure chloroform contains several units per cent, of a chlorinated
oil, lighter than water and boiling at a much higher temperature than
chloroform. A similar but different oil (heavier than water) is some-
times contained in much smaller quantity in chloroform prepared from
alcohol containing no methyl compounds.
Chloroform is not soluble in strong sulphuric acid, and, when pure,
is not acted on until after the lapse of some time, when shaken with
that reagent. Any darkening of the acid which occurs may be due to
the presence of aldehyde, wood spirit, chlorinated oils, &c. Pure chlo-
roform floats on strong sulphuric acid with a contact-surface convex
downwards, but if impure gives a plane contact-surface.
The boiling point of chloroform is a valuable indication of its purity.
Pure chloroform boils at 60*8 C. The presence of per cent, of
alcohol reduces the boiling point to 59'8 or 60 C. A boiling point
higher than 61 C. indicates the presence of amyl or butyl compounds.
In some cases the boiling point of the last portions distilled is as high
as 70 C.
Pure chloroform volatilises entirely without disagreeable smell.
The impurities are generally less volatile. Many kinds of impurity in
chloroform may be readily recognised by the disagreeable odor left on
the evaporation of the sample from a cloth or filter-paper soaked
with it.
Pure chloroform is not visibly altered when heated with solution of
potassa, though it is slowly acted on with formation of a formate and
chloride of the alkali metal. In alcoholic solution this reaction occurs
rapidly. In presence of aldehyde or acetone the solution of potassa
becomes colored brown.
Any considerable admixture of ether with chloroform would be indi-
cated by the inflammability and diminished density of the liquid.
Perfectly pure chloroform does not change the color of an alkaline
solution of permanganate of potassium from violet to green within
half a minute, but as the change is caused by alcohol equally with
more objectionable impurities, the reaction has little practical value.
The most delicate test for the presence of alcohol in chloroform is
that of A. Lieben, as modified by Hager. The sample should be
agitated with five measures of water, the liquid passed through a wet
filter, and the filtrate examined as described under " alcohol."
Caustic potash is quite insoluble in dry chloroform, but dissolves
sensibly in presence of water or alcohol. If, therefore, a piece of stick
CHLOROFORM.
237
potash be fused on a loop of platinum wire, and introduced into some
of the chloroform contained in a dry test-tube, the liquid will not
acquire the power of turning red litmus paper blue, unless water or
alcohol be present. If more than a trace of alcohol be present, the
decanted chloroform, when shaken with water, yields a liquid which
gives a blue precipitate with a solution of sulphate of copper. To use
this test with certainty to distinguish between water and alcohol, the
sample must be first shaken with recently-ignited potassium carbonate.
This treatment will remove water but not alcohol, so that if the chlo-
roform still possesses the power of dissolving caustic potash alcohol
must be present.
Oudemanns (Zeitsch. Anal. Chem., xi. 409) determines the proportion
of alcohol contained in commercial chloroform by shaking 10 c.c. of
the sample in a flask with an excess of pure dry cinchonine. The
flask is kept for an hour at a temperature of 17 C., with frequent
agitation. The liquid is then passed through a dry filter, and 5 c.c.
of the filtrate evaporated to dryness in a small hand beaker. The
following are the number of milligrammes of residual alkaloid yielded
by 5 c.c. of chloroform containing various proportions of alcohol :
Residue.
Alcohol.
Residue.
Alcohol.
Milligrammes.
21
Per cent.
Milligrammes.
260
Per cent.
6
67
1
290
7
111
2
318
8
152
3
343
9
190
4
346
10
226
5
Stoedeler has suggested fuchsine for detecting alcohol in chloroform.
The sample becomes colored red if alcohol be present, the depth of
color varying with the proportion of alcohol. The author found
(Analyst, ii, 97) that, even after agitation with chloride of calcium,
the chloroform became colored on adding fuchsine, but by agitating
the sample with one-fifth of its bulk of strong sulphuric acid, and
subsequently removing traces of the latter by shaking with dry pre-
cipitated carbonate of barium, the chloroform was obtained so pure as
to give only a very slight coloration with fuchsine. This purified
chloroform could then be used in a similar manner to ether (see page
179), for determining small proportions of alcohol in chloroform.
Chloroform may also be purified from water, alcohol, and ether by
agitating with sulphuric acid as above, separating the acid, shaking
238 CHLOROFORM.
the chloroform with a strong solution of sodium carbonate, and, lastly,
distilling it over freshly burnt lime.
When the quantity of alcohol in chloroform exceeds 1 or 2 per cent.,
the proportion may be determined with tolerable accuracy by shaking
20 c.c. of the sample in a graduated tube with 80 c.c. of water. If the
chloroform be pure it will sink to the bottom in clear globules, but in
the presence of alcohol the liquid and the surface of the drops will
become dim and opalescent. The reduction in the volume of the
chloroform shows the proportion of alcohol in the amount taken. The
addition of a few drops of solution of potassa destroys the meniscus,
and enables the volume to be read more accurately. - The aqueous
liquid may be tested for sulphuric acid by barium chloride ; for free
chlorine or hypochlorous acid by starch and iodide of potassium ; for
hydrochloric acid by silver nitrate; and the presence of alcohol defi-
nitely proved by the iodoform test.
The proportion of alcohol present in chloroform can in some cases
be ascertained from the density. According to C. Remys (Archiv der
Pharm., [3] v. 31) pure chloroform has a density of 1*500 at 15 C.,
the presence of i per cent, of alcohol reducing the density by '002
and J per cent, by "008. According to A. H. Mason, chloroform con-
taining 1 per cent, of alcohol has a density of T497 at 15 '5 C. The
chloroform of the British Pharmacopoeia has a density of 1'49.
Chloroform containing amyl or butyl compounds has a higher density
than 1-500.
The present United States Pharmacopeia prescribes the following tests for
chloroform intended for medicinal purposes :
If 20 c.c. of chloroform be poured upon a clean, odorless filter laid flat upon
a warmed porcelain or glass plate, and the plate be rocked from side to side
until the liquid is all evaporated, no foreign odor should become perceptible as
the last portions disappear from the paper, and the paper should possess no
adventitious odor.
If 10 c.c. of chloroform be well shaken with 20 c.c. of distilled water and
the liquid be allowed to separate completely, the water should be neutral to
litmus-paper, and should not be affected by silver nitrate or potassium iodide.
If to about 5 c.c. of chloroform contained in a dry test-tube of about 10 c.c.
capacity, about 4 c.c. of perfectly clear saturated solution of barium hydroxide
be added without agitation, and the test tube be then corked and set aside in a
dark place for six hours, no film should be visible at the line of contact of the
two liquids (absence of products of decomposition in chloroform, which may be
otherwise pure).
If 40 c c. of chloroform be shaken with 4 c.c. of colorless concentrated sul-
phuric acid in a 50 c.c glass -stoppered cylinder during twenty minutes, and the
liquids be then allowed to separate completely so that both are transparent, the
CHLOROFORM. 239
chloroform should remain colorless and the acid should appear colorless or very
nearly so when seen in a stratum of not less than 15 mm. in thickness.
If 2 c.c. of the sulphuric acid, separated from the chloroform, be diluted with
5 c.c. of distilled water, the liquid should be colorless and clear, and while hot
from the mixing should be odorless, or give a faint vinous or ethereal odor.
When further diluted with 10 c.c. of distilled water it should remain clear and
should not be affected by silver nitrate solution.
If 10 c.c. of the chloroform, separated from the acid, be well shaken with 20
c.c. of distilled water, and the liquid be allowed to separate completely, the
watery portion should not be affected by silver nitrate solution.
Chloroform has marked antiseptic powers and is especially convenient for
preserving urine samples. A few drops well shaken with 100 c.c. will be suffi-
cient to preserve the liquid for an indefinite time. An excess should be avoided,
as the globules collect at the bottom of the bottle and interfere with the exami-
nation of the sediment. It does not interfere with nor imitate any of the com-
mon tests except with copper solutions and by fermentation. The bismuth and
phenylhydrazin tests give no result with a solution of chloroform in urine free
from sugar. Diabetic urine in an active state of fermentation is brought to
quiescence by addition of chloroform. The liquid may be freed from the pre-
servative by adding water and boiling down to the original volume. L.
SPIRIT OF CHLOROFORM, B.P., is a solution of chloroform in 19
measures of rectified spirit (55 O.P.) and should have a density of
"871. A lower specific gravity may be due to deficiency of chloroform
or to the use of spirit of 60 O.P. " Chloric Ether" is a spirituous
solution of chloroform of very varying strength.
The proportion of chloroform present in spirit of chloroform, "chloric
ether," and similar preparations, may be ascertained with accuracy by
introducing into a narrow graduated tube 20 c.c. of the sample and
30 c.c. of dilute sulphuric acid (1 to 6) colored with a little fuchsiue.
A cork is then inserted and the contents of the tube thoroughly
shaken. When the chloroform has separated, the tube is tapped to
cause any floating globules to sink, and about 10 c.c. of petroleum
spirit is cautiously poured on the surface of the acid. The cork is
reinserted, and the volume of petroleum spirit employed is carefully
noted, when the contents of the tube are well mixed by agitation.
After separation the volume of petroleum spirit is again observed,
when its increase will be due to the dissolved chloroform. Better re-
sults are obtainable in this way than without petroleum spirit, but
great care is necessary to avoid error from expansion or contraction
through alteration of temperature. Hence, before observing the
volume of petroleum spirit originally used, and again before the final
reading, the tube should be immersed in a cylinder of cold water for a
short time. The process gives inaccurate results when the proportion
240
METHYLENE DICHLORIDE.
of chloroform exceeds about 30 per cent. In such cases the method
given on page 238 should be employed.
The chloroform in mixtures of chloroform and alcohol may also be
determined by decomposition with alkali in the manner described on
page 183.
Methylene Bichloride. Methylene Bichloride. CH 2 C1 2 .
This substance is the second member of the series of products arising
from the action of chlorine on marsh gas, as shown in the annexed
table.
Methylene dichloride is obtained by exposing the vapor of methyl
chloride in admixture with chlorine to the action of daylight, in a
large glass globe. The products are passed through two Woulffe's
bottles, and then into a flask surrounded by a freezing mixture. The
former chiefly retain chloroform, while the methylene dichloride con-
denses in the flask. It may also be obtained by the reduction of
chloroform in alcoholic solution by zinc and hydrochloric acid.
Formula.
Name.
Boiling
Point.
C.
Specific Gravity.
TH
Methane * marsh gas
V^iA 4
CH 3 C1
CH 2 C1 2
CHC1 3
Chlormethane ; methyl chloride,
Dichlormethane ; methylene dichloride, .
Trichlormethane * chloroform
-23
41-6
61'
/ '999 at -30
I -952 at
l'36atO
( 1-500 at 15
CC1 4
Tetrachlorm ethane ; carbon tetrachloride, .
78'
{ 1'526 atO
f 1'630 at
\ 1'599 at 15
Methylene dichloride is a powerful anaesthetic, but is said to have
a depressing effect. Being more expensive than chloroform, the latter
liquid is sometimes substituted and sold for the former, which it closely
resembles in odor. The two bodies may be distinguished by their
specific gravity and boiling points. The dichlormethane burns with
a smoky flame and dissolves iodine with brown color, while chloroform
unmixed with alcohol burns with great difficulty, giving a green-edged
flame, and dissolves iodine with reddish-violet color.
A mixture of alcohol and chloroform has been substituted for
methylene dichloride. On shaking the sample with water, the alcohol
would be dissolved, and the chloroform would then be recognisable by
its density.
IODOFORM. 241
Bromoform, CHBr 3 .
This body closely resembles chloroform, but boils at 150 to 152 C.
Its density is 2'9 at 12 C., or, according to E. Schmidt, 2-775 at 14'5
C. It solidifies at 9 C.
Caustic potash converts bromoform into chloride and formate of
potassium. By the action of alcoholic potash, gas is evolved, con-
sisting of one volume of carbon monoxide and three of ethylene ;
thus : CHBr 3 + 3KC 2 H 5 O = 3KBr + 2H 2 O + CO + 3C 2 H 4 .
Bromoform is not unfrequently present in commercial bromine, even
to the extent of 10 per cent. It may be detected by fractional dis-
tillation of the bromine on the water-bath, or by treating the sample
with excess of solution of potassium iodide, and then adding sufficient
sodium thiosulphate (hyposulphite) to take up the iodine set free.
The characteristic odor of bromoform then becomes apparent.
lodoform, CHI 3 .
lodoform is produced in Lieben's test for alcohol (page 90). It
may be conveniently prepared by heating 1 part of iodine, 1 of alco-
hol, 2 of crystallised sodium carbonate, and 10 of water to about 70
to 80 C., till decolorised, when the iodoform separates as lemon-yellow
powder, which may be filtered from the liquid, washed with cold water,
and dried.
lodoform is a light yellow, shining, crystalline solid, having a per-
sistent odor resembling saffron, or a solution of iodine in chloroform.
It has a density of 2'0, sublimes at a gentle heat without change,
distils with vapor of water, and volatilises sensibly at ordinary tempera-
tures. Heated strongly, it is decomposed with formation of violet
vapors of iodine, and deposition of carbon.
lodoform is nearly insoluble in water (1 part in 13,000) and dilute
alkaline and acid liquids; sparingly soluble in rectified spirit (1 in 80),
but more readily in absolute alcohol (1 in 25) ; and with facility in
ether, chloroform, and carbon disulphide. It is also dissolved by many
essential oils, and sparingly by glycerin, benzene, and petroleum spirit.
lodoform is employed in medicine as an antiseptic dressing and for
other purposes. In its chemical reactions iodoform closely resembles
chloroform. Its microscopic appearance is very characteristic, its
usual forms being hexagonal plates, stars, and rosettes.
lodoform may be extracted from urine and other aqueous liquids by
agitation with ether. On allowing the ethereal layer to evaporate
spontaneously, the iodoform may sometimes be recognised by examin.
ing the residue under the microscope. If no distinct forms are
16
242 IODOFORM.
observable, the residue should be taken up with a little absolute
alcohol, and three or four drops of the clear solution added to a
minute quantity of a solution of phenol in caustic soda. The mixture
is cautiously heated, when a red deposit will be formed at the bottom
of the tube, soluble in dilute alcohol with crimson color (Lustgarten,
Jour. Chem. Soc., xliv. 243).
COMMERCIAL IODOFORM.
On agitation with water, iodoform should not yield a liquid pre-
cipitable, after filtration, by barium chloride or silver nitrate. It
should leave no soluble residue on ignition in the air; and should be
wholly soluble in boiling alcohol, but insoluble in brine.
Picric acid has been used as an adulterant of iodoform (Pharm.
Jour., [3] xiv. 493). It may be detected by agitating the sample with
dilute solution of caustic soda or carbonate of sodium, carefully
neutralising the filtrate with acetic acid, and adding potassium nitrate,
when a yellow precipitate of the sparingly soluble potassium picrate
will be thrown down. The iodoform may also be separated by treating
the sample with caustic soda solution and agitating the liquid with
chloroform, when only the picric acid will remain in the aqueous
liquid. Picric acid may also be detected by the reddish-brown colora-
tion produced on heating the cold aqueous solution of the sample with
potassium cyanide.
SUGARS.
UNDER the generic name of sugars is included a large number of
bodies occurring naturally in the animal or vegetable kingdoms, or
produced from the so-called glucosides by the action of ferments or
dilute acids.
The sugars constitute a group of closely-allied bodies, in many cases
distinguishable from each other only with considerable difficulty, while
their quantitative separation is frequently impossible in the present
condition of chemistry.
As a class, the sugars are crystallisable, readily soluble in water,
somewhat less soluble or wholly insoluble in alcohol, and insoluble in
ether and other solvents immiscible with water.
A sweet taste is possessed by nearly all sugars, to a greater or less
extent, though in some of the rarer saccharoids the character is very
feebly marked. Glycerol and glycol have a sweet taste, and, like the
sugars, are polyatomic alcohols, but the same analogy of constitution
does not extend to glycocine (the so-called " sugar of gelatin"), or to
the sweet salts of lead and yttrium.
In many cases the sugars exert a powerful rotatory action on a ray
of polarised light, the direction and extent of the rotation being pecu-
liar to each sugar. Hence the optical activity is a valuable means of
estimating and differentiating sugars, and is fully discussed in a special
section.
CONSTITUTION AND CLASSIFICATION OF
SUGARS.
Most of the sugars have the constitution of hexatomic alcohols, or of
aldehydes or ethers derived therefrom. Thus mannite, which is
a-hexone alcohol, C 6 H 8 (OH) 6 , by limited oxidation with platinum-
black yields the corresponding aldehyde, C 6 H 6 (OH) 6 , which is a true
sugar called mannitose. Conversely, by the action of nascent hydro-
gen, the aldehyde mannitose can be again reduced to mannite. Mannite
also results from the reduction of dextrose and Isevulose, which are
sugars isomeric with mannitol ; while the action of nascent hydrogen
243
244 SUGARS.
on another isomer, galactose, results in the production of dulcite, or
/3-hexone alcohol, isomeric with raannite.
The saturated alcohols of which mannite, C 6 H U O 6 , is the type, form
the class of sugars called saccharoids. Their characters are detailed
more fully in the table on the next page.
The aldehydes of the bodies of the last group constitute the im-
portant class of sugars called glucoses, C 6 H 12 O 6 . These have them-
selves, to some extent, the characters of alcohols.
The oxygen-ethers or first anhydrides of the glucoses constitute the
class of sugars called saccharoses, C^H^On, of which cane sugar is the
type. The conversion of saccharoses into glucoses by hydrolysis is
readily effected, but the reverse change has not been realised (unless
very recently).
By the action of heat on the glucoses and saccharoses the elements
of water are eliminated, and other anhydrides result. Thus dextrose,
C 6 H 12 O 6 , yields glucosau, C 6 Hi O 5 .
The following tables show the distinguishing chemical and physical
characters of the principal sugars, which are arranged in the three
classes of saccharoids, glucoses, and saccharoses.
In order to abridge the descriptions as much as possible, initial letters
are used in the tables, the characters given after them referring to the
properties or reactions of the sugars when examined or treated in the
respective manners indicated below :
(a) Specific gravity of the sugar.
(b) Character of the crystals and general appearance of the sugar.
(c) Action of heat on the sugar.
(d) Solubility of the sugar in water, and taste of the solution.
(e) Solubility of the sugar in alcohol.
(/) Products of the action of moderately concentrated nitric acid
on the sugar.
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Erythro-mar
246
PROPERTIES OF GLUCOSES.
73 o
K*2i**S
1 .J~.3g;i
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ilil
PROPERTIES OF GLUCOSES.
247
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248
PROPERTIES OF SACCHAROSES.
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PROPERTIES OF SACCHAROSES.
249
=
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5^ tn *t3_.=? a 7S rt S
ill P.
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250 SUGARS.
Isolation of Sugars.
The general methods by which sugars are isolated in the proximate
analysis of animal and vegetable substances depend much on the
nature of the associated bodies. Principles of separation commonly
utilised are : the removal of albuminoid bodies by heat or precipita-
tion ; the precipitation of dextrin and other gummy matters by alcohol ;
the removal of organic acids and various other matters by lead acetate ;
concentration of the saccharine fluid with a view to promoting crystal-
lisation ; and the detection and estimation of the sugars present by their
reactions as reducing agents, and their relations to polarised light. A
third mode of determination is based on the specific gravity of the
saccharine solution. Other useful processes for estimation or differen-
tiation are based on the behavior of the sugars with yeast, and on
treatment with concentrated and dilute acids, &c. These general
methods will be described in the following sections, before dealing
with the special application of these and other processes to the exam-
ination of particular sugars or saccharine. substances.
RELATIONS OF THE SUGARS TO POLARISED
LIGHT.
The greater number of sugars possess the property of altering the
plane of polarisation of a ray of light. The power is possessed not
merely by the solid sugars, but also by their solutions, the rotatory
action exerted by the latter being approximately, but not strictly, pro-
portional to their concentration, or in other words to the number of
molecules of dissolved sugar which the ray of light is caused to tra-
verse.
The principle of construction of polarimeters, and the optical
activity of various organic substances are described at length on pages
34 to 41.
Specific Rotatory Powers of Sugars.
The strength of a cane-sugar solution which will produce the same
deviation, when examined in a tube 2 decimetres in length, as a plate
of quartz 1 millimetre in thickness, has been determined by various
observers. Clerget estimated it at 16*471 grm. of sucrose in each 100
c.c. of solution. Dubrunfaut reduced the amount to 16'390 grm.,
while the weight 16'350 grm. was the result of the investigations of a
commission consisting of Pouillet, Barreswil, Schlosing, and Duboscq.
SUGARS.
251
The directions now issued with the instrument specify the last-named
amount as that to be used in verifying the scale. Recently Girard
and De Luynes have given 16*190 grm. of cane sugar per 100 c.c. as
the equivalent of 1 millimetre of quartz. Tollens (Ber., 1877, 1403),
in a very elaborate paper, gives 16'337 grm. as the standard amount. 1
The deviation of the D line produced by 1 millimetre of quartz is 21
40', according to Broch, or 21 48', according to Girard and De
Luynes. The mean of these two determinations is 21 44' 21*73.
Fig. 12. 2
Employing this figure in the formula for specific rotatory power given
on page 39, the value of S D for cane sugar in solutions containing about
16 grm. per 100 c.c. may be found as follows :
100 X 21 -73
2 X 16-337
= 66 -50.
1 The corresponding amount for the Ventzke-Soleil instrument is 26*086 grm. in
100 c.c.
2 The accompanying illustration (fig. 12) shows the appearance of a new instrument of
the Laurent type, having an ingenious optical modification due to Mr. Thos. Bayley. It
has given satisfaction in the hands of the writer and others, and is obtainable at a com-
paratively moderate price from P. Harris & Co., Birmingham.
252 SUGARS.
As stated already, the concentration of the solution sensibly
affects the specific rotation of sugars, and not always in the same
direction. Thus, strong solutions of sucrose cause a less deviation
than the same amount of sugar would in more dilute solutions, while
with dextrose the reverse is the case. On this account, recorded values
for S must not be interpreted too strictly in cases in which no mention
is made of the concentration of the solution. The importance of this
point is well shown by the following determinations by Hesse l of the
value of S D for cane sugar in solutions of various strengths :
Grm. of Sucrose Ar , f
per 100 c.c. Value of SD "
1 67-95
2 67*39
3 67-05
6 66-67
10 66-50
20 66-45
The exact apparent specific rotatory power may be found, for solu-
tions of strengths varying from 1 to 10 grm.of cane sugar per 100 c.c.,
by the following formula, in which c represents the number of grm.
of sugar in each 100 c.c. of the solution: S D = +68'65 '828c +
115415c 2 '00541666c 3 . Beyond a concentration of 10 grm. of sugar
per 100 c.c. of the solution, the decrease is pretty regularly '005 for
each unit of sugar. 2
The values of Tollens and Hesse for the specific rotation of
cane sugar agree with those of Tuschmidt, (Jimr. /. Praet. Chem ,
[2] ii. 235) who obtained 66"42 (apparently for somewhat concentrated
solutions), and Backhoven, who obtained the same result (Ibid. [2]
viii. 277). Schmitz, again, has found 66'42 and 66*53 as the value of
S D when c = 10 (Ber., 1877, 1414), and, lastly, Tollens (Ibid. [2] viii.
1403) gives -}-66 '48 as the correct value for S mo in the case of cane
sugar. These results all correspond closely, and point conclusively to
a value of -f66'5 for cane sugar in solutions of a concentration from
10 to 20 grm. per 100 c.c. It must be remembered that this is the
apparent specific rotation for the concentration in question ; the absolute
1 Annal. der Chemie, clxxvi. 95. These determinations have been recently disputed
by Tollens, who finds a very slight decrease in the rotatory power of very dilute solutions
(Ber., xvii. 1751).
2 Calculated from the formula in the text the value of SD for cane sugar when c = 10
is 66-4948. Tollens has recently proposed the formula S D =66'S86 + 0'015035c
0'0003986c 2 . By this, if c = 10, S D = 66-4966.
SUGARS. 253
value of S D for cane sugar being, according to Tollens, -j-63 0- 90, and
according to Schmitz, -j-64'16.
Although the apparent specific rotatory power of cane sugar for
the D line may be considered to be accurately ascertained, the same
cannot be said of the value for the transition-tint. This is doubtless
due in part to the fact that the transition-tint is not a ray of definite
refrangibility, and even differs with different observers.
These are insurmountable difficulties in the way of obtaining a con-
stant value for Sj, and hence all determinations made by instruments
intended for observing the transition- tint must be regarded as of sec-
ondary value only. This is well shown by the discordant factors pro-
posed by different observers for calculating S D to Sj in the case of cane
sugar. 1
The mean of the more trustworthy of these determinations gives a
value for Sj not greatly different from -(- 73'8, which is that generally
adopted. If this be accepted as the specific rotation of cane sugar for
the transition-tint, then S D and Sj may be calculated into each other by
the following factors, which are those adopted in this work :
I- w -"'*! --
In the following table are given the most reliable determina-
tions of specific rotation of some more important species of sugars.
1 The following figures illustrate this fact. For convenience, the value of SD is uni-
formly taken at + 66 0> 5, and the product obtained by multiplying this constant by the
factor or fraction represents the value of Si.
SD X Factor = Sj Authority.
f 1-129 75-08 ................ Landolt- Montgolfier.
24
= 73-21 ................ Girard and De Luynes.
ZI'oU
24
= 74*09 ..... .......... Brown and Heron.
1-091 = 72-55 ................ Calderon.
1-049 = 69-96 ................ Weiss.
The factor of Calderon is remarkable. It is deduced from determinations made by him
in Berthelot's laboratory with the view of revising that chemist's value for Sj (= 73'8).
Calderon found, for 10 to 20 per cent, solutions of cane sugar, SD = 67'1 and Sj = 73'2
(Compt. rend., Ixxxiii. 393). Brown and Heron do not state the grounds of their adoption
of the ratio employed by them. Holzer (Ber., xv. 1938) gives the factor of Weiss as 1*034,
which is even more anomalous than the value given in the table. Holzer found that the
value of SD was not materially affected by the addition of picric acid or other coloring
matters to the solution, but when white light was employed the rotation was affected in a
very marked degree.
254
SUGARS.
The optical properties of the rarer sugars are shown in the tables on
page 245 et seq. 1 It will be observed that the figures given below are
the apparent or sensible specific rotatory powers for solutions containing
10 per cent, or so of the solid sugar. The figures printed in bolder
type are the result of direct determinations, the others being calcu-
lated by means of the 'ratio
| = Ml.
S D
It is not certain, however, that this ratio is correct in its application to
all species of sugar. 'The signs -f- and signify dextro- and few-rota-
tion respectively. It must not be forgotten that the crystals of sugars
(other than cane) are not usually anhydrous when deposited from aque-
ous solutions. The formulae given in the following table show the
condition of hydration of the sugars to which the values for specific
rotation apply :
Apparent Specific Rotatory Power.
Species of
Sugar.
Formula.
Reference.
So.
Sj.
Cane sugar, . . .
Maltose, ....
gjHjA,
+ 66-5
+ 139-2
+ 73-8
+ 154-5
See page 250.
Milk sugar, . .
CjoHooOn 4" HO
+ 52-7
+58-5
Galactose, . . .
C^HioOg
+ 81-3
+90-2
Sucro-dextrose,
C 6 H 12 6
+ 52-7
+ 58-5
Levulose, ....
C 6 H 12 6
-98'8 at 15 C.
-52-7 at87'2C.
-109-7 at 15 C.
- 58-5 at 87 -2 C.
\ Deduced.
J See next page.
Invert sugar, . .
2C 6 Hi 2 6
-23-65 at 15 C.
- at 87'2 C.
-25 -6 at 15 C.
- at 87-2 C.
j- See beiow.
The values given in the above table are those for the rotations pro-
duced by solutions of the various sugars which have been heated or
kept for some hours. If this condition be not observed, the curious
phenomenon of bi-rotation will cause the results to be considerably
higher. It is not improbable that some of the discrepancies in the ob-
servations of the specific rotations of certain of the sugars originated
in a neglect of this precaution.
According to Tuschmidt, Casamajor, and many other observers, 2
1 According to Thomsen the rotatory power of the carbohydrates in solutions of infinite
dilution (c = 0), multiplied by the molecular weight, is always some multiple of the con-
stant number 19 (Joiir. Soc. Chem., xl. 245), but his views have not met with very gen-
eral acceptance.
2 As expressed in the text the statement is Casamajor's. Tuschmidt gives the formula:
gt = _ (27-6 - 0*320. That is, the rotatory power of invert sugar is -27*6, less 0'32 for
each degree centigrade above zero. Thus, at 15 C. the rotation would be - 27'6 - (-.32 X 15)
= -22-8, against -23-05, the number adopted in the test.
SUGARS. 255
a solution of cane sugar which, before inversion, shows a deviation of
-f- 100 divisions, aft&i' inversion has a levo-rotation of 36'5 divisions
at 15 0.
The value given in the table for the specific rotation of invert sugar
is based on this fact, also taking into account the increase in the weight
of solids caused by the inversion of the cane sugar to glucoses. 1
From the value for invert sugar thus found, that of levulose was
calculated by the equation, 25*6 X 2 -|- 58-5 = 1097. 2
PRACTICAL OPTICAL SACCHARIMETRY.
For the application of the rotatory action exerted by sugars and
allied bodies on a ray of polarised liquid to the examination of sac-
charine substances, it is necesary that the body shall exist in solution,
and that the solution be free from suspended matter and also fairly free
from color, though this last condition is less essential with the instru-
ments with which a sodium lamp is used than with those which
employ white light.
It will be convenient first to describe the method of estimating cane
sugar in a commercial product containing no other optically active
substance, after which its determination in presence of invert sugar
will be dealt with, and subsequently the employment of the polari-
meter for estimating other kinds of sugar will be described.
Polarimetric Determination of Sucrose in the Absence of
other Optically Active Bodies.
For the purposes of saccharimetry, it is found convenient in practice
to employ a constant weight of each sample. The weight to be taken
varies from 16'19 to 26'07 grm., according to the instrument to be
employed, and to a lesser degree with each particular instrument.
With SoleiPs saccharimeter the standard weight is 16*350 grm., and
with other instruments, showing directly the percentage-content of real
sugar in the sample, weights closely approximating to 16*337 grm.
are usually employed. With polarimeters furnished with the Ventzke
1 The equation used was :
2173 X 73-8
-36-5X 66^5-
Sj= -= 25-59 at 15 C.
16-337 100
2 The corresponding value for 14 C. is 110'5, against 106 as generally taken.
256 SUGARS.
scale, however, the standard weight is 26*048 grin. 1 With instruments
employing sodium light, and graduated only in angular degrees,
18*800 grm. is a more convenient weight to use.
PREPARATION OF THE SOLUTION OF SUGAR FOR THE POLARIMETER.
Having carefully mixed the sample to obtain a fair average
specimen, the standard quantity is weighed out and introduced care-
fully into a 100 c.c. flask. About 50 c.c. of water are then added, and
the liquid carefully agitated until the whole of the sugar has passed
into solution.
If the liquid be clear and colorless it is merely necessary to dilute
the liquid to exactly 100 c.c., mix it well by agitation, and at once
introduce it into the tube of the polarimeter. But if the liquid be
colored to any notable extent, as is usually the case with commercial
sugars, it is essential that it should be decolorised before being sub-
mitted to optical examination. The necessary clarification may be
effected by means of animal charcoal, hydrated alumina, or basic
acetate of lead.
Animal charcoal is employed by adding to the solution of the sugar
(prepared as above described, and diluted to exactly 100 c.c.) about
one-fourth of its bulk of powdered bone-black, which must be fresh
and free from hygroscopic water. The liquid is well agitated with the
black for a few minutes and then passed through a dry filter. This is
a preferable mode of using charcoal to the French plan, in which the
granular bone-black is placed in a vertical tube closed at the lower
end by a plug of cotton-wool, and the sugar solution passed through
the column of charcoal. In using this method, the first portions of
the percolated liquid must be rejected, as the charcoal absorbs sugar
as well as coloring matter. It is highly probable that the tendency to
absorption is the cause of many of the discrepancies in sugar assays,
but by making the optical determination on the latter portion of the
percolate the error due to the absorption of sugar by the charcoal may
be completely eliminated.
The source of error may be avoided altogether by employing the
following method of clarification, which is very efficacious even under
extremely unfavorable conditions : Weigh out the normal quantity
of sugar and dissolve it in about 50 c.c. of water in a flask holding
i In the original Soleil-Ventzke instruments the scale was so divided that a solution of
cane sugar, of a density of I'lO at 17'5 C., observed in a tube 20 centimetres in length,
rotated 100 divisions. A solution of sugar of the above density is obtained by dissolving
26-048 grm. in water and diluting the liquid to 100 c.c.
SUGARS. 257
100 c.c., as described above. According to the quality of the
sample, the solution will be (1) colorless but cloudy, (2) yellow, (3)
brown, or (4) almost black. In the first case, add about 3 c.c. of a
cream of hydrated alumina and one drop of basic acetate of lead
solution. 1 In the second case, the same volume of alumina may be
used, but the lead solution increased to 3 or 5 drops. In the third or
fourth case add about 2 c.c. of a 10 per cent, solution of sodium
sulphite, and then the lead solution gradually, with constant shaking,
till no further precipitate is produced. 2 Whichever mode of clarifica-
tion be adopted, the liquid is well agitated, and allowed to stand at
rest for a few minutes, to ensure the complete separation of any
precipitate. The flask is then filled nearly to the mark with water,
and the froth allowed to rise to the surface, when it is destroyed by the
cautious addition of a few drops of spirit or a single drop of ether.
Water is then added exactly to the mark, the contents of the flask
thoroughly mixed by agitation, and the liquid filtered through a dry
filter.
Another mode of clarification, recommended by Schiebler, and
very simple and good in all ordinary cases, is as follows : Solutions of
alum or aluminium sulphate and of basic lead acetate are prepared of
equivalent strengths, so that on mixing equal measures and filtering no
sulphate remains in solution. To the solution of sugar 5 c.c. of each
of these liquids is added, the mixture shaken, made up to 100 c.c., and
passed through a dry filter.
Some exceptionally dark cane sugars, and most beet-root molasses,
are not sufficiently decolorised by either of the above methods. In
such cases a double normal quantity should be weighed out, and the
solution clarified by sodium sulphite and basic lead solution, as before
described, a rather larger quantity of the latter liquid being employed.
The solution is made up accurately to 100 c.c., filtered, and 50 c.c. of
1 This alumina cream is prepared by pouring a solution of alum into excess of a hot
solution of washing-soda, collecting the precipitate in a linen bag, washing well with
boiling water, and mixing it with enough water to form a thin cream.
The solution of basic acetate of lead is prepared by grinding together in a mortar Ib.
of recently ignited litharge, 1 Ib. of acetate of lead, and enough water to render the
whole pasty. The mixture is next boiled with three pints of water, and the solution
filtered and preserved in well closed bottles.
2 If, as is often recommended, a considerable excess of lead solution be added, some of
the precipitate is apt to be redissolved, and the solution becomes opalescent and filters
with difficulty. The presence of lead in the solution is said to affect the results, having a
tendency to cause somewhat excessive readings, though the lead solution itself has no
optical activity.
17
258 SUGARS.
the filtrate treated with a saturated solution of sulphurous acid 1 until
the liquid smells strongly of the gas. About 2 grm. of purified animal-
charcoal 2 are then added, the liquid well shaken, made up exactly to
100 c.c., and filtered. By proceeding in this manner, a perfectly color-
less or lemon-yellow solution may be obtained from the worst samples. 3
METHOD OF EMPLOYING THE POLARIMETER.
The solution of sugar having been clarified, if necessary, by one of
the foregoing methods, the tube of the polarimeter (2 decimetres in
length) is rinsed with a little of it, and then completely filled with the
liquid. A glass plate is then cautiously placed on the top, and secured
by screwing home the brass cap. This being done, the cap should be
somewhat loosened to avoid any chance of pressure being exerted on
the contents of the tube. The tube with its contained saccharine solu-
tion is then placed between the polariser and analyser of the sac-
charimeter, when an optical disturbance will be observed, the extent of
which will depend on the amount and nature of the sugar in solution.
The polarimeter is then adjusted until the neutral point is reached,
or, in other words, until the optical disturbance produced by the
introduction of the saccharine solution is compensated. The rotation
required to produce this effect is then read off and recorded.
Polarimeters intended for use in saccharimetry are usually gradu-
ated so that the percentage of cane sugar in the sample examined is
shown without calculation, which is not the case if the instrument be
graduated in circular degrees only.
According to Biot, a plate of quartz 1 millimetre in thickness pro-
duces rotation of exactly 24 circular degrees for the transition-tint.
This rotation is taken as the standard in the Soleil and Soleil-Duboscq
saccharimeters, and the 24 degrees are divided into 100 equal parts, so
that each one of the divisions is equivalent to 0'24 circular degrees.
A cane sugar solution contained in a 2-decimetre tube must have a
concentration variously estimated at 16'19 to 16*35 grm. in 100 c.c. of
the liquid to produce a rotation equal to that caused by 1 millimetre of
1 Instead of employing a saturated solution of sulphurous acid it is convenient to bubble
through the liquid a little sulphur dioxide, now sold in syphons by Boake & Co.
2 This is prepared by boiling 1 Ib. of freshly ground bone-charcoal in half a gallon of
common yellow hydrochloric acid diluted with one gallon of water. The liquid is filtered
through a linen bag, and the residue washed with hot water till free from acid, dried, and
ignited to full redness in a closed crucible. It is bottled while still warm, and kept care-
fully dry.
3 See the articles on analysis of beet-root juice and molasses for precautions necessary
for the removal of foreign optically active bodies from these substances.
SUGARS. 259
quartz. In practice, a solution of sugar, varying in strength from
16-190 to 16-350 grm. of the solid in each 100 c.c. according to the
practice of the instrument maker, is introduced into the polarimeter,
and the point of neutrality marked as 100. The distance between this
point and the zero point is then divided into 100 equal parts. Hence
with each particular saccharimeter should be employed a solution of
sugar of the same concentration as that used for its graduation. By
doing this the percentage of cane sugar contained in any impure
sample free from other active bodies can be ascertained by dissolving
the standard weight to 100 c.c. and noting the number of divisions
through which the light is rotated when the solution is interposed in a
2-decimetre tube. The saccharimeters employing sodium-light are
usually graduated in a similar manner, but the 100 divisions corre-
spond to about 21'73 angular degrees, instead of 24 as in those instru-
ments using the transition-tint. In all cases it is desirable to verify
the standard weight of sugar said to cause a rotation through 100
divisions of the scale, and, if proved correct, this weight should be
invariably employed in subsequent experiments. As stated on page 250,
16'337 grm. for 100 c.c. is the exact quantity of sugar producing a
rotation in a 2-decimetre tube equivalent to that caused by 1 milli-
metre of quartz, and this quantity will be the same whether the instru-
ment be constructed for the sodium-light or for the transition-tint.
Most instruments are now graduated both in circular degrees and in
percentages of cane sugar. If the polarimeter employed be graduated
in the former manner only, the percentage of real sugar in a sample
may be ascertained by comparing the rotatory power of its solution
with that of an equally concentrated solution of pure cane sugar. 1
Thus, if the solutions be made by dissolving in water 20 grm. each of
the standard sugar and the sample, and making the liquids up to 100
c.c. each, then, in a 2-decimetre tube the standard solution should
give an angular rotation of -j-26'6 degrees for the sodium ray. 2 Hence,
if the angular rotation produced by the solution of the sample was
only 25'5 degrees, the percentage of sugar contained in it was 95'87,
according to the proportion
1 Sugar crystals, or white sugar candy, crushed to powder, and dried first by pressure
between layers of filter paper, and then by exposure for a short time to a temperature of
100 C., will furnish a very good standard.
_ 100 CT_ 100 a
2 According to the equation on page 39, 66'5~ / y c 2 X 20' wnence a = 26*6.
260 SUGARS.
Even this simple calculation may be avoided, for, if the weight of the
25 X 20
sample taken be . = 18'800 grm., the angular rotation produced
in a 2-decimetre tube will be exactly 25 degrees for the D line, and
hence each degree of angular rotation will represent 4 per cent, of
sugar in the sample.
For the determination of sucrose in saccharine liquids, such as cane
and beet-juice, the formula becomes
_ 100 a
~7S~
For S should be substituted either 66'5 or 73*8, according as the
instrument employs the sodium ray or white light. Thus, if the liquid
has caused an angular deviation of 19'0 when examined in the
2-decimetre tube with a Laurent instrument, then :
C _19X100_19QO_ 14 . 29
2 X 66-5 133
Therefore, the juice contained 14*29 grm. of cane sugar in each
100 c.c.
If the polarimeter be merely graduated in sugar-units the strength
of juice will be found by multiplying the units of sugar indicated by
the standard weight of sugar with which the instrument is intended to
be used, and dividing the product by 100. Thus, if with a Ventzke
instrument a rotation equal to 72 sugar units has been observed,
then :
Concentration = 72 X 26 ' 48 = 72 X '26048 = 18'76.
Determination of Sucrose in presence of Glucose.
Clerget's Process.
While the polarimeter is capable of accurately indicating the pro-
portion of cane sugar present in a liquid containing no other optically
active substance, its readings may be below the truth, or actually
negative, if the liquid contain a notable amount of certain other
varieties of sugar, or other active bodies. Hence, in such complex
liquids the direct reading of the polarimeter is erroneous, but by
operating in a manner first suggested by Clerget the indications may
still be relied on.
The different varieties of glucose are unaffected by heating with
dilute acid, while cane sugar is, by such treatment, converted into a
SUGARS. 261
mixture of equal parts of sucro-dextrose or dextro-glucose, and sucro-
levulose or levo-glucose. C 12 H 22 Oii -f- H 2 O 2C 6 H 12 O 6 . The product
is called inverted or invert sugar, of which 100 parts are produced by
the hydration or " hydrolysis " of 95 parts of cane sugar.
While the effect of increase of temperature on the rotatory power
of cane sugar and sucro-dextrose is almost inappreciable, in the case
of levulose the temperature is a most important factor. The same
remark applies to invert sugar, the levulose of which diminishes in
rotatory power to the same extent as if it were unmixed with dextrose.
On this account the rotatory power of invert sugar decreases regularly
with increase of temperature till at 87*2 C. it is optically neutral, and
at still higher temperatures exerts a dextro- rotatory power.
Serious discrepancies exist in the rotatory power of sucro-dextrose as
determined by different observers, but fortunately this uncertainty
does not affect the accuracy of ordinary sugar assays, for the change
caused by the inversion of a solution of cane sugar has been accurately
ascertained, irrespective of the exact measure of the rotatory powers of
the two glucoses to the combined influence of which the effect is due.
It has been found by various observers that a solution of cane sugar
which before inversion causes a deviation of 100 divisions to the right,
after inversion has a fevo-rotatory power of 39 divisions at 10 C., and
consequently has undergone an optical change equivalent to a rotation
through 139 divisions. Owing to the diminished optical power of levu-
lose at high temperatures, the change by inversion is less the higher the
temperature at which it is observed, decreasing by one division for each
increase of 2 C. Thus at C. the change by inversion would equal
144 divisions, and the value for any higher temperature may be found
by the equation :
Hence at 15 C., the change by inversion is 136*5 divisions for a
solution previously reading -f- 100 ; or the number representing the
change by inversion, however expressed, multiplied by the factor "7326
(= ) shows the corresponding rotation caused by the sucrose
loO'O /
in the original solution, whence its proportion of cane sugar may be
readily deduced.
The above factor and equation may be conveniently combined as
follows : C is that part of the rotation produced by the uninverted
liquid which is really due to the cane sugar contained in it, and D
262 SUGARS.
is the change in the polarimetric reading caused by the process of inver-
sion. Then :
C= 100 D
144- 1
Thus, if a saccharine solution show at 16 C. a rotation of -j- 23'0 cir-
cular degrees before inversion, and after inversion a tevo-rotatory action
of 7'2 degrees at 16 C., then by the equation :
c _ 100 X 30-2 _ 3020 _ 2
144-19. 186
2
Thus of the 23 circular degrees of rotation produced by the original sugar
solution 22 -26 were really due to cane sugar, and should be calculated
to that substance, while the remaining -}- 0*74 of rotation was due to
dextrose or some other dtoro-rotatory substance not capable of inver-
sion by the means employed for the purpose.
In employing the foregoing method of examining saccharine liquids
containing any considerable quantity of invert sugar, it is essential that
the temperature at which the observation of the original rotation was
made should be identical with that at which the reading of the inverted
solution is taken, otherwise an error would be produced from the altered
optical activity of the invert sugar originally present. Some observers
have held that the invert sugar present in raw cane syrup is optically
inactive, but this statement has been disproved by Meissl.
The rotation due to cane sugar having been ascertained, the amount
of that substance present in the solution may be found as described on
page 259.
In the above arguments the fact is left out of consideration that in-
version usually involves increase in the bulk of the saccharine liquid.
In practice, the increase is neutralised by taking the reading of the in-
verted sugar in a tube 22 centimetres in length instead of 20, as with
the original liquid. The 22 centimetre tube, intended for the observa-
tion of the rotation of the inverted sugar, should be furnished with a
short vertical tube to allow the insertion of a thermometer, so that the
temperature of the liquid during the observation may be accurately
ascertained. 1
i The increase in the volume of the solution can be avoided by inverting with crystal-
lised oxalic acid. A good way of avoiding change of temperature is to employ a polar-
ising tube surrounded with cold water, on the plan of a Liebig's condenser.
SUGARS. 263
THE INVERSION OF SUGAR for polari metric purposes is best accom-
plished in the following manixer : The sugar solution is clarified and
made up to a definite volume in the manner described on page 256,
and its rotating power observed by the polarimeter. 50 c.c. of the
solution are then mixed with 5 c.c. of pure fuming hydrochloric
acid of about 1'16 sp. gravity. This is best done in a flask having two
marks on the neck, one at 50 c.c. and a second at 55 c.c. The flask
is next heated on a water-bath till its contents have acquired a tem-
perature of 68 C., an operation which should be arranged to occupy
about ten minutes. The solution is then cooled down by immersing
the flask in cold water, and if colored, may be shaken with a very
little bone-black and filtered. The liquid is then poured into the 22
centimetre tube, and its rotation observed by the polarimeter in the
manner already described. (For other methods of inversion, see
below.)
Clerget's method is applicable to the estimation of cane sugar in
such complex saccharine liquids as contain no bodies other than cane
sugar, the optical activity of which is modified by heating with dilute
acid under the conditions sufficient to insure the inversion of cane
sugar. But it must be borne in mind that instances may occur in
which such changeable substances are present. Thus the mixture of
dextrose, maltose, and dextrin known as " starch-sugar " undergoes a
change in optical activity by heating in solution with dilute acid, and
there exist in molasses sensible quantities of optically active bodies,
which may undergo modification by treatment with acid. Hence the
results of Clerget's method must be received with caution when applied
to such products.
It must also be borne in mind that the presence of various substances,
themselves optically inactive, has a tendency to modify the rotatory
powers of saccharine liquids, though interference from this cause is
not likely to occur in practice. 1
1 The presence of alcohol in solutions of cane sugar does not materially alter the rota-
tory power, but it reduces the rotation of invert sugar. Free caustic alkalies notably
reduce the rotation of saccharine solutions, but on neutralisation with acetic or phosphoric
acid the original optical activity is restored. Baryta, strontia, and lime also lower the
rotating power of sugar solutions. The neutral carbonates of the alkali metals have but
a slight influence, and the acid carbonates none at all. Chloride of sodium present in
equal quantity to the cane sugar in a 10 per cent, solution of the latter, reduces the
rotation from 67'0 to 65-3 ; and in a solution containing 20 grm. of sugar and 20
of salt per 100 c.c. the rotation is only 61 0- 0. According to Muntz, the sulphates,
nitrates, phosphates, and acetates of the light metals alter the polarimetric reading
from 2 to 3 per cent., when they are present in the proportion of 20 or 30 parts to 100 of
sugar.
264 SUGARS.
Polarimetric Determination of Sugars other than Sucrose.
The optical estimation of all rotating sugars may be effected on
principles similar to those already described for determining sucrose,
provided that no interfering substance be present. The method of
clarifying colored solutions is in all cases much the same as that
found effective with cane sugar on page 256, and the directions need
not be repeated.
In preparing solutions of sugar other than sucrose for examination
with the polariraeter, if the instrument is merely graduated in cane-
sugar units it is desirable to employ the ordinary standard weight of
sugar, but the indications require to be translated into those of the
particular species of sugar under examination. This may be done by
multiplying the observed sugar-indication by 66*5, the value of S D for
cane sugar, and dividing it by the specific rotatory power (S D ) for the
sugar under treatment. The concentration of solutions of unknown
strength may similarly be ascertained.
When an instrument graduated in circular degrees is used, it is
simpler to make a solution containing 20 grm. of the sugar per 100 c.c.,
and examine it in the usual way in a thickness of 2 decimetres. The
percentage of sugar in the sample will then be found by dividing the
specific rotatory power into the circular angle of rotation, and multi-
plying the number thus obtained by 250. 1
INFLUENCE OF TEMPERATURE, REACTION, &c.
In examining solutions of sugars with the polarimeter, it must be
borne in mind that the optical activity of certain species of sugars is
modified more or less by the temperature, concentration, and other
circumstances already alluded to. Hence, to ensure the best results,
the solution should have a concentration of 10 to 20 grm. per 100 c.c.,
and the temperature should be as near 15 C. as possible, unless some
other temperature be deliberately chosen, and its effects duly allowed
for. The presence of free acid in moderate amount does not influence
the rotatory power of sugars, but any alkaline reaction must be care-
fully neutralised before taking the observation.
Bi-RoTATiON is a term employed to signify the curious change in
optical activity which is undergone by the solutions of certain sugars
when kept or heated. The change in optical activity is probably due
to the existence of two modifications of bi-rotating sugar, a and /?, the
1 c = a . This gives the pure sugar in 100 c.c. of the solution or in 20 grin, of the
2 S
sample, and the percentage will be five times this.
SUGARS. 265
first of which is present in freshly-made solutions, but undergoes con-
version into /5 in the course of a few hours at the ordinary temper-
ature, or immediately on heating the liquid. In some cases (e.g.,
dextrose and milk sugar), the freshly-made solution has a greater
optical activity than after keeping, whilst in others (e.g., maltose)
the rotation increases on standing. To avoid the error due to bi-
rotation, the solution of a solid sugar (other than sucrose) should
always be heated to boiling before introducing it into the observing
tube. It is desirable to heat the solution before finally making it up
to an exact volume.
SPECIFIC GRAVITY OF SACCHARINE SOLUTIONS.
An aqueous solution of cane sugar, containing 10 grm. of the
solid in each 100 c.c., has a density of 1*038 -6 at 15'5 C. (=60
R). The weight of water in 100 c.c. of this solution is 103*86
10-00=93-86 grm. As this would occupy 93'86 c.c., the volume
occupied by the 10 grm. of sugar is 6'14 c.c., whence the
specific gravity of the sugar in a state of solution is =1'628,
a figure which agrees closely with those obtained in a similar
manner for other carbohydrates.
From careful determinations it appears that solutions of equal
strengths containing different carbohydrates have approximately the
same, though not strictly identical, specific gravities. In other words,
the density of the solution depends chiefly on the amount of solid
dissolved, and not on the percentage of carbon in the liquid. As a
consequence of this fact, it is found that solutions of cane sugar
increase very sensibly in density on inversion by dilute acid, or a
small quantity of yeast, and a similar increase of density is observed
by the hydrolysis of maltose. 1
1 The increase in the density of cane sugar solutions by inversion has a practical bear-
ing of an unpleasant character, as some brewers have discovered to their cost, the duty
on worts being levied on the content of saccharine matter as indicated by the specific
gravity. Hence, if, from the presence of traces of acids or ferments, the dissolved sugar
gradually undergoes inversion, the brewer will be liable to an increased duty. Oc-
casionally he has been charged with having surreptitiously added more sugar to his wort,
though the real nature of the change ought to be known to the Excise. Direct estimation
of the solid matter in the solution appears to confirm the calculation from the density,
owing to the fixation of the elements of water in the inversion of the sugar. By com-
pletely inverting the solution with acid (making due allowance for the increase of
density due to the acid used), calculating the sugar from the density and deducting ?) Solutions containing 10 grin, of the solid in 100 grm. weight
of liquid ; and,
(c) Solutions containing 10 grm. of the solid in 100 c.c. measure
of the solution.
The figures refer in 'all cases to densities at 15'5C. ( = 60 F.),
water at the same temperature being taken as 1000.
Substance in
Solution.
Formula.
Specific Gravity of Solutions
containing
Observer.
4-21 per
cent, of
Carbon.
6
10 grm.
solid per
100 grm.
c
10 grm.
solid per
100 c.c.
Dextrose
C 6 H 12 6
2C 6 H 12 6
CioHjjaOn
CjoHoaOn
CioHooOu
arCioHooOjo
1042-1
1042-0
(1042-4
1 1042-1
(1042-3
1040-6
(1040-6
I 1040-3
(1040-1
( 1040-8
J 1040-0
(1041 1
1041-2
1041-2
(1038-3
< 1039-0
(10392
1039-1
1034-9
1040-0
1039-9
1040-3
1040-0
1040-2
1040-6
1040-6
1040-3
1040-1
1040-8
1040-0
1041-1
1038-9
1040-4
1040-0
1041-1
1041-0
1041-3
1039-0
10385
1038-4
1038-8
1038-5
1038-7
1039-1
1039-0
1038-6
1039-3
1038-5
1039-5
1037-5
1038-9
1038-5
1039-5
1039-4
1039-7
1037-5
F. Salomon.
A. H. Allen.
G. H. and R.i
A. H. Allen.
Chancel.
O. Hehner.
G. H. and R.i
Brix ; Gerlach.
Brown and Heron. 2
Brown and Heron. 2
O'Sullivan, 1876.3
O'Sullivan, 1879.3
Chas. Graham.
Muspratt.
G. H. and R.i
G. H. and R.i
O'Sullivan, 1876.3
O'Sullivan, 1879.3
H. T. Brown, 1884.
Brown and Heron. 2
G. H. and R.3
Starch glucose, ....
Invert sugar,
Milk sugar
Cane sugar,
Maltose
Malt extract,
,, pale, . .
,, brown, .
Dextrin,
Starch paste, .....
Caramel,
In practice it is convenient to assume the solution-densities of the
carbohydrates in the table to be uniformly 1038'6, for a concentration
1 Report on Original Gravities, 1852, by Graham, Hofmann, and Redwood.
2 Jour. Chem. Soc., xxxv. 569 et seq.
8 O'Sullivan's original figure for the solution-density of maltose was 1038*5 (Jour.
Chem. Soc., xxx. 130), and he adopted the same figure for dextrin but in a recent letter
this chemist informs the writer that he- now takes 1039*5 as the density of solutions of
maltose and dextrin containing 10 grm. of the solid per 100 c.c., the lower figure being
a consequence of the extreme difficulty of obtaining these carbohydrates in a condition
of absolute dryness and purity.
SUGARS. 267
of 10 grm. per 100 c.c. This is Brown and Heron's figure for cane
sugar, 1 and is not far from the mean of the whole table.
The density of solutions of dextrin and the chief kinds of sugar
being almost identical, it follows that the sum of them present in an
aqueous solution may be found approximately by allowing an increase
of 3'86 in density for each 1 grm. of sugar or other carbohydrate in
100 c.c. of the liquid. For very dilute solutions of cane sugar this
figure is correct, 1 but for those containing more than 12 of solids per
100 volumes, the divisor 3'85 gives still closer results. If W be the
weight of the solid carbohydrates in 100 c.c., and D be the density of
the solution at 60 F. (compared with water as 1000), then the value
of W may be found by the equation
W = D ~ 1QQO = (D 1000) X '2597.
3*85
From the number thus found for W (= the number of grm. of
solids in 100 c.c.) the weight of solid carbohydrates in 100 parts by
weight of the liquid (w) may be found by multiplying \V by 1000, and
dividing the product by the density of the liquid :
n ,_10QQ X W
By the Inland Revenue Act of 1880, the specific gravity of standard
wort was fixed at 1057 at a temperature of 60 F. Hence, such wort
contains 14*8 grm. of solids per 100 c.c., or 148 Ibs. per 100 gallons; 2
for
1057 1000
3-85
= 14-8.
This result gives, by the second equation, 14'0 parts of solids in 100
parts by weight of the liquid ; for
= 14 .
1057
1 Brown and Heron (Jour. Chem. Soc., xxxv. 644) have laid down a curve by which
the strength of cane sugar solutions can be readily ascertained in all cases of less density
than 1150.
2 It is surprising how difficult it is for an unscientific mind to grasp the true relations
between weight and volume. Thus, the provisions of the Inland Revenue Act re-
lating to density were at first wholly incomprehensible to the majority of brewers. A
very common fallacy was to suppose that a barrel of wort which weighed 20 Ibs. more
than the same barrel would if filled with water, must necessarily contain 20 Ibs. only of
dry extract.
268
SUGARS.
For all saccharine solutions of moderate strength the foregoing
formulae will answer every purpose. Solutions of invert sugar respond
to the formulae up to about 20 per cent, of contained solid, but more
concentrated solutions should be diluted with a known proportion of
water before applying the method.
Tables showing the densities of concentrated solutions of cane sugar
have been published by Gerlach, Scheibler, Balling, and Brix. The
following figures are chiefly those of Gerlach, and will answer every
purpose :
Cane Sugar
percent, by
weight.
Sp. Gravity
at 17 -5 C.
Cane Sugar
per cent, by
weight.
Sp. Gravity
at 17'5 C.
Cane Sugar
per cent, by
weight.
Sp. Gravity
at 17'5 C.
10
^0401
34
^1491
58
7-2782
11
0443
35
1540
59
2840
12
0485
36
1590
60
2899
13
0527
37
1641
61
2959
14
0570 *
38
1691
62
3019
15
0613
39
1742
63
3079
16
0656
40
1794
64
3139
17
0700
41
1845
65
3200
18
0744
42
1897
66
3262
19
0788
43
1950
67
3324
20
OH32
44
2003
68
3386
21
0877
45
2056
69
3449
22
0922
46
2109
70
3512
23
0968
47
2163
71
3575
24
1014
48
2218
72
3639
25
1060
49
2272
73
3703
26
1106
50
2327
74
3768
27
1153
51
2383
75
3833
28
1200
52
2439
80
4159
29
1248
53
2495
85
4499
30
1296
54
2552
90
4849
31
1344
55
2609
95
5209
32
1393
56
2666
99
. '5504
33
1442
57
2724
CORRECTION OF DENSITIES OF SACCHARINE SOLUTIONS FOR TEM-
PERATURE. In breweries it is often convenient to ascertain the
density of the wort at a temperature above that of 60 F. (= 15 '5
C.), in which case the specific gravity as observed by the hydrometer
can be calculated into the corresponding number for a temperature of
60 F. in the following manner :
To unity add '004 for every degree of specific gravity above 1000
(
inverted, and neutralised if necessary, is added to the hot Fehling's
solution, and the water kept boiling in the outer beaker for twelve
or fourteen minutes. If the blue color of the solution be com-
pletely destroyed within the first few minutes it can be restored by
quickly adding more of the Fehling's solution, but it is much safer to
commence the assay again, using a smaller amount of the saccharine
liquid. After twelve or fourteen minutes the precipitated cuprous
oxide is rapidly filtered, washed with boiling well-boiled water, dried,
and ignited in porcelain. Strong ignition for five or six minutes in
an open crucible ensures the conversion of the red precipitate into the
black cupric oxide (CuO), and treatment with nitric acid is hence
rarely necessary. The oxide of copper must be cooled under a desicca-
tor and weighed as rapidly as possible, as it is extremely hygroscopic.
Although the above method is very satisfactory, some chemists prefer
to weigh the cuprous oxide direct, or to redissolve the precipitate,
either before or after ignition, and deposit the metallic copper on the
inside of a platinum crucible by electrolysis.
The details of manipulation just given are those recommended by
O'Sullivan (Jour. Chem. Soc., xxx. 131) for the estimation of maltose
in beer- worts, &c. The determination of milk sugar by Fehling's
solution requires certain modifications to insure accuracy, and is best
effected as described under " Lactose."
The following factors may be employed for calculating the weight
of copper or oxide of copper obtained to the corresponding quantities
of the principal kinds of sugar.
Glucose,
C 6 H 12 6 .
Cane Sugar,
doH^On
(after inversion).
Milk Sugar,
CioHgoOn.
Malt Sugar,
QisHoaOn.
Cu,
Cu 2 0, ....
CuO, ....
5634
5042
4535
5395
4790
4308
7707
6843
6153
9089
8132
7314
Thus, if a solution of O'l grm. of a sample of cane sugar has been in-
verted and precipitated as above described, and the resultant CuO
weighs 0*198 grm., then the total quantity of sugar (expressed as cane
sugar) is
0-198 X '4308 = -085298 = 85'3 per cent.
SUGARS. 285
TlTRATION BY PAVY's AMMONIACAL CUPRIC SOLUTION.
This modification of the ordinary mode of using Fehling's solution
for the estimation of reducing sugars is based on the fact that in pres-
ence of a sufficient excess of ammonia the cuprous oxide is not pre-
cipitated, but forms a colorless solution, so that the end of the reaction
is indicated by the decolorisation of the blue liquid. As the ammo-
niacal cuprous solution is extremely oxidisable, the blue color being
restored by oxidation, it is necessary to avoid access of air. This is
best done by attaching the nose of the Mohr's burette containing the
sugar solution to a tube passing through the india-rubber stopper of a
flask containing the copper solution. A second tube conveys the steam
and ammoniacal gas into a flask of cold water. It is desirable to allow
the end of the tube to dip into a little mercury placed at the bottom
of the water, so as to prevent any tendency to "suck back." A still
better arrangement is to pass (by a third tube) a slow current of
hydrogen or coal-gas through the flask containing the boiling copper
solution.
To prepare the ammoniacal solution, 120 c.c. of the ordinary
Fehling's solution (see page 280) should be mixed with 300 c.c. of
strong ammonia (sp. gr. *880), and with 400 c.c. of caustic soda solu-
tion of 1*14 sp. gr. ( 12 per cent.). The mixture is then made up
to 1 litre. 100 c.c. measure of this solution has the same oxidising
power on glucose as 10 c.c. of the ordinary Fehling's solution, that is,
it corresponds to '050 grm.
In carrying out the process, 100 c.c. of the above solution are
placed in the flask, a few fragments of pumice or tobacco-pipe added,
the tubes and burette adjusted, and the liquid brought to ebullition.
The sugar solution is then gradually run in from the burette, the
boiling being continued regularly. The process is at an end when the
blue color of the liquid is wholly destroyed. The end- reaction is
very sharply marked, but the reduction occurs more slowly than with
the ordinary Fehling's solution. The process is often a very useful
one, especially for the rapid assay of impure saccharine liquids such
as beer-worts.
Pavy's solution is said to possess a different oxidising power on
maltose and lactose from that exerted by Fehling's test. Its reaction
on invert sugar is, under the above-described conditions, only five-
sixths of that exerted by Fehling's solution. Hence 120 c.c. of the
latter are employed in making the ammoniacal solution, instead of
100, as would be the case if they were strictly equivalent.
286 SUGARS.-
O. Hehner has shown (Analyst, vi. 218) that the presence of a
varying proportion of salts, such as alkaline tartrates and carbonates,
gravely affects the accuracy of the indications obtained by Pavy's
solution.
Reaction of Sugars with Solutions of Mercury.
Several methods have been described of determining glucoses by
their reducing action on mercuric solutions, an alkaline solution of
potassio-mercuric cyanide being recommended by Knapp ; an alkaline
solution of potassium mercuric iodide by Sachsse ; and a solution of
mercuric acetate by Hager. The first two of these reagents have
valuable qualities.
KNAPP'S MERCURIC SOLUTION is strongly recommended by Mu'ller
and Hager for determining the glucose in diabetic urine, the process
being conducted in the following manner:
A standard solution is prepared by dissolving 10 grm. of pure dry
mercuric cyanide in water, adding 100 c.c. of caustic soda solution of
1-145 sp. gr., and diluting the liquid to 1000 c.c. 10 c.c. of this
liquid are reduced by 0'025 grm. of diabetic sugar (dextrose). 10 c.c.
of the standard solution are diluted with 20 to 30 c.c. of water, and
the liquid heated to the point of boiling. The urine, previously diluted
with water to five or ten times its volume, is then run in from a
burette till the whole of the mercury is precipitated. When the pre-
cipitate has settled, a drop of the supernatant liquid, which has a
more or less yellow color, is transferred by a glass tube to a piece of
thin, pure white, Swedish filter paper. The paper is held over a bottle
containing fuming hydrochloric acid, and then over a vessel contain-
ing strong solution of sulphuretted hydrogen. The slightest trace of
mercury is shown by the production of a light-brown or yellow stain.
It is desirable to compare a drop of the original liquid side by side
with that which has been subjected to the treatment with the acid gases.
By thus working, the slightest trace of mercury remaining in the
liquid may be detected. Of course it is desirable to repeat the titra-
tion. Knapp's solution undergoes no change on keeping.
For the analysis of ordinary glucose solutions, 40 c.c. of Knapp's
reagent should be diluted to 100 c.c. and the sugar solution (not
stronger than per cent.) run in as quickly as possible.
An alkaline solution of mercuric cyanide has been employed by
H. W. Wiley for oxidising and destroying dextrose and maltose while
leaving dextrin unchanged.
SACHSSE'S MERCURIC SOLUTION is prepared by dissolving 18 grm.
SUGARS.
287
of pure dry mercuric iodide in a solution of 25 grm. of potassium
iodide. To this a solution of 80 grm. of caustic potash is added, and
the solution diluted to 1 litre. 40 c.c. of this solution are boiled in a
basin, and a standard solution of the sugar gradually added. The end
of the reaction is attained when a drop of the supernatant liquid
ceases to give a brown color with a drop of a very alkaline solution of
stannous chloride. The end of the reaction is well defined, and the
results are accurate when pure dextrose or inverted sugar is worked
with, though differing with each. 1 In presence of cane sugar the
results are quite erroneous. By reducing the proportion of caustic
potash from 80 grm. to 10 grm. per litre, Heinrich finds that glucose
may be accurately determined in presence of very varying amounts of
cane sugar. .
The solutions of Knapp and Sachsse cannot advantageously replace
that of Fehling for ordinary purposes, but occasionally they are capa-
ble of being applied with great advantage. This is owing to the fact
that they are unequally affected by the different kinds of reducing
sugars, and even the two mercurial solutions exhibit essential differ-
ences in this respect. The subject has been recently investigated by
Soxhlet (Jour. Prac. Chem., [2] xxi. 227 ; and Jour. Chem. Soc.,
xxxviii. 758), who gives the following table. The numbers must not
be interpreted too rigidly, but regarded as roughly comparative rather
than absolute determinations of reducing power.
' *
Fehling.
Knapp.
Sachsse.
Dextrose .
100
100
100
Invert sugar
96*2
99 '0 (100 9 )
124'5
Levulose . .
92*4
102'2 (100 9 )
148'6
70-3
64-9
70-9
Lftcto-glucose
93*2
83*0
74*8
Inverted-milk sugar
96'2
90'0
85'5
61 '0
63*8
65'0
Some of Soxhlet's results are not accepted as accurate (see page 289),
and further investigation of the subject is much wanted. His observa-
tions are very suggestive of possible means of differentiating various
sugars.
Influence of Variable Conditions on the Reducing Power
of Sugar Solutions. In all experiments on the reducing power of
1 40 c.c. of Sachsse's solution is reduced by 0-1342 grm. of dextrose, or 0*1072 of invert
sugar.
288 SUGARS.
sugar on metallic solutions, it is important to operate as far as possible
under constant conditions. Apparently unimportant variations, as
time occupied in the experiment, amount of free alkali, presence of
excess of the metallic solution, concentration of the liquid, and other
conditions liable to change with every experiment, are all factors more
or less concerned in the results obtained, and rigidly accurate results
thus become impossible in many cases likely to occur in the practical
analysis of saccharine liquids. The variations due to some of the
above causes have been studied by Soxhlet (Jour. Prac. Chem., [2]
xxi. 227-317), a very full abstract of whose original paper has been
published in English by C. H. Hutchinson (Pharm. Jour., [3] xi. 721).
Soxhlet finds that the reducing power of sugar for alkaline copper
solutions is only constant under exactly the same conditions, and that
if the same amount of sugar act in one case on an amount of copper
solution which it is just able to reduce, and in another on an excessive
quantity, the reducing equivalent will in the first case be found to be
considerably less than in the second. Evidently, therefore, if a solu-
tion of sugar be added by small quantities at a time to a copper solu-
tion, as in an ordinary volumetric estimation, the amount of reduction
effected by the first quantities added will be greater than that produced
by the last. To avoid the error due to this cause Soxhlet employs the
sugar and copper solutions in the exact proportions necessary for their
mutual reaction, ascertaining the volumes requisite by a series of
approximating experiments. 1
It will be seen from Soxhlet's results that dilution of the Fehling's
solution very sensibly affects the reducing power exerted by the sugar.
Thus one equivalent of invert sugar in 1 percent, solution reduces 10*1
equivalents of CuO when the undiluted cupric solution is employed,
but 9'7 equivalents only when Fehling's solution is diluted with four
measures of water. It will also be observed that Soxhlet's results show
a slight but very sensible difference between the reducing power of
dextrose and of invert sugar, and this difference becomes more marked
1 These were made by adding to a carefully measured quantity of Fehling's solution
(prepared fresh daily), at the boiling point, a certain amount of a one per cent, or one-half
per cent, solution of the sugar. The reaction was allowed to continue for a specified time,
when the liquid was passed through a plaited filter, and a portion of the filtrate acidulated
with acetic acid, and tested with potassium ferrocyanide. If a reddish-brown coloration
or precipitate resulted, the experiment was repeated, a somewhat larger quantity of sugar
solution being employed, and so on until a measure of sugar solution was found that would
exactly suffice for the decomposition of the copper solution, while if 0*1 c.c. less of sugar
solution were employed a sensible quantity of copper was found in the filtrate. Hence
the volume of sugar solution required was ascertained to within 0*1 c.c.
SUGARS.
289
when the reducing power of levulose is calculated therefrom. 1 This
difference, if a real one, is of an exceedingly important nature, as it is
calculated to vitiate very many of the analyses of saccharine matters
on record. It is therefore greatly to be regretted that Soxhlet's con-
clusions are very seriously diminished in value by the questionable
method adopted by him for effecting inversion. 2
The following results were obtained by Soxhlet by operating in the
manner described. The sugar solutions contained 1 grm. of the solid
in 100 c.c. The figures represent the weight of the sugars in grammes
required for the reduction of 100 c.c. of Fehling's solution, used undi-
luted or mixed with one, two, three, or four measures of water.
Time of
Weight of Sugar oxidised by 100 c.c. of
Fehling's Solution.
Kind of Sugar.
Heating in
Minutes.
Undi-
luted
Equal
Bulk of
Two
Measures
Three Four
Measures Measures
Water.
Water.
Water. Water.
Dextrose 1
(anhydrous) J
2
4750
4825
4880
4920
4940
Invert sugar, ....
2
4940
5030
5090
5140
5150
Levulose )
(calculated) /
2
5130
5235
5300
5360
5260
Milk sugar 1
(dried at 100) {
6
676 Unaffected by dilution.
676
Lacto-glucose, \
(dried at 100) /
2
511
.
-
.
533
Maltose . .
3 to 4
778 '
740
The same objection applies to Soxhlet's experiments on the reducing
power of invert sugar on the mercurial solutions of Knapp and Sachsse
In these cases, also, he found that the reducing equivalent was notably
influenced by the concentration of the solution and the proportion of
alkali present, and that any other variation in the conditions of work-
ing was likewise liable to influence the results.
1 According to Allihn the reducing powers of levulose and dextrose are identical, if the
heating with Fehling's solution be continued for half an hour.
2 This was done by dissolving 9*5 grm. of purified cane sugar in 700 c.c. of water,
adding 100 c.c. of one-fifth normal hydrochloric acid, and heating on the water-bath for
thirty minutes. The solution was then exactly neutralised by caustic soda, and diluted
with water to 1000 c.c. Soxhlet found that '5 grm. (=='475 of cane sugar) of inverted
sugar so obtained reduced 101'2 c.c. of undiluted Fehling's solution, while with more pro-
longed heating with the same amount of acid the product reduced 100'5 c.c. of copper
solution, and this was further reduced to 100*2 when 300 c.c. measure of the standard acid
was employed, and the heating continued for ninety minutes.
19
290
DISTINCTIVE TESTS FOR SUGARS.
I 55
M?i s
IsS-SHS M
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3.22
ih
f-i O rC
9
3 11^
2 2 II
-
I 8
&*&
,T3 OB
; HT3
1 C8 '
s-cs
Us
1
3
OJ .
^^
co
11
3 8
ft (
^O
1 ||!
o o ft e
^ ^^3 ^
x x fe s
-S 5 $
O^R
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rC T3
-;
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O 3
-~ M
!!
II
11
5^
IS
C8 _r ff tX'd O
eJri'li-l
:IP^-
o -2 ^ b
SUGARS. 291
RECOGNITION OF THE PRINCIPAL KINDS OF
SUGAR.
When a sugar has been isolated in a condition of tolerable purity,
it may be recognised by the special characters described in the tables
of properties on page 245, with the aid of the additional details of
manipulation given in the subsequent sections.
The detection or identification of a sugar by its reactions is greatly
simplified by applying the tests in a systematic manner, and the fol-
lowing method of examination may be of service for distinguishing
qualitatively between the more common species of sugar. For reasons
of practical convenience the reactions of dextrin are also given.
From an inspection of the table, it appears that all the substances
referred to therein are optically active. Hence it is not possible to
have an inactive solution containing a notable quantity of one of the
above sugars. If levulose were present together with a certain pro-
portion of one of the other sugars, the solution might exhibit no rota-
tion at first, but would do so on heating, owing to the reduced optical
activity of levulose in hot liquids.
Levulose always occurs in practice in presence of more or less dex-
trose, and in such cases is best detected by the change in the optical
activity of the solution on heating. Other distinctions between levu-
lose and dextrose will be found under " levulose."
The presence of a glucose of some sort is indicated^by the behavior
of the sugar with tests 2 and 8.
Milk Sugar is only met with in products derived from milk. It is
peculiar in having its optical activity and cupric oxide reducing power
increased by treatment with dilute acid, and in yielding mucic acid on
oxidation with nitric acid. Physically it is distinguished from other
sugars by its crystalline form and sparing solubility in cold water.
Cane Sugar is well characterised by its behavior with tests 1, 3, 4, 5,
6, and 7.
Maltose when unmixed with dextrose is distinguished from the latter
by reactions 2 and 6, but if dextrose be also present only a quantita-
tive application of tests 3, 4, 6, and 7 will suffice for the detection of
maltose.
Dextrin, which often occurs together with maltose, may be detected
in mixtures of the two by gradually adding a large excess of strong
alcohol, when it is precipitated in flocks which often adhere to the
sides of the beaker as a gummy mass. Dextrin is said to be unaffected
in its optical activity by boiling with a concentrated alkaline solution
292
SUGARS.
of mercuric cyanide, by which treatment maltose and dextrose are
oxidised and destroyed.
The value of the tests depending on the reduction of alkaline cupric
solutions and observations of optical activity is greatly diminished
when the experiments are merely of a qualitative nature, whereas an
intelligent interpretation of the quantitative indications of these tests
will allow of the better known sugars being not only detected but actu-
ally determined in presence of dextrin and of each other.
FOE THE DETERMINATION OP SUGARS IN ADMIXTURE, the cupric
oxide reducing power (K) and specific rotatory power (S) should be
determined under the following circumstances :
In the original solution of known concentration.
In the solution after treatment with invertase.
In the solution after heating for some hours with dilute sulphuric
acid.
The following table shows the relative cupric oxide reducing
power (K) (determined gravimetrically) of the principal sugars,
that of dextrose being taken as 100 ; and the specific rotatory power
(S) of the solutions of the original substances, and of the inverted
solutions thereof, corrected for increase in volume. The values given
are in all cases calculated for the anhydrous substance, and the volume
of the solution is assumed to remain unchanged, any dilution being
duly allowed for. The characters attributed to gallisin are also given
in the table :
Dextrose.
Levu-
lose.
Milk
Sugar.
Maltose.
Cane-
Sugar.
Dextrin.
Gallisin
CUPRIC OXIDE REDUCING
POWER (= K).
a. Of original solution, .
b. After treatment with
100
100
67-8
62
45-6
invertin,
100
100
67-8
62
105-3
45-6
c. After heating with acid,
100
100
97-7
105-3
105-3
111-1
SPECIFIC ROTATORY POW-
ER (for Sodium ray = SD).
a. For original solution, .
+ 52-7
98-8
+ 55-8
+ 139-2
+ 66-5
+ 198
+ 84
6. After treatment with
invertin
+ 52-7
98-8
+ 55'8
+ 139-2
24'3
+ 198 (?)
+ 84
c. After heating with acid,
+ 52.7
98-8
+ 71-0
+ 55-0
24-3
+ 58-5
It must be borne in mind that the figures representing the cupric
oxide reducing powers after treatment with invertin or dilute acid are
not the values of K for the original weights of substance, but for the
products of the inversion. Thus, on heating with dilute acid, 9 parts of
dextrin yield 10 of dextrose, and hence the value of K after the
SUGARS. 293
treatment is not 100, but 100 X-^-. Similarly, when milk sugar, mal-
y
tose, or cane sugar undergoes hydrolysis, the resultant glucoses are
20
' = 105*27 per cent, of the weight of the original sugar, and hence
iy
the reducing powers and optical activity of the solutions are corres-
pondingly increased. In the latter case, the figures in the table repre-
sent the rotation produced by the products of the hydrolysis, and not the
actual value of S D for those products.
In determining the values of K and S D it is necessary to know the
amount of sugar employed in the operation. This is best ascertained
by evaporating to dryness a known measure of the solution employed
for the determinations, but in some respects there is an advantage in
calculating the strength of the solution from the density. The con-
centration of solutions of pure cane sugar can be accurately ascer-
tained by dividing the excess of density over that of water by 3'86, as de-
scribed on page 267, but this divisor is not strictly accurate for solutions
of other carbohydrates. In practice, it is sometimes very convenient
to follow the practice of Brown and Heron (Jour. Chem. Soc., xxxv.
569 et seq.), and assume all solutions of carbohydrates to have the den-
sity of cane sugar solutions of the same strength, using appropriately
modified figures to express the values of K and S D . As the true den-
sity of a solution of dextrin containing 10 grm. of the dry solid in 100
O.Q
c.c. measure is!039'4, the value of S^ will be 198 X Q rr= + 194 -
oy4
Similarly, the value of S D3 . 86 for maltose will be -f- 136*4.
The following is a description in outline of the mode of procedure
which should be adopted in the application of the foregoing principles
to the analysis of one of the most complicated saccharine mixtures
likely to be met with in practice. It assumes the presence in ad-
mixture of dextrose, levulose, sucrose, maltose, dextrin, and gallisin,
together with water and mineral matter. Such a mixture would be
represented by honey which had been adulterated both with cane
sugar and glucose-syrup.
The total solids are estimated by evaporating a known measure of
the solution to dryness in a flat dish. On deducting the ash left on
igniting the residue the amount of the organic solids will be ascer-
tained. The solids may also be deduced from the density of the solu-
tion by dividing the excess above 1000 by 3'86.
The dextrin may be precipitated by pouring the aqueous solution
gradually into a large excess of rectified spirit. After standing till
294 SUGARS.
the precipitate is completely settled, the liquid is poured off and the
dextrin estimated in the residue by direct weighing, or deduced from
the solution-density or optical activity of the re-dissolved residue.
The gallisin may be estimated by distilling the alcoholic solution
obtained in b, fermenting an aliquot part of the residual liquid, and
treating the filtered solution left after complete fermentation by
Fehling's solution.
The rotation due to the sum of the optically active bodies present is
ascertained on the clarified solution at 15 C.
The levulose is estimated from the change in the rotatory power of
the solution on heating.
The sucrose is estimated from the change produced in the rotatory
power of the solution by treatment with invertase. The result is
confirmed by the change in the cupric oxide reducing power of the
solution caused by the action of the invertin.
The cupric oxide reducing power of the original solution is deter-
mined gravimetrically by Fehling's solution. From the value for K
thus obtained that due to any gallisin found after fermentation is
deducted, and from the remainder is subtracted the reduction due to
any levulose present. The difference is the reducing power due to
the dextrose and maltose. The sum of their weights having been
ascertained by deducting the levulose, sucrose, dextrin, gallisin, and
ash from the total solids, the amounts of maltose may be calculated by
subtracting the value of K for the two bodies from the sum of the
percentages of the two, and dividing the difference by G'38. 1 The
maltose thus found is subtracted from the sum when the percentage of
dextrose will be arrived at. Further information on the estimation of
dextrose and maltose in admixture is given in the section on " Com-
mercial Glucose."
CANE SUGAR.
Sucrose. Saccharose. Saccharon. Cannose. Diglucosic
Alcohol.
French Sucre de Canne. German Zucker.
Cane sugar is found ready-formed in the sugar-cane and many
1 If K be the cupric oxide reducing power due to the two bodies, and P the sum of the
percentages of maltose (m) and dextrose (rf), then:
K=d+-62m; P = m+d; P K = '38m; and m = P ~ K
'38
SUGARS. 295
grasses, in the sap of many forest trees, in the root of the beet and the
mallow, and in several other plants. It is also found in many seeds,
and notably in walnuts, almonds, hazel nuts, barley, coffee beans, &c.
Most sweet fruits contain sucrose together with invert sugar, but some
contain only the former. 1 The nectar of flowers contains both, but
the presence of any notable proportion of cane sugar in honey is
exceptional.
Cane sugar forms large transparent colorless crystals, having the
form of a monoclinic prism, and familiar in commerce under the names
of " crystal-sugar " and " sugar-candy." The crystals have a specific
gravity of about 1*6, and are unchangeable in the air.
Cane sugar exercises a powerful rotatory action on a ray of polar-
ized light; the apparent rotatory power in 10 per cent. solutions being
+ 66 -5 for the D line, and + 73'8 for the transition-tint. The
optical properties of cane sugar are fully described in the section on
the " Kelationsof the Sugars to Polarised Light."
At a temperature of about 160 C. (320 F.) cane sugar melts, and
on cooling forms a transparent amber-colored solid known as barley
sugar. This modification gradually loses its transparency from spon-
taneous crystallisation, but the change may be retarded, though not
altogether prevented, by the addition of a small proportion of vinegar
to the melted sugar. 2
When heated a little above 160 C. cane sugar is converted without
loss of weight into a mixture of dextrose and levulosan. CuMaOj] =
C 6 H 12 O 6 -f- C 6 H 10 O 5 . 3 At a higher temperature water is given off, the
1 For the extraction of sucrose from plant-products on a small scale, the fine substance
should be boiled with strong alcohol, the solution filtered hot, and allowed to cool, when
the cane sugar will usually crystallise out, or can be caused to do so after concentrating
the solution. If invert sugar be also present, Peligot and Buignet recommend the fol-
lowing method : Add to the juice an equal measure of alcohol to prevent fermentation
by keeping, filter, treat the filtrate with milk of lime in excess, and again filter. Boil the
liquid, when calcium sucrate separates in amount corresponding to two-thirds of the whole
cane sugar present. The precipitate is filtered off, washed well, diffused in water, and
decomposed by carbonic acid. The solution is filtered, evaporated at a gentle heat to a
syrupy consistence, decolorised by animal charcoal, and mixed with strong alcohol till it
becomes cloudy, when it is set aside to crystallise. If the solution, after treatment with
carbonic acid, yields a turbid filtrate, solution of basic lead acetate is added, the liquid re-
filtered, and the excess of lead separated by sulphuretted hydrogen.
2 Barley sugar appears to be a definite allotropic modification of cane sugar comparable
to viscous sulphur.
3 On dissolving the product in water and fermenting the solution- with yeast the dex-
trose is destroyed, and by evaporating the liquid the levulosan may be obtained as an
uncrystallisable syrup, which appears to become converted into levulose on boiling with
water or dilute acid.'.
296 SUGARS.
dextrose being probably converted into glucosan, C 6 H 10 O 5 , the next
stage being the formation of caramelan, C 12 H 18 O 9 , which is an amor-
phous highly deliquescent substance, colorless when pure, having a
bitter taste, and incapable of being reconverted into cane sugar by
hydrolysis. Above 190, dark colored bodies are produced, some of
which are soluble and others insoluble in water or alcohol. 1
At a still higher temperature, inflammable gases are evolved, the
decomposition being attended with a highly characteristic smell.
Cane sugar is soluble in about one-half of its weight of cold water,
forming a very sweet viscid liquid known as syrup. In boiling water
it is soluble in all proportions. 2 An aqueous solution of sugar on being
subjected to prolonged ebullition acquires an acid reaction, usually
becoming less viscid and losing irrecoverably its power of crystallisa-
tion. The liquid then contains invert sugar. When heated with
water under pressure to 160 C. sucrose is decomposed with production
of formic acid, carbon dioxide, and carbon.
Cane sugar is almost insoluble in absolute alcohol, but dissolves in
rectified spirit of wine with moderate facility, and readily in weaker
alcoholic liquids. Weak spirit dissolves more than would be taken up
by the water of it alone, but strong spirit dissolves less than would be
dissolved by the water of the spirit separately. It is insoluble in
ether, chloroform, carbon disulphide, petroleum spirit, or oil of turpen-
tine, but dissolves in glycerol and all aqueous liquids. The action of
dilute acids results in the formation of the mixture of glucoses called
invert sugar. Strong sulphuric acid acts violently, charring it and
causing abundant evolution of gas.
Nitric acid acts upon cane sugar in a manner dependent on its con-
centration and other conditions. With one part of sugar and three of
nitric acid of 1*25 to 1*30 sp. gr., the product formed at 50 C. is
wholly saccharic acid, C 6 H 10 O 8 , but at a boiling heat oxalic acid,
C 2 H 2 O 4 , is the chief product. If stronger nitric acid be em-
i These constitute the substance known as caramel, or " burnt-sugar," which is also
obtainable from dextrose, and is employed for tinting cognac, rum, vinegar, &c., and for
other coloring purposes. The dark color of stout is due to the presence of carameloid
bodies in the burnt malt from which it is brewed.
The changes undergone by cane sugar on heating furnish a good example of "cumula-
tive resolution," thus :
H 2 O = -CcH^Oe + C 6 H 10 O 5 . Levulosau .
CoH l8 6 + C 6 H 10 5 H 2 = 2C 6 H 10 5 . Glucosan.
2C 6 Hi 5 H 2 = Ci 8 H 18 9 . Caramelan.
2 For information respecting the density of aqueous solutions of cane sugar, see
page 265.
SUGARS. 297
ployed, these bodies undergo further oxidation with formation of
carbonic acid. Cold fuming nitric acid converts cane sugar intonitro-
sucrose, which probably contains C 12 H 18 (NO 3 ) 8 Oii. (Elliott, Jour.
Amer. Chem. Soc., iv. 147.) Glacial acetic acid forms several acetyl
derivatives, having the constitution of sucrosic acetates.
When cane sugar is rubbed in a mortar with caustic potash or soda
it undergoes no visible change, a property which distinguishes it from
the glucoses. Similarly, the solution of cane sugar undergoes no imme-
diate change when mixed with alkali and raised to the boiling point.
The rotatory power of the alkaline liquid is temporarily diminished,
but is restored to its original amount on neutralising the solution by
an acid. When fused with caustic potash it yields oxalate and acetate
of potassium and other products.
According to Wanklyn, cane sugar is oxidised in a definite manner
when boiled with a strongly alkaline solution of potassium perman-
ganate, with formation of oxalic and carbonic acids, the reaction
being
C 12 H 22 O n + 20 = 4C 2 H 2 4 + 7H 2 + 4CO 2 .
Cane sugar does not immediately reduce Fehling's solution at a boil-
ing temperature, but on prolonged ebullition precipitation of cuprous
oxide gradually occurs.
SUCRATES.
Cane sugar possesses considerable solvent powers for certain metallic
oxides, with which it forms definite compounds. Thus, lime, magnesia,
and litharge dissolve with some facility in syrup, but are completely
reprecipitated by passing a current of carbonic acid gas through the
liquid. Metallic lead is attacked by sugar solutions, slowly in the cold,
but more quickly at a boiling heat, the lead passing into solution.
Several sucrates of calcium are known. The solution of calcium
sucrate has an alkaline and bitter taste, and forms the liquor calcis
saccharatus of pharmacy. On mixing syrup with a concentrated solu-
tion of baryta, a crystalline precipitate is obtained, having the com-
position C 12 H 22 BaO 12 = BaO,C 12 H 22 O n , or C 12 H 21 (Ba.OH)O n . This
compound may be re-crystallised from boiling water, separating in
brilliant scales resembling boric acid. Its sparing solubility in cold
water has been utilised in the treatment of saccharine juices, pure cane
sugar being readily obtainable by decomposing the barium sucrate by
sulphuric acid. On adding strontium hydroxide to a boiling 15 per
cent, solution of sugar, the compound C 12 H 20 (Sr.OH) 2 On begins to sep-
arate, and when 2J molecules of strontia have been added almost the
298 SUGARS.
whole of the sugar will be precipitated. The granular sucrate may be
washed with hot water, and decomposed by carbonic acid. This pro-
cess is now employed in recovering sugar from molasses.
Cane sugar resembles tartaric and citric acids in its power of pre-
venting the precipitation of ferric and cupric oxides by alkalies, and
the reaction has even been employed quantitatively.
With sodium chloride, cane sugar forms a crystallisable compound
of the formula C 12 H 22 O n + NaCl + 2H 2 O. A solution of this body
has a less powerful rotatory action on polarised light than corresponds
to the sugar contained in it, whilst the optical power of a solution of
the compound 2C 12 H 22 On -f- 3NaI -f- 3H 2 O is directly proportional to
that of the contained sugar.
By the action of a small quantity of yeast (Saccharomyces cerevisice)
sucrose in solution is transformed into invert sugar. A larger propor-
tion of yeast converts the sugar into alcohol, carbon dioxide, and other
products, the process being that known as the alcoholic or vinous fer-
mentation.
Detection of Cane Sugar.
Cane sugar is detected more readily by its physical properties than
by its chemical reactions. The following are the leading characters of
service in the recognition of cane sugar :
The sweet taste of the substance or solution.
The dextro-rotatory action of the solution on polarised light.
The form of the crystals.
The characteristic odor produced on heating the solid substance.
The production of saccharic and oxalic acids by the action of mod-
erately concentrated nitric acid.
The formation of alcohol by the prolonged action of yeast on the
warm solution.
The increase in the reducing power of the liquid on Fehling's test
after inversion of the sugar by treatment with dilute acid, and the
change in the rotatory power of the solution by inversion.
The similar change in the reducing and rotating power of the
solution by treatment with invertin. This reaction is very character-
istic.
For information respecting the distinctive tests for cane sugar, milk
sugar, maltose, and glucoses.
The greater number of the foregoing properties and reactions of
cane sugar receive more precise recognition in the following section
on the
SUGARS. 299
Determination of Cane Sugar.
Cane sugar may be determined by a variety of methods, which may
be conveniently classified according to the principles on which they
are based.
Determination of Sugar from the Density of the Solution. For the
employment of this method it is, of course, essential that the solvent
should be water, and that sensible quantities of foreign matters should
be absent ; if volatile, like alcohol, they may be removed by distillation.
The method is constantly applied in sugar-works, not so much for
ascertaining the amount of sugar in the juice as to obtain an estimate
of the foreign matters associated with it; the actual sugar being really
determined by other methods, and a corresponding deduction made
from the percentage of " apparent sugar " present. On page 265 et
seq. full directions are given for deducing the proportions of cane sugar
contained in aqueous saccharine solutions of various densities.
The percentage of sugar by weight having been ascertained, the
number of pounds of sugar per gallon of the syrup may be found by
multiplying the specific gravity by one-tenth of the percentage by
weight, and dividing the product by 1000.
Determination of Cane Sugar by weighing as such. This method is
employed in Payen's and Scheibler's methods of sugar- assay ing, and in
a few other cases.
The Determination of cane sugar by fermentation is fully described on
p. 275 et seq.
The Determination of sucrose by its reducing action after previous in-
version to glucose is usually effected by heating it with hydrochloric
acid (p. 263), neutralising with sodium carbonate, and estimating the
resultant glucose by one of the processes described in the section on
the " Keducing Action of Sugars." For every 100 parts of glucose
thus found, 95 parts of cane sugar must be reckoned.
The Determination of cane sugar by observation of the rotatory action
of its solution on a ray of polarised light has already been fully
described.
For the determination of sucrose in presence of other kinds of sugar,
methods a, c, d, and e are incapable of direct application. If em-
ployed both before and after inversion, methods d and e afford very
satisfactory means of determining cane sugar, provided that no other
body is present which is apt to suffer alteration in its reducing power
or optical activity by heating with dilute acid. This is not always the
case, but, under such conditions, the substitution of invertin for dilute
300 SUGARS.
acid, as suggested by Kjeldahl, renders it possible to effect the solution
of this somewhat difficult problem.
INVERTASE is a soluble enzym or zymase existent in yeast. It has
the property of rapidly and completely effecting the transformation of
cane sugar into invert sugar, but is without sensible action on dextrose,
levulose, maltose, or milk sugar. Its behavior towards dextrin is not
so certainly negative.
For effecting the inversion of cane sugar by invertase, Kjeldahl
(Zeits. Anal. Chem., xxii. 588) treats 50 c.c. of the sugar solution with
a little concentrated alcoholic solution of thymol, and adds a little
yeast previously washed and ground up with water. The thymol com-
pletely prevents fermentation without interfering with the action of the
enzym. The mixture is allowed to remain for twenty-four hours at
a temperature of about 50 to 52. It is then diluted to 100 c.c., fil-
tered, and the cupric oxide reducing power and optical activity esti-
mated. From the increase in the former and the change in the latter
the amount of cane sugar present in the original solution can be
determined.
H. T. Brown modifies the foregoing process by grinding well-washed
yeast in a mortar with a little water and ether or chloroform, and
adding a small quantity of the product to the sugar solution, previously .
saturated with ether or chloroform. The liquid is then kept at a tem-
perature of 30 C. for half an hour, when it is filtered and examined
as before. If chloroform has been employed it must be got rid of by
heating the liquid before adding Fehling's solution.
Malt-extract is also without inverting action on maltose, but cannot
conveniently be substituted for invertase in the above process, as the
action of diastase is not sufficiently powerful.
Commercial Sugar.
The sugar of commerce is principally obtained from the sugar cane *
(Saccharum officinarum), but almost equally large quantities are manu-
1 The process of manufacturing sugar from the cane is shortly as follows : The cane is
crushed between rollers and the expressed juice allowed to flow into a large vessel in which
it is heated nearly to its boiling point. Lime is then added, when a coagulum is formed
which consists chiefly of earthy phosphates, a peculiar albuminous principle, and mechan-
ical impurities. The clear liquid is rapidly evaporated, and, when sufficiently concen-
trated, transferred to a shallow vessel to crystallise. The crystals are drained from the
dark-colored syrup known as molasses or treacle, and form the raw or muscovado sugar of
commerce. From this intermediate product, refined sugar is obtained by redissolving the
crystals in hot water, clarifying by filtration through animal charcoal, evaporating under
reduced pressure, crystallising,
which is then heated until the contents of the tube have reached the
point of ebullition. The urine to be tested is treated with an equal
measure of ammonium hydroxide, and filtered from the precipitated
phosphates. A known volume of the filtrate is then further diluted
with a definite measure of water, according to the proportion of sugar
supposed to be present, and then added drop by drop to the boiling
hot Pavy's solution by means of a small burette or graduated pipette,
until the disappearance of the blue color indicates the termination of
the reaction. If 10 c.c. of Pavy's solution were employed, the volume
of urine required to decolorise it contains 0'005 grm. of sugar.
Experiments by Mr. G. Bernard Brook show that unclarified
healthy human urine may exert a reducing action on Pavy's solution
equal to that of a liquid containing from O'l to 0'3 per cent, of glu-
cose. G. Stillingfleet Johnson finds the reduction to vary from 0'15 to
0'19 grm. per 100 c.c., and ascribes about one-fourth of this to uric acid
(removable by lead acetate) and the remainder to creatinin (removable
by mercuric chloride).
It is evident, therefore, that Pavy's method, applied in the ordinary
manner, will give misleading results when only small quantities of
sugar are in question. As to Fehling's test, although, by the foregoing
modified mode of application, the indications are much more definite
and the delicacy of the reaction is correspondingly increased, there
still remains the disturbance due to the presence of creatinin. On
adding Fehling's solution to a solution of this substance, a green
liquid is produced, and on boiling a yellow coloration is observed,
without, however, any separation of cuprous oxide. It is this behavior
which causes interference with the detection of glucose, the combina-
tion of the yellow and blue colors resulting in a green, and in addition
the creatinin compound is said to have the power of preventing the
precipitation of cuprous oxide by glucose.
A better separation of creatinin can be effected by a method pro-
posed by Maly and improved by G. Stillingfleet Johnson. Sixty c.c.
of the urine to be tested should be boiled for five minutes with 15 c.c.
of saturated mercuric chloride and 3 c.c. of saturated sodium acetate
solution, and the liquid filtered hot. The precipitate is washed twice
and the filtrate boiled for ten minutes with zinc-dust and again filtered.
GLUCOSE. 349
The precipitate is washed and the filtrate diluted to 120 c.c. with am-
monium hydroxide (specific gravity 0'960). This liquid has half the
concentration of the original urine, and is added from a burette to not
more than 50 c.c. of boiling Pavy's solution. The requisite washing of
the mercuric and zinc precipitates can be avoided if 50 c.c. of the
urine be boiled with solid mercuric chloride and sodium acetate, the
liquid filtered, the filtrate boiled with zinc-dust and again filtered,
and a known volume of the last filtrate mixed with an equal measure
of strong ammonium hydroxide. 1
Experiments made by Mr. G. Bernard Brook in the foregoing
manner, upon urine from apparently healthy persons, showed that the
purified liquid exerted a reducing action on Pavy's solution corre-
sponding to the presence of from 0'05 to 0'13 grm. of glucose per 100
c.c. of the original urine, which yielded crystals of phenylglucosazone
by the phenylhydrazine test. A slight residual reduction after the
mercury treatment has often occurred, and it is highly probable that
these urines, limited in number, contained traces of sugar ; but
Johnson has obtained entirely negative results, which implies that
many of the urines he examined could be added to Pavy's solution,
after purification by mercury, without causing the slightest reduction
in the color.
As all the methods of detecting sugar in urine which are based on
the reducing action of glucose are more or less vitiated by the pres-
ence of other reducing bodies, a special reagent for glucose has an
exceptional value. This exists in phenylhydrazine, which, when
added as a solution of the hydrochloride to a liquid containing
glucose, to which sodium acetate has been also added, gives a yellow
precipitate of phenylglucosazone. To apply the test, von Jaksch
recommends that 50 c.c. of the suspected urine, previously freed from
albumin, should be treated with 2 grm. of sodium acetate and from 1
to 2 grm. of phenylhydrazine hydrochloride, and the liquid heated to
100 C. for half an hour ; or 10 to 20 drops of phenylhydrazine and
the same volume of 50 per cent, acetic acid may be employed. On
cooling, the phenylglucosazone separates as an amorphous or crystal-
line precipitate of a yellow or brick-red color. If amorphous, the
precipitate should be dissolved in hot alcohol, and the solution diluted
with water and boiled to expel the alcohol, when the glucosazone will
i This treatment serves the double purpose of keeping the zinc in solution and furnish-
ing a constant but gradually added supply of ammonia during the subsequent titration
with Pavy's solution. The additional ammonia has been proved by Mr. C. GK Moor to
have no prejudicial effect on the accuracy of the results obtained.
350 GLUCOSE.
be obtained in the form of characteristic yellow needles, melting at
205 C., nearly insoluble in cold water, more soluble in hot, moder-
ately soluble in alcohol, and dissolved by glacial acetic acid to
form a laevo-rotatory solution. According to von Jaksch, no sugar
can be detected by this test in the urine of persons poisoned by
arsenic, potassium hydroxide, or sulphuric acid ; but the presence
of sugar seems constant in the urine of those poisoned by carbon mon-
oxide.
Instead of operating in the manner prescribed by von Jaksch, the
phenylhydrazine test may be applied in the following simple manner,
which is substantially that recommended by C. Schwartz (Phar. Z&it.,
xxiii. 465) : 10 c.c. measure of the urine is heated to boiling and treated
with half its volume, or a sufficiency, of a 10 per cent, solution of
neutral lead acetate. The liquid is boiled and filtered hot. Solution
of caustic soda, in amount sufficient to redissolve the precipitate which
first forms, is added to the filtrate, and then as much phenylhydrazine
hydrochloride as will lie on the point of a penknife is dropped in.
The liquid is boiled for some minutes and strongly acidulated with
acetic acid. In presence of much sugar an immediate yellow turbidity
or precipitate will be formed, but if only minute traces be present a
yellow coloration is first produced, which on cooling and standing
changes to a turbidity. In all cases considerable time is required for
the complete separation of the glucosazone, but the qualitative indica-
tion is readily and quickly obtained.
Unfortunately the phenylhydrazine test does not appear susceptible
of being applied quantitatively, though, of course, the intensity of the
reaction and the amount of precipitate afford a fair indication of the
proportion of sugar present.
In all doubtful cases the indications furnished by the production of
a turbidity or precipitate with the above test should be confirmed by
obtaining the glucosazoue in a crystallised form, examining it under
the microscope, and, when possible, determining its melting point. I
have found that it is readily dissolved by ether from its acidulated
aqueous solutions. On separating and evaporating the ether the glu-
cosazone can be dissolved in alcohol, and crystallised by adding water
and* evaporating as already described. As small a proportion as 0*05
per cent, of sugar can be positively detected in urine by the phenyl-
hydrazine reaction.
Both dextrose and levulose yield identically the same glucosazone.
The only other constituents of urine which simulate the behavior of
DEXTROSE. 351
glucose with phenylhydrazine are glycuronic acid and its com-
pounds. 1
Glycuronic acid is a syrupy liquid, miscible with alcohol or water.
When the aqueous solution is boiled, evaporated, or even allowed to
stand at the ordinary temperature, the acid loses the elements of water
and yield the anhydride or lactone (C 6 H 8 O 6 ), which forms monoclinic
tables or needles, having a sweet taste and melting at 167. It is in-
soluble in alcohol, but dissolved by water to form a solution which is
dextro-rotatory ([a] D = -j- 19'25), prevents the precipitation of cupric
solutions by alkalies, and powerfully reduces hot Fehling's solution,
the cupric oxide reducing power being 98'8 compared with glucose as
100. The acid is dextro-rotatory ([a] D = -f 35), but many of its com-
pounds are laevo-rotatory. It reduces Fehling's solution on heating,
and precipitates the metals from hot alkaline solutions of silver, mer-
cury, and bismuth. With phenylhydrazine, glycuronic acid forms a
yellow crystalline compound, melting at 114 to 115 C. and resembling
closely phenylglucosazone. When oxidised with bromine glycuronic
acid yields saccharic acid, which can be again reduced to glycuronic
acid by treatment with sodium amalgam. It is distinguished from
glucose by not undergoing the alcoholic fermentation when treated
with yeast. On the other hand, when fermented in presence of cheese
and chalk it yields lactic and acetic acids.
[To obtain satisfactory results, the phenylhydrazine hydrochloride must be of
good quality It should be in light fawn-colored scales with an odor recalling
geranium. If pasty and brown, with a strong unpleasant odor, it is unfit for
use. It is said to be liable to cause an inflammation of the skin. L.]
Dextrose. Dextro-glucose. Sucro-dextrose.
French Sucre de raisin. German Traubenzucker.
This species of sugar, often called simply " glucose," and also known
as " starch -sugar," may be produced in various ways, of which the fol-
lowing are the chief:
a. By the hydrolysis of starch, dextrin, cane sugar (together with
1 Glycuronic acid contains CeHioOy; or, COH(CH.OH) 4 .COOH. The substance doubtless
has its origin in the dextrose of the body, to which compound it is closely related. It was
first obtained in the conjugated form of campho-glycuronic acid, in the urine of dogs to
which camphor had been administered, and subsequently as uro-chloralic acid after the
administration of chloral. It is remarkable for its tendency to form ethereal or glucosidal
compounds when appropriate substances are introduced into the body. Traces of such
compounds probably occur normally in urine, especially indoxyl- and skatoxyl-glycuronic
acids, in addition to the combination with urea, having probably the constitution of uro-
glycuronic acid, which is the ordinary form in which glycuronic acid exists in urine.
352 DEXTROSE.
Isevulose), or some gums, by means of dilute acids, diastase, or in-
vertin.
b. By treating linen rags or similar vegetable matter with sulphuric
acid.
c. By decomposing the so-called glucosides (e.g., salicin, gallotannic
acid, araygdalin, phloridzin, &c.), by treatment with dilute acids or
certain ferments. 1
Dextrose occurs ready-formed, together with levulose, in honey. It
is found ready-formed in various fruits, levulose and cane sugar being
also present as a rule. The proportion of dextrose in grapes is as
high as 15 per cent.
Dextrose usually crystallises from its aqueous solution in granular,
hemispherical, warty masses or tabular crystals, containing C 6 H 12 O 6 -f-
H 2 O, but hot concentrated solutions often deposit anhydrous dextrose
in prisms. By crystallisation from hot methyl alcohol the anhydrous
sugar is obtained in transparent prismatic crystals. The hydrated
glucose becomes anhydrous below 100 C. Dextrose melts at 146,
and at about 170 C. loses water and is converted into glucosan,
C 6 H 10 O 5 , and at higher temperatures yields caramel. Dextrose is less
soluble than cane sugar in cold water, requiring 1 times its own
weight, but it dissolves in all proportions in boiling water, forming a
syrup of a sweetening power inferior to a solution of cane sugar, or
one of levulose of the same strength.
Considerable discrepancies exist in the determinations of the specific
rotatory power of dextrose as ascertained by different observers. In
certain cases it is even doubtful whether the recorded numbers apply
to anhydrous or to crystallised dextrose. The following table shows the
value of S D and Sj for anhydrous dextrose, according to the observa-
tions of various chemists. The figures refer to a solution which has
been either heated or kept for some hours, a freshly-prepared solution
of dextrose in cold water having a rotatory power about twice as great
as that shown in the table. The values printed in prominent type are
those obtained by direct observation ; the others by calculation, on the
assumption that Sj = S D Xl'll. The figures having H. affixed are
obtained by calculation from the observed rotation of the hydrated
dextrose :
1 The dextro-rotatory glucoses obtained by the action of dilute acids on the glucosides
are generally assumed to be identical with sucro-dextrose, or grape sugar, but the re-
searches of Hesse and others have thrown considerable doubt upon the accuracy of this
view.
DEXTROSE.
353
APPARENT SPECIFIC ROTATORY POWER OF j3 MODIFICATION OF DEXTRO-
GLUCOSE IN AQUEOUS SOLUTION, AS DETERMINED BY DIFFERENT
OBSERVERS.
Source of Sugar.
Value for Anhydrous Sugar of
Concentration
of Solution
employed.
Observer.
So or [a]D.
Sj or [a]j
\
-h 50-5
-f 56
9
Berthelot.
51-7
57 4
9
Bechamp.
Sucrose, . . \
52-9
58 65
5-10
Brown & Heron.
\
51-9
57-6
9
O'Sullivan.
I
51-3
57-0
?
Schmidt.
52 37
58-13
2f
Tollens.
52 74
58-54
10
) )
Starch, 1
52 99
5284
58-82
58-65
17|
9
Soxhlet.
I
52-70
58-50
10
Salomon.
Diabetic urine,
56-4
62-6
4-5-26
Hoppe-Seyler.
Starch, . . . <
51-67
51-51 (H.)
57-3
52-2
3
12
Hesse.
Grapes, . . . <
5216
51-80
57-9
57 "5
3
9
Honey, . . . |
50-97 (H.)
51-7
56-6
57-3
12
9
Salicin, . . . |
51-8
52-4 (H.)
57-4
58-2
2-12
12
Amygdalin, .
54-2 (H.)
60-1
2
Phloridzin, .
43-7 (H.)
48-5
6
It will be seen from these results that it is very doubtful whether the
dextro-glucoses obtained from diabetic urine and from some of the
glucosides {e.g., phloridziu) are identical with the sucro-dextrose from
starch, honey, or grapes. Even then there is considerable variation in
the values of different observers, possibly owing to certain of the ob-
servations having been made on freshly-prepared solutions. For
practical purposes, the value of S D for anhydrous dextrose may be
taken at -j- 52 '7, which, multiplied by I'llO, gives + 58'5 as the
value of Sj. 1
Dextrose is not affected by heating for a moderate time with dilute
acids. Prolonged treatment is said to result in the formation of prod-
ucts having the probable formula C 6 H 14 O 7 .
If dextrose be heated with a solution of caustic alkali the liquid
rapidly acquires a yellow or brown color, and on continued heating a
humus-like substance separates.
1 Tollens (Ber., xvii. 2234) gives the following formula for calculating the specific rota-
tion of dextrose in solution : S D = 52-50 + 0'018796c + 0'00051683c 2 .
23
354 LEVULOSE.
A solution of dextrose dissolves the alkaline earths, forming yellow
solutions precipitated by alcohol. By boiling with excess of lime
dextrose is rapidly acted on and destroyed.
The action of alkalies and alkaline earths on dextrose is described
more fully on p. 277.
Dextrose, when pure, is not precipitated by neutral or basic lead
acetate, but gives a white precipitate with an ammoniacal solution of
normal lead acetate.
The reaction of dextrose with alkaline solutions of copper and other
reducible metallic solutions is described on p. 279 et seq.
When heated with oxide of silver and water, dextrose yields
glycollic, oxalic, and carbonic acids, but not acetic acid.
By the action of nascent hydrogen dextrose is converted into man-
nite or mannitol, C 6 H 14 O 6 .
When quite pure, dextrose is not readily charred by concentrated
sulphuric acid, but combines with it to form antacid-ethereal salt, de-
composed by water.
With tartaric, benzoic, stearic, butyric, acetic, and other organic
acids, dextrose combines to form oily or amorphous solid products,
sparingly soluble in water, but dissolved by alcohol and ether.
Other properties and reactions of dextrose are described in the
tables on page 246. The reactions which distinguish dextrose from
levulose are given below.
Levulose. Sucro-levulose. Levo-glucose.
French. Levulose. Chyliarose. German. Linksfruchtzucker.
This species of glucose, often called " fruit-sugar," occurs together
with dextrose in honey and many fruits. A variety of levulose i&
produced by the action of dilute acids on inulin, which is probably
identical with sucro-levulose. Levulose is obtained, together with an
equal weight of dextrose, by the action of dilute acids, diastase, or
invertin on cane sugar. Levulose is not a product of the action of
dilute acids on any known glucoside.
When cane sugar is heated to 165-170 C. for some time it is
converted without change of weight into a mixture of dextrose and
levulosan, C 6 H 10 O 5 . On dissolving the product in water and treating
the solution with yeast, the dextrose ferments and the unfermentable
levulosan remains, and can be converted into levulose by boiling with
dilute acid.
The principal physical and chemical properties of levulose are
described on p. 246. It presents a close general resemblance to-
LEVULOSE. 355
dextrose, the following being the chief differences of analytical
value :
Levulose is not readily crystallisable (CWp. rend., xciii. 547), and
is more soluble in alcohol than dextrose. The aqueous solution is
much sweeter than one of dextrose, and somewhat sweeter than one of
cane sugar of the same strength. Mixed in ice-cold 5 per cent, solu-
tion with 120 per cent, of its weight of fine-powdered slaked lime (which
should be added gradually, the vessel being immersed in ice-cold water),
a milky liquid is obtained which gradually becomes pasty from the form-
ation of a difficultly-soluble calcium levulosate, CaO,C 6 H 12 O 6 ,H 2 O,
while dextrose on similar treatment yields a freely soluble compound, 1
which can be separated by filtration through linen. The residue, after
being washed and strongly pressed, may be suspended in water and de-
composed by oxalic or carbonic acid, when a solution of pure levulose
is obtained, which yields anhydrous levulose by evaporation in vaeuo
over sulphuric acid.
The respective reducing actions of dextrose and levulose on Fehl-
ing's copper solution are usually assumed to be identical. According
to Soxhlet, however, the reducing action of the former is sensibly
greater than that of the latter. Allihn states that the reducing action
of dextrose arid levulose are identical if care be taken to continue the
boiling of the solution for half an hour.
The reducing action of dextrose on Knapp's mercurial solution is
sensibly the same as that of levulose, but the latter glucose exerts a
far stronger reducing action on the solution of Sachsse, equal amounts
of the dextrose and levulose reducing 100 and 148'6 c.c. of Sachsse's
solution respectively.
When a solution of dextrose is heated with bromine water, and the
liquid then treated with silver oxide (care being taken to avoid excess
of the latter), gluconic acid, HC 6 H U O 7 , is formed, which may be ob-
tained as a syrup on evaporation. If slaked lime be added in excess
to its lukewarm solution, and the liquid filtered and heated to boiling,
the acid is almost completely precipitated as a basic calcium gluconate.
When levulose is similarly treated with bromine water and oxide of
silver it yields glycollic acid, HC 2 H 3 O 3 , the calcium salt of which crys-
tallises in silky needles, which are more soluble in hot water than in
cold. Digestion with excess of argentic oxide converts gluconic into
glycollic acid.
1 If invert sugar or honey is to be treated for levulose, the proportions of lime and
water must be modified accordingly : 10 parts of invert sugar, 6 of slaked lime, and 100
of water are then the right proportions.
356 INVERT SUGAR.
The specific rotatory power of levulose is 98 '8 for the D line
at 15 C., decreasing by - 6385 degree for each increase of 1 C. in
the temperature. At 87'2 C., the rotation is 52*7, being equal
to that of dextrose at the same temperature, but in the opposite direc-
tion.
The change in the optical activity of levulose by increase of temper-
ature affords a means of determining it in the presence of other sugars.
For this purpose, the solution, previously clarified, if necessary, and
not too dilute, is carefully neutralised, and the rotatory power observed
in a tube round which a current of very cold water is caused to circu-
late by an arrangement similar to that of a Liebig's condenser, having
an orifice for the insertion of a thermometer. The rotation and tem-
perature having been noted, a current of hot water is passed round the
tube until a constant temperature is attained, when the rotation and
temperature are again observed. If an instrument employing sodium-
light has been used and the observation made in a 2-decimetre tube,
the number of grammes of levulose in 100 c.c. of the solution may be
found by the following rule : Subtract the temperature of the cold
water observation from that of the hot water ; multiply the difference,
expressed in centigrade degrees, by 1*277 ; then the product divided
into 100 times the change in rotation by increase of temperature (ex-
pressed in circular degrees) gives the number of grammes of levulose
in 100 c.c. of the solution. 1
Invert Sugar.
French Sucre interverti. German Kriimelzucker.
Invert sugar exists largely in honey, molasses, and many fruits. It is a
mixture of equivalent proportions of dextrose and levulose, produced by
the action of heat, diastase, acids, salts, or other agents on cane sugar
and some of its isomers. 2 The conditions most favorable for its forma-
tion have already been described.
Invert sugar is an uncrystallisable syrup having a sweeter taste than
1 Suppose that the solution at 4 C. caused a rotation of - 19'0 circular degrees ; and at
96 C. the circular rotation was - 10'5. The diflerence of temperature is 92 C., and
that in optical activity 8'5. Then by the rule given in the text: ~ =
y 2 /\ 1*^77 117*4o4
= 7-24 grm. levulose per 100 c.c. In /. A. C. , January, 1896, Wiley gives a full de-
scription of the construction and use of polarimeters adapted for accurate determination
of levulose.
2 MaumenS regards ordinary invert sugar as a mixture of dextrose, levulose, and an
optically inactive sugar, the composition varying with the conditions of the inversion.
GALACTOSE. 357
cane sugar. In its chemical reactions and optical properties it behaves
strictly as a mixture of dextrose and levulose.
By treatment with lime, in the manner described on p. 355, the
dextrose and levulose of invert sugar may be partially separated.
Levulose is less readily fermentable than dextrose, and hence when a
solution of moist sugar is treated with yeast, the dextrose disappears
first.
Invert sugar is now made largely for brewers' use, being sold under
the names of " invert " or " inverse sugar," " saccharum," " malt-sac-
charum," &c. Starch sugar and cane sugar are often added. The
analysis of such products may be effected in the same manner as that
of honey, but it is generally sufficient to estimate the sugar by Feh-
ling's solution before and after inversion. These estimations give the
data for calculating the cane or uninverted sugar and the total glucose,
without distinguishing between the dextrose and levulose (see Ap-
pendix for recent analyses of invert sugar).
Galactose. Lactose. 1
When milk sugar is heated with dilute sulphuric or, preferably,
hydrochloric acid, it undergoes hydrolysis, the rotatory power of the
solution increasing from 52*7 to 67*5. The product of the reaction
is frequently stated to be lactose or galactose, but it is now definitely
proved that the action of dilute acid on milk sugar really results in
the formation of two isomeric glucoses, corresponding with sucro-dex-
trose and sucro-levulose. In the case of milk sugar, however, both of
the resultant glucoses are dextro-rotatory, and their freshly-prepared
solutions exert a stronger dextro-rotatory power than after standing or
heating. The complete separation of the two glucoses is difficult to
effect, but one of them has been satisfactorily identified with sucro-
dextrose, while the other, or galactose proper, is characterised by
yielding mucic acid instead of saccharic acid on oxidation with nitric
acid.
Galactose is less sweet than cane sugar. By reduction with sodium
amalgam it yields dulcite, whilst by heating with bromine water it is
converted into lactonic acid, C 6 H 10 O 6 , which forms deliquescent crys-
tals, and yields, when warmed with excess of lime, a basic salt, which
separates on heating the filtered liquid to boiling.
A. Rindell states the specific rotatory power of galactose in 10 per
cent, solution at 15 C. to be -j- 81'27 for the sodium ray, and for cal-
1 The name lactose is applied to milk-sugar itself, as well as to the glucose resulting
from its hydrolysis, a practice which has caused some confusion.
358 COMMERCIAL GLUCOSE.
culatmg the rotation for other temperatures and concentrations gives
the following formula : S D = -f- 83'037 + 0'199c (0*276 -0025c)<.
The mean of this value (-J- 81-27) and the number for dextrose (52'7)
gives 66-98 as the calculated rotation for inverted (hydrated) milk
sugar against 67*50 actually found.
Commercial Glucose. Starch Sugar.
Under the names of glucose, saccharum, grape sugar, starch sugar,
and other more fanciful cognomens, are manufactured and sold a
variety of starch-products in which dextrose is the leading constituent.
Commercial glucoses are employed by brewers as substitutes for malt
and cane sugar, by vinegar-makers, and large quantities are used by
manufacturers of fancy-sugars, sweetmeats, and preserves. Table-
syrups are also manufactured from starch glucose, and honey is exten-
sively adulterated with it. In America, coffee-sugar is largely mixed
with glucose, and the same sophistication has recently been practised
in this country. Starch glucose is likewise used for the manufacture of
factitious wine.
Commercial starch glucose is produced by the action of dilute acid
on starch or starchy matter, or occasionally woody fibre. In America
it appears to be wholly made from maize starch, but in Europe rice
and potato starch are frequently used. 1
As a rule, sulphuric acid is used as the converting agent, the pro-
portion employed ranging in practice from 1 to 3 per cent., according
to the kind of product desired and the details of the subsequent man-
ipulation. The starch, or amylaceous substance, is either boiled with
the acid and water in an open tank, or heated with it in strong copper
cylinders under high pressure. If the first method be adopted,
and the process arrested as soon as a cold sample of the liquid ceases
to give a blue color with iodine, the product contains a large propor-
tion of dextrin ; but if high pressure be employed, and the action
pushed further, dextrose is the chief product. In either mode of
operating, maltose and, very commonly, other products are formed in
addition to dextrose and dextrin. The acid is next neutralised by
addition of chalk or ground marble, milk of lime being added to
remove the last traces, the resultant gypsum allowed to settle, the
liquid decolorised, if necessary, by animal charcoal, and evaporated
in vacuo till it acquires a density of 1400 to 1420.
1 It is not certain that the products thus obtained are strictly identical with those
from maize starch. J. Frankel has published (through H. C. Baird & Co., Philadelphia)
A Practical Treatise on the Manufacture of Starch Sugar, based on the German of
L. von Wagner.
COMMERCIAL GLUCOSE. 359
Oxalic acid is said to be substituted for sulphuric acid by certain
firms, the resultant calcium oxalate being more insoluble than calcium
sulphate. 1 A small quantity of hydrochloric acid appears to be
employed in a few cases.
Starch glucose occurs in commerce in several forms, varying from
the condition of pure anhydrous dextrose, through inferior kinds of
solid sugar, to the condition of a thick syrupy liquid resembling gly-
cerin, which contains a large proportion of dextrin. 2
A great number of so-called analyses of commercial starch sugars
have been published, but the majority are vitiated by the employment
of faulty methods of analysis, or by an insufficient knowledge of the
constituents of starch sugar. Thus, many analysts give only the pro-
portions of dextrin and dextrose, the latter being deduced from the
cupric oxide reducing power of the sample. Such a mode of expres-
sion is gravely in error in many cases, since it ignores the presence of
maltose, which is a very important and common, if not a constant, con-
stituent of products obtained by the action of dilute acids on starch. 3
1 When the conversion is effected by sulphuric acid, the glucose solution retains a con-
siderable quantity of dissolved calcium sulphate. More complete separation occurs on
concentrating the liquid to a density of about 1240, and a further deposition ensues when
the sugar is fermented. The calcium sulphate may be very completely removed by treat-
ing the glucose solution with barium oxalate.
2 In America, the term ''glucose" is restricted to the syrupy preparations, the solid
products being distinguished as " grape sugar." The following grades are recognised :
Liquid Varieties. Glucose, mixing glucose, mixing syrup, corn syrup, jelly glucose
and confectioners' crystal glucose.
Solid Varieties. Solid grape sugar, clipped grape sugar, granulated grape sugar, pow-
dered grape sugar, confectioners' grape sugar, brewers' grape sugar.
3 Although the total percentage of matter useful to the brewer is the same whether a
commercial glucose consist wholly of dextrose or in large part of maltose, the quality of the
material, as measured by the character of the beer produced, is very different, beer brewed
from maltose being greatly superior to a glucose beer. The latter is apt to be thin and
deficient in head, very clean, and of a vinous character. Maltose gives a beer of full
body, good head, soft and creamy on the palate. It keeps well, and, owing to the gradual
after-fermentation which occurs, continues brisk and sparkling. These remarks apply to
beer brewed from acid-made maltose, as well as to malt-brewed beer.
On account of the superiority of maltose over dextrose as a brewing material, it is desir-
able to limit the action of the dilute acid used for converting the starchy matter. In
practice, it is found that a mixture of two parts of maltose and one of dextrin is the most
generally suitable for brewers' purposes. This product, which has been introduced under
the name of "dextrin-maltose," is obtained if the action of the acid be arrested when the
specific rotatory power of the solids has decreased to about + 171 for the transition-tint,
or + 151 for the sodium ray. The value of K for the solid matter should be about 42.
The proportion of solids present is ascertained by removing the sulphuric acid by a slight
excess of baryta-water and taking the density of the solution.
The dextrin of brewers' glucose is of value for giving " body " to the beer. A smaller
proportion is required for running ales than for heavier or " stock " ales.
360 COMMERCIAL GLUCOSE.
Again, many specimens of starch glucose contain a notable percentage
of unferraentable carbohydrates, apparently produced by over- treatment
with acid, and to which the formula C 6 H 14 O 7 has been attributed, but
certain of which appear to be identical with the body recently described
by Schmitt and Coblenzl (Ber., xvii. 1000, 2456 ; Jour. Chem. Soc.,
xlvi. 981, xlviii. 134), under the name of gallisin.
GALLISIN was prepared by fermenting a 20 per cent, solution of
starch sugar with yeast at 18 to 20 C. for five or six days. The
resultant liquid was filtered, evaporated to a syrup at 100, and shaken
with a large excess of absolute alcohol. The syrup thickened, but did
not mix with the alcohol. The alcohol was poured off, and the residue
shaken with a fresh quantity, and by repeating this process the unal-
tered sugar and other impurities were removed, the syrup being con-
verted into a crumbling yellowish gray mass, which by pounding in a
mortar with a mixture of equal parts of alcohol and ether was
obtained as a gray powder. It was purified by solution in water,
boiling with freshly ignited animal charcoal, filtering, evaporating to
a syrup, and repeating the treatment with alcohol and ether. The
product was dried over sulphuric acid. Thus obtained, gallisin is a
white, amorphous, extremely hygroscopic powder. Its taste is at first
slightly sweet, but after a time becomes insipid. Gallisin is readily
decomposed by heat, giving off water and carbon dioxide even at 100.
It is readily soluble in water, nearly insoluble in absolute alcohol, and
but slightly more soluble in methyl alcohol, in which respect it differs
from dextrose. It dissolves in a boiling mixture of alcohol and glacial
acetic acid, but is insoluble in ether, chloroform, or hydrocarbons.
Scheibler and Mittelmaier (Ber., 1891, p. 301) prepared gallisin by
repeated addition of a large excess of absolute alcohol to a concen-
trated syrup. E. Fischer (Ber., 1890, p. 3687) obtained " isomaltose"
(by which term gallisin is intended by some writers) by precipitating
the concentrated syrup with a large excess of alcohol and ether.
Ost (Chem. Zeit, 1896, p. 102) used the following method : A
solution, after hydrolysis of glucose by acid and subsequent fermenta-
tion, was found to contain 237 grm. of solids in 900 c.c. To this 6,000
c.c. of absolute alcohol were added, which precipitated about two-
thirds of the solids. Most of the remaining solid matter was thrown
down by the addition of 6,000 c.c. of ether. Ost designates the two
precipitates as A and B, and states that they are nearly identical in
composition. A is purified by dissolving it in a little water and adding
sufficient absolute alcohol to produce a liquid of 85 per cent, strength.
The filtrates from this mixture yield, on evaporation, syrup consisting
COMMERCIAL GLUCOSE. 361
largely of isomaltose. With the exception of a small amount of
calcium compounds, these syrups are soluble in 85 per cent, alcohol.
By treating precipitate A four successive times in this manner, 100
grm. entirely soluble in 80 per cent, alcohol were obtained, and some
was obtained by treating with absolute alcohol, filtering, and evap-
orating.
Gallisin is stated to have the composition CuH^Oio. Its concen-
trated aqueous solution is distinctly acid to litmus, and a sparingly
soluble barium compound may be obtained therefrom by adding alco-
holic baryta. Gallisin reduces nitrate of silver on heating, especially
on addition of ammonia, reduces bichromate and permanganate, and
precipitates hot Fehling's solution. Its cupric oxide reducing power
is stated to be 45'6. Knapp's mercurial solution is also reduced by
gallisin.
Gallisin is dextro-rotatory, the value for S D being stated to be
+ 80'l in 27 per cent., + 82'3 in 10 per cent., and 84'9 in 1-6 per
cent, solutions.
By heating with dilute sulphuric acid for some hours, gallisin yields
a large proportion of dextrose, but its complete conversion has not, so
far, been effected.
The presence of an unfermentable carbohydrate in starch su^ar
was long since pointed out by O'Sullivan, and Neubauer has described
two such bodies of little reducing power, one of which was soluble in
alcohol, and had a dextro-rotatory power of + 78, while the other
was not dissolved by alcohol, and had a rotation value of S D = -j- 93.
It is doubtful whether " gallisin," as hitherto obtained, is really a
definite compound, 1 but the possibility of isolating a reducing or opti-
cally active body from the liquid left after fermenting solutions of
many specimens of starch sugar cannot be ignored in considering the
composition of commercial glucose. It is probable that the proportion
of unfermentable matter has been exaggerated, and O'Sullivan states
that starch sugar manufactured by the quick-action process, using high
pressure, contains very little, if any, of such unfermentable carbo-
hydrates.
1 The value of the researches on gallisin by Schmitt and Coblenzl is discounted by
their giving a process for analysing commercial starch sugar in which the cupric oxide
reducing power of the sample is assumed to be wholly due to dextrose and gallisin. For
all that appears in their researches they might be ignorant of the existence of maltose,
though the process employed for the preparation of gallisin would not improbably lead to
its contamination with maltose if any of that sugar had escaped fermentation. A mixture
of much maltose with a non-reducing substance of comparatively low rotatory power
would give values for K and S similar to those attributed to gallisin.
362
COMMERCIAL GLUCOSE.
According to Nessler (Zeits. Anal. Chem., xx. 466), starch sugar is lia-
ble to contain an unfermentable body capable of producing unpleasant
symptoms when taken internally. His conclusions have received some
confirmation from Schmitz, Kedsie, and others. The subject has been
investigated by von Mering, who attributes the results of Schmitz to
the enormous quantities employed, and those of Nessler to the fact
that he used the unfermentable residues after they had been evapo-
rated to dryness and taken up again with water, whereby they are
changed. The United States Committee on Glucose investigated these
statements very carefully, and concluded that there was nothing of
an injurious nature in the starch sugar manufactured in America,
which is derived entirely from maize ; but their experiments did not
extend to glucose from potatoes, with which the German chemists
worked.
H. W. Landbeck has described an unfermentable, poisonous, bitter
substance, giving many of the reactions of colchicine, and which he
states is sometimes present to a considerable extent in commercial glu-
cose and badly fermented beer (Pharm. Jour., [3] xi. 832).
The following analyses of commercial glucoses, quoted by W. G.
Valentin (Jour. Soc. Arts, xxiv. 404) are amongst the most complete
and probably most reliable hitherto published :
No. 1.
No. 2.
No. 3.
No. 4.
No. 5.
Dextrose,
80*00
58'85
67'44
63'42
61*46
Maltose,
none
14-11
10'96
13 50
13'20
Dextrin,
none
1-70
none
none
none
Unfermentable carbohydrates, \
with a little albuminoids, /
Mineral matter,
Water,
8-20
1-30
10*50
9-38
1-40
14-56
4-30
1-60
15'70
8-40
1'50
13'18
8-60
1-60
15'20
100-00
100-00
100-00
100-00
100-06
Total solid matter,
89'50
85'44
84'30
86"82
84 '80
Matter of use to the brewer,
80-00
74-66
78-40
76-92
74-60
No. 1 was somewhat brown, very hard, and of English manufacture.
No. 2 was pale straw-colored, softish, French. No. 3, whitish, some-
what hard, English. No. 4, whitish, somewhat hard, German. No. 5,
white, somewhat hard, German.
The following analyses are by I. Steiuer (Dingier s Polyt. Jour.,
ccxxxiii. 262) :
COMMERCIAL GLUCOSE.
363
No. i.
No. 2.
No. 3.
No. 4.
Dextrose .
45-40
26'50
76 '00
28 '00
40'30
5'00
42'60
Dextrin,
9*30
15-90
39'80
Unfermentable carbohydrates,
Albuminoids
1-50
traces
7-00
1'80
5-30
'20
8-90
Free acid (as H 2 SOJ
08
03
'05
Mineral matter - .
"30
2"50
'40
rio
Water, . . .
15-50
6-00
13-30
7-60
100-08
100-03
100-25
100-00
Total solid matter ....
84 "42
93'97
86 '65
92 "40
Matter of use to the brewer, . .
82-70
82-70
81-00
82-40
No. 1 was of German origin, white and soft. The other samples
were English, and made from maize without previous separation of the
. starch.
These analyses are unusually elaborate, and for commercial purposes
there is no occasion to enter so much into detail. Many analysts limit
their statements to the proportions of water, ash, dextrin, and glucose,
ignoring the maltose altogether. This practice is very objectionable,
as, in an analysis so stated, not only is the maltose classed as dextrose,
but the amount of dextrin is also seriously in error. Nevertheless, the
cupric oxide reducing power of the sample is a character of considera-
ble value for the commercial classification of a glucose or for assaying
a sample during the process of conversion, provided its true meaning
be not misinterpreted. Taken together with the specific rotatory power
of a sample, and the percentage of ash and water, it often affords
ample information for commercial purposes.
H. W. Wiley (Proc. Amer. Assoc. Adv. Science, xxix., xxx.) has ob-
Jained by the analysis of thirty-five samples of glucose syrup (made by
the Peoria Grape Sugar Company, Buffalo), results of which the fol-
lowing is an epitome : *
Highest.
Specific gravity, 1440 l
K, in terms of dextrose, ........ 62.5
S D (Rotation of sample for D line), . . . 107 '99
Lowest.
1406
39-23
75-47
Average.
1414-8
52-89
92-52
1 The water in the sample of highest density (confectioners' glucose) was but 6*37 per
cent., while a sample of 1409 specific gravity contained 15'40 per cent, of water. The
reducing power was lowest in the sample of greatest optical activity, a fall of 1 degree
in the value of S D (calculated on the sample) corresponding to a rise of approximately 0'75
per cent, in the value of K. A sample which in 10 per cent, solution showed a rotation
of + 53 degrees on a cane sugar scale had also a reducing power of K = 53, a fall of 1
364 COMMERCIAL GLUCOSE.
Wiley has also determined the change occasioned in the optical ac-
tivity and reducing power of glucose syrup by heating with dilute acid.
As a result, he found the value of S D for the inverted sugar was about
-f- 54, the close approximation of which figure to the specific rotation
of dextrose = (-}- 52'7) shows that the inversion was nearly complete.
The value of K after inversion ranged from 79'00 to 9O10. It is a
misfortune that the water in these samples does not appear to have
been determined. 1
The solid varieties of commercial starch glucose have only about one-
half the rotatory power of the syrups, while their reducing power
ranges from K = 70 to K = 87. This is exclusive of the anhydrous
crystallised glucose which is now manufactured, a sample of which
contained 99'4 of real dextrose and 0'6 per cent, of water.
As already stated, analyses of commercial glucose which ignore the
presence of maltose are merely of value for comparative purposes, and
do not even approximately show the proportion of the constituents
actually present. The dextrose is usually over-stated, and the percent-
age of dextrin is also seriously in error. This is well shown by the
following results obtained by the author from a commercial glucose.
Column A. shows the composition on the assumption that all the re-
ducing sugar is glucose, the remaining organic matter being dextrin.
Column B. gives a more correct analysis of the material.
A. B.
Water, 17'77 17'77
Mineral matter, -63 '63
Dextro-glucose, 72' 60 66 '32
Maltose, &c., 10'13
Dextrin, 9'00 5'15
100-00
Total solid matter, 82 '23 82 '23
degree on the sugar scale corresponding to a rise of 1'25 per cent, in the reducing power.
In cases in which the density of the syrup differs sensibly from 1041 (corresponding to
about 15 percent, of water), Wiley corrects the cane sugar units before calculating to the
reducing power by subtracting -003 (a X d) when the density of the sample exceeds 1409,
and adding the same amount to the observed sugar-units when the density is less than
1409; a signifying the rotation of a 10 per cent, solution in sugar units, and d the differ-
ence between 1409 and the density of the sample.
1 In some cases the inversion was effected by heating the glucose solution, with 10 per
cent, by measure of sulphuric acid of 1*25 specific gravity, to 100 C. for three to six
hours. Some of the better results were obtained by increasing the temperature of the
bath to 104, by addition of salt, the heating being continued for three hours.
COMMERCIAL GLUCOSE. 365
A very useful method of assaying glucose solution in the course of
conversion consists in calculating the percentage of total solids in the
sample from the solution-density (see p. 267), deducting the reducing
power found by Fehling's solution, and calling the difference " dex-
trin, &c."
The following data, obtained by the analysis of the above sample,
illustrate the mode, first suggested by the author, of deducing the
relative proportions of dextrose, maltose, and dextrin in such pro-
ducts.
a. On carefully drying the powdered sample, first at about 60 C.,
and subsequently at 100, it lost a weight corresponding to 17 ''11 per
cent, of water ; leaving 82*23 per cent, of total solids. 1
b. On igniting the dried sample it left 0'63 per cent, of ash. Hence
the organic solids amounted to 81 '60 per cent.
c. By Fehling's test (see p. 283) the sample was found to have a
cuprie oxide reducing power (" K ") equivalent to 72*6 per cent, of
dextrose. The reducing power of maltose may be taken as -ff$ that
of dextrose.
d. A solution containing 20 grm. of the original sample per 100
c.c., observed in a 2-decimetre tube, caused a circular rotation of
-f- 23*7 for the sodium line D. Hence the value of S D for the sample
was + 59'25. 2
The values of S D for dextrose, maltose, and dextrin are respectively
+ 52'7, + 139'2, and + 198 (see Dextrin).
If S be the apparent specific rotatory power, K the cuprie oxide
reducing power of the sample, and O the percentage of organic solids,
then the percentage of maltose may be found by the following rule :
Subtract the reducing power (K) from the organic solids (O), and
multiply the difference by 198. To the product add 52'7 times the
reducing power (K) of the sample. Divide their sum by 100, sub-
tract the resultant figure from the specific rotatory power (S), and
divide the remainder by 0*313. The dividend is the percentage of
maltose, &c. t in the sample. 3
The percentage of maltose multiplied by 0'62, and the product sub-
1 As a fact the percentage of total solids in the analysis quoted in the text was deduced
from the solution-density, as stated in the first edition. The method of direct determina-
tion by drying is substituted in the test as a more accurate method of analysis.
2 SD = 23 ' 7 = 59-25. (See p. 39.)
2X^-
100
s For the sample of which the analytical data are given in the text : ;
366 COMMERCIAL GLUCOSE.
tracted from the reducing power (K), gives the percentage of dextrose
in the sample.
The sum of the maltose and dextrose subtracted from the organic
solids gives the percentage of dextrin, &c.
Applying these rules to the sample of which the analytical data
have been given, the percentages of dextrose, maltose, and dextrin are
found to be respectively 66'32, 10'13, and 5'15, together making 81'60.
Instead of ascertaining the organic solids directly, they may be
deduced from the solution-density of the sample, but in that case it is
desirable to subtract twice the percentage of ash from the total solid,
and divide the remainder by 3'94 to obtain the percentage of organic
solids. 1
Total solids 82-23
Ash -63
Organic solids (0) . . 81-60
Reducing power (K) 72-60
Difference 9'00 X 198 = 1782
Reducing power (K) 72-6 X 52-7 = 3826 Specific rotation (S) 59-25
Sum, 5608 -=- 100 = 56'08
3-17 -^ 0-313 = 10-13
per cent, of maltose.
If m be the percentage of maltose, g the dextro-glucose, and d the dextrin in the sample,
then
+ 198(0 -K)^ 013
/_ 52-
"V
; and
d = - g m.
These formulae are deducible from the data in the text. A more extended description of
the method of calculation was given in the first edition of this work.
i H. T. Brown prefers to state the values of S and K on the assumption that the divi-
sion 3-86 is uniformly correct for ascertaining the concentration of solutions of carbohy-
drates from the density. Under these conditions, the specific rotations of dextrose,
maltose, and dextrin for the transition-tint become respectively + 58*6, + 150, and
-(- 216, the value of Ks-se for maltose being 61-0.
From these data, H. T. Brown calculates the composition of the sample by the following
equations :
g = 438-9 -2-03S j3 -86-2-19K; and
i = l-64K-l-64<7.
Using these formulae for the analysis of a sample of known composition, Mr. Brown
informs the author that he obtained the following results :
Dextrose. Maltose. Dextrin.
Actual composition of sample 40-45 41-09 18-45
Found by analysis - ' 38<6 44 ' 64 16 ' 76
COMMERCIAL GLUCOSE. 367
In estimating the reducing power by Fehling's solution, the gravi-
metric method should be employed, and in the manner described on p.
283, as it was in that way the value of K for maltose was determined.
In the case of liquid samples, it is preferable to employ 10 grm.
instead of 20 grm. per 100 c.c., for the estimation of the rotatory
power. The solution of solid samples should be heated to 100 C. for
at least ten minutes before use, in order to destroy the tendency of
freshly-dissolved dextrose to exercise an abnormal rotatory action. 1
In analysing samples of commercial starch sugar by the foregoing
process, the determinations must be made with the greatest possible
care, as very slight variations in the proportion of solids, and in the
values of K and S, correspond to considerable differences in the com-
position of the sample. This is a serious defect of the method, but
another of equal, if not greater, importance is the influence which the
presence of other bodies has on the results. Too little is known of
these substances, of which " gallisin " is the type, to allow of a definite
allowance or correction being made for their presence, yet their dis-
turbing influence on the value of K and S is unquestionable. 2 Hence,
such analyses of starch sugar must not be regarded as scientifically cor-
rect, though they are very superior to those showing the total reducing
powers as dextrose, and stating the remaining carbohydrates as dex-
1 This " bi-rotatory power " is very marked in many samples of solid starch sugar, but
is not noticeable in the syrups. It is not improbably the cause of some of the discordant
results obtained by different observers of the specific rotatory power of dextrose (see
p. 353).
2 If a mixture were made of 40 parts each of dextrose and maltose, and 20 of dextrin,
the calculated optical activity and reducing power of the product would be :
SD. K.
40 per cent, dextrose at 52-7 and 100 21'OS 40
40 per cent, maltose at 139-2 and 62 55-68 24-8
20 per cent, dextrin at 198 and 39-60
Characters of the mixture 116'36 64-8
If 3 per cent, of the dextrin in this mixture were replaced by an equal weight of some
non-reducing carbohydrate of one-third the optical activity of dextrin (S D = 66) the cal-
culated value of S D for such a sample would be + 113'40, the reducing power being
unchanged. But on calculating the composition of such a sample by the rule given in
the text it would appear to contain :
Dextrose
Maltose .
Dextrin .
100-00
This is a very possible case in practice, and hence the method has a tendency to indi-
cate a proportion of maltose considerably below the truth.
368 COMMERCIAL GLUCOSE.
trin. The error falls chiefly on the maltose, the determination of
which is apt to be seriously below the truth, and in some cases a nega-
tive quantity is found.
The difficulty may be in great measure avoided by an ingenious
process due to H. W. Wiley (Chem. News, xlvi. 175), based on the
assumption that dextrose and maltose are oxidised to optically inactive
products when heated with excess of an alkaline solution of mercuric
cyanide, and that dextrin, which is not oxidised thereby, has its optical
activity unaffected. The following is the mode of operation adopted
by Wiley.
a. The cupric oxide reducing power of the sample is ascertained in
the usual way by Fehling's solution.
b. The specific rotatory power is determined by polarising a 10 per
cent, solution (previously heated to boiling) in the ordinary manner.
c. 10 c.c. of the solution employed for b (= 1 grm. of the original
sample) is treated with an excess of an alkaline solution of mercuric
cyanide, 1 and the mixture boiled for two or three minutes. It is then
cooled and slightly acidulated with hydrochloric acid, which destroys
the reddish-brown color possessed by the alkaline liquid. The solution
is then diluted to 50 c.c., and the rotation observed in a tube 4 deci-
metres in length. The angular rotation observed will be due simply
to the dextrin, the percentage of which in the sample may be calculated
by the following formula : 2
Circular rotation X 1000 X volume in c.c. of solution polarised
= Percentage of dextrin.
198 X length of tube in centimetres X weight of sample in
solution employed for mercury treatment.
The percentages of dextrose and maltose may be deduced from
the reducing power of the sample, or from the difference between the
specific rotatory power before (S) and after (s) the treatment with the
1 The mercuric solution is prepared by dissolving about 120 grm. of mercuric
cyanide and the same quantity of caustic soda in 1 litre of water, and filtering the liquid
through asbestos. 20 c.c. of this solution should be employed for samples having K less
than 65 per cent., and 25 c.c. when the reducing power is greater than this. In all cases
care must be taken to use a slight excess ^f the mercuric solution, which may be ascer-
tained by holding a piece of filter-paper with a drop of the solution on it over fuming
hydrochloric acid, and then over sulphide of ammonium or sulphuretted hydrogen water,
when a dark stain, due to mercuric sulphide, will appear on the paper.
2 If the directions in the text were adhered to, and a sample showed an angular rota-
tion of 3'2 with a tube 4 decimetres in length, then the calculation would be :
3-2X1000X50
198X40X1 = 20 ' 2 P 6r Ce
COMMERCIAL GLUCOSE. 369
alkaline mercuric solution. Using the same symbols as before, with
the addition of u for the unknown and presumed inactive organic
matter, the following equations result :
= y + m + d + n; K = I'OO g + 0'62m.
S = 0-527^ + l-392i + l'98d; s = l'9Srf.
From these data :
S - s = 0-527# + 1-392/H ; and 0-527K = 0'527<7 + 0-32674 ; whence
S-- 0-527 K
l-06526wi = S--0-527K; m = ^06526
The proportions of dextrose, dextrin, and inactive carbohydrates are
deduced by means which are evident.
In Wiley's process it is assumed that the indefinite carbohydrates
have no optical activity and no reducing action on Fehling's solution.
,Both these assumptions are probably incorrect, in addition to which it
has not been definitely proved that boiling with an alkaline solution of
mercuric cyanide wholly destroys the optical activity of maltose and
dextrose, while leaving that of dextrin unchanged. Nor has the action
of the mercuric solution on the indefinite carbohydrates been ascer-
tained with certainty, though they may be presumed to react like mal-
tose, since " gallisin " is stated to reduce Knapp's solution. Haas also
found that certain samples of starch glucose gave concordant results
with Fehling's and Sachsse's solutions, while in other cases the reducing
action of the latter reagent showed 10 per cent, more reducing matter
(in terms of dextrose). Haas suggests (Zeits. Anal. Chem., xxii. 219)
that the difference was due to the presence of unfermentable carbohy-
drates, but offers no proof of the accuracy of this view, and makes
no mention of maltose, which also reduces Sachsse's solution.
Wiley's process was employed by the Committee of the American
Academy of Sciences appointed to investigate the nature of commercial
starch glucose. 1 Their Report to the United States Commissioner of
Internal Revenue is a valuable contribution to the literature of the
subject. The following is an epitome of the results quoted in the
Committee's Report:
1 In a copy of the report sent to the writer by one of the members of the committee, the
following note is made respecting a sample found by Wiley's method to contain 41'5 per
cent, of dextrose, 0'6 of maltose, and 38'S of dextrin. "This sample when fermented
gave results which lead us to the belief that it contains a large amount of maltose, and
very little, if any, dextrose. From this and some other facts noticed in the course of the
work, we conclude that the method of Wiley is not applicable to products containing any
considerable percentage of maltose." Nevertheless Wiley's process is a distinct advance
toward the solution of a very difficult problem.
24
370 COMMERCIAL GLUCOSE.
SOLID FORMS. LIQUID FORMS.
Per cent. Per cent.
Dextrose, 72'0 to 73'4 34'3 to 42'8
Maltose, O'O to 3'6 O'O to 19'3
Dextrin, 4'2 to 9'1 29'8 to 45'3
Ash, 0-33 to 0-75 0'32 to T06
Water, 14'0 to 17'6 14'2 to 22'6
Probably a more certain method of estimating the dextrin in com-
mercial glucose would be to employ the following method recommended
by C. Graham : Dissolve 5 grm. of the sample in a small quantity of
hot water, and add the solution drop by drop to 1 litre of nearly abso-
lute alcohol. Dextrin is precipitated, and on standing becomes
attached to the sides of the beaker, while maltose, gallisin, and dextrose
are soluble in the large quantity of alcohol employed. If the solution
be then decanted from the precipitate the dextrin in the latter can be
ascertained by drying and weighing, or by dissolving it in a definite
quantity of water and observing the solution-density and rotation.
The alcohol is distilled off from the solution of the sugars, and the
residual liquid divided into aliquot portions, in one of which the gal-
lisin may be determined after fermentation with yeast, while others are
employed for the observation of the specific rotation and reducing
power, which data give the means of calculating the proportions of
maltose and dextrose in the sample. In the absence of gallisin these
may also be deduced from the increase in the reducing power caused
by heating with dilute acid for several hours (p. 272).
The method indicated in the last paragraph is probably the best
existing for the complete analysis of starch glucose, but it must be ad-
mitted that no reasonably simple process has hitherto been suggested
which will enable the constituents of all kinds of commercial glucose
to be ascertained with a fair approximation to accuracy. 1
When cane or invert sugar is also present, as is frequently the case
in confectioners' glucose syrup and factitious honey, the problem is
still more complete, though an approach to its solution is given on p.
293. The estimation of starch glucose when employed as an adulterant
of commercial cane sugar is described on p. 309 et seq.
The water in commercial glucose may be determined by one of the
methods described on p. 302 et seq., but a high temperature must be
carefully avoided. H. W. Wiley has communicated to the author the
following method of determining the water in* commercial glucose.
The process is also applicable to molasses, honey, &c. : Two grm. of
the sample is treated in a flat platinum dish with a few centimetres of
1 For an advance in this direction see footnote on p. 384.
COMMERCIAL GLUCOSE. 371
dilute alcohol (40 per cent.) until, completely dissolved, when a weighed
quantity (10 to 15 grm.) of dry sand (previously washed and ignited)
is added, and thoroughly mixed with the liquid by means of a weighed
glass rod. The dish is then heated over boiling water for one hour,
when the contents are moistened with about 5 c.c. of absolute alcohol
and further heated to 100 for ten minutes. The dish is then heated
to 110 in an air-bath for fifty minutes, and weighed.
The ash of commercial glucose should not exceed 1 per cent, of the
weight of the sample, and should be almost wholly free from iron,
which is objectionable in brewing materials. It usually consists
chiefly of calcium sulphate, 1 but this is not invariably the case. Some-
times the sulphate of calcium is removed by treating the concentrated
solution of the glucose with barium oxalate, in accordance with a pro-
posal of E. Luck.
The nitrogenous matter of glucose can be determined, if desired, by
ignition with soda-lime. The amount of nitrogen found, multiplied by
6"33, gives the albuminoid matter. Fair comparative results may be
obtained by Wanklyn's "albuminoid ammonia" process (see p. 131).
Mere traces of nitrogenous matter should be present in good glucose,
though it is true that some favorite commercial brands contain a nota-
ble proportion of albuminoids.
Free Acid ought to be wholly absent from commercial glucose,
though many specimens possess normally a slightly acid reaction,
which is probably due to acid phosphates.
The foregoing analyses show the composition of commercial glucoses
up to about 1885, and indicate the presence of unfermentable matters
up to about 9 per cent. Analyses given by Moritz and Morris (" Text-
Book of Brewing "), show similar amounts of unfermentable matters in
five samples of glucose of unknown origin, while the three samples of
maize-glucose are stated to contain 15*59, 14*71, and 15*90 per cent,
of gallisin, in addition to about 1 per cent, of proteids.
ANALYSES OF MAIZE-GLUCOSES, WITH DUE ALLOWANCE FOR GALLISIN.
Dextrose,
Maltose,
Dextrin
A.
50-58
14-19
1'76
B.
48-84
14-88
1*80
C.
47-71
12-29
2'98
Gallisin
15'59
14'71
15'90
Ash,
Albuminoids, . . .
Water
1-44
1-18
16*49
1-36
0-86
18'84
1-39
0-81
20*77
101-23 101-29 101-85
J. S. C. Wells made, on behalf of the United States Committee (p. 369), a number of
372 COMMERCIAL GLUCOSE.
That no gallisin or similar unfermentable substance is present natu-
rally in maize or rice is shown by the following analyses given by
them :
Husked Rice. Maize.
Water, 14 '41 per cent. 17'10 per cent.
Starch, 77'61 59'00 ,,
Fat or Oil, 0'51 ,, 7'00
Dextrin and Sugar, ... . . ,, T50 ,,
Nitrogenous matters, . . 6'94 ,, 12'80 ,,
Cellulose and Fibre, ... 0*08 ,, 1'50
Ash, 0-45 ,, 1-10
100-00 100-00
The 14 per cent, of " passive matter " present in malt-extract is not
of the nature of gallisin. O'Sullivan mentions albuminoids and pen-
toses as among its constituents, but states that it requires further study.
Commenting on these figures, Moritz and Morris remark : " The
quality of a commercial glucose can be judged by the following
analytical standards : the dextrose and maltose should together exceed
80 per cent., the dextrin should not exceed 3 per cent., the albuminoids
1'5 per cent., the correct proportion of gallisin can only follow a much
more extensive knowledge of this substance than now exists, and there
should not be more than a trace of fatty matter."
It is noteworthy that the three samples of maize-glucoses, in par-
ticular, stated by Moritz and Morris to have been analysed by
"one of us," and presumably typical specimens, are far from com-
plying with their standard of quality, nor do some samples of American
maize-glucose of high quality, said to be superior to the highest 'class
English glucose, come up to the standard.
In the Jour. Fed. Inst. Brew., March, 1897, Mr. Arthur L. Stern
gives the following analyses of glucose:
12345
Water, 10'5 9'9 15'7 17'8 16'0
Dextrose, 80'0 70'0 67'4 64'9 65'3
Maltose, 5'1 ll'O 12'4 2'1
Dextrin, .......... . . . . 4'3 1'2
Unfermentable bodies, . . 8'2 14'8 4'3 not det. 14'3
Ash, 1-3 0-2 1-6 0-6 I'l
lOO'O 100-0 100-0 100-0 100-0
analyses of the ash of samples of commercial starch glucoses (Report, p. 24). The compo-
sition varied very greatly, and the results showed clearly that calcium sulphate was by no
means the nearly constant constituent of glucose-ash which it is commonly assumed to be.
In not a few cases the proportion of chlorides exceeded that of the sulphates. Careful
search was made for metallic impurities, but with wholly negative results.
COMMERCIAL GLUCOSE. 373
Commenting on these results, Stern says : " No. 1 is a very good
sample, and much better than is usually sold. No. 2 is now largely
sold, and is a well-made article. No. 3 is not properly converted.
No. 4 is a specimen of bad analysis, as owing to the neglect to deter-
mine the unfermentable matter, the figures are completely valueless,
and, no doubt, part of the maltose and dextrose shown in reality
includes these substances. No. 5 is a fairly well-made sample, but the
water and ash are excessive. It will be seen that of the above sam-
ples only No. 1 comes up to the requirement of Messrs. Moritz and
Morris, of containing a minimum of 80 per cent, of dextrose plus
maltose. Stern states that either dextrin or maltose on the one hand,
or the decomposition-products of dextrose on the other, are always
present, and usually both. Some ash and usually some nitrogenous
bodies are found. Nitrogenous matter should be present in only small
quantities ; even a small percentage is an indication that the sugar was
prepared from imperfectly purified material. We may look upon the
unfermentable residue (gallisin or isomaltose) as an impurity of glucose
with little, if any, sweetening power. It must not be confounded with
another body which Lintner and Dull (Ber., xxvi. 2533) isolated from
the transformation-products of starch by diastase, and also called
isomaltose. Their statements have given rise to a great deal of dis-
cussion, and appear likely to be considerably modified before being
accepted. Several investigators deny the existence of isomaltose in pure
malt-beer, but Dr. Moritz thinks that isomaltose may exist in high-
dried malt.
In an article by J. Brossler (Bingl. Polyt. Jour., 1893, cclxxxvii. 231),
in discussing the question whether commercial glucose manufactured
from starch or potatoes should be permitted to be added to wine, he
gives the following summary of analyses of commercial glucose:
German and Austrian
Glucose. American Glucose.
Dextrose, 64 '3 per cent. 73 '4 per cent.
Unfermentable compounds, ... 18*0 ,, 9'1 ,,
Water, . . . . : 17'0 17'6 ,,
Ash, 0-7 07 ,,
The author has confirmed some of the experiments of Dr. Schidro-
witz on the isolation of an unfermentable, optically-active substance
from samples of beer brewed with glucose, and the very much smaller
optical activity of the unfermentable residue from all-malt beer.
374 COMMERCIAL GLUCOSE.
Exception has been taken to these experiments on the ground that malt-
infusion or diastase should have been used in addition to yeast to get rid
of any malto-dextrin present, but this precaution was taken in a series
of control-experiments, with results practically identical with those
given by Dr. Schidrowitz. It is not at all certain that gallisin would
be precipitated by using alcohol in the manner in which it was employed
by Dr. Schidrowitz, since Ost and other observers similarly recover it
from liquids to which a large excess of alcohol has been added. Cer-
tainly it is not proper to assume, as Dr. Moritz has done, that because
a sample of so-called gallisin in his possession was found not to be sol-
uble in alcohol of 90 per cent, strength, that the gallisin would be pre-
cipitated from a syrup by adding alcohol in quantity sufficient to bring
the strength up to something less than 90 per cent. It does not
follow that the optically-active, unfermentable residue found by
Schidrowitz was actually or wholly gallisin. All that is certain is
that by operating in the manner described by him, beers manufac-
tured with glucose were capable of being distinguished from all-malt
beers.
In addition to the method of Schidrowitz the following differences
between all-malt beers and substitute-beers may assist in their discrimi-
nation.
1. The 14 per cent, of " passive matter " peculiar to malt-infu-
sion.
2. The proportion and nature of the nitrogenous matters. Thus, by
the action of certain ferments, albumin is readily peptonised, but the
action goes no further. On the other hand, by the action of acids the
molecule is further broken down, with formation of tyrosine, leucine,
and other crystallisable bodies.
3. The isolation of gallisin, which is always present to a greater or
less extent in commercial glucose, and often in considerable propor-
tion.
4. The presence of humin matters in invert-sugar produced by
acid.
5. The proportion and nature of the ash-constituents. This datum
has already been utilised by Mr. R. Bannister for the differentiation of
malt-vinegar from sugar- vinegar, and it is clearly equally applicable
to beer.
[The following statement of methods of analysis of brewing-sugar is from a
paper by G. H. Morris (abstract J. S. C. /., June, 1898). The text is from an
advance proof sent by Mr. Allen. L.]
COMMERCIAL GLUCOSE. 375
In the methods given in the " Text-Book of the Science of Brewing,"
by Moritz and Morris, the calculation of the percentages of the
different sugars is based on the assumption that 1 grm. of dextrose,
levulose, maltose, and " gallisin " reduce 2'205, 2'037, 1/345, and 0'992
grm. respectively of copper oxide, these numbers being based on the
values given by C. O'Sullivan. Heron has pointed out that the equiva-
lent of 1 grm. of dextrose, levulose, or invert-sugar is 2'26 grm. of
copper oxide, thus maintaining that these three sugars have the same
reducing powers.
The determination of the amount of available sugar is one of the
most important estimations in the analysis of brewing sugars ; and, as
this depends largely on the reduction of Fehling's solution, the author
has given in detail the mode of procedure. The conditions under which
all determinations should be made are: The use of Fehling's solution,
containing 34'6 grm. of recrystallised copper sulphate, 173*0 grm. of
Rochelle salt, and 65 grm. of anhydrous sodium hydroxide per litre.
The copper sulphate and alkaline tartrate solutions are kept separate,
and mixed in equal volumes immediately before being used. The
degree of dilution of the copper solution, after taking into account the
volume of the sugar added, should be 1 part of Fehling's solution to 1
part of water, 50 c.c. of the undiluted Fehling being used in each
experiment, and made up to 100 c.c. An amount of the reducing
sugar should be taken which will give a weight of copper oxide lying
within the limits of 0'15 to 0'35 grm. The diluted Fehling's solution
should be heated in a beaker in a bath of boiling water until the tem-
perature is constant ; then the weighed or measured solution of reduc-
ing sugar added, and the heating in the water-bath continued for
exactly twelve minutes, the beaker being covered with a clock-glass.
The filtration should be performed as rapidly as possible, either through
a Soxhlet tube under reduced pressure, or through a carefully-folded
filter paper. In the former case, the reduced cuprous oxide is oxidised
to cupric oxide and then reduced to copper in a stream of hydrogen.
In the latter case, the filter and its contents are burnt in the usual way,
and weighed as cupric oxide. A correction must be made for the
slight amount of reduction which Fehling's solution always undergoes
on heating, and if filter papers are used, it is necessary to determine
and allow for the copper retained in the tissue of the paper. Working
under these conditions, it was found that 1 grm. of dextrose, levulose,
and maltose, reduced 2*578 to 2*338, 2*310 to 2*211, 1-380 to 1'362
grm. respectively of copper oxide, the exact amount depending upon
376 COMMERCIAL GLUCOSE.
the quantity of copper reduced in the standard volume of Fehling's
solution. The method of calculation previously adopted must, there-
fore, be modified, and in place of a fixed factor, one corresponding to
the amount of reduction in each case be taken.
Attention is drawn to the fact that commercial invert-sugar and
glucose contain a certain amount of unfermentable matter, having a
cupric-reducing and optical action. It has been usual to make a
correction for this matter in the case of glucose, but not, however, with
invert-sugar. Several determinations are given, showing the properties
of this unfermentable matter in both sugars.
The following is a routine process for the analysis of brewing
sugars : The ash is determined by burning a weighed quantity of the
sugar in the usual way, and calculating the amount obtained as a per-
centage of the sample. The albuminoids are estimated by Kjeldahl's
process, and the albuminoids calculated from the ammonia obtained
by the usual factors. The water is estimated by dissolving 10 grin.
of the sugar in 100 c.c. of water, taking the gravity, and calculating
the total solids by the 3'86 divisor. The solid so obtained requires to
be corrected for the higher solution density of the ash, which, accord-
ing to Heron, and confirmed by the author, may be taken at 8. The
most convenient way of doing this is to multiply the solid matter of
the 10 per cent, solution by 10, to convert it into a percentage, and
then to deduct from it the percentage of ash. 100, minus the number
thus obtained, gives the percentage of water. The reducing power is
carried out as described above. A polarimetric reading of a 10 per
cent, solution, which should be made with boiling water and allowed
to stand eighteen hours, is taken at 68 F. in a 200-mm. tube, and the
specific rotatory power calculated, after correcting for any cane sugar
which may be present. Both the values so obtained then require to
be corrected for the reducing power and opticity of the unfermentable
residue. The percentages of the sugars are now calculated by means
of the equation
[a] D D [a] D L = b x 100
in which x D = the gram-value of dextrose expressed in either CuO
or Cu, x L = the gram-value of levulose expressed in the same way,
a = the CuO or Cu reduced by 100 grm. of the sample, b = specific
rotatory power ([] D ) calculated on the sample.
In order to determine the amount of cane sugar, 50 c.c. of the 10
COMMERCIAL GLUCOSE. 377
per cent, solution are digested with a small quantity of washed and
pressed yeast at 125 F. for five hours. The solution is cooled, a little
alumina added, made up to 55 c.c., filtered, and the rotation deter-
mined at 68 F. ; the reading is increased by one-tenth, to correct for
dilution, and the difference between the corrected and the original
reading divided by 5*02 gives the cane sugar in solution, from which
the percentage may be calculated. (5*02 is the number of divisions of
the Soleil-Ventzke-Scheibler polarimeter, which a solution of 1 grm. of
cane sugar in 100 c.c. of water, read in a 200-mm. tube, lost on being
converted into invert-sugar by yeast or acid.) To estimate the unfer-
mentable matter, 50 c.c. of the 10 per cent, solution are placed in a
100-c.c. flask and sterilised ; 2 or 3 grm. of washed and pressed yeast
are added, and the mixture fermented at 75 F. When fermentation
is over, alumina is added and the whole made up to 100 c.c. After
filtration the copper reduction is determined on 25 c.c., and the rota-
tion observed in a 200-mm. tube. The results are expressed on the
same basis as those of the original solution, and deducted from the
latter. In order to directly obtain the percentage of the unfermentable
residue, a portion of the liquid may be evaporated to expel the
alcohol, then made up to the original volume and the gravity taken.
From this the solid matter is obtained by the 3'86 division, and the
result multiplied by 20, in order to bring to a percentage on the
original sample. It is then necessary to subtract the percentage of
albuminoids, and twice that of the ash, to get the amount of solid
matter contained in the unfermented residue. This residue also con-
tains the non-volatile products of fermentation, and these must be
corrected for. According to Pasteur, the non-volatile products
amount to from 4 to 5 per cent, of the sugars fermented ; therefore 4
per cent, of the total sugars obtained as above is deducted, and the
remainder gives approximately the true unfermentable matter. With
commercial sugars it is, however, unnecessary to make this determina-
tion, and it is sufficient to take the difference between the sum of the
sugars, ash, albuminoids, and water, and 100 as representing the unfer-
mentable residue. In the case of glucoses this residue includes the
"gallisin " and dextrin. The constants of the former are not, in the
opinion of the author, sufficiently well established to admit of direct
estimation. The latter can, if necessary, be directly determined by
making a second fermentation with a small quantity of cold-water malt
extract, and calculating the difference between this and the ordinary
fermentation as dextrin. It is only necessary to do this when par-
tially converted products are being dealt with.
378
COMMERCIAL GLUCOSE.
The extract is estimated from the 10 per cent, solution in the usual
way.
The paper concludes with the following optical constants and cupric-
reducing tables used in the preceding calculations :
Eotation in 10 Per Cent.
Solution at 20 C. [a] D
Absolute.
Reading in the 200-mrn.
Tube in the Soleil-Ventzke-
Scheibler Polarimeter for
1 Grin, in 100 c.c.
Dextrin,
Maltose,
Cane su^ar . ...
202-0
138-0
66 '5
Divisions.
11-66
7-97
3'84
Dextrose,
Levulose,
Invert sugar,
52-8
-92-0
-19-6
3-05
-5-31
-1-13
KEDUCING VALUES OF VARYING QUANTITIES OF CARBOHYDRATES UNDER
STANDARD CONDITIONS.
Maltose.
Maltose in
Mgrm.
Cu weighed
in Grin.
CuO weighed
in Grm.
Maltose in
Mgrm .
Cu weighed
in Grin.
CuO weighed .
in Grm.
70
0-0772
0-0966
190
0-2072
0-2593
75
0-0826
0*1034
195
0-2126
0-2661
80
0-0880
0-1102
200
0-2180
0-2729
85
0-0934
0-1169
205
0-2234
0-2797
90
0-0988
0-1237
210
0-2288
0-2865
95
0-1042
0-1305
215
0-2342
0-2933
100
0-1097
0-1373
220
0-2397
0-3000
105
0-1151
0-1441
225
0-2451
0-3068
110
0-1205
0-1509
230
0-2505
0-3136
115
0-1259
0-1576
235
0-2559
0-3203
120
0-1313
0-1644
240
0-2613
0-3272
125
0-1367
0-1712
245
0-2667
0-3340
130
0-1422
0-1779
250
0-2722
0-3407
135
0-1476
0-1848
255
0-2776
0-3475
140
0-1530
0-1916
260
0-2830
0-3543
145
0-1584
0-1983
265
0-2884
0-3610
150
0-1634
0-2051
270
0-2938
0-3678
155
0-1692
0-2119
275
0-2992
0-3747
160
0-1747
0-2186
280
0-3047
0-3814
165
0-1801
0-2254
285
0-3101
0-3882
170
0-1855
0-2323
290
0-3155
0-3950
175
0-1909
0-2390
295
0-3209
0-4017
180
0-1963
0-2458
300
0-3264
0-4085
185
0-2017
0-2526
305
0-3318
0-4154
HONEY.
Dextrose.
379
Sugar in
Mgrm.
Cu weighed
in Gnu.
CuO weighed
in Grm.
Sugar in
Mgrm.
Cu weighed
in Grm.
CuO weighed
in Grin.
50
01030
0-1289
130
0-2585
0-3241
55
01134
0-1422
135
0-2675
0-3354
60
01238
0-1552
140
0-2762
0-3463
65
0-1342
0-1682
145
0-2850
0-3573
70
0-1443
0-1809
150
0-2934
0-3673
75
0-1543.
0-1935
155
0-3020
0-3787
80
0-1644
0-2061
160
0-3103
0*3891
85
0-1740
0-2187
165
0-3187
0-3966
90
0-1834
0-2299
170
0-3268
0-4098
95
0*1930
0-2420
175
03350
0-4200
100
0-2027
0-2538
180
0-3431
0-4302
105
0-2123
0-2662
185
0-3508
0-4399
110
0-2218
0-2781
190
0-3590
0-4501
115
0-2313
0-2600
195
0-3668
0-4599
120
0-2404
0-3014
200
0-3745
0-4689
125
0-2496
, 0-3130
205
0-3822
0-4792
Levulose.
Sugar in
Mgrru.
Cu weighed
in Grm.
CuO weighed
in Grm.
Sugar in
Mgrm.
Cu weighed
in Grm.
CuO weighed
in Grm.
50
0-0923
0-1155
130
0-2390
0-2997
55
0-1027
0-1287
135
0-2477
0-3106
60
0-1122
0-1407
140
0-2559
0-3209
65
0-1216
01524
145
0-2641
0-3311
70
0-1312
0-1645
150
0-2723
0-3409
75
0-1405
0-1761
155
0-2805
0-3587
80
0-1500
0-1881
160
0-2880
0-3622
85
0-1590
0-1993
165
0-2972
0-3726
90
0-1686
0-2114
170
0-3058
0-3828
95
0-1774
0-2224
175
0-3134
0-3939
100
0-1862
0-2331
180
0-3216
0-4032
105
0-1952
0-2447
185
0-3297
0-4134
110
0-2040
0-2558
190
0-3377
0-4234
115
0-2129
0-2669
195
0*3457
0-4335
120
0-2215
0-2777
200
0-3539
0-4431
125
0-2303
0-2817
205
0-3616
0-4534
Honey.
French Meil. German Honig.
Ordinary honey is a saccharine substance collected and stored by a
particular species of bee (Apis mellifica}, but its production is common
to various species of bees, besides other hymenopterous insects, such as
wasps and certain species of ants. 1
1 The Mexican honey-ant (Myrmecocystus Mexieanut) secretes a syrup of nearly pure
invert sugar, but slightly acid, apparently from the presence of formic acid.
In a substance allied to honey called tuzma, found in Ethiopia, and said to be the product
380 HONEY.
The specific gravity of virgin honey ranges from 1425 to 1429, and
that of honey from old bees from 1415 to 1422. According to Buch-
ner, the density sometimes reaches 1440.
When honey is examined under the microscope, crystals of dextrose,
scales from butterflies' wings, spores of fungi, and different kinds of
pollen may be observed. The last bodies, if sufficiently identified,
may lead to a knowledge of the country whence the honey was de-
rived.
Chemically, honey is essentially a concentrated aqueous solution of
certain sugars, dextrose and levulose being the most important con-
stituents. Occasionally a small percentage of sucrose appears to be
normally present, especially in the new honey from bees fed on cane
sugar, 1 but after a time this constituent undergoes inversion by the
trace of acid or some ferment present in the honey. According to
James Bell, honey contains from 5 to 10 per cent, of a substance which
undergoes conversion to glucose only by prolonged treatment with acid
(maltose, gallisin ?). Soubeiran and Dubrunfaut also state that honey
contains certain undefined sugars, and the same conclusion is deducible
from the analytical results of other observers.
Besides the true sugars, honey contains a sensible quantity of the
saccharoid mannite, C 6 H U O 6 (see Table on p. 245), which may be iso-
lated by fermenting a solution of the honey with excess of yeast, filter-
ing, evaporating the filtrate to a low bulk, adding excess of boiling
alcohol, evaporating the filtered liquid to dryuess, extracting the resi-
due with boiling alcohol, concentrating the resultant solution, and
precipitating the mannite therefrom by addition of ether.
The other constituents of honey are water, small quantities of wax,
pollen, mineral matter, traces of flavoring and bitter substances, organic
acids, &c. Formic acid appears usually to be present in honey.
Several observers have published figures showing the composition of
honey, the most complete analyses being those of J. Campbell Brown
(Analyst, iii. 269). E. Sieben (Zeits. Anal. Chem., xxiv. 135), and O.
Hehner (Analyst, ix. 64), have determined certain of the constituents
in a large number of samples of honey, and J. Bell in a few (Foods,
part i. p. 116). A. H. Hassall has also published analyses of four
of an insect like a large mosquito, A. Villiers found 32 per cent, of glucoses (the dextrose
being somewhat in excess), no sucrose, 27'9 per cent, of a kind of dextrin, 3*0 of mannite,
2*5 of mineral matter, a non-nitrogenous bitter principle, and 9*1 of unidentified sub-
stances (Compt. rend., Ixxxviii. 292).
1 On the other hand, the nectar of plants contains a considerable quantity of an invert-
ible sugar, which is probably sucrose (Chem. News, xxxviii. 93).
HONEY.
381
samples of honey. The following is an epitome of the results of these
chemists :
J. C. Brown.
E. Sieben.
0. Hehner.
J. Bell.
A. H. Hassall.
Dextrose, ....
31-77 to 42-02
22-23 to 44-71
Levulose, . . .
33-56 to 40-43
32-15 to 46-89
Total Glucoses, .
68-40Ho 79-72
67 -92 to 79-57 l 61'42to75'34
66-57 to 74-04
79-48 to 82-50
Sucrose, ....
t
none to 8 -22
f
none to 5-29
Wax, Pollen, and
Insoluble mat-
ters,
trace to 2*10
.
traces
Ash,
0-07 to 0-26
i
018 to 0-49
0-02 to 0-30
Water expelled
at 100 C., . .
15-50 to 19-80
16-28 to 24-95
12-43 to 23-26
17-10 to 23-32
1
U n d e t ermined
matters ( b y
[ 13-63 to 19-56
difference), . .
4-95 to 11 -00
1-29 to 8-82
8-48 to 19-17
7-67 to 10-79
J
The undetermined matters of Bell's analyses included the unidentified
sugar previously mentioned, while Campbell Brown collected a consider-
able quantity of water, which he found to be driven off above 100 C.
Although the figures representing the other constituents show a con-
siderable range of variation, the great majority of samples of honey are
of a remarkably constant character, the glucoses ranging from 70 to
80 per cent., the water from 17 to 20, and the ash from O'lO to 0'25.
In normal honey, the dextrose and levulose are present in approxi-
mately equal proportions, but if the honey has crystallised in the comb
the runnings therefrom will be deficient in dextrose, and hence will
be strongly levo-rotatory. It is held by experienced bee-keepers that
all genuine honey will eventually crystallise, and hence that honey
warranted to remain syrupy is probably adulterated.
ANALYSIS OP COMMERCIAL HONEY.
Honey is frequently adulterated, the most common sophistication
being the addition of glucose syrup, a dextrine-saccharine liquid
obtained by the action of dilute acid on starch. A factitious honey is
sometimes manufactured wholly from glucose syrup, with addition
of minute quantities of formic acid, and flavors to give the prepara-
tion a flavor of honey. Cane sugar and invert sugar have also been
used as adulterants of honey, and molasses is said to have been occa-
sionally added. The addition of mineral matters, such as clay or
gypsum, is improbable.
1 In this analysis there was also found 2*2 per cent, of cane sugar, but Dr. Brown con-
siders that the appearance of sucrose as a constituent is as probably due to error of experi-
ment as to its actual presence in the specimen, which was one of Jamaica honey. Dr.
Brown's figures for dextrose and levulose have been re-calculated with his consent.
382 HONEY.
The proportion of water in honey may be determined as in molasses
(p. 302), or by the method of Wiley, described on p. 370. A useful
check on the result is obtained by calculating the solids from the
density of a 20 per cent, solution of the sample, as described on
p. 267.
The ash of genuine honey is usually very trifling in amount. If in
excess of 0'3 per cent., it should be tested for calcium sulphate, the
presence of which, in notable quantity, is an almost certain indication
of adulteration by starch glucose or invert sugar. In fact, the pres-
ence of notable traces of sulphates is the only way in which an addition
of invert sugar to honey can be inferred. Sulphates may also be
detected by the direct addition of barium chloride to the aqueous
solution of the sample. A high ash containing a notable proportion of
chlorides points to a probable adulteration with molasses.
The insoluble matter of honey may be determined as in sugar. It
usually consists of wax, pollen, &c., and should be carefully examined
under the microscope. Starch, which is not a normal constituent of
honey, will be readily recognised in the residue by its reaction with
iodine, and, if present in quantity, points to an adulteration of the
sample with flour or other farinaceous substance, the exact nature of
which will be indicated by its microscopic appearance.
Gelatin, if present, will be left undissolved on treating the sample
with spirit, and will be recognised by its odor on ignition, and the
reaction of its aqueous solution with tannin.
Dextrin, which is not found in genuine honey, but is a constituent of
commercial glucose syrup, may be detected by diluting the honey with
an equal measure of water, and gradually adding strong spirit, stirring
constantly until a permanent turbidity is produced. In samples adul-
terated with glucose syrup a heavy gummy deposit will soon form, but
with genuine honey only a slight milkiness is produced.
Saccharine additions to honey can only be detected by a careful
examination of the action of the sample on polarised light, and its
behavior with Fehling's and other reducible solutions. The following
table shows the specific rotatory power and cupric oxide reducing
power of mixtures of cane and invert sugar, containing 82 per cent, of
the solid and 18 per cent, of water, and of average glucose syrup, as
compared with genuine honey. The table also shows the changes pro-
duced in solutions of the above saccharine matters by the action of
invertase (p. 300), by prolonged heating with dilute acid (p. 272), and
by fermentation with yeast (p. 275) :
HONEY.
383
Cane Sugar
82ft Water
18ft
Invert Sugar
82ft Water
18ft
Average
Glucose Syrup.
Genuine
Honey.
SPECI ric ROTATOR Y POWER
FOR SODIUM KAY.
Original substance, ....
After treatment with in-
vertin,
After prolonged heating
with dilute acid, ....
After fermentation with
-f 54-5
19-9 at 15
19-9 at 15
18-9 at 15
18'9 at 15
18-9 at 15
inactive -1
+ 92 to 100
little altered
+ 45
very notably
-I- 2 to 3
little altered
little altered
I to + 4
CUPRIC OXIDE REDUCING
POWER.
Original substance, ....
After treatment with in-
86-3
82
82
dextro-rotatory
53
little altered
61 to 82
little altered
After prolonged heating
with dilute acid,
86-3
82
82
little altered
After fermentation with
yeast, . . . .
very notable
to 2
According to the table, there is a sensible difference between the
rotation of invert sugar and genuine honey, but unfortunately this dis-
tinction does not always hold good, for if the honey has crystallised in
the jcomb some of the dextrose is apt to remain there, and the honey
drained therefrom will contain excess of levulose, and be more strongly
levo-rotatory than is indicated by the figures in the table. Unless,
therefore, the ash be excessive, or happen to contain calcium sulphate
(p. 371), the positive recognition of added invert sugar is next to
impossible.
Any considerable proportion of cane sugar in honey would be indi-
cated by the strong dextro- rotation of the sample, changed to left-
handed rotation on treatment with invertin or dilute acid. The
proportion of cane sugar can be estimated from the extent of the change
in the rotatory and reducing power of the sample caused by treatment
with invertin, or, iu the absence of glucose syrup, by inversion with
dilute hydrochloric acid, as on p. 263. As already stated, a small per-
centage of sucrose appears sometimes as a constituent of genuine honey.
Glucose syrup is still more dextro-rotatory than cane sugar to com-
mence with', the optical activity falling to about one-half by prolonged
treatment with acid, while the products left after fermentation are
still notably dextro-rotatory. In the absence of added cane and invert
sugar, an approximate estimation of the proportion of glucose syrup in
honey may be made by reckoning 1 per cent, of the adulterant for
every degree of dextro-rotatory power possessed by the original sample.
Of course, it must not be forgotten that a dextro-rotation of a few
384 GLUCOSIDES.
degrees is observable in some samples of genuine honey. 1 The saccha-
rine liquid secreted by fir-cones, &c., is said to be notably dextro-
rotatory.
Glucosides.
The name glucoside is applied to numerous bodies possessing the
1 Sieben, in a recent valuable paper (Analyst, x. 34), gives the following methods of
examining honey for starch glucose: For the fermentation test, 25 grm. of the sample are
dissolved in water, the solution diluted 200 c.c., and fermented for forty-eight hours at the
temperature of the room with 12 grm. of German yeast free from starch. Alumina cream
(p. 257) is then added, the liquid diluted to 250 c.c. and filtered. 200 c.c. of the clear
filtrate should then be evaporated to 50 c.c., and examined in the polarimeter. As
already stated, pure honey gives a residue after fermentation which is optically inactive,
or nearly so, while the residue from an adulterated sample is strongly dextro-rotatory.
Sieben states that, operating as above described, a sample adulterated with 20 per
cent, of starch sugar will show a rotation of + 7'2 when examined in a 2-decimetre
tube with a Wild's polarimeter, while a sample containing 50 per cent, of starch sugar
will rotate -f 22*2 under the same conditions. After observing the optical activity,
25 c.c. of the (fermented and concentrated) solution employed for the experiment should
be heated on the water-bath with 25 c.c. of water and 5 c.c. of concentrated hydro-
chloric acid. The liquid is then neutralised, made up to 100 c.c., and the sugar deter-
mined in 25 c.c. by Fehling's solution. The glucose thus found, when multiplied by 40,
gives the dextrose corresponding to the unfermentable carbohydrates of the sample.
Honey containing 10 per cent, of starch sugar shows 3'24 per cent, of dextrose from the
unfermentable matters, while 20 per cent, gives 6*39, and 40 per cent. 8-85 of dextrose.
Unfortunately, all these figures assume the presence of constant proportions of unferment-
able carbohydrates in honey and starch sugar.
Another method of detecting starch sugar in honey, described by Sieben as being very
delicate, is as follows : 14 grm. of honey are dissolved in about 450 c.c. of water, and any
sucrose inverted by heating the solution with 20 c.c. of semi-normal hydrochloric acid.
The liquid is then neutralised, and made up to 100 c.c. 100 c.c. of Fehling's solution are
next titrated with the saccharine solution, of which 23 to 26 c.c. will be required; and
then another quantity of 100 c.c. of Fehling's solution is boiled with, a measure of the
honey solution less by 0*5 c.c. than was previously found necessary for the reduction of the
copper. By this means the sugars are oxidised without the non-reducing carbohydrates
being affected. The liquid is filtered through asbestos, the filter washed slightly with hot
water, and the filtrate neutralised with strong hydrochloric acid. One-tenth of its measure
of fuming hydrochloric acid is then added, and the solution is heated on the water-bath
for one hour, nearly neutralised with concentrated solution of soda, and made up to 200 c.c.
After cooling, the liquid is passed through a dry filter, and 150 c.c. of the filtrate boiled
with 120 c.c. of Fehling's solution and 20 c.c. of water. The dextrose corresponding to
the non-reducing carbohydrates is calculated from the cuprous oxide precipitated. Sieben
states that when treated in the above manner the metallic copper corresponding to the
cuprous oxide precipitated by genuine honey does not exceed 0*002 grm., while with 5 per
cent, of starch sugar the copper precipitated weighs *020 ; with 10 per cent., *040 ; with 20,
090 with 40, "190 and with 60, '330 grm. These figures again assume the presence of a
constant proportion of non-reducing carbohydrates in the starch sugar used as the adul-
terant.
The foregoing methods of examination would probably yield interesting and valuable
results if employed for the analysis of unmixed starch glucose.
GLUCOSIDES. 385
common property of yielding a glucose, C 6 H 12 O 6 , as one of the products
of their treatment with water and a dilute acid. Thus salicin, when
boiled with dilute sulphuric acid, yields dextrose and the alcohol-like
body saligenol or saligenin.
C 13 H 1S 7 + H 2 O = C 6 H 12 O 6 + C 7 H 7 O.OH.
A similar decomposition of the glucosides often occurs by the agency
of certain peculiar ferments occurring in the plant, together with the
glucoside. These ferments have a very limited power of producing
such decompositions, their influence being exerted only on a few gluco-
sides of closely-related composition.
The glucoses obtained from the glucosides have been identified with
sucro-dextrose in a few instances, but in many cases their exact nature
is uncertain.
Some of the glucosides are of interest from a pharmaceutic and toxi-
cologic point of view, but few of them, except gallotannic acid and the
glucoside of mustard, commonly require to be assayed. Their analytic
characters have in most cases been but very imperfectly studied. From
the alkaloids they may, as a rule, be separated by acidulating the
aqueous solution with sulphuric acid, and agitating with a mixture of
chloroform and ether, which extracts the glucosides without affecting
the sulphates of the majority of the alkaloids. The alkaloids which
cannot thus be separated are usually weak bases.
STARCH AND ITS ISOMERS.
In the vegetable kingdom, and to a minor extent in the animal
kingdom, there exist a number of carbohydrates having in common a
composition represented by the empirical formula C 6 Hi O 5 , but their
physical and chemical characters point in many cases to a multiple of
this formula as the true representation of the constitution of the mole-
cule.
The carbohydrates of the starch group are non-volatile bodies, and,
with perhaps one or two exceptions, are amorphous. As a class they
are insoluble in alcohol, though the greater number of them are dis-
solved by water, forming solutions which usually exert a marked rota-
tory action on a ray of polarised light. They are neutral in reaction,
and form but few definite compounds or metallic derivatives. The
carbohydrates of the starch group are very numerous, and apparently
capable of isomeric modification. Owing to their physical characters,
and feebly-marked chemical affinities, it is often extremely difficult to
obtain them in a state of purity.
None of the members of the group reduces Fehling's solution when
boiled with it. By treatment with acids they yield sugars among
other products, and then reduce the cupric solution.
Many of the members of the group are of little practical interest,
and their analytical reactions have been very incompletely studied.
The following table serves to show the comparative characters of the
more important members of the group, and cellulose, starch, and
dextrin are described more fully in subsequent sections. Elsewhere
will be found tables for the general proximate analysis of plant-prod-
ucts; and under the head of "Gums" a short description of pectinous
matters.
386
AMYLOSES.
387
Ill i
|*t i
jinj
3f'E.l S
Mil*
ZUill
o> J- o a, cr
aw 'o.HsSta
.23*8 ^^-^
4J| Is
S =-2 ***
'
^1
1
l-'l
o
^s o
^r.
5 a
I I
S C
i
g
;.So = S*a3S
S I
I 1
I I
II P
ill
"S-c o
8-5
I'! H
:| . "14!
'-Hs '-32
'
c ^ ^ S - o
c? w
388 CELLULOSE.
CELLULOSE. C 6 H 10 O 5 .
Cellulose constitutes the essential part of the solid frame-work or
cellular tissue of plants, and hence is an especially characteristic prod-
uct of the vegetable kingdom. The outer coating of Ascidian animals
is, however, apparently identical with cellulose.
Cellulose occurs nearly pure in cotton, linen, and the pith of certain
plants. Swedish filter-paper, linen rags, and cotton-wool are still purer
forms of cellulose.
Cellulose is closely related to starch, and is most probably directly
formed from it ; but it is more stable than starch, and is not readily
rendered soluble.
Cellulose is a white, tasteless, odorless, non-volatile body of about
1*45 specific gravity. It is insoluble in water and all ordinary men-
strua, but dissolves, as first observed by Schweitzer, in a strong solution
of cupric oxide in ammonia.
SCHWEITZER'S REAGENT, which may be regarded as a solution of
cuprammoniurn hydroxide, is prepared by leaving copper turnings
partially immersed in ammonia, with access of air or cupric hy-
droxid maybe precipitated from a cold solution of cupric sulphate by
adding excess of caustic soda, and the well-washed precipitate dissolved
to saturation in ammonia. On treatment with the resultant solution,
cellulose becomes gelatinous, and on agitation gradually dissolves,
forming a viscid solution which may be filtered after dilution with
water. 1 On neutralising the filtrate with hydrochloric acid the cellu-
lose is separated in a flocculent state resembling hydrated alumina,
which when dried forms a brittle, greyish, horn-like mass. Carbonic
acid also precipitates the solution, as do sugar, salt, and even copious
dilution with water.
The solution of cellulose in Schweitzer's reagent is decomposed by
dialysis. It is levo-rotatory, a 1 per cent, solution showing a
specific rotation of 20 for the light transmitted, which bears to the
sodium ray the ratio 1 : 1*85. The optical activity is not strictly pro-
portional to the cellulose dissolved, increasing somewhat more slowly
than the concentration of the solution. Cellulose from different sources
exhibits the same optical activity.
According to Fremy, three varieties of cellulose exist, all of which
are soluble without coloration in cold sulphuric acid of 1*78 specific
i The action of ammoniacal solutions of cupric and zinc oxides on cellulose has been
applied on a large scale by C. R. Alder Wright to the manufacture of the " Willesden "
products (Jour. Soc. Chem. Ltd., iii. 121).
CELLULOSE. 389
gravity, to form a solution which, after dilution with water and boil-
ing, is found to contain glucose ; they are distinguished by their
behavior with the cupric solution ; thus:
Cellulose; constituting the greater part of cotton and the utricular
tissue of certain fruits, as the apple, is dissolved immediately by the
cupric reagent.
Paracellulose ; forming the epidermis of leaves and the utricular
tissue of certain roots, is not soluble in the cupric solution till after
boiling with very dilute hydrochloric acid.
Metacellulose, or fungin; found chiefly in agarics and lichens, is
not dissolved by the cupric reagent even after treatment with acid, but
is easily soluble in nitric acid and in hypochlorites, and is distinguished
from the above varieties of cellulose by its solubility in cold sul-
phuric acid diluted with 4 or 5 equivalents of water.
Cellulose is not altered by cold dilute alkaline solutions, but in con-
centrated caustic potash or soda it swells up and gradually dissolves,
being apparently converted into dextrin and ultimately into sugars.
Cellulose absorbs an appreciable amount of barium hydrate when
immersed in dilute baryta water.
By heating to a high temperature with caustic potash, cellulose
yields methylic alcohol and potassium oxalate.
When heated with a solution of a hypochlorite containing free alkali,
or with soda and a ferricyanide, cellulose forms oxidation-products
which are soluble in the alkaline liquid.
Cellulose does not undergo the ordinary alcoholic fermentation with
yeast, but in presence of a little albuminoid matter it is converted by
the ferment of the pancreas into acetic and isobutyric acids, methane
and carbon dioxide being simultaneously evolved (Tappeiner, Ber.
xvi., 1734).
If cotton-wool or filter-paper be heated at 180 C. for several hours
with about six or eight parts of acetic anhydride, it is entirely dissolved
and converted into a triacetate, C 6 H 7 (C 2 H 3 O)3O5, which may be sepa-
rated by pouring the syrup into water; it is a white powder, optically
inactive, soluble in strong acetic or sulphuric acid, and very readily
converted into cellulose and potassium acetate by boiling with dilute
caustic potash. Other acetyl-derivatives of cellulose have been
obtained.
HYDROCELLULOSE, C 12 H 22 O U , is the product of the action of mineral
acids (e.g., sulphuric acid of 1'42 sp. gr., or fuming hydrochloric acid),
and many other reagents on cellulose. It always retains the form of
the cellulose from which it is derived, but differs therefrom in being
390 CELLULOSE.
extremely friable,. more readily affected by reagents, and in the readi-
ness with which it combines with coloring matters.
Cellulose undergoes gradual change by prolonged boiling with dilute
acids, being converted into hydrocellulose, and is even affected by
boiling water alone, especially if heated under pressure.
Cold concentrated sulphuric acid dissolves cellulose, converting it
first into a body (? hydrocellulose) which gives a blue color with
iodine, and swells up in water without dissolving; a dextrinoid sub-
stance is next produced, and if the liquid be then largely diluted and
boiled, sugars are formed which reduce Fehling's solution. If cellu-
lose be heated with concentrated sulphuric acid, charring at once
occurs.
By treating cellulose with cold sulphuric acid previously diluted
with half its measure of water, it is converted into a substance called
amyloid, which, after washing with cold water, is extraordinarily
tough. This fact is utilised for the production of "parchment paper."
Chloride of zinc may be substituted for the sulphuric acid.
Cellulose is not colored by iodine solution alone, or at most only
assumes a yellow or brownish color, but in presence of hydriodic acid,
potassium or zinc iodide, zinc chloride, sulphuric or phosphoric acid, it
is colored blue by iodine. Concentrated sulphuric acid and zinc
chloride especially favor the production of the blue color, doubtless
owing to the formation, of amyloid. 1 If cellulose be first treated with
one of the above reagents, and then freed from it by washing, no blue
color is produced on adding solution of iodine.
By treatment with cold nitric acid of 1*42 specific gravity, cellulose
is remarkably toughened, without losing its fibrous structure or becom-
ing nitrated. With stronger acid, cellulose is converted into nitro-
substitution products which are described on p. 399 el seq.
By boiling with moderately concentrated nitric acid, cellulose is
converted into oxidation -products, some of which have a close analogy
to the original substance, but differ from it in certain remarkable
respects.
OXYCELLULOSE appears to vary somewhat in composition according
to the mode of preparation, but an apparently definite substance of the
formula Ci 8 H 26 O 16 was obtained by Cross and Bevan (Jour. Soc. Chem.
Ind., iii. 206) from several different sources. The cellulose was boiled
with nitric acid containing 50 per cent, of HNO 3 , whereby it was
1 Schulze's reagent, by which cellulose is colored blue, may be prepared by adding 6
grin, of iodine and the same weight of potassium iodide to 100 c.c. of a solution of zinc
chloride of 1'8 specific gravity.
CELLULOSE. 391
largely oxidised to oxalic acid, but yielded 30 per cent, of oxycellulose
in the form of a fine white powder, readily soluble in dilute alkalies
and reprecipitable from the solution in a pectous form on addition of
acids, salts, or alcohol. Oxycellulose dissolves in concentrated sul-
phuric acid with pink coloration, and yields a gummy dextro-rotatory
substance resembling ordinary dextrin. By the action of concentrated
nitric acid mixed with sulphuric acid, oxycellulose yields a nitro-
compound of the formula C 18 H23(NO 2 )3Oi 6 .
The action of hypochlorites on cellulose, which has an important
practical bearing on the theory and practice of bleaching cotton and
linen goods, has been studied by M. G. Witz. By the extreme action
of the reagent, the cellulose is converted into a white, friable powder,
which is a variety of oxycellulose. If the action of the bleachiug
solution be duly controlled the cellulose is unchanged in appearance,
but is now found to be remarkably modified in its relation to coloring
matters. Thus all the basic coal-tar dyes (and notably methylene blue)
dye oxycellulose without requiring a mordant, while the dyes of acid
character do not exhibit the slightest affinity for it. The absorptive
power of oxycellulose for vanadium is so great as to withdraw it from
a solution containing only one-billionth of the metal, and the combina-
tion can be demonstrated by printing the tissue with aniline-black
mixture.
The oxidation of cellulose by hypochlorites seems to depend on the
presence of free acid, 1 even the atmospheric carbonic acid having a
notable influence. When once converted into oxycellulose, no reduc-
ing agent (e.g., thiosulphate) will restore the fibre to its original con-
dition. By immersing dyed oxycellulose-tissue in a bleaching liquid,
the dye can be made to disappear, and the fibre can be re-dyed of any
color by immersion in the solution of a suitable coloring matter.
When an oxycellulose tissue is boiled with Fehling's solution cu-
prous oxide is formed, and becomes deposited in firm union with the
fibre, dyeing it an orange color.
DETERMINATION OF CELLULOSE.
In consequence of its occurrence in association with bodies of a closely
allied nature, the accurate determination of cellulose is often a tedious
operation, and some, at least, of the processes prescribed for the pur-
pose yield arbitrary rather than accurate results.
1 If paper be written on with a solution of potassium chlorate acidulated with hydro-
chloric acid, oxycellulose is formed, and on immersing the paper in a solution of a basic
coal-tar dye the writing will appear in color.
392 CELLULOSE.
From starch, cellulose is best separated by boiling the substance with
water containing 1 per cent, by measure of sulphuric acid. The liquid
is filtered when a drop taken out gives no coloration with iodine solu-
tion. In cases where the use of acid is objected to, the substance
should be boiled with water, and the unfiltered liquid mixed with an
equal measure of cold infusion of malt. The starch will be wholly dis-
solved by keeping the liquid at a temperature of 60 C. for a short
time.
The separation of cellulose from sugar, dextrin, and other substances
soluble in water presents no difficulty. Albuminoids may be separated
by treatment with warm water containing 1 per cent, of caustic alkali.
They may be determined by igniting the substance with soda-lime.
For the determination of cellulose in wood, vegetable fibres, and sub-
stances to be used for the manufacture of paper, Mu'ller recommends
the following process : 5 grin, weight of the finely-divided substance
is boiled four or five times with water, using 100 c.c. each time. The
residue is dried at 100 C., weighed, and exhausted with a mixture of
equal measures of benzene and strong alcohol, to remove fat, wax,
resin, &c. The residue is again dried, and boiled several times with
water to every 100 c.c. of which 1 c.c. of strong ammonia has been
added. This treatment removes coloring matter and pectous sub-
stances. The residue is further bruised in a mortar, if necessary, and
is then treated in a closed bottle with 250 c.c. of water, and 20 c.c. of
bromine water containing 4 c.c. of bromine to the litre. In the case of
the purer bark-fibres, such as flax and hemp, the yellow color of the
liquid only slowly disappears, but with straw and woods decolorisation
occurs in a few minutes. When this takes place, more bromine water
is added, and this is repeated till the yellow color remains and bromine
can be detected in the liquid after twelve hours. The liquid is then
filtered, and the residue washed with water and heated to boiling with
a litre of water containing 5 c.c. of strong ammonia. The liquid and
tissue are usually colored brown by this treatment. The uudissolved
matter is filtered off, washed, and again treated with bromine water.
When the action seems complete, the residue is again heated with
ammoniacal water. This second treatment is sufficient with the" purer
fibres, but the operation must be repeated as often as the residue
imparts a brownish tint to the alkaline liquid. The cellulose is thus
obtained as a pure white body. It is washed with water, and then
with boiling alcohol, after which treatment it may be dried at 100 C.
and weighed.
Bevan and Cross (Chem. News, xlii. 77), substitute a treatment with
CELLULOSE. 393
chlorine gas for the repeated digestion with dilute bromine water pre-
scribed in the foregoing process. A single repetition of the treatment
is then always sufficient, and the results obtained are concordant with
those given by the bromine process. Bevan and Cross also find that
by boiling the chlorinated fibre for a few minutes in a 5 per cent, solu-
tion of sodium sulphite, and then in a 1 per cent, solution of caustic
potash, pure cellulose is at once obtained, the results by this method
being 5 per cent, higher than those yielded by Muller's process.
Analysis of Woody Tissues.
Cellulose is associated in woody tissues with ligneous, cuticular, and
intercellular bodies. These have the following analytical char-
acters :
LIGNIN, VASCULOSE, or ligneous matter cements the fibres and
cells together, and constitutes the hard part of woody tissue. The
harder the wood the larger the proportion of lignin contained in it.
Lignin contains more carbon than cellulose, having the composition
C 18 H. 20 O 8 , according to Freray, and Ci 9 H 18 O 8 according to Schuppe
(Pharm. Jour., [3] xiv. 52), while other observers appear to have
analysed more hydrated bodies. It is doubtful whether lignin is a
definite compound. 1 It is a light yellow substance, which retains the
structure of the tissue from which it has been prepared. It has a
density of 1/5, and is insoluble in all neutral liquids, as also in cold
sulphuric acid of 1*78 specific gravity, and in ammonio-cupric oxide
solution. It is also undissolved by alkalies under ordinary conditions,
but dissolves when heated with them under pressure at 130 C., with
formation of a brown liquid, from which acids precipitate black flocks
of a complex composition. By fusion with caustic potash lignin is
immediately converted into ulmic acid, while cellulose, when similarly
treated, yields acetic and oxalic acids. The acetic acid produced in
the distillation of wood appears to be derived chiefly, and the methyl
alcohol wholly, from the vasculose. .Treatment with dilute nitric acid,
chromic acid, permanganate, chlorine, or bromine, converts lignin into
bodies soluble in dilute alkalies, and partly even in water and alcohol.
1 (See abstract of researches by M. Singer in Jour. Chew. Soc., xlii. 1122.) According
to Erdmann, pine wood consists of glucolignose, CsoI^Oa, which can be obtained pure
by treating the finely-rasped wood successively with very dilute acetic acid, hot water,
alcohol, and ether. Traces of cellulose are next removed by Schweitzer's reagent when
pure glucolignose remains. This is a glucoside, which on boiling with dilute hydrochloric
acid yields glucose and lignin. Bente has confirmed Erdmann's formula for glucolignose,
which he also prepared from poplar wood, but he differs from Erdmann as to the propor-
tion of glucose formed by the action of acid.
394 CELLULOSE.
The products are resinous acids, of which those first formed are nearly
insoluble in alcohol, while the final products are soluble both in
alcohol and in ether. Lignin undergoes a similar change by atmos-
pheric oxidation, as observed in the decaying of wood.
The presence of ligneous matter in vegetable tissues, such as hemp,
flax, or paper, may be detected by exposing the wet substance to the
action of chlorine or bromine, and then immersing it in a neutral
solution of sodium sulphite, when a fine purple coloration will be pro-
duced.
Ligneous matter is generally stated to be capable of detection by
moistening the substance with an aqueous solution of aniline sulphate,
which produces an intense yellow coloration. More accurate observa-
tions, however, have shown that the reaction is really dependent on the
presence of products of the oxidation of cellulose, and does not occur
if the tissue has been previously boiled in a solution of sodium
sulphite.
A more certain and delicate test for vasculose consists in moistening
the tissue with a solution ( per cent.) of phloroglucinol, and then
adding hydrochloric acid, when an intense red-violet coloration will
be produced if lignin be present. The phloroglucinol may be
replaced by resorcinol, orcinol, pyrocatechol, and similar bodies, but
they are less convenient and reliable.
According to Reichl, if woody fibre be boiled with a solution of
stannic chloride mixed with a few drops of pyrogallol, a fine purple
coloration is produced.
CUTOSE, or cuticular substance, constitutes the greater part of cork,
and the fine- transparent membrane covering the exposed parts of
vegetables. It contains a high percentage of carbon (C = 68*29 ;
H = 8*95), and yields suberic acid, C 8 H U O 4 , on oxidation with nitric
acid of 1'20 specific gravity. Cutose is insoluble in cold sulphuric
acid of 1'78 specific gravity, and in the ammonio-cupric solution
which dissolves cellulose. On the. other hand, it dissolves slowly in a
hot dilute solution of sodium hydrate or carbonate, forming a solution
from which acids precipitate a yellowish, flocculent substance, fusible
below 100, soluble in alcohol and ether, and having the same compo-
sition as cutose. If the alkaline solution be saturated with common
salt, a cutose-soap rises to the surface. From the researches of
Urbain, cutose appears to be composed of stearocutic acid, C28H 48 O 4 ,
with five equivalents of oleocutic acid, CuB^O*.
PECTOSE occurs in the utricular tissues of fruits and roots. It is
insoluble in water, but is converted into soluble pectin by boiling
CELLULOSE.
395
with dilute hydrochloric acid. The solution obtained is precipitated
by alcohol.
CALCIUM PECTATE forms part of the membrane which binds the
cells together. On treatment with cold dilute hydrochloric acid,
pectic acid is liberated, and this may be dissolved in dilute alkali, and
reprecipitated by an acid.
The following table gives a general outline of the method of
analysing the insoluble portion of woody tissue. The sample should
be in the form of sawdust or shavings, or otherwise finely divided :
All soluble matter having been previously removed by treatment with water, the sample is
dried at 100, and exhausted (preferably in a Soxhlet's tube, with ether, and then with
alcohol.
>>.
Solution may
contain res-
ins, col or-
ing matters,
&c., deter-
mined by
weighing the
residue left
on evapora-
tion.
Residue. Digest with cold, very dilute hydrochloric acid. Wash, and
treat the residue with a cold dilute solution of caustic soda.
Solution con-
tains alka-
line pectate,
from which
insolublepec-
tic acid may
be precipi-
tated by add-
ing HC1.
Residue. Boil with dilute hydrochloric acid.
Solution. Pre-
cipitate of
pectin on ad-
dition of al-
cohol.
Residue. Treat with cold sulphuric acid
of 1'78 specific gravity.
Solution
contains
products
formed
from the
cellulose.
Residue. Boil with dilute
caustic soda solution.
Solution
contains
culose.
Residue consists
of liqnin. sol-
uble in alkali
after treat-
nient with
dilute nitric
acid.
An alternative method, which is recommended by Urbain for the
analysis of wood, consists in exhausting 20 grm. of the sample with
ether and alcohol, then by distilled water, and by water made slightly
alkaline by potash to remove soluble substances and pectic, compounds,
and finally with very dilute hydrochloric acid, which dissolves the
lime and other mineral matters. The purified wood is weighed and
treated with Schweitzer's cupric solution, and the residue washed, dried,
and weighed. The loss is cellulose. The residue is boiled with weak
hydrochloric acid for a few minutes, and again repeatedly treated with
the ammonio-cupric reagent to dissolve the paracellulose. The residue,
after washing, consists of pure vasculose. The results may be confirmed
by dissolving out the two varieties of cellulose together by sulphuric
396 CELLULOSE.
acid, and weighing the residual vasculose, or by removing the vascu-
lose with cold dilute nitric acid, boiling with ammonia, and weighing
the residual cellulose. Some varieties of wood, e.g., boxwood, yield
no true cellulose when analysed, the insoluble portion being composed
entirely of paracellulose and vasculose.
Pith parenchyma contains the same constituents as wood, and may
be analysed in a similar manner. Purified elder-pith contains 37 per
cent, of cellulose, 38 of paracellulose, and 25 of vasculose.
The following figures show the percentage results obtained by
Urbain on applying the foregoing method to the analysis of typical
woods, &c.:
Water and Cellulose and
Extractives. Paracellulose. Vasculose.
Poplar, .......... 18 64 18
Oak, 19 53 28
Box, . . 38 28 34
Ebony, 45 20 35
Iron-wood, 33 27 40
Walnut shell, 31 25 44
Cocoa-nutshell, 17 25 58
Cork contains cutose in addition to the constituents of wood. After
purification, the cutose may be estimated from the loss of weight
undergone on boiling the sample with dilute caustic alkali. Urbain
found in common cork: water, 2; matters soluble in ether or alcohol,
9 ; matters dissolved by water, dilute ammonia, and dilute hydrochlo-
ric acid, 5; cutose, 43; vasculose, 29; cellulose and paracellulose, 12
per cent.
Root-tissue contains paracellulose, vasculose, and often pectose in
addition. The last may be dissolved by boiling the purified tissue
with weak hydrochloric acid, and the vasculose and paracellulose
separated as before.
The parenchyma of leaves is chiefly cellulose, and may be separated
from the epidermis, fibres, and vessels by maceration with water or by
treatment with Schweitzer's cupric reagent. The epidermis is com-
posed of two closely-united membranes, the outer consisting of cutose
and the inner of paracellulose. The latter can be dissolved away from
the former by treatment with Schweitzer's reagent after boiling with
dilute hydrochloric acid, or by treatment with cold sulphuric acid
diluted with 3J equivalents of water. The petals of flowers contain
the same insoluble constituents as leaves.
The fibre of jute, for the characteristic constituent of which the
CELLULOSE. 397
name of bastose has been suggested, presents many peculiarities. It
appears to consist of about 70 per cent, of cellulose, with a consider-
able quantity of a body allied to lignose. Jute fibre has formed the
subject of a series of interesting papers by Bevan and Cross (Chem.
News, xlii. 79, 91 ; xliv. 64; xlvii. Ill ; Jour. Soc. Chem. Lid., i. 129 ;
iii. 206, 291 ; Jour. Chem. Soc., xlii. 18).
Recognition of Vegetable Fibres.
As vegetable fibres, when thoroughly bleached, all consist of nearly
pure cellulose, chemical tests are not available for distinguishing one
kind from another ; but, owing to the impossibility of wholly removing
the incrusting matter on the large scale, it is possible to distinguish
between certain fibres, such as cotton and linen.
By far the best and most reliable means of differentiating vegetable
fibres is to examine their structure with a microscopic power of 120 to
150 diameters.
The filaments of cotton appear under the microscope as transparent
tubes about "04 millimetre in diameter, flattened and twisted round
their axis, and tapering off to a closed point at each end. A section
of the filament resembles somewhat a figure of 8, the tube, originally
cylindrical, having collapsed most in the middle, forming semi-tubes
on each side, which give to the fibre when viewed in certain lights
the appearance of a flat ribbon with a hem or border at each edge.
The uniform transparency of the filament is impaired by small irregu-
lar figures, in all probability wrinkles or creases arising from the dessi-
cation of the tube. The twisted and corkscrew form of the dried
filament of cotton distinguishes it from all other vegetable fibres, and
is characteristic of the fully ripe and mature pod, M. Bauer having
ascertained that the fibres of the unripe seed are simply untwisted
cylindrical tubes, which never twist afterwards if separated from the
plant ; but when the seeds ripen, even before the capsule bursts, the
cylindrical tubes collapse in the middle, and assume the form already
described. This form and character the fibres always retain, under-
going no change through the various operations of spinning, weaving,
bleaching, printing, and dyeing, nor in all the subsequent domestic
processes of washing, &c., and even the reduction of the rags to pulp
for the manufacture of paper effects no change in the structure of the
fibres.
Linen, or flax fibre, appears under the microscope as hollow cylin-
drical tubes, open at both ends, and having a diameter of about *02 of
a millimetre. The fibres are smooth, the inner tube very narrow, and
398 CELLULOSE.
joints or septa appear at intervals, but they are not furnished with
hairy appendages as is the case with hemp. The jointed structure of
flax is only perceptible under a very excellent instrument, and with
judicious management of the light.
When flax fibre (linen) is immersed in a boiling solution of equal
parts of caustic potash and water for about a minute, and then
removed and pressed between folds of filter paper, it assumes a dark
yellow color, whilst cotton when similarly treated either remains white
or becomes a very bright yellow. The same solution of potash em-
ployed cold colors raw flax orange-yellow, whilst raw cotton becomes
grey.
When flax or a tissue made from it is immersed in oil, and then
strongly pressed to remove the excess of the liquid, it remains trans-
parent, while cotton similarly treated becomes opaque.
Phormium tenax, or New Zealand flax, may be distinguished from
ordinary flax or hemp by the red color produced on immersing it in
nitric acid of 1'32 sp. gravity, containing lower oxides of nitrogen.
A reddish color is also developed if New Zealand flax be immersed
first in strong chlorine water and then in ammonia.
In machine-dressed New Zealand flax the bundles are translucent
and irregularly covered with tissue. Spiral fibres can be detected in
the bundles, but less numerous than with sizal. The bundles are flat,
and numerous ultimate fibres project from them. In Maori-prepared
Phormium the bundles are almost wholly free from tissue, and there
are no spiral fibres.
Hemp fibre resembles flax, but has a mean diameter of about '04
mm., and exhibits small hairy appendages at the joints.
With manilla hemp the fibrous bundles are oval, nearly opaque, and
surrounded by a considerable quantity of dried-up cellular tissue com-
posed of rectangular cells. The bundles are smooth, very few partly
detached ultimate fibres are seen, and no spiral tissue.
Sizal forms oval fibrous bundles surrounded by cellular tissue ; a
few smooth ultimate fibres projecting from the bundles. Sizal is more
translucent than manilla, and is characterised by the large quantity
of spiral fibres mixed up in the bundles.
Jute fibre appears under the microscope as bundles of tendrils, each
of which is a cylinder with irregularly thickened walls, the thickening
often amounting to a partial interruption of the central lumen. The
bundles offer a smooth cylindrical surface, to which fact the silky
lustre of jute is due, and which is much increased by bleaching. By
the action of sodium hypochlorite, the bundles of fibres can be disin-
CELLULOSE. 399
tegrated so that the single fibres can be more readily distinguished
under the microscope. Jute is colored a deeper yellow by aniline sul-
phate than is any other fibre, and responds strongly to the bromine
and sulphite test.
In examining fibres under the microscope the tissue should be cut
up with sharp scissors, placed on a glass slide, moistened with water,
and covered with a piece of thin glass.
Cellulosic Nitrates.
Nitric acid of 1'2 specific gravity has little or no action on cellulose
in the cold, but when heated converts it into oxalic acid, oxy-cellulose,
and other products.
With cold nitric acid of greater strength cellulose is converted into
various nitro-substitution products or cellulosic nitrates, the constitu-
tion of which depends on the strength of the acid employed. Thus,
with acid of moderate strength (1*45 specific gravity), mononitro-
cellulose, C 6 H 9 (N0 2 )O 5 , is the chief product. With a mixture of
equal volumes of strong sulphuric acid (1*85 specific gravity) and
nitric acid of 1'42 specific gravity, dinitro-cellulose, C 6 H 8 (NO 2 ) 2 O 5 ,
is obtained ; while if the strongest nitric acid be employed and
strong sulphuric acid also added, the product is trinitro-cellulose,
All the cellulosic nitrates are soluble in strong caustic soda, under-
going partial saponification with formation of cellulose and sodium
nitrate. Concentrated sulphuric acid displaces the nitric acid almost
completely, even in the cold. By the action of reducing agents, such
as ferrous chloride or acetate or potassium sulphydrate, the cellulosic
nitrates are converted into cellulose even by digestion at the ordinary
temperature. By boiling with a solution of stannous oxide in caustic
potash, the nitro-celluloses are dissolved with conversion into cellulose,
which is precipitated in flocks on neutralising the liquid.
The nitric peroxide, NO 2 , contained in specimens of nitrocellulose
may be determined by reducing the substance with a ferrous salt, and
measuring the nitric oxide, NO, evolved (Champion and Pellet, Comp.
rend., Ixxxiii. 707). A flask of 250 c.c. capacity is fitted with a
1 Curiously discrepant statements are made as to the action of solvents on the nitro-
celluloses. Several chemists, in addition, deny that any more highly nitrated product
can be obtained than corresponds to the formula C 12 Hi 5 (N0 2 )50io, or according to Vieille
(Compt. rend., xcv. 132) Ca^^NO^nOoo, but Abel has shown that the preparations to
which the first of these formulae was ascribed had been imperfectly purified. On the
whole, the balance of evidence seems in favor of the formula given in the text.
400 CELLULOSE.
caoutchouc stopper, through which pass two tubes, one leading to a
pneumatic trough, while the other is a funnel-tube drawn out to a
point and provided with a tap. The portion of this tube below the
tap is filled with distilled water, while the funnel itself contains about
50 c.c. of a mixture of hydrochloric and sulphuric acids. 1 0'5 grm.
of the sample is placed in the flask together with about 5 grm. of
ammonium ferrous sulphate and 50 c.c. of water. The flask is then
closed and the liquid boiled till the air is expelled. The acids in the
funnel are then allowed to run slowly into the flask, when the boiling
is .continued as long as gas is evolved. The nitric oxide gas liberated
is collected over soda solution, its volume measured, corrected for
pressure and temperature, and calculated to weight.
The number of cubic centimetres of gas at C. and 760 mm.
pressure multiplied by 0*62693, gives the weight of nitrogen in milli-
grammes, which, multiplied by T72649, gives the equivalent weight
of NO 2 .
The nitric peroxide in gun-cotton may be determined by treating
the sample with sulphuric acid and mercury, as in Crum's process of
estimating nitrates in water. If conducted in a nitrometer, and the
volume of gas compared with that yielded by a standard sample
or -nitre solution, as suggested by the writer (Analyst, v. 181), the
process is very simple. A weighed quantity of the gun-cotton is
placed in the cup of the nitrometer, and there dissolved in concen-
trated sulphuric acid. The resultant solution is then allowed to enter
through the tap and is agitated with the mercury.
DINITRO- CELLULOSE, C 6 H 8 (NO 2 ) 2 O 5 , or Ci 2 H 16 (NO 2 ) 4 O 10 , constitutes
the pyroxylin of the British Pharmacopoeia, and differs from the mono-
and the trinitro-derivatives by being soluble in a mixture of three
measures of ether and one of rectified spirit, employed in the propor-
tion of 48 c.c. to 1 grm. of pyroxylin. The solution thus obtained is
known as collodion (Collodium, B.P.), and is a colorless liquid, which
rapidly evaporates on exposure to the air, leaving a transparent film
of dinitro-cellulose, insoluble in water or rectified spirit.
Pyroxylin is also soluble in acetone and in glacial acetic acid, and
is precipitated in very voluminous flocks on diluting either of these
solutions with water.
Collodion receives one of its principal applications in photography.
It is now employed in the form of an emulsion for the preparation of
dry plates. In addition to the constituents of the collodion, these
1 The apparatus used for the assay of ethyl nitrite is also convenient.
CELLULOSE. 401
emulsions generally contain argentic chloride, bromide or iodide, with
the products of their formation from silver nitrate and the haloid
compounds of potassium and sodium. On diluting the emulsion with
water and filtering from the precipitated pyroxylin and insoluble
silver salts, excess of argentic nitrate may be detected by the addition
of hydrochloric acid to a portion of the filtrate, and excess of alkaline
bromides, &c., by adding silver nitrate to the remainder of the solu-
tion. From the precipitate, after washing with alcohol, the pyroxylin
may be dissolved out by digestion with ether-alcohol, and the insolu-
ble silver salts dried, weighed, and further examined. Some collodion
emulsions contain wood spirit and acetic acid, and various sensitisers
or preserving agents are liable to be present. Among those said to be
more commonly used are gallic acid, pyrogallol, tannin solutions (such
as tea and coffee infusions), cinchonine, cane sugar, glucose, glycerin,
albumin, gelatin, and resins, especially colophony and shellac.
Celluloid, or "artificial ivory," is prepared on a large scale by treat-
ing pyroxylin with melted camphor or spirit of camphor, or by the
simultaneous action of methyl or ethyl alcohol and camphor on
pyroxylin. Various coloring agents and inert matters may also be
present.
Celluloid cannot be caused to explode by heat, friction, or percus-
sion. When brought in contact with flame it burns like paper, and
continues to smoulder after the flame is extinguished, the camphor
being distilled off with production of thick smoke, while the nitro-
cellulose undergoes incomplete combustion.
Celluloid dissolves in warm moderately concentrated sulphuric acid,
but is carbonised by the strong acid. It is readily soluble in glacial
acetic acid, and on diluting the solution with water both camphor and
pyroxylin are reprecipitated. It is rapidly soluble in warm moder-
ately concentrated nitric acid (4 volumes of fuming acid to 3 of water),
and is also dissolved with ease by a hot concentrated solution of caustic
soda. Ether dissolves out the camphor from celluloid, and wood spirit
behaves similarly. Ether-alcohol (3 : 1) dissolves both the nitro-
cellulose and camphor, leaving the coloring and inert matters as a
residue. The ash of celluloid ranges from 1*3 to 2'2 per cent, and the
density from 1'310 to 1'393.
TRINITRO- CELLULOSE, C 6 H 7 (NO 2 ) 3 O 5 or C 12 H U (NO 2 ) 6 O 10 , is obtained
by treating cellulose in the cold with the strongest nitric acid (1*52
specific gravity) mixed with two or three times its bulk of concen-
trated sulphuric acid. The product is thrown into water and washed
with scrupulous care. Trinitro-cellulose retains the form and appear -
26
402 CELLULOSE.
ance of the original cellulose from which it is prepared, but is found
to have lost the property of depolarising light. It is somewhat hygro-
scopic, and becomes highly electrical when rubbed or pulled out
briskly. Trinitro-cellulose is insoluble in water, alcohol, ether, and all
mixtures of alcohol with ether. It is dissolved, however, by a mixture
of ether, ammonia, and potash, and by methyl or ethyl acetate (acetic
ether). In dilute acids it is insoluble.
Trinitro-cellulose is dyed by rosaniline, indigo, &c., in the same
manner as are animal fibres.
Trinitro-cellulose, if dry, inflames when a light is applied, and burns
very rapidly with a large, luminous, and wholly smokeless flame.
When subjected to strong percussion it detonates with extreme violence,
whether it be wet or dry.
Gun-cotton, when carefully made, consists almost wholly of trinitro-
cellulose. It may be purified from foreign matters and lower nitro-
derivatives by treatment with ether-alcohol (3 to 1).
THE ASSAY OF GUN-COTTON is sometimes of importance with a view
of judging of its tendency to decompose. Pure trinitro-cellulose will
keep indefinitely, but the presence of free acid, dinitro-cellulose, or
fatty or waxy matters, renders it more or less unstable, and, therefore,
unsafe.
Free add may be detected by treating 20 grm. weight of the gun-
cotton with 50 c.c. of cold water. After twelve hours the water may
be pressed out, filtered, and tested with litmus paper. If any trace of
acidity be detected 25 c.c. of the liquid may then be titrated with
decinormal caustic alkali. The remainder of the liquid may be em-
ployed to ascertain the nature of the free acid. If sulphuric acid be
present, a small fragment of filter paper immersed in the solution will
be charred on evaporating the liquid to dryness at 100 C. If nitric
acid be the free acid, it may be detected by mixing the liquid with an
equal bulk of pure sulphuric acid, cooling thoroughly, and placing a
crystal of ferrous sulphate in the mixture. A brown tint will be
developed in the neighborhood of the crystal, if any nitric acid or
nitrates be present.
Dinitro-cellulose and foreign nitro-compounds may be detected by
treating 5 grm. of the sample, previously dried at 100 C., with 100
c.c. of a mixture of three parts of ether and one of rectified spirit.
The mixture is shaken frequently during twelve hours, and is then
rapidly filtered through loosely-packed glass-wool, the filtrate evapo-
rated at a gentle heat, and the residue weighed.
Unaltered cellulose may be estimated by treating the gun-cotton left
STARCH. 403
undissolved by the ether-alcohol with acetic ether, which dissolves the
trinitro-cellulose and leaves the unchanged cotton. An alternative
plan is to prepare a solution of sodium stannite by adding caustic soda
to a solution of stannous chloride till the precipitate at "first formed is
just redissolved. The liquid thus obtained, when boiled with gun-
cotton, dissolves the nitro-compounds, without affecting the unchanged
cellulose.
The nitric peroxide, NO 2 , contained in samples of gun-cotton may be
determined as described on p. 399.
The ash of gun-cotton may be determined by melting some pure
paraffin wax, at a gentle heat, in a platinum capsule, adding a known
weight of the sample, and igniting from above. The mixture burns
quite gently.
Some varieties of gun-cotton contain metallic nitrates, those of
potassium and barium being usually employed. Potassium and
sodium chlorates may also be found. Such admixtures may be re
moved by treating the sample with water, and recognised in the
filtered solution by the methods of mineral analysis.
STARCH. (C 6 H 10 O 5 )7i. 1
French Fecule. German Starke.
Starch is found in cells in every part of plants, except in the top of
the bud and the extremity of the rootlets. Although an especially
characteristic product of the vegetable kingdom, starch-like sub-
stances are also met with in certain parts of animals.
Pure starch is a white, glistening, tasteless, and odorless powder. It
is fixed in the air, and is not volatile or crystallisable. Ordinary air-
dried starch contains about 18 per cent, of water, a proportion corre-
sponding to the formula C 6 H 10 O 5 -f- 2H2O. 1 When dried in vacuo the
1 Nageli attributes to starch the formula C 36 H 62 3 i + 5H 2 = 6C 6 H 10 5 ,H 2 0. Sachsse
regards ordinary starch as a hydrate of the composition 0361160030,1120 + 12Aq. Both
these investigators ground their opinion on the amount of sugar produced by the action
of acid, but Schulze has gone into the subject very carefully and fully confirms the
empirical formula a;C 6 H 10 5 . Salomon obtained 111 per cent, of dextrose from potato
starch, which points to a formula of xC6H 10 Os ; but from rice starch he could only obtain
107 per cent, of dextrose together with 4 per cent, of other products. Pfeiffer and
Tollens attribute to starch the formula C 24 H 40 20 , or C^H^O^, and deduce this from the
composition of the sodium and potassium compounds, which contain respectively 3'44 per
cent, of Na, and 5'25 per cent, of K ; but on the other hand, they consider dextrin and
inulin to have the composition C 12 H 20 U , or C^H^On, so that the molecules of starch and
inulin are not of the same size. The experiments of Brown and Heron point to the
presence of C 72 in the molecule of starch.
404 STARCH.
product contains C 6 H 10 O 5 -f H 2 O, and by heating to 100 or 110 C.
in a current of dry air, anhydrous starch is obtained as a highly
hygroscopic powder.
Starch is not dissolved without change by any known solvent. 1 It
is quite unacted on by cold water, alcohol, or ether. When heated
with water to a temperature varying according to the origin of the
starch, it swells up and forms a paste. When the mixture is largely
diluted with hot water almost perfect solution seems to occur, though
it is doubtful how far this is really the case. The solution is strongly
dextro-rotatory (S, = -f- 222), and contains soluble starch. By
heating with pure water, even under pressure, starch is not trans-
formed into sugar.
When boiled with dilute acids starch is readily converted into a
mixture of dextrin and maltose, prolonged treatment resulting in
further hydrolysis and formation of dextrose. A solution of starch
undergoes a similar change when treated with malt-extract, even in
the cold, but solid starch is unaffected by malt-extract.
By treatment with cold nitric acid starch yields nitro-derivatives,
but on heating with the reagent it is converted into oxalic acid and
other products.
When treated with a solution of caustic potash or soda containing
to li per cent, of the alkali, starch swells up enormously and forms
a tenacious paste which is soluble in water, the solution yielding with
cupric sulphate a blue precipitate, which does not blacken on boiling
and is soluble in pure water. Ammonia does not gelatinise starch.
SOLUBLE STARCH or AMIDULIN is produced by boiling starch with
water. A solution is thus obtained which may be rendered quite clear
by addition of a little caustic alkali. It is strongly dextro-rotatory.
Starch solution is one of the most perfect colloids known, and has a
very high viscosity.
Soluble starch is not only obtained by boiling starch with water,
but also by heating it to 100 C. with glacial acetic acid, or to 190
with glycerol. It is the first product of the action of dilute acids or
malt-extract on starch. It is uncertain whether it is chemically or
only mechanically distinct from the insoluble form of starch. Starch
solution is perfectly neutral to litmus, but yields sparingly soluble
1 According to Bungener and Fries (Dingl. Polyt. Jour., ccxlix. 133) boiling water
containing 1 per cent, of salicylic acid readily dissolves starch, forming a thick syrupy
mass, which, on cooling, deposits " tabular crystals of starch." If finely ground barley be
boiled for three quarters of an hour with 30 parts of water containing 1 per cent, of
salicylic acid, and the hot opalescent liquid filtered, the solution will contain all the
starch, which may be converted by dilute aid and determined in the usual way.
STARCH. 405
precipitates with lime and baryta water. On exposure to the air,
starch solution gradually decomposes, with formation of lactic acid.
Structure of Starch Corpuscles.
Starch occurs in plants in the form of minute granules, which gen-
erally possess a concentrically stratified structure, similar to that of
an onion. These granules consist chiefly of a body called granulose,
together with a closely allied substance known as ainylo-cellulose or
starch-cellulose, and water and traces of mineral matter. Starch-
cellulose occurs in largest proportion in the outer layers of the
granule, and probably constitutes the whole of the external coating.
Owing to this protective coating, starch granules are wholly unacted
on by cold water, as the internal granulose, though slightly soluble, is
highly colloidal. When the outer layer of the granule is ruptured, as by
grinding the starch with sand, water acts readily on it, and the liquid
gives an intense blue color with iodine. By treating starch paste with
malt-extract, the insoluble starch-cellulose may be obtained pure, and
then is found to give only a dirty yellow color with iodine. Saliva
(owing to the ptyalin contained in it), and at a temperature of 50 to
60 C., pepsin, organic acids, very dilute hydrochloric or sulphuric
acid, and a saturated solution of sodium chloride containing 1 per
cent, of hydrochloric acid, all dissolve out the granulose and leave
the arnylo- cellulose intact. By boiling with water, starch-cellulose is
mostly converted into soluble starch, leaving, however, a portion
.which obstinately resists the action of water, but is readily dissolved
by dilute alkali. Amylo-cellulose differs from ordinary cellulose in
being insoluble in Schweitzer's reagent. By repeated alternate treat-
ment of potato-starch in the cold with very dilute alkali and acid, the
cellulose may be removed, when the residue dissolves in hot water to
form a perfectly clear solution. Solid starch corpuscles, when treated
with iodine solution, are colored intensely blue, the reagent readily
penetrating the coating of cellulose and thus reaching granulose.
Young small corpuscles of starch appear to be invariably spherical,
but as they grow older they may become lenticular, ovoid, or poly-
gonal. The shape and size of the starch corpuscles are often highly
characteristic of the plant by which they were produced, and this fact
is frequently taken advantage of for identifying the presence of starch
from particular sources.
MICROSCOPIC IDENTIFICATION OF STARCHES. When a sample is to
be examined under the microscope for the identification of its starch,
a minute quantity should be placed, on a glass slide with the point of
406 STARCH.
a knife. If in a powdered state, or readily reducible to powder, a
preferable plan is to stir the sample with a dry glass rod, and tap the
rod on the glass slide. A drop of distilled water or diluted glycerin
(1 of glycerin to 2 of water) should then be added, and if the unpow-
dered structure be employed it should be broken up by careful mash-
ing with the point of a knife. A glass cover is then put on, and any
superfluous moisture removed by blotting paper. The specimen is now
ready for observation. Somewhat oblique light should always be em-
ployed, and the power should vary from a i to -|- inch, using a B eye-
piece furnished with a micrometer-scale, the value of the divisions of
which have been previously ascertained. Too high a magnifying
power should be avoided, especially in a first examination.
The points to be observed in the microscopic observation of starches
are (a) The shape and size of the granules. (6) The position and
character of the hilum. (c) The concentric markings. (cT) The ap-
pearance under polarised light. The two first observations are toler-
ably simple, but the examination for rings requires care, the markings
being rarely visible without very cautious manipulation of the illumi-
nation and movement of the fine-adjustment, and then only in a few
granules at the same time. Natal arrowroot and turmeric starches
are almost the only two which show well-developed rings on nearly
every granule. Wheat, on the other hand, shows no rings, even in
the best light. When the hilum is situated near the centre of the
granule, the rings are usually complete, but when the hilum is near
one end of the granule only a segment of each ring is visible.
Although the size of starch-granules is a highly important character,
it must be remembered that great variation occurs between individual
granules, and that it is only the general or average size of the corpus-
cles which is usually recorded. Variation in size of the starch-
granules is very marked in the case of the potato, in which the
corpuscles range from 0*0025 of an inch in length down to less than
0-0002 (0-063 millimetre to less than 0*005).
Examination with polarised light, either with or without the use of
a selenite plate, is a valuable auxiliary means of identifying starches,
but many of the statements made in books, such as the black cross
being observable in the case of certain starches only, must be consid-
ered as merely applicable to the precise conditions under which the
observations referred to were made. With proper manipulation, all
starches appear to show the black cross, and an ignorance of this fact
has led many into error. Some starches show much more color than
others when examined under the polarising microscope. For observa-
STARCH. 407
tion of starches by polarised light it is often desirable to employ a
highly-refracting mounting medium, and for such purposes water may
be advantageously replaced by diluted glycerin, glycerin jelly, Canada
balsam, oil of anise, carbon disulphide, &c.
W. H. Symons (Pharm. Jour., [3] xiii. 237) has recorded a number
of observations of the conditions under which starch-granules of differ-
ent origins undergo tumefaction by the action of heat and dilute
alkaline solutions. In some cases, the behavior is sufficiently charac-
teristic to serve as a means of differentiating the starches.
Much has been written on the microscopic appearance of starches,
and some observers profess to be able to distinguish starch of almost
every origin. To the observer who has not made a special study of
the morphology of starches, these distinctions are in many cases wholly
unrecognisable, and as the minute points of difference are almost in-
capable either of description or delineation, the only safe method of
discriminating starches is by a careful comparison of the sample with
specimens of known origin and purity, making the observations under
exactly similar conditions as to illumination, magnifying power, and
mounting medium. These standard specimens should not be perma-
nently mounted, but kept in an air-dry state, and a minute quantity
mixed with water or other medium when required for use. As a rule,
it is quite unnecessary to prepare the pure starches for comparison, a
direct employment of the air-dried tissue answering every purpose.
Very complete tabular schemes for the recognition of starches by
the microscope have been devised by Muter, (Organic Materia Medica,
2nd edition) and Vohl (Ber., ix. 1660). 1 Of course, they in no way
enable the observer to dispense with the requisite experience in obser-
vation, but they much facilitate the recognition by drawing the atten-
tion to the more characteristic features of the starches.
The following arrangement of starches, based on their microscopic
appearance, is based on that of Muter. According to his method, the
starches are arranged in five classes. 2
1 Hassall's work on Food and its Adulterations, and J. Bell's Analysis and Adultera-
tions of Food, contain numerous woodcuts showing the microscopic character of starches.
Valuable articles on the identification of starches have been published by H. Pockling-
ton (Pharm. Jour., 3rd series, vol. iii. p. 663; vol. iv. p. 352; vol. vi. pp. 501, 662, 741),
and J. W. Tripe (Analyst, vol. iv. p. 221).
2 In order that mistakes may not be made in differentiating starches by the scheme, it
is important to bear in mind that the appearances described apply to the following condi-
tions of examination, namely, observation with oblique light ; use of water as a medium,
and a T 4 u inch power, and B eye-piece ; and, when polarised light is used, the use of a red-
green selenite plate with diluted glycerin as a mounting medium.
408
STARCH.
I. THE POTATO GROUP includes such oval or ovate starches as give
a play of colors when examined by polarised light and a selenite plate,
and having the hilum and concentric rings clearly visible.
II. THE LEGUMINOUS STARCHES comprise such round or oval
starches as give little or no color with polarised light, have concentric
rings all but invisible, though becoming apparent, in many cases, on
treating the starch with chromic acid, while the hilum is well marked,
and cracked or stellate.
III. THE WHEAT GROUP comprises those round or oval starches
having both hilum and concentric rings invisible in the majority of
granules. It includes the starches from wheat and some other cereals,
and a variety of starches from medicinal plants, such as jalap, rhubarb,
senega, &c.
IV. THE SAGO GROUP comprises those starches of which all the
granules are truncated at one end. It includes some starches used for
food, together with those from belladonna, colchicum, scammony,
podophyllum, canella, aconite, cassia, and cinnamon.
V. THE RICE GROUP contains the starches all the granules of which
are polygonal in form. It includes the starches from oats, maize,
buck-wheat, rice, pepper, and ipecacuanha.
The following table gives further particulars respecting the micro-
scopic appearance of the more important starches. The figures
expressing the sizes are micro-millimetres (l-1000th millimetre), but
they may be converted into ten-thousandths of an inch by multiplying
them by the factor '3937.
In the case of elongated starches, the figures expressing the size have
reference to the mean of the longer and shorter diameters.
Origin of
Starch.
Diameter
in micro-
milli-
metres.
Characteristic Shape
of Granules.
Other Characters.
CLASS I.
.
Canna, or
47-132
Irregular oval, or
Hilum annular and eccentric.
tous - le -
oyster-shaped.
Rings incomplete, very fine,
mois.
narrow, and regular. Alkali
develops lines and hilum.
Well marked and regular
cross with polarised light.
Potato.
Very
Small granules,
Hilum, a spot, generally near
variable ; \ circular ; the
smaller end. Rings in larger
usually
larger ovate, or
granules numerous and com-
between
oyster-shaped.
plete. Very distinct cross
60 and
towards smaller end, and
100.
brilliant colors with polar-
ised light.
STARCH.
409
Origin of
Starch.
Diameter
in micro-
milli-
metres.
Characteristic Shape
of Granules.
Other Characters.
Maranta-
10 to 70;
Somewhat ovoid or
Hilum, near one end, either
arrowroot.
average
mussel - shaped,
circular or linear, and often
36.
tending to tri-
cracked. Rings numerous
angular in larger
and always visible, but not
granules. Some-
strongly marked. Well-de-
times irregular,
fined cross towards larger end
with a nipple-
with polarised light, and bril-
like projection
liant colors.
at same end as
hilum.
Natal-arrow-
33 to 38
Broadly ovate, or
Hilum, a crack, eccentric.
root.
occasionally cir-
Rings very distinct under
cular, with irreg-
water.
ular projections.
Curcuma -
30 to 61
Resembles maran-
Hilum, an eccentric dot or circle.
arrowroot.
ta. Elongated, or
Indistinct segments of rings.
oval with irregu-
Heat or alkali deforms gran-
lar projections.
ules very irregularly.
CLASS II.
Bean.
. nearly
Reniform or oval.
Hilum, stellate Often becom-
uniform
ing a longitudinal furrow.
34
Smaller granules predomi-
nate.
Pea.
very
Reniform or oval.
Hilum elongated. Not distin-
variable
guishable from bean in mixt-
18 to 28
ures.
Lentil.
28
Reniform or oval.
Hilum elongated and very
clearly defined. Rings mod-
erately distinct.
CLASS III.
Wheat.
very
Circular or nearly
Chiefly of two sizes, large and
variable
so, and flat-
very small. Shows a cross in
2 to 52
tened.
glycerin with polarised light,
but very slightly in water.
.
Faint rings and colors are
visible on the most elliptical
granules.
Barley.
fairly .
Closely resembles
Not certainly distinguishable
uniform
wheat ; some
from wheat in mixtures of
13 to 39
granules slight-
the two.
ly angular, or
elliptical.
Rye.
2 to 38
Closely resembles
A few granules show a three or
wheat.
four armed fissure extending
nearly to the circumference.
Oat.
Large oval gran-
The compound granules break
ules, showing
up by attrition into polygonal
polygonal divi-
granules (see Class V.).
sions.
410
STARCH.
Origin of
Starch.
Diameter
in micro-
milli-
metres.
Characteristic Shape
of Granules.
Other Characters.
Acorn.
19
Circular or slightly
Eccentric hilum developed by
oval.
chromic acid.
CLASS IV.
Arum.
14
Truncated with
Hilum eccentric.
two facets.
Tacca-
9 to 19
Resembles tapioca.
Distinct hilum, linear and often
arrowroot.
starred. Very varied shape.
often resembling maize, but
has sharp angles.
Sago.
25 to 66
Ovate, or trun-
Hilum, a circular spot or crack
cated oval.
at convex end ; faint rings.
Well-defined cross, and often
colors with polarised light.
Prepared sago shows large
,
oval depression ; with polar-
ised light characters less
definite than the raw.
Tapioca.
8 to 22
Kettle-drum, or
Hilum, a dot or short slit, nearly
circular.
central. Well defined cross
and colors with polarised
light. Characters of prepared
tapioca are less definite.
CLASS V.
Rice.
5to8
Pentagonal or hex-
Angles sharply defined. Dis-
agonal, occasion-
tinct hilum with a very high
ally triangular.
power, and cross visible in
larger granules with polar-
ised light.
Buckwheat.
5 to 20
Resembles oat and
No rings, but distinct central
depend-
rice, but angles
hilum, as spot or star. Well-
ing on
more rounded.
defined cross, with polarised
variety.
light. Granules often com-
pound.
Oat.
4 to 30
Triangular to hex-
Rings and hilum invisible ex-
agonal, a few
cept under very high powers.
small and round,
Faint cross by polarised light.
or apple - pip
shaped.
Maize.
7 to 20
Circular to poly-
Hilum central, as a well-de-
hedral, usually
fined star or crack. Rings
with rounded
nearly invisible. Distinct
angles.
cross and faint colors with
polarised light.
Dari.
19
Small elongated
. . .
hexagons.
Pepper.
to5
Resembles rice,
Shows hilum with very high
but majority de-
power. Granules often in
cidedly smaller.
motion. Forms large com-
pound granules of very irreg-
ular form.
LLLRN, VOU I.
1. Potato Starch 4. St. Vincent Arrowroot j. Rio Arrowroot
2. Bermuda Arrowroot 5. Sago of Commerce 8. Tapioca
3. Tous les Mois 6. Port Natal Arrowroot q. Maize
STARCH. 411
ARROWROOT of commerce is the starch derived from plants of the
genus Maranta, belonging to the order Marantacece. The most import-
ant member of the group is Maranta arundinacea, which is a native of
the West India 'Islands and South America, but is now cultivated in
Africa, Ceylon, and other hot countries. Three other species of
Maranta are recognised, namely, M, allonym and M. nobilis, which
grow in the West Indies, and M. ramosissima, a native of the East
Indies. For trade purposes, arrowroot is distinguished by the name
of the island or country producing it. Thus we have Bermuda, St.
Vincent, Natal, Cape, Mauritius, and Rio arrowroots.
The starch corpuscles of the different species and varieties of
Maranta differ considerably in their microscopic appearance (see Plate
opposite), while certain varieties are closely simulated by the starches
from plants other than the different species of Maranta. This is the
case with the starch of Curcuma angustifolia, sometimes called East
Indian arrowroot.
Arrowroot is liable to adulteration with a variety of cheaper
starches, though the practice is now far less common than formerly.
The principal starches which have been employed, either as substitutes
for arrowroot or for mixing therewith, have been those of potato, sago,
tapioca, curcuma, and tous-les-mois. Tacca and arum starches are
also stated to have been employed, but they are not known at present
in the English market.
The microscope affords the only satisfactory means of distinguishing
maranta starch from the starches above mentioned, and even then the
detection of certain admixtures is a matter of considerable difficulty.
Potato 1 and tous-les-mois starches are distinguished by their large size,
and regular and well-developed concentric rings, and potato, in addi-
tion, by the hilum being situated near the smaller end of the granules.
Sago, tacca, arum, and tapioca are distinguished by the truncation of
the granules. Curcuma starch closely resembles marauta, but the
granules of the former are more irregular in size and shape, and also
more pointed and transparent.
THE CEREAL STARCHES may be divided into two well-defined
groups, wheat, barley, and rye starches being circular, or nearly so,
while the starches of rice, maize, buck-wheat, and oat are polygonal.
i Besides its microscopical appearance, potato starch is said to be distinguished from
maranta starch in the following respects : 1. When mixed with twice its weight of
strong hydrochloric acid, maranta starch produces an opaque white paste, while the paste
produced by potato starch is transparent and jelly-like. 2. Potato starch evolves a pecu-
liar and disagreeable odor when boiled with dilute sulphuric acid. 8. An acrid oil may
be extracted from potato starch, but not from that of maranta.
41 2 STARCH.
THE LEGUMINOUS STARCHES present very close resemblances, and
are generally indistinguishable from each other when in admixture.
Determination of the Proportion of different Starches in admixture.
The following is the best method, in the opinion of the author, 1 for
ascertaining the extent to which oatmeal is mixed with barley or
wheat-flour, and is a type of the process to be employed in other cases.
Genuine pearl-barley is ground finely in a mortar, and a series of
standards made by mixing the flour with definite proportions of genu-
ine oatmeal. Mixtures containing 5, 10, 15, 20, 30, and 40 per cent,
of barley, respectively, will be found convenient in practice. The
sample of oatmeal to be examined is thoroughly mixed, and 0*1 grm.
weighed out and ground in an agate mortar, with a little water.
When the mixture is perfectly smooth it is rinsed into a small conical
glass, and diluted with water to 10 c.c. Two of the standard mixtures
(say the 10 and 20 per cent, mixtures) are then treated in a precisely
similar manner. A drop of the sample and one of each of the stand-
ards are then placed on glass slides and covered with thin covers.
Care must be taken that the starches and water are thoroughly
agitated, so that the drops taken shall be representative, and it is
important that the drops themselves shall be of exactly the same size.
These conditions are best ensured by immersing in the liquid a short
piece of glass tube drawn out to a fine point, blowing down it so as to
mix the sample thoroughly by means of the air-bubbles expelled, and
then allowing a drop of the liquid to fall from the orifice on to the glass
slide. The same tube is then employed to take drops of the standard
mixtures. The cover glasses must all be of equal size, and sufficiently
large to take up the whole of the drop, as none of the liquid must be
removed. The slides being prepared, the number of barley granules
visible in twelve successive fields is noted. The standards are then
similarly observed, the operation being repeated until a standard
1 Dr. James Bell, from whose little book on Foods (part ii.) much of the information
in the text on arrowroot and other starches has been gathered, gives the following method
for estimating starches in admixture: "The sample is first rubbed in a mortar and
passed several times through a sieve. A small quantity, say 0'05 of a grain, is then
weighed out and placed on a glass slide, where it is worked into a thin paste with about
two drops of water. A thin covering glass, measuring about H inch by 1 inch, is then
placed over the paste, and moved about the slide until the paste is equally distributed and
all under the covering glass. With a i-inch objective, the number of granules is counted in
nine fields, as fairly as possible representing the entire slide. The process is repeated till a
correct idea of the composition of the sample is obtained. Standard mixtures approxi-
mately representing the sample are made up and treated in exactly the same way, and
from a comparison of the results the percentage of foreign starch is computed."
STARCH. 413
mixture is found, the barley granules in twelve fields of which are
equal or nearly equal in number to those counted in the sample. The
proportion of wheat or barley in the sample will then be approxi-
mately the same as that in the standard it agrees with.
Detection and Determination of Starch.
For the detection of starch existing in the solid state, no method is
so good as the microscopic recognition of the corpuscles, the origin of
which may usually be identified in the manner already described.
The microscopic examination may be advantageously supplemented
by adding a drop of iodine solution to the slide, when each of the
true starch granules will assume a blue color, which renders their
recognition easy. In some cases, as when roasted coffee is mixed with
beans or acorns, the microscopic detection of the starch becomes diffi-
cult, but may still be effected in the following manner : The coffee is
boiled with water for a few minutes, and the solution is decanted or
filtered from the insoluble matter. The liquid is next thoroughly
cooled, and cold dilute sulphuric acid is added. A solution of potas-
sium permanganate is then gradually added till the brown color is
nearly or entirely destroyed, when the decolorised liquid is tested with
iodine. A blue color is obtainable in this way with coffee containing
only 1 per cent, of roasted acorns.
Sometimes it is desirable to remove the coloring matter from the
solid substance before examining it for starch. If cold water fail to
effect this, alcohol should be tried, and subsequently other solvents.
The cases are rare, however, in which the starch cannot be observed
microscopically after successive treatments of the substance with cold
water and alcohol.
In aqueous solution, starch yields a precipitate with ammoniacal
acetate of lead having a composition represented approximately by
the formula C 12 H 18 Pb2"O n . Tannin gives a white precipitate with
starch solution, disappearing on warming and re-appearing as the
liquid cools. Soluble starch is completely precipitated by adding
alcohol to its aqueous solution.
The most characteristic reaction of starch solution is the violet or
indigo-blue coloration which it gives with iodine. The colored body
does not appear to be a definite compound of starch with iodine, and
hence is best called iodised starch. The best form in which to employ
the reagent is as a very dilute solution of iodine in iodide of potas-
sium. The starch solution should be perfectly cold. On heating the
liquid it is decolorised, but on cooling the blue color is restored, though
414 STARCH.
not with the same intensity as before. In employing the reaction
as a test for starch it is necessary to remember that it is only pro-
duced by free iodine. Hence any free alkali should be neutralised by
cautious addition of cold dilute acid, and any reducing or oxidising
agent got rid of if possible. The best way of testing for starch is to
add the iodine solution gradually to the slightly acid liquid until
either a blue color appears or the liquid remains permanently colored
yellow by the free iodine. If the latter effect is produced and yet no
blue coloration is obtained no starch can be present.
The only organic body liable to interfere when the test is performed
in the foregoing manner is erythro-dextrin, which itself produces a'n
intense reddish-brown coloration with iodine, which is apt to mask a
feeble starch-reaction. The affinity of iodine for starch is, however,
greater than its affinity for erythro-dextrin, and hence if a very little
iodine solution be employed the blue color due to starch will alone be
developed, the brown coloration becoming apparent on a further addi-
tion of the reagent. By cautiously adding very dilute ammonia, or
gradually heating the liquid, the brown color can be destroyed while
the blue remains. 1
THE DETERMINATION OF STARCH is effected in different ways
according to the nature of the substance in which it occurs. In
wheat flour a convenient but very rough plan is to place a weighed
quantity of the sample in a sieve, and allow a stream of water to
trickle over it, kneading well all the time. When the water runs
away clear, it is allowed to stand, and, when the starch has all settled
out, the water is poured off and the deposited starch collected, dried
at 110, and weighed.
In plant-products, such as wheaten-flour, oatmeal, cocoa, &c., the
determination of starch may be effected as described elsewhere. The
conversion of the starch into dextrose by boiling with dilute acid
and estimation of the resultant glucose by Fehling's solution, is a
process giving fairly good results if carefully conducted, but there
is a danger of the estimation being low from incomplete conversion to
dextrose or the formation of secondary non-reducing bodies. 10
parts of dextrose thus found correspond to 9 parts of anhydrous
starch. The change to dextrin and maltose is easily made, and may
be effected either by heating the starch with dilute acid or by the
1 Neither the brown color of a solution of iodised erythro-dextrin nor the blue of
iodised starch shows any absorption bands when examined by the spectroscope. Accord-
ing to Bondonneau, iodised starch has a definite composition represented by the formula
(C 6 H 10 6 )l5.
STARCH. 415
action of diastase. When very accurate estimations of starch are
required this is probably the best process to employ. It is applicable
to all the cereals, raw as well as malted, and is conducted by C. O'Sul-
livan (Jour. Chem. Soc., xlv. 1) in the following manner : A fair
sample of the grain is taken and 5'1 grm. weighed roughly and
ground to a fine flour in a clean coffee-mill. 5 grm. of the powder is
placed in a flask of about 120 c.c. capacity thoroughly wetted with
rectified spirit, and 25 c.c. of ether added. The flask is corked and
agitated occasionally, and after a few hours the ether is decanted
through a filter and the residue washed by decantation with three or
four fresh quantities of ether. To the residue 80 to 90 c.c. alcohol,
specific gravity 0'90, are added, and the mixture kept at 35 to 38 C.
for a few hours with occasional shaking. The alcoholic solution, when
clear, is decanted through the filter used in filtering the ethereal solu-
tion, and the residue washed a few times by decantation with alcohol
of the strength and at the temperature indicated. The residue in the
flask, and any little that may have been decanted on to the filter, is
then treated with about half a litre of cold water. In about twenty-
four hours the supernatant liquid becomes clear, when it can be grad-
ually decanted through a filter. The solution filters bright, but, in
the case of barley and oats, exceedingly slowly at times ; the malted
grains, as well as wheat, rye, maize, and rice, yield solutions requiring
no excessive time to filter. The residue is repeatedly washed with
water at 35 to 38, but this treatment does not completely free barley
and oats from a-amylan, which body dissolves with the greatest diffi-
culty at this temperature. The residue is then transferred to a 100
c..c. beaker, and the portion adhering to the filter washed off by open-
ing the filter- paper on a glass plate and removing every particle by
means of a camel's-hair brush, cut short, and a fine-spouted wash-
bottle. When the transference is completed, the beaker, which should
not now contain more than 40 to 45 c.c. of the liquid, is heated to 100
for a few minutes in the water-bath, care being taken to stir well when
the starch is gelatinising to prevent " balling" or unequal gelatinisa-
tion. After this the beaker is cooled to about 62, and 0'025 to 0'035
grm. diastase 1 dissolved in a few cubic centimetres of water, added.
1 The diastase employed is prepared as follows : 2 or 3 kilogrm. of finely-ground
pale barley-malt are taken, sufficient water added to completely saturate it, and when
saturated to slightly cover it. When this mixture has stood three or four hours, as much
of the solution as possible is pressed out by means of a filter-press. If the liquid is not
bright it must be filtered. To the clear bright solution rectified spirit is added as long as
a flocculent precipitate forms, the addition of the alcohol being discontinued as soon as
the supernatant liquid becomes opalescent or milky. The precipitate is washed with
416 STARCH.
On keeping the liquid at 62 to 63 for a short time, the starch is
completely converted into maltose and dextrin, and a drop of the solu-
tion no longer gives a blue coloration with iodine, but it is desirable
to continue the treatment for about an hour after the disappearance
of the starch, as the solution then filters more readily. The liquid is
then heated to boiling for ten minutes, and filtered, the residue being
carefully washed with small quantities of boiling water. The filtrate
is cooled, and made up to 100 c.c. and the density observed. The
maltose is then determined by Fehling's solution, and the dextrin
deduced from the rotatory power of the solution. The maltose found,
divided by 1*055, gives the corresponding weight of starch, which,
added to the dextrin found, gives the total number of grammes of
starch represented by 100 c.c. of the solution. 1 The sum of the dex-
trin and maltose found directly ought to agree fairly well with the
total solid matter estimated from the density of the solution, after
making allowance for the weight of diastase employed.
The foregoing process, involving as it does the preparation of dias-
tase, is not always a convenient one to employ, and in such cases the
following modification will be found of service, though it does not aim
at so high a degree of accuracy as the method prescribed by O'Sulli-
van. Any fat and essential oil having been removed by treatment
with ether, the substance is treated with a saturated solution of sali-
cylic acid in cold water. This will dissolve alkaline salts, sugar,
dextrin, &c. The liquid is filtered, and the residue washed with deci-
normal caustic soda (4 grm. NaHO per litre) to remove salicylic acid
and albuminoids. The residue is rinsed off the filter with warm water,
the liquid heated to boiling while constantly stirred, so as to gelatinise
the starch, and the product treated with a known measure of recently-
prepared and filtered cold infusion of malt, of which the specific gravity
alcohol of 0*86 to 0'88 specific gravity, dehydrated with absolute alcohol, pressed between
cloth to free it as much as possible from that liquid, and dried in vacuo over sulphuric
acid, until the weight becomes constant.
Prepared in this way the substance is a white, friable, easily soluble powder, retaining
its activity for a considerable time. The preparation usually sold as diastase is useless for
this work.
1 In very accurate experiments, it may be well to estimate the a-amylan present in the
solution. For this purpose, 75 c.c. of the above solution should be evaporated to about
30 c.c., cooled, and 60 c.c. of rectified spirit added. A few drops of hydrochloric acid are
then added, and the opalescent liquid stirred, when a flocculent precipitate will probably
be produced. This is allowed to subside and the clear supernatant liquid is decanted off.
The residue is then washed with alcohol of 0'S6 specific gravity, dehydrated by treatment
with strong alcohol, and collected on a tared filter. It is then dried in vacuo over sul-
phuric acid, and afterwards in dry air at 100 C., being subsequently weighed.
STARCH. 417
has been previously ascertained. The mixture is kept at a temperature
of about 60 to 63 C., with occasional stirring, until a drop taken out
with a glass rod and added to a drop of diluted iodine solution on a
porcelain plate shows no blue or brown coloration. The solution is
then filtered, made up to a definite volume, and its specific gravity
accurately ascertained. From the excess of the density over water is
subtracted the density due to the infusion of rnalt used, allowance
being made for the increased volume of the liquid, when the difference
represents the density due to the starch dissolved, and this number
divided by 4 < 096( = 3'95 X 1'037) gives the number of grammes of
starch in each 100 c.c. of the solution. 1
For technical purposes it is sometimes desired to determine the
proportion of starch existing in potatoes. This can be done in a
rough and ready manner by ascertaining the specific gravity of the
tuber. The un peeled potatoes, freed from dirt, are placed in a solu-
tion of salt, which is then diluted with water till some of the indi-
vidual Itubers sink, while others just float. The density of the saline
solution, as ascertained by a hydrometer, is then equal to the average
specific gravity of the potatoes. Another method consists in taking 5
kilogrm. of the potatoes, and then weighing in water. The weight
in water divided into the original weight in air gives the specific
gravity. Tables have been compiled for ascertaining the percentage
of starch from the specific gravity of the potatoes. The most com-
plete table is that of Heidepriem (Jour. Chem. Soc., xxxii. 233), for
which may be substituted the following formulae, in which W is the
weight of 5 kilogrm. of potatoes immersed in water.
(W 285) -052 -f- 7'13 = percentage of starch ; and
(\y 285) '052 + 14'35 percentage of solid matter.
Diastase Method for Starch, A. 0. A. C. Extract from 2 to 5 grm. of the
finely powdered substance with ether, bring the extracted residue on to a filter,
or into a Gooch crucible, and wash with 150 c.c. of 10 per cent, alcohol, and
then with a little strong alcohol. Place the residue in a beaker with 50 c.c. of
1 Thus, suppose 10 grm. of the sample be taken, and, after treatment with ether and
salicylic acid and soda solutions in the manner described, the residue be treated with 50
c.c. of water and 5 c.c. of infusion of malt of 1060 sp. gravity; the liquid being subse-
quently made up to 100 c.c. and found to have a density of 1033. Then, the correction
due to the malt-extract will be = 3 ; this, subtracted from the difference
100
between the density of the solution and that of water (1033 1000 = 33) leaves 30 as the
excess-density caused by the solution of the starch of the sample ; and this figure, divided
by 4-096, gives 7'324 grm. per 100 c.c., or in the 10 grm. taken ; or 73'24 per cent, of
starch in the sample.
27
418 STARCH.
water, immerse the beaker in a boiling water-bath, and stir constantly until all
the starch is gelatinised, cool to 55, add from 20 to 40 c.c. of malt extract and
maintain at this temperature until the solution no longer gives the starch re-
action with iodine : Cool and make up directly to 250 c.c., filter, bring 200 c.c.
of the filtrate into a ten-ounce flask with 20 c.c. of 25 per cent, hydrochloric
acid (sp. gr. 1*125), connect with a reflux condenser, and boil for two hours and
a half, exactly neutralise while hot with sodium carbonate, avoiding excess,
cool and make up to 500 c.c. Mix the solution well, pour through a dry filter,
and determine the dextrose in an aliquot part by Allihn's method. The figure
for dextrose multiplied by 0'9 will give the amount of starch.
[The method for preparing the malt-extract is not given in the official bul-
letin, nor is attention called to the fact that malt-infusions will contain some
reducing sugar. Commercial malt extracts are often without diasiatic power ;
it is better to use diastase or taka-diastase. The latter can be readily obtained
in a form free from reducing sugar and very active. As a rule, amylolytic
enzymes are most active in solutions slightly alkaline to litmus.
Wiley and Krug have investigated the methods for estimating starch, and
consider that the diastatic process is the best. The material must be ground
very fine, and the preliminary extraction with ether must not be omitted. The
treatment with diastase should be repeated after boiling and cooling to 50 C.
The undissolved residue should not show any starch granules when stained with
iodine and examined under the microscope. L.]
Commercial Starch is usually obtained from wheat, rice, maize,
or potatoes. This statement applies simply to the varieties of starch
sold under that name, for arrowroot, tapioca, sago, and farinaceous
foods often consist of starch in a condition of considerable purity.
The origin of a specimen of starch can usually be ascertained by
observing its appearance under the microscope.
Commercial starch is generally very pure, though occasionally it
may contain traces of vegetable fibre and of albuminoid matters.
Starch often occurs in commerce in irregular elongated lumps,
having a basaltic-like structure. This appearance is especially char-
acteristic of wheat starch, the small admixture of gluten causing the
granules to cohere. An admixture of potato starch with wheat
starch prevents agglutination, and tends to cause the starch to fall to
powder.
The ash of commercial starch should be very trifling in amount.
Its determination serves to detect any mineral additions.
The proportion of water in air-dried starch averages about 18 per
cent., but is liable to considerable variation. It may be determined
by drying the starch in a vacuum over sulphuric acid, till constant,
and then in a current of dry air at 100. Saare has described a
method of approximately estimating the water in potato starch, which
DEXTRIN. 419
consists in placing 100 grin, of the sample in a 250 c.c. flask, filling
the flask to the mark with water at 17'5 C., and observing the weight
of the contents. There is no occasion to employ the large quantities
of starch and water recommended by Saare. He gives a table (Jour.
Soc. Chem. Ind., iii. 527) by which the proportion of water is directly
shown, but the following rule may be employed instead : From the
weight of the starch and water contained in the bottle subtract 250,
and divide the difference by 0'3987, when the quotient will be the
percentage of starch in the sample. This instruction applies to the
quantities of starch and water prescribed by Saare, but the following
is a more general expression of the rule :
Contents of bottle in grams minus capacity of bottle in c.c. (the number of grammes of
= 1 anhydrous starch in weight
3987 (.of sample taken.
DEXTRIN.
Amylin. (C 6 H 10 O 6 ).
Dextrin is a product obtained by treating starch or amylaceous
bodies in certain ways. The following modes of treatment cause a
formation of dextrin :
By heating starch or flour to a temperature varying from 210 to
280 C., till it acquires a yellow or brownish color. The change is
greatly facilitated by moistening the starch with dilute nitric acid,
and then slowly drying the paste and heating it for some time to about
110 to 150 C.
By boiling starch with dilute sulphuric acid till the cooled liquid
no longer gives any coloration with solution of iodine.
By treating gelatinised starch with warm water and a small quan-
tity of malt-extract.
The first process is employed for the manufacture of solid dextrin,
which is known in commerce by the name of British gum, gommeline,
starch-gum, &c. The other processes result in a simultaneous forma-
tion of maltose, as described elsewhere. The former is used for the
preparation of commercial glucose, and the latter reaction takes place
in mashing malt for the manufacture of beer.
Several, and not impossibly many, varieties of dextrin exist, all
being apparently formed by the breaking up of the highly complex
starch molecule by treatment with dilute acids or ferments. There is
no ready method of distinguishing the different varieties with certainty,
except that one kind, or possibly class, of dextrin gives a reddish-
420 DEXTRIN.
brown color with solution of iodine, while the other kind or class pro-
duces no coloration. The erythro-dextrin, the kind giving the brown
color with iodine, is an intermediate product of the formation of achro-
dextrin from starch. 1
The best method of applying the iodine reaction as a test for erythro-
dextrin is to divide a very weak solution of the iodine in iodide of
potassium into two parts, and place the slightly yellow liquid in adja-
cent test-tubes or glass cylinders. On then adding the solution to be
tested to one, and an equal measure of water to the other, any brownish
coloration will be readily observed. In presence of starch, the blue
color is apt to obscure the brown tint produced by the erythro-dextrin.
This may be avoided to some extent by employing the iodine solution
somewhat in excess, so as to get a full development of the brown
color.
Pure dextrin is a white amorphous solid. It is tasteless, odorless,
and non-volatile. Dextrin is very deliquescent, and dissolves in an
equal weight of cold water to form a syrupy and strongly dextro-
rotatory liquid 2 which is miscible with 1 J measures of proof spirit.
By strong spirit, if used in sufficient quantity, dextrin is completely
separated from its aqueous solutions.
Cold concentrated sulphuric acid dissolves dry dextrin without
color, but charring takes place on warming. By boiling with dilute
acids, dextrin yields maltose and ultimately dextrose (see p. 273). 3
Hot nitric acid of T35 specific gravity converts dextrin in part into
oxalic acid, whereas the natural gums yield mucic acid under similar
conditions.
Dextrin is distinguished from starch by its solubility in cold water ;
from soluble starch by yielding no blue color with iodine when tested
as described on p. 413, and no precipitate with baryta water; from
maltose and dextrose by not reducing Fehling's solution ; from starch,
soluble starch, gelatin, and egg-albumin by not yielding a precipitate
1 According to Musculus and Meyer (Jour. Chem. Soc., xl. 570), erythro-dextrin is a
variety of soluble starch. They obtained the intense red color which characterises erythro-
dextrin when a half per cent, solution of soluble starch was added to a solution of a higher
dextrin which gave a pure yellow-brown color with iodine.
2 SD = 200 and Sj=222. These corrected figures for the specific rotation of dextrin
are somewhat higher than those given in previous paragraphs.
8 According to Musculus and Meyer the re-conversion of dextrose into a variety of dex-
trin can be effected by dissolving the glucose in strong sulphuric acid, heating the mixture
to 60 till it becomes brown, and then throwing it into a large quantity of absolute alco-
hol. On boiling the product with water a yellow amorphous mass is formed having the
characters of dextrin.
DEXTRIN. 421
with tannin ; from albumin, by not being coagulated by heat or
mineral acids.
Dextrin is separated from starch and cellulose by solution in cold
water ; coagulable albuminoids may then be separated by raising the
faintly acid solution to boiling. An ammoniacal solution of acetate
of lead added to the cold and dilute liquid is stated to precipitate the
dextrin, leaving the sugar in solution. The precipitate may be dried
at 100 C., and is said to have the formula PbO,C 6 H 10 O 5 . Another
method consists in precipitating the dextrin by means of a large pro-
portion of alcohol, washing the precipitate with rectified spirit, and
drying it at 110 C. After weighing, the dextrin should be ignited,
and the resultant ash deducted from the total weight obtained.
The proportion of dextrin present in a solution also containing mal-
tose arid dextrose may be determined by observing the rotatory action
of the liquid, together with its specific gravity, and reducing action on
Fehling's solution. Further information on the determination of dex-
trin will be found on pp. 273, 291 to 295, 330 to 332, 365 to 370, and
373.
Commercial Dextrin.
Commercial dextrin, or "British gum," is now manufactured exten-
sively by moistening starch or flour with a mixture of dilute nitric
and hydrochloric acids, and then exposing it to a temperature of 100
to 125 C. Either nitric or hydrochloric acid singly may be substituted
for the mixture, or oxalic acid may be employed.
Commercial dextrin is a white, yellowish, or light brown powder.
It consists largely of erythro-dextrin, and hence its aqueous solution
gives a brown coloration with iodine, unless this reaction is obscured by
the blue color produced by a considerable proportion of soluble starch.
For most purposes this admixture is unobjectionable, provided that it
does not exceed 12 or 15 per cent. Unaltered starch may be recognised
by the microscope and its insolubility in cold water. Reducing sugars
(maltose) are nearly always present in commercial dextrin, and may
be detected and estimated by Fehling's solution.
Many mixtures of starch and dextrin are employed as thickening
agents in calico-printing, &c. "Gloy" consists essentially of farina
mixed with a solution of magnesium chloride.
Dextrin syrups are largely employed by confectioners. Their
examination is described on p. 298 et seq.
The method of distinguishing commercial dextrin from gum arabic
is described on p. 426.
422 GUMS.
GUMS.
French Gommes. German Gummi.
Gums are a peculiar class of bodies occurring in the juices of plants.
They are perfectly non-volatile, have little or no taste, are uncrystal-
lisable, and eminently colloidal. These characters render their puri-
fication very difficult, and hence but little is known of their chemical
relationships. Many of them appear to be true isomers of starch, but
others have a different composition. For convenience, various pectous
bodies are classed with the gums.
The analytical characters of the gums as a class are indicated by
the following facts, which are also applied to their separation from
similar bodies.
Gums are either soluble in, or swell up in contact with, cold water,
a character which distinguishes them from starch, cellulose, and resins.
They differ from the sugars by being incapable of fermentation by
yeast, and from the sugars and resins by their insolubility in alcohol.
From dextrin the gums soluble in water are distinguished by their
levo-rotatory power and acid reaction, and by yielding mucic acid by
treatment with moderately concentrated nitric acid. 1 Reichl and
Breinl state that arabin and bassorin are distinguishable from dextrin
by the blue flocculent mass they yield when heated with hydrochloric
acid and orcinol, dissolving in alcoholic potash to form a violet solu-
tion showing a green florescence. Fragments of wood, containing
only traces of wood-gum, when boiled with hydrochloric acid and
orcinol show the reaction quite distinctly. From erythro-dextrin and
starch the gums differ by giving no color with solution of iodine, and
from albuminoids they are distinguished by not yielding ammonia
when ignited with soda-lime.
The gums having been very imperfectly studied, it is impossible to
arrange them with any degree of scientific accuracy. They may,
however, be conveniently classified according to their behavior when
treated with cold water and dilute acids. Thus the gums of which
gum arabic is the type are dissolved by cold water, and are not readily
precipitated by acids. Pectin forms a jelly when its aqueous solution
is faintly acidified, while gum tragacanth merely swells up when
treated with cold water, without undergoing notable solution.
1 According to Nageli and Cramer, quince-mucilage yields no mucic acid by treatment
with nitric acid. Mucic acid gives a crimson coloration when treated with concentrated
sulphuric acid.
GUMS.
423
1
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PLANT ANALYSIS.
431
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432
PLANT ANALYSIS.
11
13
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a < 2 >
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PLANT ANALYSIS.
433
bo S
lilts
id
N
i
r-t CO
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13 *3 O
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28
434
CEREALS.
COMPOSITION OF CEREALS, &c.
A very large number of analyses of wheat and other grains have
been published by different chemists, but unfortunately many of them
are of doubtful value, owing to the defective methods of analysis
employed.
The following is the average composition of the cereal grains,
according to Charles Graham :
Old Wheat.
Barley.
Oats.
Rye.
Maize.
Rice.
Water, ....
Ill
12-0
14-2
14-3
11-5
10-8
Starch, ....
62-3
52-7
56-1
54-9
54-8
788
Fat,
1-2
2'6
4-6
2-0
4-7
o-i
Cellulose, . .
8'3
11-5
i-o
6-4
14-9
0-2
Gum and Sugar,
3*8
4-2
5-7
11-3
2-9
1-6
Albuminoids, .
10'9
13-2
16-0
8-8
8-9
7-2
Ash, ....
1-6
2-8
2-2
1-8
16
0-9
Loss, &c., . .
0-8
i-o
0-2
0-5
0-7
0-4
lOO'O
lOO'O
100-0
lOO'O
100-0
100-0
I
A. H. Church gives the following analyses by himself in illustration
of the composition of representative specimens of the cereal grains
and products therefrom :
"be
c
jL-
|
i
8-.
J
^
|
n
**** o
-4-3
*fi o
W
,5
^
~^
gfn
I
-2 a
s
a
N
I
2
E
i
1
K
O
1
s
ft
Water,
14-5
13-0
14-0
5-0
14-6
13-0
14-6
14-5
13-0
12-2
Albuminoids and other
nitrogenous bodies, . .
Starch, with traces of
Dextrin. &c..
j-11-0
1 69-0
10-5
74-3
15-0
44-0
16-1
63-0
'6-2
76-0
10-5
71-0
7-5
760
9-0
64-5
15-3
61-6
82
70-6
Fat
1'2
0'8
4-0
10-1
1-3
1-6
0-5
5-0
5'0
4-2
Cellulose and Lignose, .
2-6
0-7
17-0
3-7
0-8
2-3
0-9
5-0
3-5
3-1
Mineral matter, ....
1-7
0-7
6-0
2-1
1-1
1-6
0-5
2-0
1-6
1-7
100 -JO
100-0
100-0
100-0
100-0
100-0
100-0
100-0
100-0
100-0
For convenience of comparison, the following analyses ef other
vegetable products are given. They are selected from among a large
number published in Church's valuable work on Food:
1 100 Ibs. of oats yield about 60 of oatmeal and 26 of husks, the remainder being
water and loss.
2 The product called pearl-barley constitutes only about one-third of the whole seed.
CEREALS.
435
Buck-
wheat.
Peas.
Haricot
Beans.
Lentils.
Earth-
nuts,
Shelled.
Water,
Albuminoids, &c., . - -
Starch &c ....
13-4
15-2
63'6
14-3
22-4
51 "3
14-0
23-0
52 '3
14-5
24-0
49'0
V5
24-5
11'7
Fat,
Cellulose and Lignose, .
Mineral matter, ....
3-4
2-1
2-3
2-5
6-5
3'0
2-3
5'5
2-9
2-6
6'9
30
50-0
4-5
1-8
100-0
100-0
100-0
100-0
100-0
Potatoes.
White
Turnips.
Carrots.
Beet-root,
Red.
Yam.
Water
75 '0
92 '8
89 '0
82 "0
7'96
Albuminoids, &c., . '. .
Susar
2-3
0-5
0-5
4'5
0'4
lO'O
2-2
}'
Starch .
15'4
Dextrin, Gum, and Pec-
tose,
Fat, . . .
Cellulose and Lignose, .
Mineral matter, ....
2-0
0-3
i-o
i-o
4-0
o-i
1-8
0-8
0-5
0-2
4-3
i-o
3-4
o-i
3-0
0-9
16-3
0-5
0-9
1-5
Albuminoids of Cereals.
Of the bodies known to chemists as albuminoids or proteids,
numerous species are found in the vegetable kingdom. Although
differing somewhat in composition, the percentage of nitrogen found
in them by the soda-lime process does not vary very greatly from the
average of 15'8. Hence it is very usual to deduce the proportion of
albuminoids present by multiplying the percentage of nitrogen by 6'33
(= I, and to ignore the fact that the whole of the nitrogen of
lO'O/
plants does not exist in the form of proteids, but may be present as
true albuminoids, peptones, alkaloids, amido-acids, nitrates, &c.
Hence an expression of the proportion of the total nitrogen as " albu-
minoids " is very misleading if the analysis is to be used to judge of
the suitability of a cereal for bread-making, or as an article of diet
generally, and it is desirable therefore to acquire a more complete
knowledge of the nature and amount of the nitrogenised bodies
present than is obtainable from a mere determination of the nitrogen,
and the calculation of the amount found to its equivalent of
albuminoids. 1
1 A detailed description of the nitrogenous constituents of plants, and of the methods
of separating them, is given in Dragendorff' s Plant-Analysis, translated by H. (J.
Greenish.
436
CEREALS.
[The following account of the proteids of wheat flour is from advance sheets,
Vol. IV, sent by Mr. Allen. It is substituted for pages 363-366 of Vol. I. L.]
Proteids of Wheat.
According to the experiments of Osborne and Voorhees (Amer.
Chem. Jour., xv. 392 ; xvi. 524) the seed of wheat contains five dis-
tinct proteids, having the composition shown in the following table:
Proteid.
Proportion
Present.
Per cent.
Elementary Composition ; per cent.
Carbon.
Hydrogen
Nitrogen.
Oxygen.
Sulphur.
Globulin 1 ("Edes->
tin"), f
Albumin * (" Leu- >
cosin"), j
Proteose, l . . . .
Gliadin . . .
0-6 to 0-7
0'3 to 0-4
'- 0-3
4.25
4-0 to 4-5
51-03
53-02
51-86
5272
52-34
6-85
6-84
'6-82
6-86
6-83
18-39
16-80
17-32
17-66
17-49
23-04
22-06
-~ * -
24
21-62
22-26
0-69
1-28
*- *_ -
00
1-14
1-08
Glutenin, ....
It will be observed that the first four of these proteids are present
in very small proportion, and the two last are constituents of the
"gluten" of wheat.
GLUTEN.
When wheaten flour is kneaded in a stream of water, the starch is
gradually washed away, and there remains a sticky cohesive mass
which is very rich in nitrogen. This mass, which is generally de-
1 EDESTIN is a proteid of the globulin class, precipitated from its saline solutions by
dilution, and probably more perfectly by removing the salts by dialysis. Edestin solu-
tions are also precipitated by saturation with ammonium or magnesium sulphate, but not
by saturation with sodium chloride. Edestin is partially precipitated from its solutions
by boiling, but is not coagulated below 100 C. Edestin also exists in barley, rye, and
probably in sunflower seeds.
LEUCOSIN is an albumin coagulating at 52 and precipitated from its solutions by
sodium chloride or magnesium sulphate, but not precipitated by completely removing
salts by dialysis in distilled water.
PROTEOSES. After dialysing away the salts to precipitate the globulin, and coagu-
lating the albumin by heat, the filtered liquid was saturated with sodium chloride. On
concentrating the solution by boiling, a coagulum was gradually formed, having the com-
position shown in the table, and amounting to about 0'3 per cent, of the wheat-kernel.
The filtrate contained another body of proteose character which was not obtained in a
pure state, but by precipitating the concentrated liquid with alcohol, and determining the
nitrogen in the precipitate obtained, was estimated at 0-2 to 0'4 per cent, of the seed.
Both these substances and the coagulum are regarded by Osborne and Voorhees as
unquestionably derivatives of some other proteid in the seed, presumably the proteose
first mentioned.
CEREALS. 437
scribed as " crude gluten," has a brownish tinge, is almost tasteless,
gives an odor on burning resembling that of burnt horn or feathers,
and on destructive distillation yields the same products as animal
proteids. It is insoluble in cold water, and in a 10 to 15 per cent,
solution of common salt, but dissolves partially in alcohol and in
boiling water.
Crude gluten consists of a mixture of proteids with small quantities
of lecithin, fat, phytosterin, starch, cellulose, fibre, and mineral
matter. The proteids of gluten have been the subject of numerous
researches, with curiously discordant results. Their nature has been
re-investigated in a masterly manner by Osborne and Voorhees
(Amer, Chem. Jour., xv. 392), who find that only two proteids of defi-
nite character can be detected in gluten, namely : glutenin, which
is a body substantially identical with the gluten-casein of earlier
investigators, and gliadin, remarkable for its solubility in dilute
alcohol. They can find no evidence of the existence of mucedin or
gluten-fibrin described by Ritthausen as constituents of crude gluten,
and they strongly dissent from the views of Weyl and Bischoff and of
Sidney Martin (Brit. Med. Jour., 1886, ii. 104) that gluten does not
pre-exist in flour, but is a product of the action in presence of water
of a soluble ferment or zymaze on other proteids of the grain.
GLUTENIN is prepared by Ritthausen by boiling crude gluten
several times with alcohol of 0'890 specific gravity, when the gliadin
dissolves and a residue is obtained consisting of glutenin with some
impurities. This product should be dissolved in very dilute ( T 2 ^ per
cent.) solution of caustic potash, and the proteid reprecipitated by
exactly neutralising the solution with acetic acid. Osborne and Voor-
hees then direct that the precipitate should be treated in succession
with alcohol and ether to remove traces of fat, &c., and then redis-
solved in very dilute alkali, the solution filtered clear through close
paper, and the glutenin reprecipitated by exact neutralisation. 1
When purified in the above manner, glutenin forms a greyish-white
1 Unless glutenin be treated in the manner described in the text, the impurities are not
removed and the product has a variable composition.
Glutenin was first described by Taddei under the name of zymom. Liebig, as well as
Dumas and Cahours, named it plant-fibrin. Ritthausen, who obtained the substance sub-
tantially pure, called it gluten-casein. Weyl and Bischoff regarded it as an albuminate
form of a myosin-like globulin, which body pre-existed in the grain and was converted
into glutenin by the action of a ferment. Sidney Martin held the same view, and he and
Halliburton caused confusion by designating the proteid as gluten-fibrin. This name had
already been employed by Ritthausen for a body soluble in dilute alcohol which he
described as existing in gluten.
438 CEREALS.
mass which is not sticky. When dried at 100 it forms a slightly
brownish, horny substance, which slowly recovers its original condition
by contact with water. In a moist state, glutenin readily undergoes
decomposition, soluble proteids being first formed, and subsequently
products of a very offensive character. 1 Glutenin is practically in-
soluble in cold water or cold alcohol, but appears to be slightly soluble
in these solvents when warmed. After dehydration with absolute alcohol
and drying over sulphuric acid, glutenin is soluble in very dilute alkalies
(as O'l per cent, solution of caustic potash) and in very dilute acids
(e.g., 0'2 per cent, hydrochloric acid), with the exception of an in-
soluble residue, the amount of which depends on the condition of its
preparation. Thus, when freshly precipitated and in the hydrated
state, glutenin is extremely and completely soluble in the slightest
excess of caustic alkali, and in somewhat greater but still very slight
excess of acid. In this condition, glutenin is also soluble in the slightest
excess of ammonia or sodium carbonate solution. After drying over
strong sulphuric acid the substance dissolves only partially in a 0*5
per cent, solution of sodium carbonate.
Glutenin also dissolves with facility in cold dilute organic acids
(acetic, citric, tartaric). From its solutions in alkalies and dilute acids
it is thrown down by exact neutralisation. Glutenin is precipitated
from its solutions by cupric acetate, or by saturating its solution with
common salt. In sulphuric acid diluted with an equal measure of
water, glutenin dissolves on boiling with brownish color, which persists
on standing. On diluting the solution a clear liquid is obtained. In
concentrated hydrochloric acid, glutenin dissolves to a slightly yellow-
ish solution, which becomes of a deep violet color on standing.
GLIADIN' is readily dissolved out of wheaten flour or gluten by hot
1 G. Emmerling (Ber., xxix. 2721) describes the result of experiments on the de-
composition of wheat-gluten by proteus vulgaria. The gluten was prepared by kneading
out the starch from wheat-flour, and treating the crude product with malt-extract, the
residue after this treatment being washed with alcohol and ether. The purified substance,
suspended in water with calcium carbonate, potassium phosphate, and magnesium sul-
phate, was sterilised and treated with a pure culture of proteus. In four days a copious
evolution of gas had occurred. The gas had the composition C0 2 46,H38, and N16 per
cent. After six days the strongly alkaline fluid was distilled in a current of steam. The
distillate contained phenol and trimethylamine ; dimethylamine and other liquid bases
were not found. The residue contained betaine, acetic acid, and butyric acid, but not pro-
pionic acid. Egg albumin was also treated with staphylocnccus pyogenes aureus ; indole,
skatole, phenol, formic acid, acetic, propionic and higher fatty acids were obtained from
this decomposition.
2 This proteid was first discovered in 1805 by Einhof, and in 1820 was named by Taddei
gliadin on account of its resemblance to glue. By Liebig it was called plant-gelatin, and
CEREALS. 439
dilute alcohol. In the hydrated condition, gliadin is a soft, sticky
substance, which can be readily drawn into threads ; but when dehy-
drated by means of absolute alcohol and subsequent treatment with
ether, and dried in vacua, it forms a white, friable mass which can be
readily reduced to powder. If moistened with a little water or dilute
alcohol and then dried, gliadin forms thin, transparent sheets resem-
bling gelatin, but somewhat more brittle.
When treated with a little cold water, gliadin forms a sticky mass,
and dissolves somewhat on addition of a larger quantity. It is much
more soluble in boiling water, forming an opalescent solution, but
partially separates again on cooling. The aqueous solution of gliadin
is coagulated on boiling, and the precipitate formed is insoluble in
dilute alcohol or in 0'2 per cent, caustic alkali solution. A solution of
gliadin in pure water is instantly precipitated by adding a very minute
amount of sodium chloride.
If previously-moistened gliadin be treated with water containing a
little common salt, a very viscid product is obtained, which adheres
persistently to everything with which it comes in contact, but with a
stronger solution of common salt (10 per cent.) a plastic mass is
formed which is not adhesive. Gliadin is quite insoluble in absolute
alcohol, but up to a certain point becomes increasingly soluble as the
alcohol is diluted, after which the solubility again diminishes. Thus,
alcohol of 70 per cent, dissolves an almost infinite amount of gliadin,
but the proteid is precipitated by adding either much water or strong
alcohol to this solution. Gliadin is precipitated from its solutions
either in strong or in weak alcohol by adding a few drops of sodium
chloride solution, the completeness of the precipitation depending on
the strength of the alcohol and the amount of salt added. The pre-
cipitation is least complete from alcohol of 70 to 80 per cent.
Gliadin dissolves readily in extremely dilute acids and alkalies,
and is precipitated, on neutralisation, in a condition apparently
unchanged either in composition or properties. Gliadin gives the
general proteid reactions with nitric acid, Millon's reagent, and the
biuret test. When dissolved in strong hydrochloric acid, gliadin
gradually develops a violet coloration. Warm 50 per cent, sulphuric
acid gives a similar reaction, the color becoming much more intense
by Dumas and Cahours glutin. The mucin of De Saussure and of Berzelius must also be
considered as impure gliadin, and the products called by Ritthausen gluten-fibrin and
mucedin were apparently simply impure or altered preparations of his plant-gelatin or
gliadin, which, owing to the strength of the alcohol used, were more soluble in the hot
than in the cold liquid.
440 CEREALS.
on boiling. Gliadin is precipitated from its solutions by tannin, basic
lead acetate, and mercuric chloride. 1
Gliadin is entirely distinct in composition and properties from the
alcohol-soluble proteids of maize and oats.
On reference to the table of analyses, it will be seen that gliadin
and glutenin show a very close agreement in ultimate composition,
and Osborne and Vorhees suggest that they may be two forms of the
same proteid, one soluble in dilute alcohol and the other insoluble
(Amer. Chem. Jour., xv. 458).
CRUDE GLUTEN from wheat-flour consists 'essentially of glutenin
and gliadin, both these proteids being essential for its formation.
According to the view of Osborne and Voorhees, the gliadin forms a
sticky mixture with water, and the presence of the salts natural to
the wheat-flour prevents its ready solution. It tends to bind the par-
ticles of flour together, rendering the dough and gluten tough and
coherent. The glutenin imparts solidity to the gluten, evidently
forming a nucleus to which the gliadin adheres, thus preventing its
solution by water. A mixture of one part of gliadin with ten of
starch forms a dough, but yields no gluten, the gliadin being washed
away with the starch on treatment with water. On the other hand,
flour freed from gliadin gives no gluten, there being no binding
material to hold the particles together.
Soluble salts are also necessary in forming a gluten-mass, since
gliadin is readily soluble in distilled water. In water containing
salts it forms a viscid, semi-fluid mass, which acts very powerfully in
holding together the particles of flour. The mineral constituents of
the seeds are apparently sufficient to accomplish this purpose, for
a firm gluten can be obtained by washing a dough with distilled
water.
In the opinion of Osborne and Voorhees, " no ferment-action
occurs in the formation of gluten, for its constituents are found in the
flour having the same properties and composition as in the gluten,
even under such conditions as would be supposed to remove com-
pletely antecedent proteids or to prevent ferment-action." They con-
sider that " all the phenomena which have been attributed to ferment-
action are explained by the properties of the proteids themselves as
they exist in the seed and in the gluten."
1 Osborne and Voorhees instance the case of ze'in, the principal proteid of maize, which
is wholly insoluble in water and in absolute alcohol ; but if water be present solution in
alcohol at once takes place, the amount of ze'in dissolved depending, within certain
limits, on the quantity of water present.
CEREALS. 441
So far as is known, wheat is the only seed the flour of which yields
a tough, elastic gluten-mass on treatment with water. 1 It is the
gliadin which imparts to wheat-flour the property of forming a stiff,
elastic dough, capable of retaining vesicles of gas, and thus producing
a light and porous loaf. The absence of more than traces of gliadin
from the glutens of barley, oats, and rye is the reason why the flours
from these sources do not form a plastic mixture with water, and hence
do not make good bread. 2 Gliadin is absent, or nearly so, from legu-
minous seeds, but is said to be present in the juice of the grape
and other fruits, being held in solution by tartaric or other vegetable
acid.
An impure gluten is obtained as a waste-product in the manufac-
ture of starch.
Gluten has a high food-value, and bread made from it has been
specially recommended as a substitute for ordinary bread in cases of
diabetes. This so-called " gluten-bread " is in many cases very unfit for
its intended use. Thus, if the starch of flour be reduced by special
treatment from 70 to, say, 60 per cent., the product is evidently unfit
for use by diabetic patients, who might equally well reduce their con-
sumption of ordinary bread by one-seventh. On the other hand,
if the "gluten-bread" be practically free from starch, it fails to
satisfy the craving for starch which attends its total prohibition, and
may be advantageously replaced by more appetising forms of proteid
food.
1 M. Weybull (Chem. Zeit., xvii. 501) attributes the inferior quality of the rye-bread
of 1892 partly to a deficiency, and partly to a changed condition of the gluten. In such
case, the defect may be remedied by an admixture of wheat-flour, or by the employment
of some substance which precipitates the soluble-constituents of the gluten. Alum and
copper sulphate have this effect, but are inadmissible. Hence Weybull recommends the
addition of at least 1 per cent, of common salt, or the employment of skimmed milk
instead of water.
2 As rye-flour yields no gluten mass when kneaded in a current of water, A. Kleeberg
(Chem. Zeit., xvi. 1071) has proposed to detect an admixture of wheaten flour with rye-flour
as follows : Place as much of the flour as will lie on the point of a knife on an object-
glass of 7'5 cm. by 2-5 cm., add 5 to 6 drops of lukewarm water (40 to 50 C.), and stir well.
The quantity of water has to be so large that the particles of flour still float in the water.
The mixture of water and flour is spread over three parts of the object-glass and another
object-glass placed on it in such a way that the dry ends protrude on either side. Press
the two glasses well, wipe off the liquid, and slide the top glass to and fro several times.
During the pressing of the glasses white spots will be observed if wheaten flour be present,
which, on being rolled, form " vermicelli " ; these are short and thin if the quantity of
wheat present is small, and become thicker and longer with increasing amounts of
wheaten flour. An admixture of 5 per cent, of wheat-flour is said to be thus recognisable
with certainty.
UNIVERSITY
442 CEREALS.
To ascertain the proportion of crude- gluten obtainable from flour,
50 grm. 1 of the sample should be triturated in a mortar with 30
c.c. of water. The dough produced should leave the mortar without
a trace adhering. After standing at rest for three or four hours, the
mass should be placed in a fine linen cloth, which is then tied up
tightly and gently kneaded with the fingers, while a fine stream of
water is permitted to flow on to it. The kneading and washing are
continued until the water which runs away is found to be clear, and
hence free from starch. The gluten is then removed from the cloth
and dried slowly at 110 to 120 C. Gluten from good flour is
elastic and but little colored ; that from damaged or inferior flour
adheres to the cloth, is with difficulty united into a single mass, and
has less consistency and a higher color than the product from good
flour. 2
M. Boland has pointed out (Compt. rend., xcvii. 496) that the pro-
portion of gluten obtained from the same flour varies with the mode
of operation and the amount of washing. A more hydrated gluten is
yielded by flour from soft or old wheat than from hard, and by fresh
paste than by paste which has stood several hours before washing.
In order to avoid these sources of error, it is recommended that 50
grm. of the flour should be mixed with 25 grm. of water, and the
paste allowed to stand for twenty-five minutes. It is then divided into
two equal portions, one of which is washed immediately, while the
other is allowed to stand for an hour. As soon as the wash-water is
clear, the glutens are tightly pressed and weighed, after which they
are washed for another five minutes and again weighed. Four num-
1 When the gluten is not to be subsequently examined in the aleurometer it is prefer-
able to operate on 10 grm. of the flour, instead of on the larger quantity recommended
in the text. Jago recommends the use of 30 grm. of flour and 25 c.c. of water. He
ties up the dough in a piece of fine silk, such as is used for dressing flour, about a foot
square, and kneads it in a basin of water instead of under a tap, replacing the water as
long as starch continues to wash through.
2 The following alternative method of determining the yield of gluten is recommended
by Wanklyn and Cooper: 10 grm. weight of the sample is mixed on a porcelain plate
with 4 c.c. of water, so as to obtain a homogeneous dough. This is placed in a conical
measure or other suitable vessel, 50 c.c. of water added, and the dough manipulated with
a spatula so as to expel the starch -granules. The water is decanted off, a fresh quantity
added, and the kneading repeated till no more starch is extracted from the gluten. The
mass is then removed and kneaded in a little ether, after which it is spread out in a thin
layer on a platinum dish and dried in the water-oven till the weight is constant. The
crude gluten contains ash equal to about '3 per cent, of the flour, and fat equivalent to
I'OO of the flour. These may, of course, be directly determined in the crude gluten, if
desired.
CEREALS. 443
bers are thus obtained, and 4he mean of these is taken as the true
yield of moist gluten. The best flours give a moderately high yield
of gluten, but the product is highly elastic, and firm and springy to
the touch. Gluten from inferior flour is soft and sticky and possesses
but little toughness.
It is sometimes an advantage to ascertain the behavior on heating
of the crude gluten obtained as above. This may be effected by
means of the aleurometer, an instrument devised by Boland. It con-
sists of a brass cylinder, about five inches in length, furnished with a
graduated piston. Adjustable caps are fitted to both ends of the cyl-
inder, the whole length of which represents 50 ; but the stem of the
piston is graduated from 25 to 50 only, since it is capable of descend-
ing only half way down the cylinder. This contrivance constitutes the
aleurometer proper, and is designed for. use in a baker's oven. For
laboratory purposes, the aleurometer is immersed in a bath of oil, which
is maintained by means of a spirit-lamp at a temperature of 150 C.
As pointed out by W. Jago, it is important that this temperature
should be kept constant during the operation, and hence it is desirable
to fix a thermostat to the apparatus.
In using the aleurometer, from 30 to 50 grm. of the flour should be
made into a paste with half its weight of water, and then washed in
the manner already described. Seven grm. weight of the freshly pre-
pared gluten is then rolled in a little starch, and placed in the
cylinder, the inside of which should be greased to prevent the gluten
from adhering. The piston is then pushed down till it registers 25,
and the cylinder is heated in a baker's oven or immersed in the oil-
bath maintained at 150 for ten minutes, when the source of heat is
withdrawn, and the gluten allowed to remain undisturbed for another
ten minutes. On then examining the apparatus, the gluten will be
found to have expanded and forced up the piston to an extent depend-
ent on its quality. Good flour yields a gluten which will expand to
four times its original volume, but the expansion never exceeds the
limit of 50 on Boland's scale. With damaged flour, the gluten does
not swell much, but becomes viscous or nearly fluid, adheres to the
cylinder, and sometimes exhales a disagreeable odor, whereas good
gluten has merely the odor of hot bread. If the gluten does not alter
the position of the piston, which therefore will continue to register 25,
the flour may be considered unfit for bread making.
With practice in the use of the aleurometer, very fair results may
be obtained, though no fine distinctions are possible. A further
knowledge of the character of the gluten is obtainable by drying the
444 CEREALS.
swollen product, as taken from the aleurometer, in the water-oven for
twenty-four hours. On the average, three parts of moist gluten yield
one part of the dry substance.
K. W. Kunis, of Leipzig, has devised an instrument, called by him
the farinometer, which is intended for use with the dough made from
the flour to be tested, instead of necessitating the previous separation
of the gluten, as in Boland's process. The apparatus, which resembles
the aleurometer, is furnished with an automatic heat-indicator, and is
said to yield reliable results in practised hands.
Instead of preparing the gluten, valuable information respecting the
bread-making capacity of a sample of flour may be obtained very
simply by ascertaining the quantity of water a definite weight will
require to form a dough of standard consistency. The test is conducted
as follows : A weight of 25 grm. of the sample of flour is placed in an
evaporating basin and 17 c.c. of cold water added to it from a burette,
the flour and water being well mixed together by means of a spatula
or glass rod. On moulding the paste between the fingers it is easy to
determine whether the dough is too stiff" or too thin. In the latter
case, too much water has been added, and another trial must be made,
using a smaller measure. If the paste be too stiff, more water may be
added and well mixed with the dough, but it is better to make another
test with an increased amount of water. This should always be done
before coming to a conclusion as to the strength of the flour, and it is
better to leave the dough for one hour before deciding. It is easy to
compare the relative strengths of two or more samples of flour by this
test, but in the absence of a standard it is difficult without practice to
decide exactly when the paste is of a proper consistency. The results
are usually expressed in quarts of water required per sack of flour. In
London, the sack of flour is taken as weighing 252 Ibs., that is, 9
stones; but in some provincial districts a weight of 280 Ibs. ( = 10
stones) is reckoned as one sack. As a quart of water weighs 2'5 Ibs.,
each quart required by a sack of 252 Ibs. is practically 1 per cent.
Operating on 25 grm. of flour, as directed above, each c.c. of water
employed will represent four quarts to the sack of 9 stones ; or, with
the addition of one-ninth, the gallons of water per sack of 10 stones.
Jago regards a flour which requires 68 quarts of water per sack of 252
Ibs. as of standard quality. A sack of such flour will make 95 four-lb.
loaves or 380 Ibs. of bread.
It appears from the facts already set forth that the proteids of
wheat and other cereals may be classed broadly as soluble and insol-
uble, the latter being concerned in the formation of a tough, elastic
CEREALS. 445
gluten, while the former are rather detrimental than otherwise in the
production of bread.
In analysing plant-products, it is very important that the nitrogen-
ised constituents should undergo little or no alteration during the
process of extraction. Schulze and Barbieri consider this may be
best effected by extracting the substance first with cold water and then
with hot water, or else with dilute alcohol.
Chas. Graham has pointed out that a constant ratio exists between
the proportion of soluble proteids and the dextrin and sugar found on
analysing the flour, and that the longer the flour is digested in cold
water the greater the proportion of soluble proteids, and hence of
dextrin and sugar, becomes.
Graham has suggested the following simple method of making
rough comparative estimates of the soluble proteids of different
samples, which, with certain modifications, is as follows: 10 grm.
weight of the flour is treated with 40 c.c. of cold water, and the
mixture allowed to stand for exactly one hour. The liquid is then
passed through a dry filter, the first portions being rejected. 20 c.c.
measure of the filtrate (= 5 grm. of flour) is then treated with an
equal measure of methylated spirit, when a precipitate of soluble
proteids will be produced, the amount of which will depend on the
quality of the flour, the best specimens giving the smallest precipitate.
A more accurate estimation of the soluble proteids may be made by
filtering the liquid, evaporating 20 c.c. of the filtrate to dryness at
100 C., and weighing the residue of sugar, &c. The weight thus
obtained is subtracted from that found by evaporating 10 c.c. of the
original aqueous solution of the flour, when the difference will be the
weight of soluble proteids precipitated by the methylated spirit. It
is necessary to adhere strictly to one hour, or other constant time, for
the digestion of the flour with water, as higher results are obtained if
the treatment be prolonged. Operating in the foregoing manner,
J. W. Downs informs the author that the matter dissolved by cold
water from flour ranges from 6'7 in samples of the lowest quality to
3'5 per cent, in the highest quality of flour, the average being about
5 or 5J per cent.
CEREALIN. The husk of wheat and other cereals contains a soluble
nitrogenised ferment or enzyme called cerealin. This body exerts
a powerful hydrolytic action on starch, rapidly converting it into dex-
trin and other soluble bodies.
The presence of cerealin in wheat-bran renders " whole meal " un-
suitable for making bread by fermentation with yeast, unless special
446
CEREALS.
precautions be taken, though aerated bread can be prepared from it.
The cerealin acts like malt extract, causing a rapid conversion of the
starch into dextrin and sugar, and materially modifies the behavior
of the flour in the aleurometer.
Mineral Constituents of Cereals.
The following table shows the percentage of ash or mineral matter
contained in nine different fractions obtained by grinding wheat con-
taining 1'634 per cent, of mineral matter. The numbers given are the
average results of the examination of twenty-eight samples, the experi-
ments extending to the products of three separate years. It appears,
therefore, that of the total ash of the grain, amounting to 1'634 per
cent, of its weight, '483 occurs in the first three products (" fine
flour"), and that in the first five taken together the ash amounts to
723. These three products constitute upwards of 80 per cent, of the
weight of the original grain, and their mixture fairly represents the
composition of good seconds flour, with an ash of *86 per cent. Even
with the addition of products 6 and 7 of the following table, the ash
of the flour only amounts to about 0'9 per cent. Hence it may safely
be assumed that no sample of flour in which bran is not very notably
present ever yields a higher ash than TOO per cent. The ash of fine
flour is more often below 0*70 per cent, than in excess of that number,
and of late years the writer has often found it as low as 0'50 per cent. :
Yield from 100
Parts of Meal.
Percentage of
Ash in Products
Distribution of
Total Ash.
1. Fine Flour,
2.
411
18'6
69
71
284
132
9'2
73
067
Products 1, 2, and 3 together,
4. "Tails,"
70 2 1
5'3
71
1'03
483
054
5. " Fine Sharps " or " Middlings"
8'8
2'12
186
Products 1 to 5 together, . . .
6 " Coarse Sharps " . .
84-3
3'4
86
4'18
723
142
7. "'Fine Pollard "
2'4
5'65
'136
8. " Coarse Pollard "
6'5
6'47
420
9. "Long Bran,"
3'0
7-11
213
1-634
1 There seems to be an error here, but a careful inspection of the original tables has
failed to detect its nature. With the exception of the line commencing " Products 1 to 5
together," the numbers in which have been calculated by the writer, the figures are taken
from the original paper by Lawes and Gilbert (Joujr. Chem. Soc., x. 27).
CEREALS. 447
The amount of ash of cereals is not influenced in any definite manner
by the nature of the soil, and the same is true of the composition of the
ash, the predominance of any particular constituent in the soil by no
means leading to an excessive proportion of the same substance in the
ash of the plant. (See a laborious series of analyses of the ashes of
wheat-grain and straw, by Lawes and Gilbert, Jour. Chem. Soc., xlv.
305 to 407.)
The difference in the proportion of ash yielded by the grain, chaff,
and straw of cereals is strictly confined to the silica ; if this be deducted,
the remainders present no perceptible difference.
The percentage of ash yielded by barley and oats is somewhat
higher than that from wheat, while rye and maize yield about the
same as wheat, and rice far less. 1
Adulterations of Flour and Bread.
The adulterations to which bread and wheaten flour are liable are
of two kinds : admixture with the flour or meal of other cereals, and
addition of mineral substances. The first kind of sophistication can,
as a rule, only be ascertained by a patient examination under the
microscope, and there are cases in which even this plan fails to be
1 The composition of the ash of the whole grain of wheat and other cereals has been
studied by Lawes and Gilbert, Chevalier, Way and Ogston, &c. The following are the
general practical conclusions deducible from the numerous analyses recorded :
The proportion of potash is very variable, but .useless as a means of distinguishing the
ash of different grains. The lime ranges from 1 to 10 per cent. Baryta has been found
in Egyptian wheat. The magnesia varies much, but in wheat-ash is pretty constant,
fifty-three samples analysed by various chemists showing a range from 9*1 to 14'3, with a
mean amount of 12 P 11 of MgO in 100 of ash. The ferric oxide in wheat-ash was found by
Way and Ogston to range from 0*1 to 3'3 per cent., but Lawes and Gilbert (Jour. Chem.
Soc., xlv. 305) never found a proportion sensibly in excess of 1 per cent., which number
doubtless includes any trace of alumina which may have been present. Meunier finds
from 0-69 to 1'75 per cent, of ferric oxide in wheat-ash, with an average of I'll per cent.
Alumina is present only in minute traces, the proportion in genuine wheat-flour ash
rarely exceeding 1 per cent., and even this is probably due to adherent dirt. The silica
in the ash of wheat, rye, maize, and rice is generally very low, rarely reaching 5, and
being usually less than 2 per cent, of the total. 'In barley-ash, on the other hand, Cheva-
lier found from 17*3 to 32-7, the usual amount being about 24 per cent., while the ash of
oats contains from 40 to 50 per cent, of silica. Except in the larger proportion of silica
the ashes of barley and oats resemble wheat-ash in every essential respect. The phos-
phoric acid (PaOs) in wheat-ash varies from 40 to 55, with a very constant average of 49
to 50 per cent., which is 10 per cent, more than is present in the ash of barley, and 20 per
cent, in excess of the usual proportion in oats. On the other hand, the ash of maize or
rye contains 40 to 50 per cent, of P^O^, and in rice-ash the proportion is still larger. In
estimating phosphoric acid in cereals it is necessary to fuse the ash with sodium carbonate,
to convert the pyrophosphates into orthophosphates.
448 CEREALS.
of service. Mineral adulterants may occasionally be used to increase
the weight or bulk of the article, but such employment of them is
now practically obsolete, and their use is limited to increasing the
whiteness and apparent quality of the bread made from the flour.
Alum is the addition usually made for this purpose, but plaster of
Paris and similar materials are occasionally employed.
MINERAL ADDITIONS TO FLOUR AND BREAD.
In the case of flour, a determination of the ash affords a sufficiently
accurate means of detecting and determining mineral adulterants,
with the exception of alum, which is usually employed in too small a
quantity sensibly to affect the percentage obtained. With wheaten
flour, any higher ash than 0'7 per cent, should be regarded with great
suspicion, but in the case of oatmeal 2 per cent, or somewhat more is
a normal proportion.
In consequence of the ease with which the mineral adulterants of
flour can be separated from the sample, it is rarely necessary to deter-
mine any of the constituents of the ash, but in the case of bread this
procedure will be found important.
The best means of separating any mineral adulterants from flour
or oatmeal is to place 100 grm. (or 4 ounces) of the sample in a
dry cylindrical separator, furnished with a tap below and a stop-
per above. About 200 to 250 c.c. of methylated chloroform should
then be added, and the whole thoroughly shaken together and then
left at rest for some hours, or until the flour has risen to the surface
of the chloroform. Any mineral adulterant present will then be
found to have sunk to the bottom of the chloroform, and on running
off a little of the liquid through the tap will pass with it. The small
quantity of chloroform thus obtained may be diluted with more
chloroform in a smaller separator, and again allowed to settle. The
second deposit may still contain a little bran and other organic mat-
ters, but will consist chiefly of sand from the mill-stones, dirt, and any
alum, plaster of Paris, or other mineral powder heavier than chloro-
form that happened to be in the sample. The deposit is tapped off
and the bulk of the chloroform having been got rid of by decantation
or filtration, the last traces are driven off by a current of air assisted
by very gentle heat, and the residue is weighed. It is next examined
under a microscope, using a low power, with the view of detecting
particles of alum or other crystalline matter. The residue is then
dissolved in a little cold water and the liquid filtered. The residue
should be ignited and weighed. It will contain the dirt and mill-
CEREALS. 449
stone dust of the sample, mixed with any plaster of Paris, chalk, barium,
sulphate, or other mineral adulterant insoluble, or nearly insoluble, in
water. If the amount found does not exceed O'l per cent, of the
weight of flour it need not be further examined. The portion of the
chloroform deposit soluble in cold water will contain any alum present
in the original flour. On evaporating the aqueous liquid to dryness
the alum will be left, and may be recognised by its astringent taste,
reaction with logwood, and the form of any crystals which may have
been produced. Its amount may be accurately ascertained by deter-
mining the sulphates or aluminium, and calculating to the equivalent
in alum.
In the case of bread, oatcake and other products obtained by add-
ing water to the ground cereal, the chloroform treatment is not avail-
able for the detection of mineral adulterants.^ In this case it is neces-
sary to estimate the ash, and not unfrequently to make a partial
analysis of it.
The mineral additions liable to be made to bread and other prepara-
tions of the cereals include the following substances : 1. Common salt.
2. The ingredients of common salt, added in the form of hydrochloric
acid and sodium bicarbonate. 3. Baking powders ; of very variable
character, but usually containing sodium bicarbonate and tartaric
acid. Acid phosphate of calcium and certain compounds of alu-
minium are also contained in some baking powders. 4. Lime water.
5. Magnesium carbonate. 6. Alum and equivalent preparations con-
taining aluminium. 7. Plaster of Paris. 8. Whiting. 9. Barium
sulphate.
Of this somewhat formidable list, the compounds of aluminium and
the sulphates of barium and calcium are the only additions to which
grave exception can be taken when only small proportions are used,
though the earthy carbonates must be regarded as objectionable to
some extent.
Alum, or an equivalent preparation containing aluminium, is by far
the most common mineral adulterant of bread, though its use has
greatly decreased of late years. Its action in increasing the white-
ness and apparent quality of inferior flour is unquestionable, though
1 The chloroform test has been applied by L. Siebold to the examination of certain
drugs (Analyst, iv. 19), of which the following, when free from mineral additions, were
found to float entirely on the surface of the liquid : gum arable, gum tragacanth, starches,
myrrh, Barbadoes aloes, jalap, saffron, cinchonas, nux vomica, mustard, white pepper,
capsicum, and guarana. The following drugs only partially float on the chloroform, the
last two chiefly subsiding : gamboge, scamrnony, soccotrine aloes, opium, liquorice-root,
ginger, colocynth, cousso, ipecacuanha, cinnamon, and cardamoms.
29
450 CEREALS.
the cause of its influence has not been clearly ascertained. Whether
there be sufficient foundation for the statements made respecting the
injurious effects of alumed bread on the system is still an open ques-
tion. The proportion of alum which may be present is a factor too
often overlooked. 1
Alum can be detected in bread or flour, even when present in very
small proportion, by the careful application of the logwood-test, which
was first proposed by Hadow, but modified and greatly improved by
Horsley, and further worked out by J. Carter Bell. To prepare the
tincture of logwood required for the test, 5 grm. of freshly-cut log-
wood chips or shavings should be digested in a closed bottle with 100
c.c. of methylated spirit.
To test for alum in flour, 10 grm. of the sample should be mixed in
a glass basin or wide beaker with 10 c.c. of water. 1 c.c. of the log-
wood tincture and an equal measure of a saturated aqueous solution
of ammonium carbonate are then added, and the whole mixed to-
gether thoroughly. If the flour be pure, a pinkish color, which
gradually fades to a dirty brown, is obtained ; whereas, if alum be
present, the pink is changed to lavender or actual blue. As a precau-
tion, it is desirable to set the mixture aside for a few hours, or, heat
the paste in the water-oven for an hour or two, and note whether the
blue color remains.
To test for alum in bread, 5 c.c. of the logwood tincture should be
diluted with 90 of water and 5 c.c. of saturated carbonate of ammo-
nium solution added. Then, without delay, the mixture is poured
over about 10 grm. of the bread contained in a glass dish or clock-
glass. After about five minutes, the liquid is drained away and the
bread slightly washed and dried at 100 C. If alum be present, the
bread will assume a lavender or dark blue color, which becomes still
more marked on drying. With pure bread, the reddish color first
obtained fades to a buff or light brown. With care and a little
practice the test is very satisfactory, and is so delicate that even 7 grs.
1 Dr. James Bell, in his useful little book on Foods (part ii. page 138), writes :
" Whichever view be held, there can be little difference of opinion that the safest course to
adopt is to regard the addition of alum as unnecessary in the process of baking, and that
when it is found its presence should be dealt with as a clear case of adulteration. Alum
is not added to bread to improve its fitness as food, but simply to lead the public to infer
from its whiteness and general appearance that the bread has been made from a better
description of flour than has really been the case."
As the best descriptions of flour, and those that do not require the adventitious aid of
alum, are those which contain most gluten, it is evident that the use of alum gives a false
idea of the nutritive value of the flour.
CEREALS. 451
of alum to the 4 Ib. loaf can be detected. With moderate propor-
tions of alum, the depth of color produced will roughly indicate the
amount of the adulterant present. 1
A. Wynter Blyth modifies the logwood test by treating the flour or
bread with a moderate quantity of cold water, and immersing small
strips of gelatin in the liquid. After twelve hours the gelatin strips
are removed and immersed in the alkaline solution of logwood, when,
if alum be present, they acquire a blue color of a much more decided
tint than is obtainable from the original sample. If desired, the
gelatin strips may be washed, dissolved in hot water, and the absorp-
tion-spectrum of the solution observed.
Determination of Alum in Bread. Of the constituents of alum, the
element most generally of service for its determination in bread is the
aluminium. Pure wheat grain appears to be wholly destitute of
aluminium compounds, but commercial wheat flour to which no alum
has been added is apt to contain small but sensible traces of aluminium
derived from extraneous mineral matter. Such aluminium is present
as silicate, and gives no blue color with the logwood test. On the
other hand, all the ordinary methods of quantitatively estimating the
alum are incapable of distinguishing between the aluminium present
as silicate and that existing in a soluble form. Hence it is usual to
make a correction for the aluminium present as silicate. This is diffi-
cult to do with any approach to accuracy, but it may be taken as a
rule that from the amount of alum calculated from the total aluminium
in the bread should be subtracted a weight equal to the silica found,
when the difference will be approximately the true amount of alum
added.
The following method should be employed for the determination of
the total alumina and silica in bread: 100 grm. weight of the sample
is dried at 100 C., and then incinerated. This is best done by heat-
ing it in a platinum tray (about 5 inches by 3) in a gas-muffle, but
may also be effected in a platinum dish or large crucible placed over
1 In employing the logwood test for alum, it is very important that the tincture of
logwood should be freshly prepared, and that the test should be made immediately after
mixing the logwood tincture with the solution of ammonium carbonate. Inattention to
these essential points has caused the failure of several chemists to obtain the blue colora-
tion with specimens undoubtedly containing alum. The subsequent drying also should
never be neglected. With proper care, the test is exceedingly delicate, 0'02 per cent, of
alum causing a distinct shade of blue, while with three or four times this proportion the
reaction is wholly beyond question.
On the other hand, a blue coloration of bread and flour by an ammoniacal solution of
logwood does not infallibly prove the presence of a soluble aluminium compound, as
several other mineral additions produce a somewhat similar reaction.
452 CEREALS.
a bunsen. The heat should be moderate, so as to avoid fusion of the
ash. The process is completed by adding pure sodium carbonate and
a little nitre, and heating the mixture to fusion. The product is
rinsed out with water into a beaker, acidulated with hydrochloric acid,
and evaporated to dryness. The residue is taken up with dilute acid,
and the liquid filtered from the silica, which is washed, dried, and
weighed. To the solution, dilute ammonia is added till the precipitate
barely redissolves on stirring, when a slightly acid solution of ammo-
nium acetate is added, and the liquid raised to the boiling point.
After a few minutes' heating the solution should be set aside for some
hours, when its appearance should be observed. 1 The precipitate of
iron and aluminium phosphates should be filtered off, washed, and
redissolved in the smallest possible quantity of hydrochloric acid. The
resultant solution is poured into an excess of an aqueous solution of pure
caustic soda contained in a platinum or nickel vessel. After heating
for some time, the liquid is considerably diluted and filtered. The
filtrate is acidulated with hydrochloric acid, ammonium acetate and
a few drops of sodium phosphate added, and then a slight excess of
ammonia. The liquid is kept hot till all smell of ammonia is lost,
when it is filtered, and the precipitated aluminium phosphate washed,
ignited, and weighed. Its weight, multiplied by 3*713, gives the
ammonium alum, or by 3*873 the potassium alum in the 100 grm. of
bread taken. The amount so found requires a correction equal to the
percentage of silica obtained. 2 By multiplying the percentage of alum
by 280, the number of grains of alum per 4 Ib. loaf will be obtained.
The number of milligrammes of A1PO 4 per 100 grm. of bread gives,
without calculation, a close approximation to the number of grains of
ammonium alum per 4 Ib. loaf. 3
Throughout the foregoing process the use of porcelain vessels should
1 If gelatinous, it probably consists solely of iron and aluminium phosphates, but if
granular more or less of the earthy phosphates have probably been co-precipitated. In
such a case the precipitate should be separated, redissolved in dilute hydrochloric acid,
And the solution again neutralised with ammonia, and treated with ammonium acetate.
2 The writer has endeavored to devise a method of extracting alumina from bread in
such a manner as to render unnecessary the questionable correction for the aluminium
existing as silicate. Very encouraging results were obtained by a process based on the
solution of the starch by malt extract, destruction of the soluble carbohydrates by yeast,
acidulation of the liquid by nitric acid, followed by nitration, evaporation of the liquid,
ignition of the residue, and precipitation of the aluminium as phosphate in the usual way.
A. Wynter Blyth has extracted the greater part of the aluminium of the alum by soak-
ing the bread in dilute hydrochloric acid.
3 At the present time ammonium alum is almost unknown in the market, while for some
years it was equally difficult to meet with potassium alum.
CEREALS. 453
be wholly avoided, and care should be taken that the alkaline liquids
are not heated in glass. The caustic soda employed should be scru-
pulously free from alumina.
Plaster of Paris has been found in flour by Fairley, and has been
met with by the author in muffins to the extent of 1 per cent, of their
weight. In oat-cake it is said to be occasionally present to the extent
of 10 per cent, and upwards. From flour, plaster of Paris is readily
separated by treatment with chloroform.
The presence of plaster of Paris in bread is recognised by the high
total ash, and the high proportion of calcium contained in it. The
sulphates of the ash do not afford a means of accurately determining
the amount of plaster present, as the albuminoids furnish a notable
quantity of sulphates on igniting the cereals. On the other hand,
mere traces of sulphates exist ready formed in the cereals, and hence
their determination in the unignited bread affords a means of estimat-
ing the plaster present. This method, though theoretically perfect,
presents some difficulties in practice, owing to the difficulty of obtain-
ing a solution of the sulphates fit for precipitation with barium chloride.
The best way is to soak 12*20 grm. of the bread for some days in 1200
c.c./of cold distilled water till mould commences to form on thesurface
of the liquid. The solution is strained through coarse muslin, and the
filtrate treated with 20 c.c. of carbolic acid distilled over a small
quantity of lime. The whole is then raised to the boiling point and
filtered through paper. 1 litre of the filtrate is then slightly acidulated
with hydrochloric acid, and precipitated in the cold by barium
chloride. 237 parts of BaSO* represent 136 of plaster of Paris. Ex-
periments conducted in the author's laboratory with the view of testing
the accuracy of this process gave very satisfactory results.
Sulphate of Copper was formerly employed as an adulterant of bread,
especially in foreign countries, and a recent instance of its employment
in this country has been recorded by W. F. Lowe (Analyst, ix. 109).
This objectionable addition can be detected, even when present in but
very minute proportion, by soaking the bread in a solution of potas-
sium ferrocyanide acidulated with acetic acid, when a purplish or
reddish-brown coloration will be produced if copper be present. The
amount of copper may be determined by moistening 100 grm. of the
bread with sulphuric acid, igniting, and estimating the metal in the ash.
Very minute proportions of copper have been stated to exist nor-
mally in wheat-ash, but it is doubtful whether its presence was not due
to the practice, formerly very common, of steeping the corn in a solu-
tion of copper before sowing it.
454 CEREALS.
ORGANIC ADULTERANTS in flour are best detected by the micro-
scope, but in bread the process of baking so alters the structure of the
starches as to render the microscopic indications of very little value.
For the detection of certain additions to flour, A. E. Vogl shakes 2
grm. of the sample with 10 c.c. of alcohol at 70 per cent., to which
^th of hydrochloric acid has been previously added. Both the color
of the flour and that of the liquid are then observed, but the reaction
is often developed only on standing, and in other cases is promoted by
heating. Pure wheat or rye-flour remains white, and the liquid also
remains colorless, or shows merely a yellowish tint in the case of coarse
qualities. Pure barley and oatmeal give a straw-yellow liquid.
Corn-cockle 1 colors the liquid a full orange, pea-flower an orange-red,
and vetches and beans give a fine purple-red color. Mildewed wheat
is said to give a purple-red, and ergotised wheat a blood-red coloration.
According to C. Hartwich, the presence of rhinanthine in flour or
bread may be detected by boiling an alcoholic solution of the sample
with hydrochloric acid, when the liquid will assume an intense green
color on cooling, if rhinanthine be present. 2
Some admixtures, such as haricot beans, are stated to give a colora-
tion varying from orange-yellow to very dark-green on mixing the
meal with a dilute solution of ferric chloride, while pure wheat flour
only acquires a pale straw color when similarly treated.
1 Corn-cockle occasionally occurs in cereals to a considerable extent. It imparts a bitter
taste to the bread, and is said to be injurious. If the ineal be passed through a sieve
having naeshes 1 millimetre in diameter, the corn-cockle husks will remain on the sieve
and be recognised by their dark color. The starch-granules of the corn-cockle are very
small (about 0'006 millimetre in diameter), but not otherwise characteristic. Petermann
suggests that corn-cockle should be sought for by digesting 500 grm. of the meal in a litre
of 85 per cent, alcohol, and filtering the solution whilst hot. The filtrate is precipitated
by addition of absolute alcohol, the precipitate dried, and taken up by cold water. This
extract is again precipitated by alcohol, the precipitate dried, when, if of a yellowish-
white color, bitter burning taste, and soluble in water, it consists of saponin derived from
corn-cockle.
2 Rhinanthine is a glucoside occurring in the seeds of the yellow rattle (RhinantJius
crista yalli), a plant often found mixed with rye.
ACID DERIVATIVES OF ALCOHOLS, AND
VEGETABLE ACIDS.
This numerous and important class of organic bodies contains a
great variety of acids, some of which occur ready-formed in plants,
and the synthesis of which has not been hitherto effected in the labo-
ratory. In addition to these, there are many which can also be
obtained artificially, and others again which are purely artificial
products.
All the acids treated of in this division are compounds of carbon,
hydrogen, and oxygen. When a metallic salt of one of them is
ignited in the air it leaves the metal, sometimes in the free state (as
the salts of silver) but more frequently in the form of oxide. If the
organic salt be a compound of one of the metals of the alkalies or
alkaline-earths, on ignition in the air the corresponding carbonate is
obtained. If this be dissolved in standard acid, the diminution in the
acidity of the liquid will be equivalent to the organic acid previously
present. This fact is often utilised for the indirect determination
of vegetable acids (see methods on p. 459), and is applicable in
presence of sulphates, chlorides, &c. The substance or solution must
be neutral in reaction before ignition, or, if not so, must be brought
into that condition. Nitrates interfere, as, on ignition in contact with
organic matter they yield carbonates, together with decided traces of
cyanides.
The following table shows the manner in which the neutral solu-
tions of the potassium or sodium salts of the acids of this division are
precipitated by cold neutral solutions of barium, calcium, and ferric
chlorides, by lead acetate, and by silver nitrate. In all cases, the
reactions refer to moderately concentrated solutions of the salts.
When the precipitate is somewhat soluble in water, so as to render its
production questionable, the letter P is placed within parentheses.
S signifies that the substance formed is soluble, and hence that no
precipitate is obtained. Except when otherwise mentioned the pre-
455
456
ORGANIC ACIDS.
cipitates are white. In addition to the reactions with the above
metallic solutions, columns are added showing the reactions of the
organic acids with other important reagents. R signifies " Reduction,"
and 0" no effect":
TABLE SHOWING THE REACTIONS OF THE SALTS OF SOME OF
THE VEGETABLE ACIDS.
.
a
12
o5
>F * r<
*r1
V
"rt
$1
^
O
Name of
1
J3
e
1
<5
1
s
*1
CS'-H
1
%&
^3 C
Salt in
5
.tJ^ 1
??S
."S^i
jtH~bC
IS
-~S 8*2
Remarks.
Solution.
1
M
*J
1
*
g
C'S
^^
^a|
5
"1
1
i>
fi
g
|l
i
Acetate, .
S
s
Red color.
s
(P)
Smell of
Ag salt not re-
acetic acid.
duced on heal-
ing solution.
Formate, .
S
s
Red color.
s
(S)
R
CO evolved.
Ag salt or solu-
tion reduced on
heating.
Oxalate, .
P
p
S
p
p
R
CO + CO 2
A yellow precipi-
evolved.
tate sometimes
occurs on add-
ing FeCl.s.
Lactate, .
S
s
S
s
s
R
CO evolved.
See "Lactic
brown
Acid."
color.
Succinate,
(P)
(S)
Red-brown
p
p
No change.
Ba and Ca salts
Malate, . .
s
(S)
precipitate.
S
p
p
R
Darkened.
precipitated on
adding alcohol.
Ca salts insoluble
in dilute alco-
hol.
Tartrate, .
p
p
s
p
p
R
Charring.
Ag salt reduced
on heating.
Citrate, .
p
p
s
p
p
CO evolved
Ca salt precipi-
brown
tated on boiling
color.
and redissolved
on cooling.
Acouitate,
(P)
(P)
p
p
f
Ca salt is soluble
in 100 parts of
water.
Meconate,
(P)
p
Red color.
p
p
.
.
Action of oxidis-
ing agents not
recorded.
Gallate,i .
Blue-violet
p
Reduced
R
Violet-red
Salts darken
turning
on heat-
color.
rapidly in pres-
green.
ing-
ence of alkali.
Pyrogallate
Blue-violet
p
Reduced
R
R
Chars when
Salts darken
turning
wine-red.
in the
cold.
strongly
heated.
rapidly in pres-
ence of alkali.
Gallotan-
nate, 1
Blue-black
precipitate.
p
Bed need
on heat-
R
R
Dull purple
color and
Almost impossi-
ble to obtain
ing.
charring.
neutral solu-
tions.
1 Gallic and gallotannic acids properly belong to the class of vegetable acids, but their
analytical characters will be described at length with greater convenience in a separate
section. Pyrogallic acid (properly, pyrogallol) is a product of the action of heat on gallic
acid; it does not occur naturally and is not an acid.
ORGANIC ACIDS. 457
ACETIC ACID.
Hydrogen Acetate.
French Acide acetique. German Essigsaure.
C 2 H 4 2 = H,C 2 H 3 2 = C * H3 2
Acetic acid exists ready formed in certain plants, and is a frequent
product in chemical reactions. It is produced by the acetic fermenta-
tion of sugar, and by the limited oxidation of alcohol. In commerce,
the largest quantity is obtained from the products of the distillation
of wood, in the manner described under " pyroligneous acid."
Pure acetic acid is a colorless liquid, having a strongly acid and
pungent smell and taste. On cooling, it crystallises in large trans-
parent tables which melt at 16'7 C., and hence the absolute acid is
known as " glacial acetic acid." Like many of its salts, acetic acid
exhibits the property of super-fusion very readily, remaining liquid if
cooled down in a closed vessel, even below 0, but on opening or
shaking the vessel, or dropping in a fragment of the solid acid, the
whole solidifies, and the temperature rises to 16*7. A small addition
of water lowers the melting point of acetic acid very considerably, so
that an acid containing 13 per cent, of water melts below 0, and one
containing 38 per cent, of water (corresponding to C 2 H 4 O 2 -j- 2H 2 O)
has a melting point of 24 C. If still more water be added the
melting point again rises.
Absolute acetic acid boils at 119 C., and distils unchanged. In
distilling hydrated acid the last fractions are absolute or nearly
so.
Addition of water to glacial acetic acid causes evolution of heat,
and a contraction in volume ensues till the mixture contains about 23
per cent, of water, probably owing to the formation of a hydrate of
the composition, C 2 H 4 O 2 ,H 2 O. Acid of this strength has a higher
density than the glacial acid, so that either concentration or dilution
causes a diminution of gravity. This fact must not be lost sight of in
estimating acetic acid by its density. In fact, the density is not to
be relied on for the determination of acetic acid in concentrated
solution, though it is of service for the dilute acid.
The densities of mixtures in various proportions of acetic acid and
water have been determined by Mohr and by Oudemanns. According
to the latter chemist, Mohr's observations were made on an acid con-
taining 5 per cent, of water.
458
ORGANIC ACIDS.
The following table shows the density of acetic acid of different
strengths, according both to Ouderaanns and to Mohr, the tempera-
ture in each case being 15 C. (= 59 F.) :
C,H 4 O 3
Densitj
' 9
C 2 H 4 2
Deusiti
r.
per cent.
Oudemanns.
Mohr.
per cent.
Oudemanns.
Mohr.
1
1 '0007
I'OOl
21
0298
1-029
2
1-0022
1-002
22
0310
1-031
3
0037
1-004
23
0324
1-032
4
0052
1-005
24
0337
1-033
5
0067
1-007
25
0350
1-034
6
0083
1-008
26
.0363
1-035
7
0098
1-010
27
1-0375
1-036
8
0113
1-012
28
1-0388
1-038
9
0127
1-013
29
1-0400
1-039
10
.0142
1-015
30
1-0412
1-040
11
0157
1-016
31
1-0424
1-041
12
0171
1-017
32
1-0436
1-042
13
0185
1-018
33
1-0447
1-044
14
0200
1-020
40
1-0523
1-051
15
0214
1-022
50
10615
1-061
16
0228
1-023
60
1-0685
1-067
17
0242
1-024
70
1-0733
1-070
18
0256
1 -025
77
1-0748
1-0735
19
0270
1-026
80
1-0748
1-0735
20
0284
1-027
90
1-0713
1 "0730
100
1-0553
1-0635
From this table it will be seen that acid of 100 per cent, and acid
of about 43 per cent, have the same density.
The "Acetic Acid " of the British Pharmacopeia contains 33 per
cent, by weight of real acid (C 2 H 4 O 2 ), and has a density of T044.
" Dilute Acetic Acid," B.P., made by diluting one measure of the
above with seven of water, has a gravity of 1*006, and contains 4'27
per cent, of real acetic acid (C 2 H 4 O 2 ).
The " Glacial Acetic Acid " of the Pharmacopeia is said to have a
density of 1'065 to T066, and to contain at least 98*8 per cent, of real
acid. 1 It should crystallise at 1'1 C. (= 34 F.), and remain solid
till heated above 8'9 C. (=48 F.).
1 If Oudemanns' density table be correct, these characters are incompatible. All the
B.P. percentages appear, however, to be calculated from Mohr's table. On the other
hand, the writer has shown (Analyst, iii. 268) that inconsistencies exist in the part of
Oudemanns' tables referring to dilute acids, though it is decidedly preferable to Mohr's.
Of course these discrepancies are quite independent of the well-known abnormal density
of acetic acid of a certain strength.
ORGANIC ACIDS. 459
Absolute acetic acid is miscible in all proportions with water,
alcohol, and ether. It dissolves many essential oils, camphor, and
resins, phenols, gelatin, and many metallic salts insoluble in water.
Cold acetic acid is not inflammable, but the vapor given off by the
boiling liquid burns with a blue flame. The strong acid is a powerful
caustic. It does not redden litmus until mixed with water.
Acetic acid is a very stable body. The most powerful oxidising
agents attack it with difficulty. Chromic acid has no effect on it, and
a solution of chromic acid in glacial acetic acid is employed for the
oxidation of anthracene and other hydrocarbons. Nitric acid has no
reaction on acetic acid ; chlorine converts it into chloracetic acid,
H,C 2 H 2 C1O,0.
DETECTION OF ACETIC ACID AND ACETATES.
Most of the acetates are soluble in water. A few oxy-acetates
(" basic " acetates) are insoluble, and the neutral argentic and mer-
curous salts are sparingly soluble. Hence, acetic acid cannot be
determined or readily detected by precipitation. Free acetic acid
may generally be recognised by its smell and other physical proper-
ties/or it may be neutralised by caustic soda, and examined by the
following tests :
Metallic acetates give the following reactions :
Subjected to dry distillation, acetone, C 3 H 6 O, is given off, having
a highly characteristic odor.
Heated in the solid state in admixture with arsenious oxide (As 2 O 3 ),
acetates give an alliaceous and very characteristic smell of cacodylic
oxide, which body is very poisonous.
Heated with sulphuric or phosphoric acid, acetic acid is evolved.
Heated with rectified spirit of wine (not methylated) and con-
centrated sulphuric acid, a fragrant and characteristic odor of ethyl
acetate (acetic ether) is produced.
The neutral solution, on treatment with ferric nitrate or chloride
(avoiding excess}, gives a deep-red liquid containing ferric acetate.
This is decomposed on boiling, the liquid becoming colorless and
depositing reddish-brown ferric oxy-acetate. The reaction is imper-
fect if the iron solution be added in excess. The cold red liquid is
not decolorised on addition of mercuric chloride (distinction between
acetates and thiocyanates), and is not taken up by ether on agitation
(distinction from thiocyanates) ; but the color is readily destroyed on
addition of cold dilute sulphuric or hydrochloric acid (distinction
from meconates).
460 ORGANIC ACIDS.
Insoluble or basic acetates may be decomposed by boiling solution
of sodium carbonate, when the acetate will be found in the filtered
liquid as a sodium salt.
Acetates of alkaloids and nitrogenised organic bases, as a rule,
respond to the foregoing tests, but acetates of the alcohol radicles
(acetic ethers) do not usually do so. The latter are readily decom-
posed, however, by digestion with alcoholic potash or soda, and, after
distilling off the resultant alcohol, the residual liquid may be examined
for the acetate of an alkali-metal.
DETERMINATION OF ACETIC ACID AND ACETATES.
When simply in admixture with water, acetic acid may be deter-
mined by the density of the liquid.
In the absence of other free acids, free acetic acid may be deter-
mined volumetrically, by titrating the liquid with decinormal alkali.
Litmus solution may be used as an indicator, or, when dark-colored
liquids are to be assayed, litmus paper may be substituted for it.
A preferable indicator to litmus is to be found in phenolphthalein,
as acetate of sodium is quite neutral to it, while alkaline to litmus.
The end-reaction is very sharp. Highly-colored liquids, such as vin-
egar, may be largely diluted before titrating, as the delicacy of the
reaction suffers but little from such treatment.
Methyl-orange and phenacetolin are not suitable indicators for
titrating acetic acid, and with rosolic acid the end-reaction is in-
distinct.
Like the corresponding salts of other organic acids, the acetates
of the metals of the alkalies and alkaline-earths are converted into
carbonates on ignition. Hence, in the absence of other organic acids,
or of nitrates, &c., the amount of acetate originally present may be
ascertained by titrating the residue of the ignition with standard acid.
Each c.c. of normal acid required for neutralisation represents "060
grm. of C 9 H 4 O 2 in the sample.
The acetates of such metals as are completely precipitated by
sodium carbonate (e.g., calcium, lead, iron) may be decomposed by a
known quantity of it, the liquid well boiled, filtered, and the filtrate
titrated with standard acid. The loss of alkalinity represents the acetic
acid originally present as an acetate. Before employing this method,
the solution must be exactly neutralised, if not neutral already.
In presence of salts of inorganic acids, the last method is valueless,
but the following modification may be employed : The excess of car-
bonate of sodium is exactly neutralised by hydrochloric acid, the
ORGANIC ACIDS. 461
liquid evaporated to dryness, the residue gently ignited, and the result-
ant carbonate titrated with standard acid. Each c.c. of standard acid
used represents '060 grm. of acetic acid. Other organic acids will be
estimated as acetic acid.
Free acetic acid may also be determined by adding excess of pure
precipitated barium carbonate to the solution. The liquid is well
boiled, filtered, and the barium in the filtrate precipitated by dilute
sulphuric acid. 233 parts of BaS0 4 obtained, represent 120 of HC 2 -
H 3 O 2 in the sample taken. This process is applicable in presence of
oxalic, phosphoric, sulphuric, and other free acids forming insoluble
barium salts, but is useless in presence of soluble oxalates, phosphates,
sulphates, &c. The method is available in presence of alkaline chlo-
rides, &c., but not in presence of free hydrochloric acid, unless the
solution be previously treated with excess of argentic sulphate. Ace-
tates and chlorides of metals of the alkalies and the alkaline-earths do
not interfere, but acetates and other salts of iron, aluminium and other
metals precipitable by barium carbonate must be absent.
Weigert determines the free acetic acid in wine, by distilling four
or fiy^ltimes to dryness under greatly reduced pressure, and titrating
the/ distillate.
The determination of acetic acid in acetates is best effected by dis-
tilling the salt to dryness with a moderate excess of sulphuric acid, or
with acid sodium sulphate. Water should then be added to the con-
tents of the retort, and the distillation repeated. A third, and even a
fourth, distillation will sometimes be necessary, as the last traces of
acetic acid are volatilised with extreme difficulty.
In presence of hydrochloric acid or chlorides, excess of sulphate of
silver should be added before commencing the distillation.
In presence of sugar or other bodies liable to decomposition by sul-
phuric acid, phosphoric acid should be substituted for the latter. Care
should be taken that the phosphoric acid used is free from nitric and
other volatile acids. This is best ensured by adding a little ammonia,
and heating the acid to fusion in a platinum crucible.
This plan is of service for the determination of acetic acid in wine.
A measured quantity of the sample is neutralised with baryta, the
alcohol distilled off, phosphoric acid added to the residue, and the dis-
tillation repeated, the process being carried nearly to dryness. To
obtain the last traces of acetic acid, water should be added and the
distillation repeated.
For the determination of acetic acid in presence of its homologues,
see the analysis of calcium acetate.
462 ORGANIC ACIDS.
Pyroligneous Acid.
French Acide Pyroligneux, or Vinaigre de Bois. German Holz-
essig or Holzsaure.
Pyroligneous acid or wood-vinegar is the crude acetic acid obtained
by the distillation of wood. It is a very complex product, containing,
besides acetic acid, all the homologues of acetic acid from formic to
caproic acid ; crotonic and angelic acids ; furfurol ; bodies of indefinite
nature called "wood-oils"; pyrocatechol and creasol ; acetone, and
other ketones of the acetic and oleic series ; methyl alcohol and the
other constituents of wood-spirit ; &c. By neutralising the crude
product with lime and distilling, the volatile substances of indifferent
nature are removed. When partially concentrated, the solution is
faintly acidulated with hydrochloric acid, when creasote and various
tarry matters separate out; and the clear liquid on evaporation to
dryness yields a brownish residue, which is heated to about 230 C.
to decompose theempyreumatic products. On distillation with hydro-
chloric acid a comparatively pure acid may be obtained, which can be
further purified by rectification with a little potassium bichromate.
A better product is said to be obtainable by converting the acid into
a sodium salt, heating to destroy tarry matters, and distilling with
hydrochloric or sulphuric acid. 1
Pyroligneous acid varies much in strength according to the kind
and state of division of the wood used for distillation, and is also
affected by the construction of the retorts. Lopwood yields stronger
acid and less tarry and resinous matters than spent dye-woods and
sawdust, even though the same kind of wood be employed.
Pyroligneous acid from finely-divided wood has a density of 1*040
to 1*045, and contains, on an average, about 4 per cent, of real acetic
acid (H,C 2 H 3 O 2 ). The product of the distillation of lop-timber con-
tains an average of 71 per cent, of real acid.
The strength of pyroligneous acid may be ascertained by titration
with standard alkali and phenolphthalein, but the liquid is frequently
1 The empyreumatic flavor which clings so persistently to acetic acid derived from the
dry distillation of wood, is in great measure due to the presence of furfuraldehyde or fur-
fural, CsH^Oa, vapors of which are always produced if a warm mixture of sulphuric acid
and water be poured on bran or sawdust, or if bran be distilled with an equal weight of
sulphuric acid and three parts of water. If the vapors of furfurol be evolved in a beaker
covered with filter paper soaked in aniline, the latter will acquire a fine red color, which,
however, soon disappears. This reaction may be employed for the detection of furfural
which may be removed from pyroligneous acid by agitating the liquid with 2 or 3 per cent,
of benzene. The aqueous layer, after separation from the benzene, is stated to give, by a
single distillation, a very palatable table-vinegar.
ORGANIC ACIDS. 463
too dark in color to permit of the end-reaction being readily observed.
Sulphates and acetates of calcium and sodium are frequently present.
In the absence of sulphates, pyroligneous acid is best assayed by treat-
ment with excess of barium carbonate, with estimation of the dissolved
barium as sulphate.
Commercial Acetic Acid varies in strength from the nearly
absolute glacial acid to the weakest vinegar. The proportion of real
acetic acid may be ascertained by the methods already described : in
certain cases by the density ; and in the case of glacial acid by the
solidifying point.
The assay of glacial acetic acid, pyroligneous acid, and vinegar is
described in the respective sections treating of these products.
Commercial acetic acid is commonly prepared by distilling the ace-
tate of sodium or calcium with sulphuric or hydrochloric acid. It is
liable to contain the following impurities :
Sulphuric Acid and Sulphates, indicated and determined by addition
of barium chloride, which in their presence throws down white barium
sulphate. 1
Sulphurous Acid, indicated by adding barium chloride in excess,
filtering from any precipitate, and adding bromine water to the clear
filtrate. An additional precipitate of barium sulphate indicates the
previous presence of sulphurous acid, and from its weight the amount
of impurity can be calculated.
Hydrochloric Acid and Chlorides, detected and estimated by addition
of nitrate of silver.
Copper and Lead, detected by evaporating a considerable bulk of
the sample to a small volume, diluting with water, adding a few drops
of hydrochloric acid, and passing sulphuretted hydrogen, which pro-
duces a black or brown coloration or precipitate in presence of lead
or copper. If much organic matter be present, the evaporation
should be carried to dryness, and the residue ignited in porcelain.
The heavy metals are then sought for in the residue in the manner
described on p. 67. A delicate test for copper is the red-brown
precipitate or coloration produced by potassium ferrocyanide in the
original liquid, or the same concentrated and then diluted with water.
If iron be present in such quantity as to give a blue precipitate and
thus interfere with the reaction, it must first be removed by addition
of bromine water and excess of ammonia, and copper sought for in
the filtrate after acidifying with acetic or hydrochloric acid. Samples
1 For the detection and estimation of small amounts of free sulphuric and hydrochloric
acids in acetic acid and vinegar, see under Vinegar.
464 ORGANIC ACIDS.
of pickles suspected to be colored with copper should be moistened
with sulphuric acid, ignited, and the ash dissolved in nitric acid, and
tested in acid solution with potassium ferrocyanide, after separation of
the iron and phosphates with ammonia. The copper can be deter-
mined by electro-deposition on the inside of a platinum crucible by a
current from one cell of Grove's battery, or by precipitation with a
stick of cadmium. lin and zinc have been occasionally met with in
acetic acid and vinegar.
Salts of Calcium are detected by partially neutralising the solution
with ammonia and adding ammonium oxalate, which will produce a
white precipitate of calcium oxalate.
Empyreumatic and Indefinite Organic Bodies may be detected by
exactly neutralising the acid with sodium carbonate and tasting and
smelling the warmed liquid. The neutralised acid gives a precipitate
when heated to boiling with ammonio-nitrate of silver, and the original
acid darkens when heated to boiling with an equal measure of concen-
trated sulphuric acid, if the above impurities are present. 1 A. com-
parative estimate of the proportion of empyreumatic impurities pres-
ent may be made by diluting 10 c.c. of the sample to 400 c.c. with
water, adding hydrochloric acid, and titrating with permanganate till
the pink color is permanent for one minute.
General Fixed Impurities are detected and estimated by evapo-
rating of a known measure of the sample to dryness and weighing the
residue.
GLACIAL ACETIC ACID (Absolute Acetic Acid). The properties
of this substance have been already described.
Commercial glacial acetic acid should contain at least 97 per cent.
of the absolute acid. This may be ascertained by agitating 1 volume
of the sample with 9 of oil of turpentine. Complete solution occurs
if the strength is 97 per cent, or above. Samples containing 99*5 per
cent, of absolute acid are miscible with oil of turpentine in all pro-
portions. Oil of lemon, if freshly distilled, may be employed instead
of turpentine.
A more delicate test for water is to treat the sample in a dry test-
tube with an equal measure of carbon disulphide, and warm the mix-
ture in the hand for a few minutes. The liquid will be turbid if any
water be present in the sample.
i A sample of glacial acetic acid containing fully 99 per cent, of CaH^ was observed
by V. Meyer to give a deep red coloration with aniline. This property he traced to the
presence of furfurol, and from the depth of the coloration produced estimated the propor-
tion of the impurity to be 0*108 grm. per litre of the acid.
ORGANIC ACIDS.
465
The influence of various proportions of water on the melting point
of glacial acetic acid is shown in the following table by Rudorff
(Pharm. Jour. [3], ii. 241) :
Solidifying Point.
Water to 100 parts of
real C 2 H 4 O 2 .
Solidifying Point.
Water to 100 parts of
real C 2 H 4 O 2 .
-f 16'70
o-o
6-25
8-0
16-65
0-5
5-30
9-0
14-80
I'O
4-30
10-0
14-00
1-5
3-60
11-0
13-25
' 2-0
2-70
12-0
11-95
3-0
0-20
15-0
10-50
4'0
2-60
18-0
9-40
5-0
5-10
21-0
8-20
6-0
7-40
24-0
7-10
7-0
The strength of glacial acetic acid may also be determined as on
p. 460. The density is not an indication of value. Impurities may be
sought for as on p. 463.
Vinegar.
French Vinaigre. German Essig.
Properly speaking, vinegar is a more or less colored liquid, con-
sisting essentially of impure dilute acetic acid, obtained by the oxida-
tion of wine, beer, cider, or other alcoholic liquid. Sometimes the
term is improperly extended to pyroligneous acid, or " wood-vinegar,"
while acetic acid is called " distilled vinegar."
The acetification of alcohol appears to occur in two stages, the first
resulting in the formation of aldehyde, C 2 H 4 O, while this is further
changed to acetic acid, CaH/V Both reactions require the presence
of free oxygen, and in practice they occur simultaneously. Although
the reaction between alcohol and atmospheric oxygen takes place
under the influence of platinum-black and certain other bodies, the
formation of vinegar from alcoholic liquids appears in practice to
depend on the presence of an organised ferment called the mycoderma
aceti. Various mechanical arrangements are employed to expose a
large surface of the alcoholic liquid to the air, so as to diminish the
time required for acetification.
Besides acetic acid, vinegar often normally contains more or less of
other organic acids, sugar, dextrin, coloring matters, &c. The agree-
1 C H 6 + = C 2 H 4 + H 2 ; and
C~H 4 + = C 2 H 4 2 .
30
466 ORGANIC ACIDS.
able aromatic smell is doubtless due to characteristic ethers, and is
sometimes imitated by direct addition of ethyl acetate.
The " Vinegar " of the British Pharmacopeia has a density of 1*017
to 1*019, and contains at least 54 per cent, by weight of absolute
acetic acid (C 2 H 4 O 2 ). The specific gravity of vinegar is of no value
as an indication of its strength in acetic acid, as the proportion of
extractive matter varies much in vinegar from various sources. 1 The
" proof vinegar" of the Excise contains about 5 per cent, of acetic
anhydride (C 4 H 6 O 3 ), or 6 per cent, of the absolute acid, and has a
density of 1*019. By the manufacturer, vinegars of different strengths
are distinguished by the number of grains of pure dry carbonate of
sodium required for the neutralisation of one fluid ounce, Thus
"proof vinegar" is .known as "No. 24," from the fact that 24 grains
of Na 2 CO 3 are required for the neutralisation of one ounce. The
weaker qualities are Nos. 22, 20, and 18. As 60 grains of abso-
lute acetic acid, or 51 of acetic anhydride, are neutralised by 53 of
sodium carbonate, the number of grains of the real acid contained in
each fluid ounce of the vinegar can be ascertained by multiplying the
'number" of the sample byff = l'132> If the " number" be mul-
tiplied by the factor *259, the product will be the parts by weight of
absolute acid (C 2 H 4 O 2 ) in 100 measures of vinegar.
The vinegar of the German Pharmacopeia is required to contain
at least 6 per cent, of absolute acetic acid. In Russia the minimum
limit of strength is 5 per cent.; in Austria, 6; in Belgium, 5*6; in
France, 8 to 9 ; and in the United States, 4'6 per cent.
The "dilute acetic acid" of the present U.S. Pharmacopeia contains 6 per
cent, by weight of absolute acetic acid. The specific gravity is 1*008 at 15 C. L.
Hence it may be asserted that genuine vinegar of good quality does
not contain much less than 5 per cent, of absolute acetic acid, though
something depends on the origin of the vinegar, cider-vinegar being
naturally the weakest and wine- vinegar the strongest in acetic acid.
Vinegar containing less than 3 per cent, of real acetic acid may be
regarded as diluted with water, or at any rate as unfit for use.
The proportion of acetic acid in vinegar may be ascertained by
titration with standard caustic alkali, litmus-paper or phenol-
1 The excess of density of dilute acetic acid over that of water is said to be doubled on
neutralisation with lime. This fact affords a means of roughly assaying vinegar and
ascertaining the proportion of extract. Thus, if a sample have a density 1*017, increased
to 1*024 on neutralisation with lime, then the density of the pure acetic acid present would
be 1*007, and that of the " extract " I'OIO.
ORGANIC ACIDS. 467
phthalein being used as an indicator. Other methods are described
on p. 461.
WINE-VINEGAR varies in color according as its origin is white or
red wine, that derived from the former being most esteemed. It con-
tains from 6 to 12 per cent, of absolute acetic acid, has a low density
(1-014 to T022), and an extract varying from 1*7 to 2'4 per cent,
(average 2'05). If the " extract " or residue left on evaporation be
treated with alcohol, nearly everything dissolves except a granular
residue of tartar, while vinegars made from malt or sugar leave a
more or less glutinous residue, only sparingly soluble in alcohol. The
amount of " tartar " (acid tartrate of potassium) contained in wine-
vinegar averages 0*25 per cent. Its presence is peculiar to wine-
vinegar. The tartar may be proved to be such by pouring off the
alcohol and dissolving the residue in a small quantity of hot water.
On cooling the aqueous solution, and stirring the sides of the vessel
with a glass rod, the acid tartrate of potassium will be deposited in
streaks in the track of the rod. An addition of an equal bulk of
alcohol makes the reaction more delicate. Tartaric acid is occasion-
ally added to vinegar as an adulterant, in which case the residue left
on evaporation at a steam-heat is viscous and highly acid. By treat-
ment with proof-spirit any free tartaric acid is dissolved, and may be
detected in the solution by adding a solution of acetate of potassium
in proof spirit, and stirring with a glass rod. In presence of tartaric
acid, streaks, and probably a distinct precipitate, of acid potassium
tartrate will be produced. By titrating the precipitate with standard
alkali, the amount of free tartaric acid in the vinegar can be deter-
mined.
CIDER- VINEGAR is yellowish, has an odor of apples, a density of
1-013 to 1'015, and contains 3 to 6 per cent, of acetic acid. On
evaporation to dryness it yields from 1*5 to 1"8 per cent, of a mucilagi-
nous extract, smelling and tasting of baked apples, and containing
malic but no tartaric acid. Cider-vinegar gives slight precipitates
with barium chloride, silver nitrate, and ammonium oxalate. Perry-
vinegar presents similar characters. Crab-vinegar, made from the
crab-apple, is well known in Wales and the adjacent counties.
BEER- AND MALT- VINEGARS have a high density (1-021 to T025),
and yield 5 to 6 per cent, of extract, containing a notable proportion
of phosphates. The acetic acid varies from 3 to 6 per cent. Barium
chloride and silver nitrate frequently give considerable precipitates,
owing to the presence of sulphates and chlorides in the water used in
the manufacture.
468 ORGANIC ACIDS.
GLUCOSE- OR SUGAR-VINEGAR is now extensively prepared from
amylaceous materials by conversion with dilute acid, followed by fer-
mentation and acetification. Glucose-vinegar usually contains dex-
trose, dextrin, and, very often, calcium sulphate (see p. 463). Hence
it reduces Fehling's copper solution, and usually gives abundant pre-
cipitates with barium chloride and ammonium oxalate, and frequently
with silver nitrate also. When mixed with three or four times its
volume of strong alcohol, glucose-vinegar gives a precipitate of dextrin.
It is best to concentrate the sample before applying this test. Dex-
trose is best detected and determined by evaporating 50 c.c. of the
sample to a syrup and adding alcohol. The liquid is filtered, decolor-
ised by boiling with animal charcoal, again filtered, the alcohol boiled
off, and the glucose estimated by Fehling's copper solution. Glucose-
vinegar is said to be employed in France for adulterating wine-vinegar.
ARTIFICIAL VINEGAR is said to be made by mixing wine and acetic
acid (often pyroligneous). Such vinegar would give off inflammable
vapors of alcohol when boiled. Another factitious vinegar is made by
diluting acetic acid to the strength of proof- vinegar, coloring it with
burnt sugar, and flavoring it with a little acetic ether. Such a prod-
uct differs from malt-vinegar by containing no phosphates, and from
wine- and cider-vinegars in the absence of tartaric acid and malic acid
respectively.
Hehner regards the presence of aldehyde and alcohol, causing an
abundant iodoform reaction in the distillate from the neutralised
sample, as evidence of fermentation, and that the sample is true
vinegar. Vinegar made from sugar contains hardly any proteids,
while that from malt contains about 0*7 per cent. Vinegar prepared
by acid inversion of starches always contains a high ash with abun-
dance of sulphates. The ash of cane-sugar vinegar is readily fusible,
even over a moderate argand flame; that of a malt or a glucose
vinegar does not readily fuse. Sugar-vinegar yields an ash composed
mainly of potassium salts, as raw cane-sugar is employed, not refined
sugar. The estimation of potassium with a view to prove the presence
of grain vinegar is useless, since both grain and raw sugar contain
much potassium.
Alcohol always exists in a well-made fermentation vinegar, for
manufacturers stop the process before the acetification is complete.
Vinegar may diminish in strength to the extent of fully 1 per cent,
of acid in six months. If the alcohol is all destroyed the change is
likely to be much more rapid afterwards, since, in the absence of other
food, the vinegar-fungus feeds on the acetic acid previously formed.
ORGANIC ACIDS. 469
A well-made vinegar should contain alcohol, not only for keeping pur-
poses, but to ensure a gradual formation of acetic ether, just the
same as in wine after keeping. We might distinguish the fermentation
vinegar in that way. At the same time we must remember that it is
very easy to add alcohol in imitation of a fermentation vinegar. The
German manufacturers put acetic ether into their acetic acid with a
view of making it as like vinegar as possible. There is a considerable
amount of solid extract in fermentation vinegar, but in a mixture con-
taining pyroligneous acid the quantity is very much less. The solid
matter varies very much according to the perfection of the fermenta-
tion, and affords an indication of some value, though not so great as
the amount of ash, which does not vary to a great extent through the
fermentation. The proportion of sulphuric acid will afford some
information as to the probable use of glucose. The estimation of
total nitrogen is a valuable criterion. Grain vinegars contain a large
amount of nitrogen ; for although the manufacturers attempt to
remove nitrogenous matters, much is left. In estimating the total
nitrogen by the Kjeldahl method, the vinegar is evaporated to dry-
ness, or at any rate to a syrup, before adding the sulphuric acid. 25
c.c. of vinegar is a convenient quantity to employ. The nitrogen
found can then be calculated to its equivalent of proteids by the usual
factor ; but probably much of the organic nitrogen of vinegar exists
as peptones or similar soluble forms. In one case one-tenth of the
nitrogen was found to exist as ammonium salts. The proportions of
all these constituents must necessarily vary with the strength of the
vinegar. A wort which originally contained 12 per cent, of sugar
and other solids will necessarily contain more nitrogen, ash, phos-
phates, &c., than a vinegar which originally contained only 7 per
cent, of sugar. Therefore, it is desirable to adopt Mr. Hehner's plan
of calculating the various constituents upon the original solids of the
vinegar; 60 parts of acetic acid are theoretically produced from 90 of
glucose, and hence, if the acetic acid found be multiplied by 1*5, we
obtain the amount of sugar from which that acetic acid was derived.
Adding to the figure thus obtained the total extractive matters still
contained in the vinegar, we obtain a number representing the
" original solids " of the wort. Thus, if a vinegar contain 5'2 per
cent, of acetic acid and 2'8 of extract, the original solids will be
7'8 +2-8 = 10'6. If the vinegar itself contained 0'08 of nitrogen,
the original solids will contain
0-08 X 100
Q. = 0'75 per cent.
470
ORGANIC ACIDS.
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ORGANIC ACIDS. 471
In this manner one can eliminate the differences caused by varia-
tions in the strength of various samples of vinegar, and reduce the
results to a kind of common denominator. As a matter of fact, the
loss of acetic acid in the process of manufacture averages some 30 per
cent., so that the proportion of original solids calculated in the above
manner is always below the truth. Hence a nearer approximation
to accuracy would be obtained by multiplying the acetic acid by 2'25,
instead of 1*5, before adding the extract, but the change would involve
confusion, and it is best to adhere to the mode of calculation originally
suggested by Mr. Hehner.
The frequent imitation of cider-vinegar by a mixture of acetic acid and water
with addition of coloring matter (generally caramel) has led to much investigation
as to the means of detecting the fraud. Among the more important contribu-
tions to this subject are papers by Allen and Moor (Analyst, 1893, 240), Gr. S.
Cox (Analyst, 1894, 89), and A. W. Smith (j; A. C. S., 1898, 3). Cox gives the
analytic results on 20 samples of cider-vinegar and 4 samples of unfermented
cider. The acidity of the vinegar ranged from 2 '28 per cent, to 8 '4 per cent.,
the solids from 1'34 per cent to 4'0 per cent., the percentage of ash from 0'25 to
0'52. By recalculating these results by Hehner's rule it is found that the pro-
portion of original solids of the juice ranged from 5*51 per cent, to 16 '00 per
cent, and the ash from 1*94 per cent, to 4 '88 per cent.
The distinction between unadulterated cider- vinegar and the imitation made
by adding coloring matter to dilate acetic acid can be easily made. The latter
preparation leaves but little solid residue, almost no ash, and has but little
flavor.
A. W. Smith finds that the ash of cider-vinegar differs from that of most other
vinegars in the following important points :
It commences to melt and volatilise at a comparatively low temperature and
gives to flame the potassium color unobscured by that of sodium. It is low in
chlorides and sulphates and high in carbonates and phosphates ; about two-thirds
of the phosphates are soluble in water. In the ash of other vinegars a much
lower proportion of phosphates is soluble in water. The dilution of vinegar by
natural water will be apt to reduce the soluble matter by the formation of cal-
cium and magnesium phosphates.
Smith gives the following suggestions for analysis: For solids 5 to 10 grm.
are evaporated to dryness in a flat-bottomed dish and dried to constant weight
in a water-oven. For total acidity 5 grm. are diluted to about 50 c.c. and titra-
ted with standard alkali, using phenolphthalein as an indicator. The acidity
may be reported as all due to acetic acid, the small amount of other organic acid
not being estimated specially. For ash 10 grm. are dried and burned at a low
temperature. The residue is weighed and dissolved in water, the flame-test
applied, and the presence of sulphates and chloride tested qualitatively. Unless
these are excessive as compared with samples of known purity, quantitative
determination need not be made. For phosphates and alkalinity 25 grm. are
dried and burned, the ash repeatedly extracted with hot water, and the aqueous
472 ORGANIC ACIDS.
solution titrated with acid, using methyl-orange as an indicator. The undis-
solved residue of the ash is treated with nitric acid, the solution partially neu-
tralised, and the phosphate in both solutions determined in the usual way.
Caramel is detected by mixing 10 c.c. of the sample with 25 c.c. of paralde-
hyde and adding alcohol until the three liquids become soluble in each other.
The mixture is allowed to stand twenty-four hours, when any caramel will be
thrown down as a dark-brown, sticky mass, which, after washing with a little
absolute alcohol, will exhibit its bitter taste and reducing action on Fehling's
solution. L.
WOOD- VINEGAR is a name sometimes applied to pyroligneous acid.
AROMATIC VINEGAR is a product obtained by distilling a metallic
acetate, usually crystallised cupric acetate. The presence of acetone
and other bodies imparts an agreeable aroma. A small addition of
camphor or essential oil is often made.
MINERAL ACIDS IN VINEGAR.
Very weak vinegar is liable to a putrid fermentation, to prevent
which the addition of 1 gallon 1 of sulphuric acid to 1000 gallons of
vinegar was permitted by an Excise regulation. This addition is now
known to be unnecessary with good vinegar and is abandoned by the
best makers, though the practice is not obsolete, and the legal propor-
tion of sulphuric acid has been occasionally largely exceeded. In
addition to sulphuric acid, hydrochloric acid has been occasionally
added to vinegar, but the adulteration of vinegar with mineral acids
is now very rarely practised.
For detecting mineral acids in vinegar various tests have been
devised, but the majority are either untrustworthy or deficient in
delicacy. Some are applicable to the detection of sulphuric acid
only, whilst others include hydrochloric and other mineral acids also.
The employment of barium chloride and silver nitrate, for the detec-
tion of sulphuric and hydrochloric acids respectively, has led several
analysts into error, owing to the presence naturally of sulphates and
chlorides in the water employed in the manufacture of the vinegar. 2
1 This proportion of 1 gallon to 1000 is often erroneously stated at O'l per cent.,
whereas the true proportion resulting from the above admixture is about 0'185 parts by
weight of sulphuric acid, or nearly twice as much as is generally assumed.
2 A remarkable water of this character is employed by Hill & Evans of Worcester. An
analysis of it, made in 1874 by Dr. Letheby, showed :
Total solids, 266-59 grains per gallon.
Sulphuric acid (SO 3 ), 97'14 ,,
Chlorine, 48'44 ,,
Hardness 123-5 degrees.
At the same time, Dr. Letheby determined the sulphuric acid and chlorine in two samples
of the vinegar in the store-vats at the works, and in a sample of Messrs. Hill & Evans'
ORGANIC ACIDS. 473
Another circumstance which complicates the problem is that the
addition of a mineral acid in moderate quantity merely decomposes the
acetates naturally present in the vinegar, with liberation of acetic acid
and formation of metallic sulphates or chlorides. Hence, only the
excess of mineral acid beyond that required for the decomposition of
the acetates, &c., can exist in the free state, and to the presence of
such free mineral acids only can objection reasonably be taken, unless
the mineral acid used were contaminated with arsenic.
Acetates, and most other salts of organic acids, are decomposed by
ignition into carbonates, having an alkaline reaction to litmus, while
sulphates and chlorides of the light metals are unchanged on ignition,
and possess a neutral reaction. Hence, if the ash of a vinegar have a
sensibly alkaline reaction, acetates must have been present in the orig-
inal vinegar, and therefore no free sulphuric or hydrochloric acid can
have been present. To determine the amount of free mineral acid, it
is sufficient to carefully neutralise the vinegar with standard solution
of soda before evaporation to dryness (the same process serves for a
determination of the total free acid), ignite the residue, and titrate the
aqueous solution of the ash with standard acid. If the free acid orig-
inally present were wholly organic, the ash will contain an equivalent
amount of alkaline carbonate, which will require an amount of stand-
ard acid for its neutralisation exactly equivalent to the amount of
standard alkali originally added to the vinegar. Any deficiency in
the amount of standard acid required for neutralisation is due to the
free mineral acid originally present in the vinegar. More accurate
results are obtained if the amount of standard alkali added before
evaporation is insufficient for the complete saturation of the acetic
acid, but more than enough for the neutralisation of all mineral and
fixed" organic acids which may be present. By thus proceeding, deci-
normal alkali and acid may be employed (50 c.c. of the vinegar being
used), and thus sharper readings obtained (O. Hehner, Analyst, i. 105).
The total chlorine, existing both as free hydrochloric acid and as
metallic chlorides, cannot be determined in vinegar by direct precipi-
tation with silver nitrate, other matters being thrown down simultane-
ously. For a correct determination, 50 c.c. of the vinegar should be
neutralised with alkali, evaporated to dryness, the residue ignited, dis-
vinegar purchased of a retail dealer at Bedford, and said to be adulterated. The following
were the results obtained from the samples in question :
Sulphuric Acid (S0 3 ) . Chlorine.
A. Vinegar from store-vats, 90-79 grs. per gall. 50-33 grs. per gall.
B. 92-19 49-98
C. Vinegar from Bedford, 91 70 ,, 49-42
474 ORGANIC ACIDS.
solved in water, and the aqueous solution precipitated with excess of
calcium sulphate or nitrate to remove phosphates. The filtrate from
this precipitate may be precipitated by, or titrated with, a solution of
silver nitrate.
The sulphuric acid and sulphates may be precipitated by the direct
addition of barium chloride to the diluted vinegar, but the determi-
nation has little value.
Free sulphuric acid, as distinguished from sulphates, may be deter-
mined with considerable accuracy by evaporating 100 c.c. of the vine-
gar to a small bulk, and then adding to the cold concentrated liquid
four or five times its volume of alcohol. Sulphates are precipitated,
while free sulphuric acid remains in solution. The filtered liquid is
diluted, the alcohol boiled off, and the sulphuric acid precipitated with
barium chloride. The precipitate is filtered off, washed, dried, ignited,
and weighed. Its weight, multiplied by 0*4206, gives the weight of
sulphuric acid (H 2 SO 4 ) in the quantity of vinegar taken. In a vinegar
free from chlorides this process gives results in accordance with
Hehner's process, but in their presence the mineral acid found is defi-
cient by the amount of sulphuric acid required to decompose the chlo-
rides. This difficulty may be obviated by treating the vinegar with
excess of sulphate of silver solution before evaporation, by which treat-
ment any free hydrochloric is also estimated as sulphuric acid (Analyst,
iii. 290).
An ingenious method of detecting free sulphuric acid in vinegar and
wine has been described by Casali. 20 grm. weight of the sample is
ground up in a mortar with about 80 grm. of finely powdered porce-
lain (previously treated with hydrochloric acid to remove every trace
of free alkali), so that the mixture is not moist to the touch. The
whole is then ground up with 50 c.c. of ether (previously agitated with
magnesia and water to neutralise any trace of acid), filtered, and washed
with ether. The filtrate is then shaken with a little distilled water,
the ether distilled off, and the residue precipitated with barium chloride.
0'0005 grm. of free sulphuric acid can be readily detected by this
method.
A very simple, and apparently reliable, method of detecting free
mineral acids in vinegar has been described by A. Ashby (Analyst, ix.
96). A solution of logwood is prepared by pouring 100 c.c. of boiling
water on about 2 grm. of fresh logwood chips, and then allowing the
decoction to stand for a few hours. Separate drops of this solution
are spotted on the surface of a flat porcelain dish, or on the cover of a
porcelain crucible, and evaporated to dryness over a beaker of boiling
ORGANIC ACIDS. 475
water. To each spot a drop of the suspected sample (previously
concentrated if thought desirable) should be added, and the heating
continued till the liquid has evaporated. If the vinegar be pure the
residue will be found to have a bright yellow color, but in presence of
a very small proportion of mineral acid the residue assumes a red
color.
If the proportion of mineral acid be very small, the red color is
destroyed on adding water to the residue, but is restored on evapor-
ating, except in the case of nitric acid.
Tartaric Acid in vinegar may be detected as described under Wine
Vinegar, of which it is a normal constituent.
Oxalic Add may be detected by evaporating 20 c.c. of the vinegar
to a small bulk, diluting the residue with water, and adding calcium
acetate solution, or a mixture of acetate of ammonium and chloride
of calcium. Any oxalic acid causes the formation of white oxalate of
calcium.
Arsenic has been occasionally met with in vinegar, and may be
introduced by the addition of impure hydrochloric or sulphuric acid.
It may readily be detected by Marsh's or Reinsch's test.
Lead and Copper may be detected as described on p. 66.
Zinc is occasionally present in vinegar. It may be detected by
boiling down the vinegar to dryness with nitric acid, dissolving the
residue in acidulated water, passing sulphuretted hydrogen, filtering
from any precipitate, and then adding ammonium acetate, when white
sulphide of zinc will be thrown down if the metal be present. 1 A less
satisfactory method is to neutralise the greater part of the free acid in
the original vinegar by ammonia, and then at once pass sulphuretted
hydrogen.
Cayenne Pepper, Ginger, &c., are sometimes added to vinegar to
confer pungency. They may be detected by neutralising the concen-
trated vinegar with sodium carbonate and tasting the liquid.
Flies and so called " Eels " are often found in vinegar. They are
readily detected by the microscope, and may be destroyed by raising
the temperature of the liquid to 100 C.
METALLIC ACETATES.
Many of these important salts are 'extensively used in the arts,
medicine, &c. Their analytical characters and the general methods
i In presence of iron, the white precipitate may be more or less discolored, and should
be filtered off, dissolved in bromine water, the solution nearly neutralised, boiled with
a mncmium aeetite, filtered, an 1 sulphurettel hydrogen again passed through the filtrate.
476 ORGANIC ACIDS.
adopted for their assay have been, in great measure, already described.
The following observations, therefore, have reference chiefly to the de-
tection of impurities and adulterations in commercial acetates of the
metals. Sections treating of the acetates of ethyl, amyl, morphine,
rosaniline, &c., will be found in other parts of this work.
Potassium Acetate. KC 2 H 3 O 2 . This salt exists in several vege-
table secretions. It is deliquescent, very soluble in water and alcohol,
and in solution is neutral to test-paper. It undergoes fusion when
heated to incipient redness, and at a higher temperature decomposes
and leaves a residue of potassium carbonate. The amount of acetate
present in commercial samples of the salt may be determined by the
general methods given on p. 460 et seq.
COMMERCIAL ACETATE OF POTASSIUM is liable to contain sul-
phates, chlorides, and carbonates; also salts of iron, lead, copper, and
zinc; and arsenic is occasionally present. It is sometimes intention-
ally adulterated, acetate of calcium, and sulphate, tartrate and car-
bonate of potassium being employed for the purpose.
Acetate of potassium being readily soluble in rectified spirit, any
admixture of sulphates, tartrates, or carbonates may be detected and
estimated by treatment with that solvent. Carbonate is indicated
more precisely by the alkaline reaction of the sample ; its precipita-
tion by chloride of calcium ; its power of decolorising iodised starch ;
and by the effervescence produced on adding an acid.
Sodium Acetate, NaC 2 H 3 O 2 , closely resembles the potassium salt
but crystallises with three atoms of water. It is liable to contain the
same foreign matters as the acetate of potassium*. Crude sodium
acetate often contains tarry matters derived from the pyroligneous
acid employed in its preparation. Sodium acetate has been employed
for preserving meat. Its supersaturated solution has been used for
filling railway carriage foot-warmers.
Ammonium Acetate. (NH 4 )C 2 H 3 O 2 . This salt is generally
met with in solution, but may be obtained in the solid state, when it is
apt to contain acetamide, C 2 H 3 O,NH 2 .
Ammonium acetate is liable to contain much the same impurities as
the potassium salt, and may be examined in a similar manner. It
should be wholly volatile on ignition.
Calcium Acetate. Ca(C 2 H 3 O 3 ) 2 . This salt crystallises with dif-
ficulty in prismatic needles containing one atom of water. It is
decomposed by heat into acetone, C 3 H 6 O, and calcium carbonate.
Calcium acetate should be completely soluble in water and in proof
spirit. An insoluble residue may consist of calcium sulphate, carbon-
ORGANIC ACIDS. 477
ate, &c. The solution should give no precipitate with silver nitrate
or barium chloride. Potassium ferrocyanide colors the solution blue
if the sample contain iron, and brown if copper be present.
ASSAY OF " ACETATE OF LIME." Calcium acetate is obtained in
the manufacture of acetic acid from crude pyroligneous acid. The
commercial product is often extremely impure, containing much tarry
matter ; hydrate, carbonate,^ and sulphate of calcium ; the calcium
salts of the homologues of acetic acid, &C. 1 On this account its assay
is a matter of some commercial importance, and is not so easily effected
as might appear at first sight. Thus, if the salt be ignited, and the
amount of acetic acid calculated from the weight of the residual cal-
cium carbonate, or from the amount of normal acid the residue will
neutralise, very erroneous results may be obtained. 2
A much used method of assaying crude acetate of calcium is to boil
the aqueous solution of the sample with a known amount of carbonate
of sodium, and then to filter off the precipitated calcium carbonate.
The loss of alkalinity found on titrating the filtered liquid represents
the amount of acetic acid previously in combination with the lime.
This simple process eliminates the error caused by the presence of cal-
cium hydrate or carbonate in the sample, but is liable to give results
considerably above the truth, owing to the acid character of some of
the tarry matters.
A method of assaying calcium acetate, which is much used in the
neighborhood of Manchester, has been communicated to the writer by
H. Grirashaw, who finds it very satisfactory. 10 grm. of the sample
of crude acetate of lime should be dissolved in boitfng water, and 20
grm. of crystallised sodium sulphate added. The liquid is raised to
the boiling point, cooled, diluted to 250 c.c., and allowed to stand for
six, or preferably for twelve, hours. The calcium will then have sepa-
1 W. Giles informs the writer that forrnic acid is a very common if not a constant con-
stituent of crude acetate of lime, the proportion of calcium formate sometimes reaching
4 or 5 per cent. When operating on the large scale, the presence of formates is unmis-
takable. On crystallising out sodium acetate as completely as possible, a dense syrupy
liquid is left which contains sodium formate, reduces argentic and mercuric salts, and
evolves torrents of carbonic oxide when treated with excess of sulphuric acid.
2 This is well shown by the following figures given by the late Mr. William Baker.
The results in column A were obtained by distilling the samples with phosphoric acid,
and titrating the distillate with standard alkali. The figures in column B were deduced
from the weight of the ash of the sample.
A. B.
By Distillation. By Ignition.
No. 1. Calcium acetate, 70'17 per cent. 85 '47
No. 2. 69-98 85-30
No. 3. . . 32-29 73-78
478 ORGANIC ACIDS.
rated as a crystalline precipitate of gypsum. The liquid is next fil-
tered, the precipitate washed with hot water, and the filtrate made up
to 500 c.c. 50 c.c. of this solution (= 1 grm. of the sample) should
then be evaporated to dryness at 100, and somewhat further dried
in an air-bath. The residue is ignited at a red heat over a good bun-
sen burner for half-an-hour, 1 allowed to cool, and treated with 10 c.c.
of normal hydrochloric acid, using a cover to avoid loss. The solution
is boiled well to drive off carbon dioxide, filtered, the residual carbon
washed, and the filtrate titrated with decinormal caustic alkali, using
methyl-orange or litmus as an indicator. Each c.c. of normal acid
found to have been neutralised by the ash represents 0'060 grm. of
acetic acid (C 2 H 4 O 2 ), or 0*079 grm. of calcium acetate, in the liquid
(= 1 grm. of the sample) evaporated. Great care is requisite in
conducting the titration, as a very small difference in the volume of
alkali required makes a sensible change in the result. The portion of
the sample taken for the analysis should be finely powdered, and if the
solution in water be appreciably alkaline it should be cautiously neu-
tralised with decinormal caustic alkali before adding the sulphate of
sodium. Mr. Grimshaw finds this process to give results varying from
close agreement to about 2 per cent, in excess of those obtained from
1 These are Mr. Grimshaw's directions. The writer finds a tendency to incomplete
decomposition of the acetate if too low a temperature be employed. He prefers to evapo-
rate a measure of solution representing 5 grm. of the sample, and ignite at a moderate
red heat in a muffle, subsequently moistening the ash with peroxide of hydrogen to oxidise
any sulphides which may have been formed.
A manufacturer of the acetates writes to the author as follows : " Anybody who has
worked out the manufacture of acetate of soda, by decomposing the lime salt with sodium
sulphate, is aware that, after all the acetate of sodium that can be crystallised out is
obtained, there remains a large quantity of a dark syrupy, tarry liquid, which contains
what, in the present state of our knowledge, can only be defined as tarrate of soda, or, at
any rate, much of the soda is combined with acid or acids of a non-volatile nature. In
the sodium sulphate process of assaying crude acetate of lime all this would be reckoned
as acetic acid. If the syrupy liquid be treated with as much or rather more sulphuric
acid than is requisite to form NaHS0 4 with the soda previously ascertained to be present,
an 1 the mixture distilled, only a trifling quantity of volatile acids can be obtained even
at a considerable temperature. Yet, if, as is commonly asserted, the mother liquor from
the manufacture of sodium acetate is merely a saturated solution of sodium sulphate and
acetate, crystallisation of which salts is prevented by the tarry matters present, the
greater part of the acetic acid present ought to be recoverable by adding sulphuric acid
and distilling; while, as a matter of fact, we get at first only a watery fluid, so weak as
not even to pay for the vitriol which is used, followed by torrents of sulphurous acid if
the distillation be continued ; and, if the whole distillate be rectified over sufficient bichro-
mate of potassium and sulphuric acid to destroy the 862, the yield of volatile acid is
practically nil."
ORGANIC ACIDS. 479
the same samples by distillation with phosphoric acid. 1 The results
are not vitiated by the presence of calcium carbonate or other insol-
uble calcium compounds in the sample.
R. Fresenius has devised a method for the assay of crude acetate of
calcium, the details of which are as follow : 5 grm. of the sample are
dissolved in water, and mixed with 70 c.c. of normal oxalic acid. The
liquid is then diluted with water to 250 c.c., and 2'1 c.c. extra water
added to compensate for the space occupied by the precipitated calcium
oxalate. The liquid is filtered, and 100 c.c. of the filtrate titrated with
normal alkali. In another volume of 100 c.c. the excess of oxalic acid
is precipitated with pure calcium acetate, and the precipitate filtered,
washed, moistened with sulphuric acid, and weighed. The weight of
CaSO 4 so obtained, multiplied by '9265, gives the amount of crystallised
oxalic acid in 100 c.c. of the solution ( 2 grm. of the sample). By
multiplying this result by '9523 (or the weight of CaSO 4 at once by
882), the equivalent amount of acetic acid is obtained, and by sub-
tracting this figure from the total acidity calculated as acetic acid (1
c.c. of normal NaHO = '060 grm. HC 2 H 3 O 2 ), the amount of actual
'acetic acid is found.
Calcium acetate may also be assayed by the distillation process,
which is preferable on the score of accuracy and being more strictly
comparable with results likely to be obtained by the manufacturer, but
it is commonly regarded as too tedious a method for general use. This
objection is not valid if the manipulation be conducted in the following
manner, which is essentially that communicated to the writer by Still-
well and Gladding, and an improvement on their published descrip-
tion : 1 grm. of the sample of acetate of lime is placed in a small long-
necked flask or retort, of a capacity not exceeding 100 c.c., and rinsed
in with 15 c.c. of water. The neck of the retort is inclined slightly
upwards, and is fitted with a rubber cork, through which passes a bent'
tube which serves as the inner tube of a Liebig's condenser. The
retort is also fitted with a tapped funnel through which is introduced
1 Mr. Grimshaw has suggested the fallowing process as possessing many of the advan-
tages of both the sodium sulphate and the distillation methods of assaying acetate of
lime. He treats 10 grm. of the sample with water and excess of "bisulphate " of sodium
(NaHSO.t), makes up the liquid to a known measure, filters, titrates one portion of the
filtrate with standard alkali, and evaporates an equal measure to dryness. The residue
is moistened with water, and again dried, this process being several times repeated. The
residue is then dissolved and titrated with alkali, when the difference between the volume
now required and that employed for neutralising the unevaporated liquid will correspond
to the acetic acid in the solution which was evaporated to dryness. Litmus paper is the
best indicator.
480 ORGANIC ACIDS.
a solution of 5 grra. of glacial phosphoric acid in 10 c.c. of water.
This large excess of acid dissolves all the calcium phosphate to a clear
liquid. The retort is then heated, and the process continued till the
contents are reduced to about 10 c.c., when 25 c.c. of water should be
introduced through the funnel and the distillation proceeded with till
the liquid in the retort is again reduced to about 10 c.c. The addition
of water and re-distillation are repeated three or four times, when the
liquid coming over will be found entirely free from acid reaction. The
acetic acid in the distillate is then carefully determined by titration
with decinormal caustic soda and phenol-phthalein, each c.c. of which
corresponds to 0*005 grm. ( = 0'6 per cent.) of acetic acid (C 2 H 4 O 2 ) in
the sample. 1
The phosphoric acid employed for the distillation must be free from
nitric acid, which if present may be eliminated by adding a little
ammonia, and heating the acid to fusion in platinum. If either the
phosphoric acid or the sample itself contain chlorides, some sulphate of
silver must be added to the contents of the retort. Oxalic acid may
be substituted for the phosphoric acid, the solution being filtered from
the precipitated calcium oxalate before introduction into the retort.*
Hydrochloric acid may be used instead, provided that the amount
which passes into the distillate be estimated and subtracted from
the total acidity as deduced from the titration. Sulphuric acid
should not be used, as its reaction on the tarry matters occasions the
formation of sulphurous acid, which increases the acidity of the dis-
tillate.
When pure calcium acetate is assayed by either of the foregoing
methods fairly accurate results may be obtained, but when commercial
samples are examined the errors sometimes become very serious. On
the whole, the method of distillation with phosphoric acid is the most
accurate, but, unless carefully performed, the results are liable to be
below the truth, from incomplete volatilisation of the acetic acid, while
on the other hand, they may be excessive if nitric or other volatile acid
be present in the phosphoric acid used. 2
1 Stillwell and Gladding collect the distillate in a quantity of semi-normal soda not quite
sufficient to saturate it, then add enough more to establish a faint alkaline reaction, render
just acid with 0-2 c.c. of standard hydrochloric acid, and then boil for fifteen seconds to
expel all carbon dioxide. The solution is then brought back to exact neutrality by semi-
normal soda, the total amount of which used (less 0'2 c.c. correction for the hydrochloric
acid) represents the acetic acid in 1 grin, of the sample.
Stillwell and Gladding recommend that the alkali employed for the titration should be
standardised against pure potassium hydrogen tartrate, instead of using a mineral acid.
2 The following results, obtained some years ago in the writer's laboratory from the
ORC4ANIC ACIDS. 481
As at present manufactured, crude acetate of lime usually contains
from 62 to 67 per cent, of calcium acetate, and from 1 to 8 per cent, of
insoluble matter, the remainder being water, soluble tarry matters, &c.
Magnesium Acetate. The basic acetate of magnesium has been
recommended as an antiseptic, and is said to be met with in commerce
under the name of " siuodor."
Aluminium Acetate, A1(C 2 H 3 O 2 )3. This salt is employed in
solution by calico-printers, under the name of " red-liquor." It is usu-
ally prepared by precipitating a solution of alum or aluminium sul-
phate by means of calcium or lead acetate, and filtering or syphoning
off from the precipitated calcium or lead sulphate. When prepared
by means of alum, the product necessarily contains sulphate of potas-
sium or ammonium (according to the kind of alum used), and, as an
excess of the precipitant should be avoided, aluminium sulphate is
always to be expected. Owing to sulphate of calcium being somewhat
soluble in water, it will be met with in red-liquors prepared with ace-
tate of calcium. Such red-liquor is inferior to that prepared by acetate
of lead. Good red-liquor contains from 3 to 5 per cent, of alumina,
and twice that proportion of acetic acid, and has a density of 1*120, but
it is sometimes met with as low as 1*087. Carbonate of sodium is
often added to red-liquor to neutralise excess of acid.
Iron Acetates. Both ferrous and ferric acetates are employed in
the arts. A crude variety of iron acetate is extensively manufactured
by dissolving iron in pyroligneous acid.
PYROLIGNITE OF IRON, IRON LIQUOR, or BLACK LIQUOR. For use
by calico-printers, a liquid consisting chiefly of a solution of ferrous
acetate, but always containing more or less ferric acetate, is prepared
by acting on scrap-iron by crude pyroligneous acid of 1*035 to 1*040
same sample of " acetate of lime " by different methods, show the nature and direction of
the errors to which the various processes are liable :
Acetic Acid.
Per cent.
By distillation with H 3 PO 4 , and titration of distillate, 47'4
48-0
HoS0 4 , 48-6
HoC 2 4 ,
By Fresenius's niethod, ." 53'4
53-2
By ignition and weighing the CaC0 3 , 53'2
., and titration of residue, 53'2
53-8
54-0
By boiling with NaaCOg, and titrating filtrate, 56'4
,, ,, 56'4
57-6
Improvements in the manufacture of acetate of lime render the discrepancies resulting
from the employment of different methods of assay less striking than formerly.
31
482 ORGANIC ACIDS.
specific gravity. A purified acid gives less satisfactory results. 1 The
product, which is a deep black liquid, has a density of 1*085 to 1*090,
and is concentrated by boiling till the density is about 1*120, when it
contains about 10 per cent, of iron. It is then ready for use, and is
known as " printers' iron liquor." Much iron liquor is now made of a
density as high as 1*140. For use by dyers, the liquid is not concen-
trated by evaporation, but the density is raised by the addition of fer-
rous sulphate (copperas), by which a more suitable product is said to
be obtained than is yielded by acetate of iron alone. As a 5 per cent,
solution of crystallised ferrous sulphate has a density of 1*026, the ad-
dition of 2 Ib. of copperas to the gallon of " black liquor " will raise
its density from 1*085 to 1*111. As much as 124 grm. of ferrous sul-
phate per liter has been met with in iron liquor. The sulphate may
also result from the addition of sulphuric acid to the pyroligueous acid
employed for dissolving the scrap-iron. Sulphate of iron may be de-
tected and estimated by precipitating the diluted black liquor with
barium chloride. 233 parts of the precipitate represent 278 parts of
crystallised ferrous sulphate. Black liquor is frequently adulterated
with common salt, a 5 per cent, solution of which has a density of 1*036.
It may be detected and estimated by adding nitric acid and precipi-
tating the diluted liquor with nitrate of silver. Chloride of iron may
also be present owing to the addition of hydrochloric to the pyroligne-
ous acid. Hence the chlorine must not be assumed to exist as common
salt without further examination. This is best effected by heating the
liquid with nitric acid, adding barium nitrate to separate the sulphates,
precipitating the iron and excess of barium by ammonia and ammonium
carbonate, evaporating the filtrate to dryuess, and igniting the residue,
when any common salt will remain. Tannin is stated to be added to
iron liquor.
FERROUS ACETATE is sometimes made by decomposing a solution of
ferrous sulphate by calcium acetate. The liquor has usually a density
of I'll, and contains calcium sulphate.
FERRIC ACETATE is sometimes preferred by dyers and printers to
the ferrous salt. It is occasionally prepared by decomposing iron-alum
or ferric sulphate by lead acetate. The product must be free from
excess of the lead salt, and, for some purposes, excess of ferric sul-
phate must be avoided.
i According to M. Moyret (Jour. Soc. Dyers and Colorists, i. 117) the iron exists in
black liquor both in the ferrous and ferric conditions, the intense color and keeping quali-
ties being due to the presence of a small quantity of pyrocatechol, CeH-^OH^, which is a
constituent of pyroligneous acid and forms a black compound with ferroso-ferric oxide.
ORGANIC ACIDS. 483
Tincture of Acetate of Iron is used in medicine. It is prepared by
mixing alcoholic solutions of potassium acetate and ferric sulphate,
and filtering from the precipitated sulphate of potassium.
Lead Acetates. These important salts include the neutral
acetate, Pb(C 2 H 3 O 2 ) 2 , often called " sugar of lead," and no fewer
than four basic- or oxy-acetates, all of which are more or less soluble
in water, the solutions possessing an alkaline reaction and giving a
precipitate of lead carbonate by the action of carbonic acid gas. 1 All
the basic acetates may be considered as compounds of the neutral
acetate with oxide or hydrate of lead. By suspending the substance
in water, and passing carbonic acid through the liquid as long as it
has an alkaline reaction, the lead oxide is separated as an insoluble
carbonate, and may be filtered off, washed, ignited in porcelain (apart
from the filter) till bright yellow when cold, and weighed as PbO.
The lead remaining in permanent solution exists as neutral acetate, and
may be determined by precipitation as sulphate or chromate.
A better and simpler method for detecting basic acetate in a sample
is to dissolve it in recently-boiled water, filter, and then add to the
clear solution an equal measure of a 1 per cent, solution of mercuric
chloride. A white precipitate proves the presence of basic acetate. 2
The assay may also be conducted by methods given on p. 460.
R. Fresenius recommends the following indirect method for the
assay of pyrolignite and acetate of lead : 10 grm. of the sample are
dissolved in water in a flask holding 500 c.c., 60 c.c. of normal sul-
phuric acid are added, and then water up to the mark. An extra 1-3
c.c. of water is added to compensate for the bulk of the precipitated
lead sulphate. The flask is closed, well shaken, and the liquid
allowed to settle. 100 c.c. of the clear liquid are taken out, precipi-
tated with barium chloride, and the resultant BaSO 4 collected,
washed, ignited, and weighed. Its weight, multiplied by '4206, is sub-
tracted from '588 grm. (the weight of H 2 SO 4 added to each 100 c.c. of
the liquid). The remainder, multiplied by 113'7 gives the percentage
of PbO in the sample. Another 100 c.c. of the clear liquid are
drawn off and titrated with normal soda solution, using litmus as an
indicator. Multiply the number of cubic centimetres of alkali used by
060, subtract from this the previously obtained weight of BaSO 4 mul-
1 A solution of neutral lead acetate is slightly precipitated by carbonic acid.
2 Besides their reactions with mercuric chloride, carbonic acid, and litmus, the basic
acetates of lead are distinguished from the neutral acetate by their property of being pre-
cipitated by a strong solution of nitre added in excess. The precipitate appears to be an
ortho-nitrate of lead, Pb 3 "(N0 4 )'"2.
484 ORGANIC ACIDS.
tiplied by '515 (=the free sulphuric acid expressed in terms of acetic
acid), and the remainder, multiplied by 50, will be the percentage of
acetic acid (C 2 H 4 O 2 ) in the sample.
SOLUTION OF OXY-ACETATE OF LEAD is an official remedy. It is
described in the British Pharmacopoeia as a colorless liquid of 1*26
specific gravity, alkaline reaction and sweet astringent taste ; becoming
turbid on exposure to air; and forming, with mucilage of gum arabic,
a white opaque jelly. A dilute solution is officially prepared by
mixing the above with an equal measure of alcohol, and then adding
enough water to make up 80 times the original measure. Solution of
oxy-acetate of lead is prepared by boiling 10 parts of neutral acetate
with 7 of finely-powdered litharge and 40 of water. After boiling
for half an hour, the liquid is filtered and made up to the original
bulk with water.
Cupric Acetates. Several of these salts are known and exten-
sively used in the arts. They are prepared by the action of acetic
acid on oxide or carbonate of copper, or upon metallic copper with
access of air. The neutral acetate is freely soluble in water, but
several basic acetates exist. They are of various shades of color, and
constitute the bodies known as blue and green verdigris,
VERDIGRIS of good quality is dry, soluble in dilute acetic or sul-
phuric acid, and also in ammonia. Verdigris should not contain more
than 4 per cent, of impurities. A good sample has the following per-
centage composition : cupric oxide, 43*5 ; acetic anhydride, 29.3 ;
water, 25*2 ; and impurities, 2'0.
Verdigris is frequently adulterated. Sand, clay, pumice, and
chalk ; sulphates of barium, calcium, and copper ; and salts of iron
and zinc are sometimes present. The presence of zinc in verdigris is
due to the use of sheets of brass instead of copper for corrosion by
acetic acid.
On dissolving the sample in dilute hydrochloric acid, any sand,
clay, pumice, or sulphate of .barium will be left insoluble, and may be
collected and weighed. (About 3 per cent, of insoluble matter is allow-
able in verdigris. If the residue amount to 6 per cent, the sample
is inferior. Sulphate of calcium, if present in large proportion, may be
left partially in the insoluble residue.) If the sample effervesced on
addition of acid, a carbonate is present, though it may be that of
copper. From a measured portion of the solution in acid the sulphates
may be precipitated by barium chloride, and tne BaSO 4 collected and
weighed.
For the detection of the metals, the sample should be ignited, the
ORGANIC ACIDS. 485
residue dissolved in hydrochloric acid, and the copper precipitated
from the diluted liquid by a current of sulphuretted hydrogen. In
the filtrate, the excess of sulphuretted hydrogen is destroyed by bro-
mine water, the liquid nearly neutralised by ammonia, and then boiled
with ammonium acetate. The precipitate, when washed and ignited,
leaves the iron as Fe 2 O 3 . The filtrate from the iron precipitate
is treated with sulphuretted hydrogen, and any white sulphide of
zine filtered off, carefully roasted, and weighed as ZnO. From the
filtrate, the calcium is precipitated by ammonium oxalate. The
precipitate yields calcium carbonate on gentle ignition, the weight
being equal to the chalk in the quantity of the sample taken. The
calcium may be determined more readily, but less accurately, by dis-
solving the sample in hydrochloric acid, precipitating the iron by
bromine and ammonia, and then at once treating the blue ammoniacal
filtrate with ammonium oxalate. Of course, it does not follow that
all the calcium found exists as chalk, unless sulphates are absent.
HOMOLOGUES OF ACETIC ACID. Lower Fatty
Acids.
Acetic acid is the most important and best known of the homolo-
gous series called " the fatty acids." These acids have the general
formula C n H 2n O 2 ; CJI^.AO H ; or C n H 2n+1 'COOH. The lower
members of the series are volatile liquids closely resembling acetic
acid. The higher members of the series are insoluble in water, not
volatile without decomposition, and solid at ordinary temperatures.
The fatty acid series is known incompletely up to an acid with 30
atoms of carbon, but the greater number of the members are of very
limited importance, and the recognition of the majority of them by
reagents is at present impossible.
The higher members of the fatty acid series are almost exclusively
obtained by the saponification of the fixed oils, fats, and waxes, and
hence such of them as require description will be conveniently consid-
ered in the section of this work treating of the products of saponifica-
tion of such bodies. This article is therefore limited to a considera-
tion of such of the lower members of the series as are sensibly volatile
or soluble in water, and hence liable to occur under the same circum-
stances as acetic acid.
With the exception of the first three, all the members of the acetic
series of acids are capable of isomeric modification. The number of
such modifications capable of existing increases rapidly with the
486
ORGANIC ACIDS.
number of carbon atoms in the molecules, and many such bodies have
been actually obtained. As far as is known, however, all the acids of
the acetic series obtainable from natural sources are either the normal
primary acids or the iso-primary acids. Such secondary and tertiary
acids as are known have been hitherto obtained solely by synthetical
means, and their consideration lies beyond the scope of the present work.
The following table gives the names of the normal and iso-acids of
the acetic series up to the member with seven carbon atoms. Above
caproic acid the modifications have been very imperfectly differen-
tiated. A table of the still higher members of the series will be
given in the section on " Saponification."
From this table it will be observed that the boiling points of the
normal fatty acids show a tolerably regular rise of 18 to 22 C. for
each increment of CH 2 added to the formula. The iso-acid in each
case boils at a lower temperature than the normal acid, and has also
a lower density. The specific gravity and solubility of the fatty acids,
as also the solubility of many of their metallic salts, decrease with an
increase in the molecular weight. The ethers of the fatty acids simi-
larly diminish in solubility and volatility with each increase in the
number of carbon atoms.
Empirical
Formula.
Name.
Constitutional Formula.
Boiling
Point
C.
Specific
Gravity
at C.
Solubility
in
Water.
( Misciblein
CH 2 2
Formic acid, . . .
H'COOH
100
< all pro-
( portions
G>H 4 Oo
Acetic acid, ....
CH 3 -COOH
119
Do.
c;n 6 o 2
Propionic acid, . .
( Normal butyric acid
CH,-CHvCOOH
CH 3 -(CH 2 ) 2 -COOH
140
163 . .
1-016
9817 . .
Do.
Do.
C 4 H 8 2
-< Iso-butyric acid ; or
( dimethaceticacid,
CH(CH 3 yCOOH
. . 154
. . "9598
Soluble.
f Normal pentoic or
valeric acid, . . .
CH 3 -(CH 2 ) 3 -COOH
185. .
9577 . .
/Sparingly
\ ( 1 in 30)
C 6 H 10 2
j Iso-pentoic acid; or-
| dinary valeric
acid; "or iso-prop-
CH(CH 2 )o-CH 2 -COOH
. .175
. . '9536
Do.
[ acetic acid, . . .
C 6 H 12 O 2
J Normal caproic acid
CH 3 -(CHo) 4 -COOH
205. .
9450 . .
( Nearly in-
t soluble.
1 Iso-caproic acid, .
CH(CH 3 ) 2 -(CH 2 ) 2 -COOH
. .199
. . '9310
Do.
C 7 H 14 O 2
("Normal cenanthylic")
acid . . j
CH 3 -(CH 2 ) 5 -COOH
224. .
9345. .
/Almost
(insoluble.
(iso-cenanthylic acid
CH(CH 3 )o-(CH 2 ) 3 -COOH
. .213
....
Do.
As a rule, the iso-acids present very close resemblances to the cor-
responding normal acids, their lower densities and boiling points and
greater susceptibility to oxidation being the most tangible distinctions.
In some cases, differences are observable in the solubility and crystal-
lisability of the salts.
ORGANIC ACIDS. 487
As a class, the lower member of the acetic acid series may be
separated from most other organic acids (except lactic acid), by
treating the aqueous solution with finely-ground oxide of lead in
quantity sufficient to render it slightly alkaline. On filtering, the
lead salts of most organic acids will be left insoluble, while those of
the acetic series will be found in the filtrate.
The separation of the lower acids of the acetic series from each other
cannot usually be effected very readily or perfectly, the most satisfac-
tory methods being based on the following principles :
The lowest members of the series are the most readily soluble in
aqueous liquids, formic, acetic, propionic, and normal butyric acid
being soluble in all proportions. All but formic and acetic acids are
separated from their aqueous solutions by saturating the liquid with
calcium chloride, when they rise in the form of oils. A more perfect
separation from acetic and formic acids of the acids higher than
valeric may be effected by shaking the acidulated aqueous solution
with ether, which dissolves the higher homologues together with more
or less of the lower. On agitating the ethereal layer with a strong
solution of calcium chloride the formic and acetic acid pass into the
latter, and by repeating the treatment may be perfectly removed from
the ether, with little or no loss of the higher homologues.
The lower members of the series are most chemically active. Hence,
if an amount of alkali insufficient for complete neutralization be added
to a solution containing the free acids, and the liquid be then distilled,
the higher members of the series pass over in the free state, while the
lower members remain behind as fixed salts.
Thus if caustic soda be added to a mixture of butyric and valeric
acids in quantity insufficient to neutralise the whole, and the -liquid
be then distilled, the distillate will consist of pure valeric acid and
the residue will contain mixed butyrate and valerate of sodium ; or
else the distillate will contain the whole of the valeric acid and some
butyric acid, and the residue will consist entirely of butyrate of
sodium. In either case, a portion of one of the acids is obtained free
from the other. In the first case the residue of mixed valerate and
butyrate of sodium may be treated with sufficient dilute sulphuric
acid to neutralise one-half of the soda originally used, and the mixture
redistilled, when a fresh quantity of valeric acid will be obtained,
either pure or mixed with butyric acid according to the relative pro-
portions of the two acids present in the original mixture, In the
latter case, by partially neutralising the distillate with soda, and
again distilling, a further separation may be effected, and by repeating
488 ORGANIC ACIDS.
the operation in a judicious manner two or even more of these volatile
fatty acids may be separated tolerably perfectly from each other.
Although the foregoing method is well suited to the separation of
normal butyric and valeric acids, the principle is wholly at fault when
iso-valeric acid is in question, for this acid completely decomposes
normal butyrates.
An approximate separation of the homologues higher than valeric
acid can be effected by a fractional crystallisation of their barium
salts. The following is the order in which the barium salts are
deposited : 1
From Aqueous Solutions. From Alcoholic Solutions.
1. Barium caprate.
2. ,, pelargonate.
3 ,, caprylate.
4. ,, cenanthylate.
5. ,, caproate.
1. Barium caprylate.
2. ,, oenanthylate.
3. ,, pelargonate and
caprate.
4. ,, caproate.
The aqueous or alcoholic solution of the acid is neutralised with
standard aqueous or alcoholic solution of potash (according as the
crystallisation is to be effected from an aqueous or alcoholic solution),
an amount of barium chloride equivalent to the potash is next added,
and the resultant liquid evaporated and allowed to deposit crystals.
The crops of crystals from an aqueous solution may be washed with
hot alcohol, the washings containing the salts in the reverse order of
their deposition from alcoholic solution.
Another method of detecting and estimating acids of the acetic
series when in admixture with each other is based on the different
composition of their barium salts, the process being as follows: The
free acids obtained by distillation are saturated by carbonate of
barium, or by the cautious addition of baryta water (using phenol-
phthalein to indicate the point of neutrality), the latter method
being preferable for the higher numbers of the series. In this way,
neutral barium salts are formed, which may be obtained in the anhy-
drous state by evaporating off the water and drying the residue at
130 C. These barium salts contain percentages of barium dependent
on the atomic weights of the fatty acids present. On moistening the
residue with sulphuric acid and then igniting, an amount of barium
sulphate is obtained proportional to the percentage of barium con-
tained in the salt of the fatty acid present. Instead of weighing the
1 It is very probable that this method would be much affected by a change in the
modifications of the acids. The normal and iso-varieties of the higher fatty acids are
not at present thoroughly differentiated.
ORGANIC ACIDS.
489
barium sulphate, a standard solution of baryta water may be employed
and the weight of barium (or its equivalent of BaSO 4 ) calculated from
the volume of solution employed. This method also serves as a useful
check on the determination of the weight of barium sulphate. The
following table shows the proportions of Ba contained in, and of BaSO 4
producible from, the barium salts of the lower acids of the acetic
series :
Name of Salt.
Formula of Salt.
Ba, per cent.
BaS0 4 , per cent.
Barium formate, . .
Ba,2CHO,
70-25
119-47
acetate, . .
Ba,2C 2 H 3 2
53-73
91-37
propionate, .
Ba,2C 3 H 5 2
48-41
82-13
butyrate, . .
Ba,2C 4 H 7 O 2
44-05
74-91
valerate, . .
Ba,2C 5 H 9 O 2
40-41
68-73
caproate, . .
Ba,2C 6 H n O 2
37-33
63-48
cenanthylate,
Ba,2C T H 13 2
34-68
58-98
caprylate,
Ba,2C 8 H 15 O 2
32-39
55-08
pelargonate,
Ba,2C 9 H 17 2
30-38
51-66
caprate, ,
Ba,2C 10 H 19 2
28-60
48-64
From this table it will be seen that the pure barium salts of the
lower acids of the acetic series can very readily be distinguished from
each other by estimating the percentage of barium contained in them.
In the case of mixtures of two acids the identity of which is estab-
lished, the proportions in which the two are present may be calcu-
lated from the following formula, in which x is the percentage of
barium salt of the lower fatty acid in the mixed barium salts obtained ;
P, the percentage of BaSO 4 yielded by the mixed barium salts on
treatment with sulphuric acid ; B, the percentage of BaSO 4 theoreti-
cally obtainable from the pure salt of the lower fatty acid ; and 6, the
percentage of BaSO 4 theoretically obtainable from the pure salt of the
higher fatty acid. Then :
bx 1006.
For example : suppose a mixed barium salt known or assumed to
consist of acetate and valerate to have yielded 78*45 per cent, of
BaSO 4 , when treated with sulphuric acid and ignited. Then, by the
above formula,
91-37o; = 7845 -|- 68-73z 6873
therefore 22'64z = 972
and x = 42-93.
Hence, the mixed barium salt consisted of 42'93 of barium acetate,
and 57'07 of barium valerate. From these data, and the weight of
490
ORGANIC ACIDS.
mixed barium salt found, the actual amounts of acetic and valeric
acid may be readily calculated.
The above method has been proposed by A. Dupre (Analyst, i. 4)
for approximately determining the fusel oil in spirits. In this case the
various alcohols are first converted into the corresponding acids by
oxidation with chromic acid mixture.
A most ingenious method of detecting other fatty acids in presence
of acetic acid, and estimating the proportions present, has been de-
scribed by M. Duclaux (Ann. Chem. Phys. [5], ii. 233). It is based
primarily on the curious fact that if a liquid containing any fatty acid
be distilled, each successive fraction of the distillate contains a pro-
portion of the total acid operated on which is practically constant for
the same fraction, but will vary according to the nature of the acid
employed. Thus M. Duclaux found that if 110 c.c. of a liquid con-
taining acetic acid were distilled in a retort of 250 to 300 c.c. capacity,
each succeeding 10 c.c. of distillate contained an increasing quantity
of acid, which amounted to 79 - 8 per cent, of the whole when 100 c.c.
had passed over. Each of the homologues of acetic acid has a special
rate of vaporisation, and it is a curious fact that the less volatile acids
pass over with the first portions of aqueous vapor, while acetic and
formic acids behave in an opposite manner. 1
1 The following table gives M. Duclaux's results in a concise form. The columns
headed " B." show the percentages of the total acid contained in each successive 10 c.c.
of distillate, when 110 c.c. of the liquid were distilled in a retort holding 250 to 300 c.c.
The columns headed " A." show the percentages of the total distilled acid which passed
over in each 10 c.c. when the 100 c.c. first obtained was redistilled. The determinations
of acid in the distillate were made by standard lime water :
Percentage of Total Acid contained.
Formic.
Acetic.
Propionic.
Butyric.
Valeric.
A,
B.
A.
B.
A.
B.
A.
B.
A.
B.
Per
Per
Per
Per
Per
Per
Per
Per
Per
Per
t
cent.
cent.
cent.
cent.
cent.
cent.
cent.
cent.
cent.
cent.
1st fraction of 10 c.c. .
5-5
3-5
7-5
5-9
11-3
10-5
16-8
16-4
24-5
2d
6-4
4-1
7-9
6-2
11-5
10-6
15-1
14-7
20-0
3d
6-6
4-2
8-2
6-7
11-2
10-4 13-5
13-2
T3
15-4
4th . 7-2
4'5 8'6
6-9 10-6
9-9 : 12-3
11-8
i
11-4
5th . ; 8-3
5-3 i 9-1
7-3 10-7
9-9 10-2
10-1
8-2
6th . 9-1
5'7 9-6
7-6
10-1
9-3 9-3
9-1
i
6-2
7th . 10-0
6-4 10-2
8-2
9-3
8-9 7-8
7'6
i
4-0
8th . 121
6-7 11-5
9-2
9-3
8-5 6-4
6-3 rg
3-1
9th . 14-6
9-3 | 12-4 ! 9-8
8'5
7-8 5-0
4-8 -
2-6
10th
20-2
12-8
15-1
12-1
7-5
7-0 3-6 3-5
O
1-5
Total distillate = 100 c.c.
100-0
63-5
100-0
79-8
100.0
92-8 100-0 97-5
fa
96.9
Remaining in retort = 1
36-5
20.2
7-2 . .
2-5
3-1
10 c.c. j
It appears from this table that when a solution of acetic or formic acid is distilled, the
ORGANIC ACIDS. 491
The presence of foreign matters has a sensible, but not very serious
effect on the rate of distillation. Alcohol diminishes the proportion of
acid in the first portions of the distillate, but by the time ^-Jths has
distilled the proportion of acid in the receiver is the same as in the
first portions which come over are very weak, and that the strength of the distillate rises
regularly till the end of the operation. On the other hand, propionic, butyric, and valeric
acids come over chiefly at the commencement of the process.
*When two or more of these acids are present together in a liquid, each maintains its
own characteristics when the distillation is carried out as described. Hence, not merely
the nature, but the quantities of the acids present may be ascertained by calculation at
least in certain cases. Thus, suppose the numbers obtained for the " B " column by the
distillation of a certain liquid to have been as follows: 8'6, 8-7, 8'7, 8'7, 8-8, 8'7, 8-9,
9*1, 9*7, 10'3 per cent. These results may safely be presumed to be produced by a mix-
ture of acetic acid with either butyric or propionic acid. Assume the mixture to consist
of a equivalents of acetic and p equivalents of propionic acid ; then, by the table, we
have for the 1st fraction of 10 c.c.
8-6(a + p) = 5'9a + 10'5^
.'. p =l-2o.
Proceeding in the same way with the percentages of acid found in the succeeding frac-
tions of distillate, we obtain the following series of numbers: 1*1, I'O, I'O, I'O, I'O, I'O,
TO, I'O, I'l. Hence the amount of propionic acid is the same, or slightly in excess, in
equivalents, of the acetic. For various reasons, the inferences to be drawn from the first
and last fractions are the least trustworthy. But suppose the mixture were one of acetic
and butyric acids ; then,
S'6(a + 6) = 5'9a + 16-46
.'. 6 =3-2.
Proceeding similarly with the other fractions, we obtain the following series of num-
bers : 3-1, 3-0, 2-8, 2-5, 2-5, 2'2, 2-1, 1-6, 1-3. Thus we have ten estimations of the
butyric acid, in which its equivalent amount varies from 3'2 to 1'3 times the acetic acid
present. The variation in these determinations renders the assumption of the second acid
being butyric acid absurd. Hence, the two acids were acetic and propionic in about
equivalent proportions.
In the original paper M. Duclaux gives a number of tables which materially facilitate
calculation.
In applying the method to the examination of wines, Duclaux recommends the fol-
lowing mode of procedure :
275 c.c. (=25 X 11), or a multiple of this quantity are shaken, and a current of air
passed through the liquid, in order to remove carbon dioxide. The wine is then dis-
tilled till 250 c.c. have passed over, and the distillate, after again drawing air through it,
is titrated with standard lime water. An excess of the latter is then added, and the
liquid is evaporated to about 250 c.c. in order to volatilise the alcohol. A gram of glycerin
is then added, and sufficient tartaric acid to set all the volatile acids at liberty. The
calcium tartrate is allowed to crystallise, and is then separated from the liquor, the volume
of which is again brought to 275 c.c. About 1 grin, of tartaric acid is now added, and
the liquid distilled till 250 c.c. have passed over, when the whole distillate is again
titrated. The lime water now required will bear the same proportion to that used for the
first titration, that the amount of volatile acid indicated by the first titratiun bears to the
total quantity present in the wine. The titrated liquid is now brought to 165 c.c., and
150 c.c. distilled over, after adding an amount of tartaric acid exactly equivalent to the
492 ORGANIC ACIDS.
absence of alcohol. Glycerin diminishes slightly the proportion of
acid volatilised, doubtless owing to the formation of a glycylic ether,
but the effect can be destroyed by adding tartaric acid to the contents
of the retort.
lime water used in the titration. 50 c.c. of the distillate are titrated, while the remainder
is diluted to 110 c.c., and 100 c.c. distilled over each fraction of 10 c.c. being separately
titrated. The numbers thus obtained give the necessary data for ascertaining the nature
and amount of the volatile acids present.
The following example indicates the mode of calculation : 275 c.c. of wine were taken
and distilled to A. 250 c.c. of distillate required 316 c.c. of lime water. On adding tar-
taric acid and distilling over TT> the distillate required 263 c.c. of lime water. Hence,
83*3 per cent, of the total acid passed over on distilling to T*T, and, assuming the same
proportion in the first distillation, the free acid in the original wine would have required
-^P of 316 = 379 c.c. of lime water for its neutralisation. On referring to the table on
page 490, it will be seen that, when a liquid containing acetic acid is distilled to -fa of its
bulk, about 80 per cent, of the acid passes over, while 93 per cent, of the propionic acid
distils under similar circumstances. On repeating the process, 80 and 93 per cent, of
these amounts will be respectively obtained. Hence, the third and last distillate will
&0 ^ SO ^ ^0 ^1 *)
contain 100x100x100 = Tooo = 51 ' 2 per cent ' of the total acetic acid P resent in the
Q3 X Q^l V Q^
wine, and - = 80'4 per cent, of the total propionic acid. Thus if the titra-
100 X 100 /\ 100
tion of the fractions obtained in the third distillation showed acetic and propionic acid to
be present in equivalent proportions, the equivalent amounts of these acids present in the
original wine would be as 804 to 512, or as 100 equivalents of acetic to 63*7 of pro-
pionic acid. Thus of 379 c.c. of lime water, required by the volatile acids in 275 c.c. of
100
the original wine, ~ of that quantity, or 231 c.c. were neutralised by acetic acid, and
the remaining 148 c.c. by propionic acid. From the strength of the lime water and the
atomic weights of acetic and propionic acids, the actual amounts of fatty acids present can
be readily calculated.
By this method, Duclaux proved the presence of valeric acid in perspiration and of
butyric acid in bread. He also found that the presence of butyric acid was characteristic
of wine suffering from "bitterness," and propionic acid of wine in which the fermentation
had been " pushed " too far.
The largest quantity of valeric acid found in wine by Duclaux was "006 grin, per litre.
For its discovery, 7 or 8 litres must be distilled as already described, the distillate neutral-
ised with lime, and then ?V of the sulphuric acid necessary to decompose the calcium salts
added. On redistillation, the whole of the valeric acid passes over, while 39 equivalents
out of every forty of the fatty acids present remain in the retort.
In Duclaux's process, standard baryta water might probably be advantageously substi-
tuted for the lime water, and standard sulphuric acid for the tartaric acid recommended
(except where about 1 grin, of tartaric acid is directed to be added to represent the acidity
of the original wine). This modification would allow the sulphate of barium to be filtered
off immediately instead of having to wait for the calcium tartrate to crystallise. In the
last titrations, the use of baryta water would cause the acids to be obtained in the form of
barium salts, which could be dried at 130 C., weighed, and converted into BaS04, as
described on p. 489. A very useful check would thus be obtained.
ORGANIC ACIDS. 493
The writer has no personal experience of Duclaux's process, beyond
an attempt to apply it to the assay of commercial " acetate of lime."
The salt was dissolved in water, oxalic acid added, and the calcium
oxalate filtered off. On distilling the filtrate to ^y, a tolerably con-
stant proportion of acetic acid passed over, but it was considerably
below 79'8 per cent, of the total quantity present in the sample.
Formic Acid.
Formic acid is contained in the liquid obtained by distilling ants
with water. The stings of bees and wasps, as also of stinging nettles
and hairy caterpillars, owe their irritating power to formic acid. It is
usually prepared by distilling oxalic acid with glycerin. It also results
from the decomposition of chloroform or chloral by an alkali, by the
reaction of carbon monoxide and caustic alkalies, and by the reaction of
cyanogen gas or cyanides with water, besides numerous other reactions.
Formic acid is a colorless volatile liquid, of extremely irritating
pungent odor. Absolute formic acid has a density of 1-2211 at 20
C., and boils at 100. Formic acid has a penetrating smell and
purely acid taste. When concentrated, it produces intense irritation
on the skin.
In general properties, formic acid strongly resembles acetic acid, but
it is stronger in its chemical affinities, and more readily oxidised.
The formates mostly crystallise well and are all soluble in water.
Heated with concentrated sulphuric acid they do not blacken, but evolve
pure carbon monoxide, as an inflammable gas burning with a blue
flame. A neutral solution of a formate of alkali-metal gives the follow-
ing reactions :
Nitrate of silver gives, in concentrated solutions, white crystalline
argentic formate, AgCHO 2 , which darkens on standing, and is reduced
to metallic silver when warmed. If the liquid be too dilute to allow
of a precipitate being formed, the reduction to metallic silver still
occurs on heating, a mirror being frequently formed on the sides of the
tube. In presence of ammonia the reduction is retarded or prevented.
Mercuric chloride is reduced on heating, with production of white
mercurous chloride, or grey metallic mercury, according to the propor-
tion of formate present. Acetates do not give this reaction, but ace-
tates and chlorides of alkali-metals retard or prevent the reduction.
The reduction of formate of mercury on heating may be applied to the
estimation of formic acid, and its separation from acetic acid may be
494 ORGANIC ACIDS.
approximately effected by boiling the solution of the free acids with
yellow mercuric oxide until effervescence ceases. If formic acid only
be present, the filtered liquid will be free from mercury. With a mix-
ture of the two acids, the amount of mercury which passes into solution
is equivalent to the acetic acid present. If the total acid present orig-
inally be determined by standard alkali or other means, the quantity
of formic acid may be found. Or, in presence of other acids forming
soluble mercuric salts, the excess of mercuric oxide may be dissolved
by dilute hydrochloric acid, and the residual metallic mercury weighed
and calculated to formic acid. HgO -f CH 2 O 2 = Hg -f CO 2 -f H 2 O.
Chlorine, bromine, chromic acid, permanganate, and other powerful
oxidising agents convert formic acid more or less readily into carbonic
acid.
When heated gently with alcohol and sulphuric acid, formates
generate ethyl formate, C 2 H 5 ,CHO 2 , having a fragrant odor of peach -
kernels, and boiling, when purified, at 54'4 C.
With ferric chloride, formates react similarly to acetates.
At a gentle heat, strong sulphuric acid evolves carbon monoxide
from formic acid or a formate. Strong alkalies produce an oxalate.
Formates of lead and magnesium are insoluble in alcohol, while the
corresponding acetates are soluble. Hence, acetic may be separated
from formic acid by saturating the free acids with a slight excess of
calcined magnesia or carbonate of lead, filtering, evaporating the fil-
trate to a small bulk, and adding a large proportion of alcohol.
Formate of magnesium or lead is precipitated, while the corresponding
acetate remains in solution. The process may be varied by precipitat-
ing the alcoholic solution of the acids with an alcoholic solution of
lead acetate, and washing the resultant precipitate with alcohol.
In addition to the methods already indicated, formic acid may be
determined by titration with standard alkali, or by decomposition in a
carbonic acid apparatus by sulphuric acid and bichromate of potas-
sium, the amount of formic acid present being deduced from the weight
of dry CO 2 evolved. CH 2 O 2 + O = H 2 O + CO 2 .
Propionic Acid.
p TT o RPTTO C 3 H 5 O \ r\ f C 2 H 5
M,C 3 M 5 2 - H JC -| COOH
This body, formerly called metacetonic acid, is of no commercial
importance, but its detection and separation from its homologues are
occasionally necessary.
Propionic acid is contained in crude oil of amber, in sour cocoanut
ORGANIC ACIDS. 495
milk, and in certain wines, especially when the fermentation has been
pushed too far. It is also produced by the fermentation of glycerin,
lactic acid, &c., and by a great variety of synthetical methods.
Propionic acid closely resembles acetic acid, but has an odor recall-
ing at once those of acetic and butyric acids. It boils at 140, and
has a density of '996 at 19.
The statements respecting the solubility of propionic acid are very
conflicting. According to some observers it is not miscible in all pro-
portions with water, but floats as an oil on its saturated aqueous solu-
tion ; according to others, it is not separated from its aqueous solution
by a saturated solution of calcium chloride. Both these statements
are probably incorrect.
The propionates closely resemble the acetates ; they are all soluble
in water.
The following method is described by Linnemann for the separation
of propionic acid from its lower homologues : The free acids are
evaporated to dryness with excess of litharge. The residue is then
treated with cold water, and the liquid filtered. Basic propionate of
lead dissolves, while any acrylate remains insoluble, together with
most of the acetate and formate. The solution is boiled and stirred
quickly, when the propionate separates suddenly and almost completely
as a crystalline precipitate, soluble in cold water, but which may be
filtered at a boiling heat from the remaining acetate and formate.
The propionic acid of fermentation is said not to exhibit this reaction.
For other methods of detecting and separating propionic acid, see
Duclaux's process, p. 490.
Butyric Acid.
C 4 H A = H,C 4 H 7 O 2 = C O.
Two isomeric modifications of this acid are known, differing slightly
in their physical properties.
NORMAL BUTYRIC ACID, CsHyCOOH, occurs ready-formed in
various natural products, and is frequently produced by the decompo-
sition of animal and vegetable matter. It exists as a glyceride in
butter and cod-liver oil and results from the butyric fermentation of
sugar.
Normal butyric acid is a colorless mobile liquid, having a smell at
once resembling acetic acid and rancid butter. It is soluble in water,
alcohol, and ether in all proportions, but is not soluble in concentrated
solution of calcium chloride or common salt ; hence, it may be sepa-
496 ORGANIC ACIDS.
rated from its aqueous solution by saturating the liquid with calcium
chloride, and then agitating with ether. From the ethereal layer it
may be recovered by spontaneous evaporation, or, as a salt, by agita-
tion with excess of solution of potash or soda.
For other methods of approximately separating butyric from acetic
and valeric acids see p. 486.
ISO-BUTYRIC ACID, CH(CH 8 ) 2 'COOH, occurs in carob beans, and
among the acids of castor oil. It closely resembles the normal acid
in its general properties, but has a lower boiling point and density.
Its smell is less offensive than that of the normal acid obtained by the
decomposition of butter, or by the butyric fermentation of sugar. It
requires three parts of cold water for solution, and is easily oxidised
to acetic acid and carbon dioxide when heated with chromic acid
mixture (p. 185).
All the metallic butyrates are soluble in water. Butyrate of lead is
a heavy liquid, which solidifies when cooled.
Butyrate of copper forms bluish-green monoclinic crystals, which are
sparingly soluble in water. The formation of cupric butyrate may be
employed to distinguish butyric from valeric acid.
The iso-butyrates closely resemble the butyrates, except in the cases
of the calcium and silver salts. Normal butyrate of calcium is very
soluble in cold water, but separates as a crystalline precipitate on heat-
ing the strong solution to 70. The iso-butyrate is more soluble in hot
water, and separates on cooling as a crystalline magma.
The most delicate and characteristic reaction of butyric acid or a
butyrate is the formation of ethyl butyrate on heating with alcohol and
strong sulphuric acid. The ether has a most fragrant odor of pine-
apple, and boils at 120 C.
Pentoic Acid. Valeric Acid.
C 5 H 10 2 - H,C 5 H 9 2 = C O.
Several acids of this formula are known, namely,
a. PRIMARY NORMAL PENTOIC ACID, CH 3 -(CH 2 )3'COOH, boiling
at 185 C., and having a density of '9415 at 20, is obtained, together
with paraffins and normal homologous acids, when fats are distilled
with superheated steam ; also by the action of alkalies on normal
butyl cyanide. The smell resembles that of normal butyric acid. The
calcium salt has a fatty lustre and crystallises in scales, more soluble in
cold than in hot water.
0. PRIMARY ISO-PENTOIC ACID, or ordinary Valeric Acid,
ORGANIC ACIDS. 497
CH(CH 3 ) 2 'CH 2 'COOH, occurs in dolphin and porpoise oils, in sweat,
and in various other products and secretions of animals. It exists
ready-formed in valerian-root, and many plants of the natural order
Composite. It may be obtained by the oxidation of the iso-amyl alco-
hol of fusel oil; or by the action of alkalies on iso-butyl cyanide.
Iso-valeric acid is frequently called simply " valeric acid," though the
name valerianic acid would serve better to indicate its origin, and
thereby distinguish it from other modifications of pentoic acid.
Valerianic Acid is an optically inactive and colorless oily liquid,
having an unpleasant smell resembling old cheese. Its taste is sharp
and acid, and it blanches the tongue. Valerianic acid dissolves in
about 30 parts of cold water, and is readily soluble in alcohol, ether,
chloroform, or strong acetic acid. It is almost wholly removed from
its aqueous solution by saturating the liquid with common salt or cal-
cium chloride.
Absolute valerianic acid has a density of *937 at 15, and boils at
175 C. It forms a'hydrate of the composition C 5 H 10 O 2 ,H 2 O, having a
density of '950 and boiling at 165, but it is gradually dehydrated by
distillation, the weaker acid coming off first. On the other hand, on
distilling dilute aqueous valerianic acid, the first portions of the distil-
late are most strongly acid.
f. SECONDARY PENTOIC ACID. Active Valeric Acid. Methyl-
ethyl-acetic acid, CH(CH 3 )(C 2 H 5 yCOOH. This acid resembles ordi-
nary valeric acid, but boils at 172 C. (3 degrees lower), and is easily
oxidised by chromic acid mixture into acetic acid, carbon dioxide, and
water. It is obtained by the oxidation of the levo-rotatory amyl alco-
hol of fusel oil, but the acid itself is dextro-rotatory. It also differs
from ordinary valeric acid in forming a very soluble barium salt, the
solution of which dries up to an amorphous varnish.
d. TERTIARY PENTOIC ACID, or Triraethyl-acetic Acid, C(CH 3 ) 3 -
COOH, is solid at ordinary temperatures, melting at 35'4 to a liquid
of '905 specific gravity at 50, and boiling at 163'8.
REACTIONS OF Iso- VALERIC ACID AND ISO-VALERATES.
When iso-valeric acid or an iso-valerate is distilled with sulphuric
acid and a little amylic alcohol, a fragrant ethereal liquid smelling of
apples is obtained ; this is arayl iso-valerate.
Iso-valerates are decomposed by acetic acid with formation of iso-
valeric acid and an acetate; they are also decomposed by tartaric,
citric, and malic acid. Some observers state that they are decomposed
by butyric acid, and others deny this.
32
498 ORGANIC ACIDS.
Metallic iso-valerates are mostly soluble in water. The oxy-valerates
of iron and bismuth are insoluble. Argentic and mercurous valerates
are but slightly soluble, and valerate of aluminium is insoluble.
Neither valerianic nor butyric acid gives a precipitate with an aqueous
solution of zinc acetate. This fact distinguishes them from eaproic acid,
which throws down sparingly soluble zinc caproate as a white crystal-
line precipitate.
Iso-valerate of barium crystallises easily in triclinic scales or tables
(in distinction from active valeric acid), is soluble in two parts of cold
water, and sparingly soluble in alcohol. Caprylate of barium requires
120 parts of cold water for solution, and is nearly insoluble in alcohol.
Caprate of barium is almost insoluble in water.
When concentrated valerianic acid is agitated with solution of cupric
acetate, anhydrous cupric iso-valerate separates in oily droplets, which,
in from five to twenty minutes, crystallise as greenish-blue monoclinic
prisms or octohedra of hydrated cupric iso-valerate, moderately soluble
in water and alcohol. The salt is less soluble in hot water than in
cold, and hence the saturated solution becomes turbid when heated.
This reaction distinguishes valeric from butyric acid, which forms with
a moderately strong solution of cupric acetate an immediate precipitate
or turbidity of cupric butyrate, of bluish-green color, and crystallising
in small monoclinic prisms. In using this test for assaying valerates,
the acid must first be obtained free by distilling the salt with a moder-
ate excess of sulphuric acid.
Valeric acid may be separated from most organic acids by convert-
ing it into the soluble valerate of lead. Acetic acid may be detected
by neutralising any free acid with soda, and precipitating in the cold
with excess of ferric chloride. In presence of acetic or formic acid,
the filtered liquid will have a red color. The insolubility of aluminium
valerate might probably tie employed for the separation of valeric from
acetic or formic acid.
For other methods of approximately determining valeric acid and
separating it from its homologues, see p. 485 et seq.
COMMERCIAL VALERIANIC ACID AND VALERIANATES.
The presence of alcohol, acetic acid, butyric acid, valerates, &c., in
commercial valerianic acid is indicated by the increased solubility of
the sample, which should not be greater than 1 of the hydrated acid
in 26 parts by weight of water. If the sample require more than 30
parts of cold water for solution, the presence of higher homologues, or
valeral (valeric aldehyde, C 5 H 10 O) is indicated. Acetic acid may be
ORGANIC ACIDS. 499
recognised as indicated ^n p. 498. By neutralising the sample with
an alkali, any amylic alcohol, valeric aldehyde, or neutral ethers will be
left undissolved, as a turbidity or oily layer, and the amount may be
estimated by measurement, or the mixture may be shaken with ether,
and the ethereal liquid evaporated spontaneously. The solubility of
valeric acid in a mixture of equal volumes of glacial acetic acid and
water may be employed to separate it from valeral and ethers, but not
from amylic alcohol. 1 The presence of butyric acid will be indicated
by fractional distillation, and by the composition of the salt obtained
by saturating the acid with carbonate of barium ; also by the reaction
with cupric acetate.
Valeric acid should also be tested for non-volatile impurities, sul-
phuric acid, and hydrochloric acid.
Valerianates have been somewhat extensively used in medicine,
especially the sodium, iron, zinc, and bismuth salts. They are all
more or less liable to sophistication, which in some instances is of a
very gross kind. Thus, samples of " valerianate of zinc " are occasion-
ally composed of the sulphate or acetate, and others have been met
with which consisted of butyrate of zinc impregnated with oil of vale-
rian. Valerianate of zinc is also liable to adulteration with tartaric
and citric acids, boric acid, and salts of the light metals. Similarly,
tartrate or citrate of iron flavored with valerian has been substituted
for the valerate of iron, and the sulphate of quinine for the valerate.
" Valerianate of ammonium " has been prepared by saturating chloride
of calcium with oil of valerian, and many similar frauds have been
occasionally practised.
Most of the above adulterations may be readily detected. The substi-
tution of butyrate of zinc for the valerate is best recognised by distil-
ling the salt with sulphuric acid diluted with an equal measure of water,
and then applying the cupric acetate and other tests to the distillate.
The most satisfactory ready test for valerates is to weigh or measure
the layer of free acid which separates on decomposing the solid salt
with sulphuric acid diluted with an equal measure of a saturated
aqueous solution of sulphate of zinc.
[The chemistry of lactic acid and important lactates is described in Vol. Ill,
pt. iii, p. 407 et seq.']
1 Valeric acid may be purified by dissolving in two equivalents of the crude acid one of
neutral valerate of sodium, assisting the solution by a gentle heat. On standing in a cool
place, crystals of an acid valerate of sodium are deposited, and on distilling this with sul-
phuric acid, and collecting the liquid which passes over between 125 and 138, pure
valeric acid is obtained. Lescseur.
500 ORGANIC ACIDS.
OXALIC ACID.
French Acide Oxalique; Acide d'oseille.
German Oxalsaure ; Kleesaure.
TT
Oxalic acid bears the same relation to glycol, C 2 H 4 (OH) 2 , that
acetic acid does to ethylic alcohol.
Oxalic acid occurs ready formed in various plants notably in the
Oxalis acetosella and in rhubarb. It is a frequent product of the
decomposition of animal matters, occurring largely in diseased and
occasionally in healthy urine, in certain urinary calculi, &c. It is a
product of the action of nitric acid, alkaline permanganate, and other
oxidising agents on various kinds of organic matter.
An interesting synthesis of oxalic acid, which may attain practical
importance, is the reaction of carbon monoxide on caustic alkali, with
production of a formate, and conversion of the latter into oxalate by
increasing the temperature.
In commerce, oxalic acid is always produced by one of two reac-
tions. The first is the oxidation of starch or sugar by moderately
concentrated nitric acid, with subsequent separation and purification
of the resultant oxalic acid by crystallisation, &c. This well-known
and simple method is now replaced in practice by the curious "saw-
dust process." When starch, sawdust, straw, bran, or other vegetable
matter is heated with caustic potash, an oxalate is formed. Wheat-
bran yields 150 per cent, of its weight of crystallised oxalic acid.
Soda cannot be advantageously substituted for the potash, at least
entirely, but with a mixture of the two alkalies very satisfactory
results are obtained. The product of the action is treated with water,
and the solution treated with slaked lime. The alkalies are recovered
in a caustic state, and the calcium oxalate is separated and decomposed
with sulphuric acid, the resultant oxalic acid being separated by
evaporation and crystallisation.
Oxalic acid usually occurs crystallised with two atoms of water,
C 2 H 2 O 4 + 2H 2 O, the crystals being monoclinic prisms having a density
of 1'641 at 4 C. Exposed to dry air, or in vacuo over oil of vitriol,
the crystals lose water, become opaque, and form a white powder. The
acid may also be obtained anhydrous by exposure to a gentle heat (60
to 70 C.). If at once heated to 100 C. the crystals melt, and it is
then much more difficult to drive off" the water. By dissolving
ORGANIC ACIDS. 501
ordinary oxalic acid in 12 parts of warm concentrated sulphuric acid,
and allowing the solution to stand for several days, the anhydrous acid,
H.jC 2 O 4 , is deposited in transparent crystals, which on exposure to air
absorb 2 Aq. and fall to powder.
Saturated solutions of oxalic acid lose acid at 100 C., and the
anhydrous acid may be readily sublimed. This furnishes a convenient
mode of obtaining the pure acid for analytical purposes. The acid
should previously be rendered anhydrous by heating to 60 or 70 C.,
and the temperature of the retort must be kept as constantly as possi-
ble at 157 C. If allowed to rise to 160 C., much loss of acid occurs,
and an inferior product is obtained, containing water and formic acid.
The passage of a current of dry air greatly facilitates the sub-
limation. 1
Oxalic acid is colorless and odorless, and completely volatile by heat
without charring.
100 parts of water dissolve 8 parts of crystallised oxalic acid at
10 C. and 345 parts at 90 C.
The solution has an intensely sour taste, reddens litmus strongly, and
in many respects acts like a mineral acid. It is very poisonous. It
decomposes carbonates, phosphates, chromates, and various other salts,
including fluorspar. (Powdered oxalic acid completely decomposes
common salt or calcium chloride when the mixture is heated.) Prus-
sian blue dissolves in oxalic acid to a clear blue liquid, sometimes
employed as a blue ink. Solutions of oxalic acid are permanent in
the dark, but when exposed to light the acid is rapidly decomposed.
Crystallised oxalic acid dissolves readily in cold and still more
readily in boiling alcohol. It is but slightly soluble in ether, and is
insoluble in chloroform, benzene, or petroleum spirit.
Oxalic acid is not affected by boiling with moderately strong nitric
or hydrochloric acid. Cold sulphuric acid has no action on it; but
when oxalic acid is heated with concentrated sulphuric acid, phos-
phoric acid, or either of the chlorides of phosphorus, it splits up
thus : C 2 H 2 O 4 = CO -f CO 2 + H 2 O.
When heated with glycerin, oxalic acid yields carbonic acid at a
moderate heat, and formic acid at a higher temperature. This is the
method commonly employed for producing formic acid.
1 Another simple method of purifying oxalic acid is to dissolve it in boiling hydro-
chloric acid containing 10 to 15 per cent, of real HC1. The liquid is stirred well, and
then cooled quickly to get small crystals. These are washed with small quantities of cold
water till but little hydrochloric acid remains in them. They are then redissolved in
boiling water and recrystallised. The product so obtained is perfectly pure.
502 ORGANIC ACIDS.
Chlorine combines with dry oxalic acid to form a compound of the
formula C 2 H 2 O 4 ,C1 2 , which is split up by water into hydrochloric and
carbonic acids.
Dioxides of manganese and lead oxidise oxalic acid to carbonic
acid. Auric chloride and acid solutions of permanganates react simi-
larly. In presence of a large excess of alkali, oxalic acid is not oxid-
ised by permanganate ( Wanklyn).
KEACTIONS OF OXALIC ACID AND OXALATES.
An aqueous solution of oxalic acid presents the following analytical
characters :
On addition of lime water or solution of calcium acetate, a white
precipitate of calcium oxalate, CaC 2 O 4 -f- H 2 O, is formed. The precip-
itate is very insoluble in water, and not sensibly soluble in acetic or
other organic acids. It is readily soluble in dilute mineral acids. It
is decomposed by boiling with excess of carbonate of sodium solution,
with formation of insoluble calcium carbonate and soluble sodium
oxalate. On gentle ignition, calcium oxalate evolves carbon mon-
oxide, CO, and leaves calcium carbonate. No blackening occurs in
this reaction. Solutions of soluble oxalates give the same reaction as
oxalic acid with lime water or calcium acetate, and react with calcium
sulphate or chloride in addition. If previously neutralised by ammo-
nia, oxalic acid solutions are precipitated by the two latter reagents.
With solutions of barium, oxalic acid and oxalates react in a simi-
lar manner as with solutions of calcium, but the resultant barium
oxalate is not so insoluble in water or acetic acid as the calcium salt.
On addition of dilute sulphuric acid and manganese dioxide,
warm solutions of oxalic acid and oxalates produce effervescence,
owing to the formation of carbon dioxide gas, according to the reac-
tion H 2 C 2 O 4 -f- O = H 2 O -f- 2CO 2 . The gas may be proved to be car-
bon dioxide by its reaction with lime water.
In presence of dilute sulphuric acid, a warm solution of oxalic acid
rapidly decolorises potassium permanganate. From strong solutions,
the resultant carbon dioxide escapes with effervescence.
DETERMINATION OF OXALIC ACID.
Oxalic acid may be determined with considerable accuracy by either
of the following methods, the details of which may be found in most
works on quantitative analysis :
By precipitation as calcium oxalate. The solution should be hot
and dilute, and mineral acids must be absent, or previously neutralised
ORGANIC ACIDS. 503
by ammonia. In the absence of other acids forming insoluble or
nearly insoluble calcium salts (e.g., sulphates, tartrates, citrates, phos-
phates), the solution may be exactly neutralised by ammonia, and
calcium chloride added. Any phosphate may be separated by digest-
ing the precipitate with cold dilute acetic acid. In presence of sul-
phates, calcium sulphate should be employed as a precipitant. It is
frequently preferable to have the solution acid with acetic acid, or to
precipitate the acid solution with calcium acetate, so as to avoid the
co-precipitation of other calcium salts. Almost all calcium salts are
soluble in acetic acid, except the oxalate, racemate, and fluoride. Race-
mates may be previously removed by precipitation with potassium
acetate in presence of alcohol. The separation of oxalates and fluor-
ides does not occur in practice, but, if required, the oxalate can be
determined by titrating the precipitate with standard permanganate.
The precipitate of calcium oxalate, however produced, is to be well
washed and then treated in one of the following ways:
1. It is dried at 100 C., and weighed as CaC 2 O 4 .
2. It is ignited, moistened with carbonate of ammonium, again
gently ignited, and weighed as CaCO 3 .
3. It is moistened on the filter with strong sulphuric acid, and the
whole ignited again, moistened with sulphuric acid, reignited, and
finally weighed as CaSO 4 .
4. It is ignited thoroughly, and the resultant calcium oxide and
carbonate titrated with standard acid.
5. The filter is placed in a beaker together with water and dilute
sulphuric acid, and the liquid is titrated with standard permanganate.
Of these methods, the two last are perhaps the best, because they
are the least affected by any impurity in the precipitate. Process 5
aims at the direct estimation of the oxalate, and may be applied to a
precipitate containing phosphate, carbonate, or sulphate; but tar-
trate, racemate, and most organic salts must be absent from the pre-
cipitate.
By treatment with dilute sulphuric acid and manganese dioxide in
a carbonic acid apparatus. This process is conducted precisely as in
the valuation of a manganese ore, except that excess of manganese
dioxide is used instead of excess of the oxalate. 44 parts by weight
of CO 2 lost by the apparatus represent 63 of crystallised, or 45 of
anhydrous oxalic acid.
By titration with standard permanganate. The solution of the
oxalate must be free from other readily oxidisable bodies, and should
be warm, dilute, and pretty strongly acidulated with sulphuric acid.
504 ORGANIC ACIDS.
The permanganate is added gradually, with constant stirring, until the
liquid acquires a permanent pink tint. The permanganate is prefer-
ably standardised with pure oxalic acid. Decinormal permanganate,
containing 3162 grm. KMnO 4 to the litre, is a suitable strength.
Each cubic centimeter of this solution will oxidise '0063 grm. of crys-
tallised or *0045 grm. of anhydrous oxalic acid. The process can be
employed for titrating a precipitate of calcium oxalate.
Toxicological Examination for Oxalic Acid. Oxalic acid
and its solutions are violently poisonous. The same is true of the solu-
ble oxalates. If a very concentrated solution of free oxalic acid be
taken internally, an immediate burning pain in the stomach is
observed, together with cramps and drawing up of the legs, and vomit-
ing of dark and perhaps bloody coffee-colored matters. The patient
often complains that the throat feels as if tightly bound with a cord.
Bloody purging next occurs, the tongue becomes sore, and the mouth
swollen and usually white. Numbness and tingling of the legs, twitch-
ings of the face, convulsions and delirium will be more or less marked,
while the circulation becomes very depressed, and respiration slow and
spasmodic.
With weaker solutions, the above effects are less marked ; death may
be almost instantaneous, or may be postponed for a considerable time.
Half an ounce is an ordinary poisonous dose, but a much smaller
quantity has proved fatal.
The proper antidote for oxalic acid is whiting, chalk, or magnesia,
suspended in a small quantity of milk.
After death from poisoning by oxalic acid, the mouth, throat, and
gullet will usually be found shrivelled and easy of removal. The
stomach, which is frequently contracted, often contains an intensely
acid, brown, gelatinous liquid. The mucous membrane, if death be
rapid, may appear soft and pale, but if death be long delayed it is
usually partly blackened, other portions being intensely congested, the
surface peeling off and the coats underneath being gangrenous.
Throughout the whole body, except the stomach and gullet, the blood
is fluid. Occasional cases are on record in which morbid appearances
have been nearly or entirely absent.
In cases of poisoning by oxalic acid, supposing no antidote to have
been administered, the contents of the stomach will usually be intensely
acid. (Of course, moderate acidity is the normal condition.)
The urine should always be examined when poisoning by oxalic acid
is suspected. It should be allowed to stand in a conical glass, the clear
solution subsequently decanted, and the sediment examined under the
ORGANIC ACIDS. 505
microscope for octohedral crystals of calcium oxalate. These should
be found in abundance, and may also be identified by chemical tests.
THE TOXICOLOGICAL DETECTION OF OXALIC ACID may be effected
in the following manner: The contents of the stomach, if acid, are
digested with warm water and strained through muslin, or, if possible,
through paper. To the clarified liquid, excess of a solution of basic
lead acetate is added, which will throw down any oxalic acid, together
with coloring and other organic matter. The precipitate is washed
well, suspended in water, and decomposed by a current of sulphuretted
hydrogen. The liquid is again filtered, when the filtrate will probably
be sufficiently pure to admit of the application of the characteristic
tests for oxalic acid. Of these, the most satisfactory for toxicological
purposes are the production of crystals of the free acid, and the forma-
tion of a precipitate having the properties of calcium oxalate on
addition of calcium chloride and ammonia, or of calcium acetate
alone.
Soluble neutral oxalates can readily be detected by the above pro-
cess, but a modified method must be used if a compound of calcium or
magnesium has been administered as an antidote. In such a case, the
contents of the stomach should be boiled for an hour or two, without
previous filtration, with a strong solution of an alkaline carbonate.
The liquid is filtered from the residual carbonate of earthy metal,
acidulated with acetic acid, and then precipitated with acetate of lead
as above described.
In toxicological investigations it must not be forgotten that oxalates
occur naturally in various edible vegetables, especially in rhubarb and
sorrel. Hence, if the symptoms do not indicate poisoning by free
oxalic acid, a quantitative determination of the oxalate present may
be necessary before concluding that death has ensued through poison-
ing. Free oxalic acid may be extracted from animal matters by means
of alcohol, which does not dissolve oxalates ; but " salt of sorrel " con-
sists largely of tetra-oxalate of potassium, which is decomposed by
alcohol into free oxalic acid and insoluble di-oxalate (KH 3 (C 2 O4). 2
KHC 2 O 4 + H 2 C 2 O 4 ).
In cases of poisoning by free oxalic acid, the acid extracted from the
stomach and intestines is chiefly uncombined, but that obtained from
the liver, kidneys, heart, and urine is wholly in combination.
Commercial Oxalic Acid is not liable to intentional adulteration ;
nevertheless, various impurities are frequently present, owing to care-
less manufacture or imperfect purification.
ORGANIC MATTERS other than oxalic acid are recognised by the
506 ORGANIC ACIDS.
charring or darkening of the sample when heated, or on warming with
concentrated sulphuric acid.
FIXED MINERAL IMPURITIES are left as a residue on igniting the
sample in the air. If the ignited residue effervesce on addition of dilute
acid, an acid oxalate is present in the sample. Very sensible quantities
of lead and other heavy metals are sometimes met with. 1 Sulphuric
Acid and Acid Sulphates are sometimes present in oxalic acid in con-
siderable quantity. The solution of such samples gives a white precipi-
tate of BaSO 4 on addition of barium chloride. The same impurities
are very common in commercial ammonium oxalate.
Oxalates. These salts require but little special description. The
alkali-metals form three classes of oxalates, the potassium salts having
the formulae K 2 C 2 O 4 ,H 2 O ; KHC 2 O 4 ,H 2 O ; and KH 3 (C 2 O 4 ) 2 ,2H 2 O. The
acid salts are the least soluble. The oxalates of most other metals are
insoluble, or nearly insoluble, in water. This is true of the oxalates of
barium, strontium, calcium, copper, magnesium, manganese, cobalt,
nickel, zinc, lead, silver, &c. The first four of these retain 1 atom of
water on drying at 100 C. The remainder retain 2 atoms, with the
exception of the -lead and silver salts, which are anhydrous. Ferrous
oxalate is but sparingly soluble, but ferric oxalate is readily so, at
least in presence of free oxalic acid ; hence the use of oxalic acid for
removing ink-stains and dissolving Prussian blue. All the insoluble
oxalates are soluble in dilute nitric acid, but they are generally insol-
uble in acetic acid. The determination of the oxalic acid may be
readily effected by the methods described on p. 502.
On ignition, oxalates of the metals of the alkalies and alkaline-
earths evolve carbon monoxide gas, and leave the corresponding car-
bonates. These may sometimes be further decomposed if the tempera-
ture be excessive (CaC 2 O 4 = CaO -f CO -f CO 2 ). Oxalates of the
heavy metals, when heated to redness in a close vessel, usually leave
the free metal and evolve carbon dioxide gas (NiC 2 O 4 = Ni + 2CO 2 ).
This reaction occurs even at 100 C. in the case of gold ; hence, gold
is reduced from its solutions by boiling with an oxalate.
Pure oxalates do not char on ignition.
SUCCINIC ACID.
French Acide Succinique. German Bernsteinsaure.
C ( H 8 0, = HC,H.O, = (C 'H; 2) " } * = (C.H,)" { caOH.
i In a sample of oxalic acid sold as specially purified for analytical purposes, the writer
found as much as 6'3 per cent, of oxide of lead.
ORGANIC ACIDS. 507
Succinic acid occurs naturally in amber and in certain lignites ; is
produced during the alcoholic fermentation of sugar ; and by the fer-
mentation of malic acid and many other substances, especially under
the influence of putrefying casein. Succinic acid is also produced by
the action of nitric acid on the fatty acids and their glycerides, and it
exists ready-formed in several plants.
Succinic acid may be obtained by the dry distillation of amber the
watery distillate being filtered while hot to separate oil, when crystals
of succinic acid are deposited on cooling, and may be purified by boil-
ing with nitric acid, followed by recrystallisation from water.
Succinic acid bears the same relation to butylenic alcohol that oxalic
acid does to ethylenic alcohol (glycol), and may be produced from
butylenic alcohol by oxidation. It may also be obtained by the deox-
idation of tartaric or malic acid, which contain respectively two and
one atom more of oxygen than does succinic acid.
Succinic acid crystallises in colorless, oblique rhombic prisms or
plates. When heated to 130 C. it emits suffocating fumes, and at
180 melts. When the heat is increased to 235 C. the acid boils and
sublimes as succinic anhydride, C 4 H 4 O 3 , which melts at 120 C. When
heated strongly in the air, succinic acid burns with a blue smokeless
flame.
Succinic acid is soluble in about 18 parts of cold and 0'8 boiling
water. It dissolves readily in alcohol and sparingly in ether, but is
insoluble in chloroform, benzene, petroleum spirit, turpentine, or
carbon disulphide. Nitric acid, chlorine, and chromic acid have no
action on succinic acid, and it is soluble without change in strong sul-
phuric acid. Permanganate has no action on a cold acid solution, but
hot permanganate in presence of free alkali produces oxalic acid.
REACTIONS OF SUCCINIC ACID. In its analytical characters suc-
cinic acid somewhat resembles benzoic acid, but differs from it in not
being precipitated from a strong solution of its salts by hydrochloric
acid; in being precipitated by ammoniacal chloride of barium even
from a dilute solution ; and by being insoluble in chloroform, and there-
fore not removable from an acid solution by agitation with that liquid.
Magnesium benzoate is soluble in alcohol, but the succinate is in-
soluble.
Ferric chloride, if first treated with as much dilute ammonia as it
will bear without precipitation, precipitates from neutral solutions of
soluble succinates bulky cinnamon-brown basic ferric succinate, some
free succinic acid being simultaneously produced, and the solution
acquiring an acid reaction. Benzoates, under similar circumstances,
508 ORGANIC ACIDS.
gives a flesh-colored precipitate, and cinnamates a yellow. The pre-
cipitate may be filtered off, washed, and decomposed by boiling with
excess of dilute ammonia. The filtered liquid, if mixed with barium
chloride and an equal bulk of alcohol, gives a white precipitate of
barium succinate. By the above combination of reactions, succinic
acid may be readily identified and separated from other organic acids.
The process might possibly be made quantitative. For such a pur-
pose, sodium acetate should be added to the liquid containing the iron
precipitate, and the whole boiled, the precipitate produced being first
boiled and then washed with dilute ammonia, the ammoniacal liquid
being then concentrated and precipitated by alcohol and chloride of
barium. Neutral succinates of alkali-metals may also be precipitated
pretty completely by adding barium chloride to the boiling solution.
For the determination of the succinic acid in wine, I. Maeagno rec-
ommends the following process : To 1 litre of the sample add sufficient
albumin or raw hide to precipitate all the tannin. The filtered liquid
is concentrated and treated with hydrated oxide of lead till the color
is entirely removed. The precipitate is boiled for a long time with a
10 per cent, solution of ammonium nitrate, and the liquid filtered.
The filtrate is treated with sulphuretted hydrogen, the precipitate
filtered off, the filtrate concentrated to 100 c.c., and exactly neutral-
ised with ammonia. Perfectly neutral ferric chloride is then added,
the precipitate well washed, ignited, and the residual Fe 3 O 3 calculated
to succinic acid by multiplying the weight found by the factor 1*978.
R. Kayser concentrates 200 c.c. of the wine to one-half, adds lime-
water till alkaline, filters from the precipitated calcium phosphate and
tartrate, and passes carbonic acid through the filtrate. The liquid is
boiled, filtered, and the filtrate precipitated by neutral ferric chloride.
The precipitate is washed with alcohol of *890 specific gravity, and
ignited to ferric oxide as before.
Schmitt and Hiepe consider the above process of doubtful accuracy
and recommend the one described on p. 117. Pasteur's method of de-
termining the succinic acid in fermented liquids is described in the
footnote on p. 109.
Commercial Succinic Acid has usually more or less of a brown
color, and smells somewhat of the empyreumatic oil of amber, which
impurity may be removed by agitation with petroleum ether. A fac-
titious succinic acid has been prepared by adding a little oil of amber
to tartaric acid, sal-ammoniac, or acid sulphate of potassium.
INORGANIC IMPURITIES and adulterants will be left on igniting the
substance. Cream of tartar leaves potassium carbonate on ignition ;
ORGANIC ACIDS. 509
it has been found in succinic acid to the extent of 50 per cent.
Barium sulphate may be recognised by its insolubility and other char-
acters; and boric acid by the reddish-brown color imparted to turmeric
paper, when the ash is acidulated with hydrochloric acid and the solu-
tion evaporated in contact with it. Heavy metals may be recognised
by the usual tests.
FOREIGN ORGANIC ACIDS may be detected by their special reac-
tions. Thus oxalic acid will be precipitated on adding calcium acetate
(or a mixture of calcium chloride and ammonium acetate) to the
aqueous solution of the sample; tartaric acid by potassium acetate and
alcohol ; citric acid by the precipitate formed on adding excess of lime-
water and boiling ; and benzoic acid by its solubility in carbon disul-
phide or warm petroleum spirit, and by its separation on treating the
precipitate produced in the neutralised liquid by ferric chloride with
hydrochloric acid.
Ammonium Chloride may be recognised by the tests for ammonium
salts and chlorides.
Sugar and various other impurities cause charring on warming the
substance with sulphuric acid.
A useful method of examining succinic acid is to dissolve 1 grm. of
the sample in 15 c.c. of hot rectified spirit, in which it should be com-
pletely soluble. When cold, one-half the solution is mixed with an
equal measure of chloroform, and the other with an equal measure of
ammonia. Complete admixture should occur in both cases. If the
result of the test be satisfactory, and the sample leave no sensible
quantity of ash, and does not notably darken with strong sulphuric
acid, the substance is free from admixture.
MALIC ACID.
Hydroxysuccinic Acid.
f CO.OH
CHO-HCHO -C C * H 43)" 1 n I CH.OH
\^ 4 rl 6 U5 12,^4*14^5 JJ f O 2 S CJJ
t CO.OH.
Malic acid is contained in apples, pears, and most fruits used for
domestic purposes. It is usually prepared from rhubarb stalks or
mountain-ash berries.
Malic acid crystallises in groups of four- or six-sided prisms, which
are colorless and odorless, and readily fusible. Malic acid is deliques-
cent and readily soluble in water, alcohol, and ether. The aqueous
solution has an agreeable acid taste, and becomes mouldy on keeping.
510 ORGANIC ACIDS.
In contact with ferments, especially putrid cheese, the solution of
malic acid yields succinic acid, C 4 H 6 O 4 , and acetic acid, C 2 H 4 O 2 .
Sometimes butyric acid is produced.
When heated in a small retort to about 180 C., free malic acid
melts and evolves vapors of maleic and fumaric acids, which crystallise
on the cooler parts of the retort and receiver. Fumaric acid, C 4 H 4 O 4 ,
forms slowly at 150 C., and mostly crystallises in the retort, in broad,
colorless, rhombic or hexagonal prisms, which vaporise without melt-
ing at about 200 C., and are soluble in 250 parts of cold water, and
easily in alcohol and ether. Maleic acid, C 4 H 4 O 4 , is the chief product
if the temperature be suddenly raised to 200 C. This body crystal-
lises in oblique rhomboidal prisms, which melt at 130, vaporise at
about 160 C., and are readily soluble in water and alcohol. The
behavior of malic acid on heating is of value owing to the few char-
acteristic tests for this acid.
Natural malic acid is levo-rotatory in dilute solutions, optically
inactive in a solution containing 34*24 per cent., and dextro-rotatory
in more concentrated liquids. Artificial malic acid is inactive, but is
said to be separable into two acids of opposite rotatory powers.
By the action of hydriodic acid, under pressure, malic acid is con-
verted into succinic acid. Nitric acid and alkaline solutions of per-
manganate oxidise malic acid. Concentrated sulphuric acid darkens
malic acid and malates very slowly on warming. When boiled with
dilute sulphuric acid and bichromate of potassium, malic acid evolves
an odor of ripe fruit.
None of the malates are quite insoluble in water, but few are soluble
in alcohol. Solution of calcium chloride does not precipitate malic
acid or malates in the cold (distinction from oxalic and tartari.c acids);
only in neutral and very concentrated solutions is a precipitate formed
on boiling. (Citrates are precipitated from neutral boiling solutions
by calcium chloride, unless the liquid be very dilute.) The addition
of alcohol after chloride of calcium produces a bulky, white precipi-
tate of calcium malate, CaC 4 H 4 O 5 , even in dilute neutral solutions.
Thus, if the liquid be filtered first cold (to remove oxalic and tartaric
acids), and then boiling hot (to remove citric acid), the malic acid can
be precipitated on addition of two volumes of alcohol. This precipi-
tate may contain calcium sulphate or succinate, but will be free from
formate, 1 acetate, benzoate, &c. On boiling the precipitate with a
moderate quantity of water, the malate will be dissolved, and tannate
and sulphate left almost wholly behind. The precipitate produced by
1 If more than two volumes of alcohol be added, calcium formate may be precipitated.
ORGANIC ACIDS. 511
calcium chloride and alcohol may also be tested for malic acid (after
drying it' to get rid of all trace of alcohol) by decomposing it with dilute
sulphuric acid, and boiling the filtered liquid with a small quantity of
potassium anhydrochromate (dichromate). If the liquid remain
yellow, succinic acid alone is likely to be present ; but if a green color
be produced without any odor being developed, citric acid is probably
present either with or without succinic acid. If the liquid acquire a
green color, and evolve an odor of ripe fruit, malic acid is present, and
possibly either or both succinic and citric acid in addition.
Solution of acetate of lead precipitates malic acid, more perfectly
after neutralisation with ammonia, as a white (and frequently crystal-
line) precipitate of lead malate, PbC 4 H 4 O 5 , which, on boiling for a few
minutes, melts under the liquid to a transparent, waxy, semi-solid.
This characteristic reaction is obscured by the presence of other
organic acids. The precipitate is very sparingly soluble in cold
water, somewhat soluble in hot water* Malate of lead is soluble in
strong ammonia, but is not readily dissolved by a slight excess. (Dis-
tinction from tartrate and citrate.) Malate of lead dissolves in
ammonium acetate, and on mixing the liquid with two volumes of
alcohol is reprecipitated. (Lead succinate remains in solution.)
The precipitate of lead malate may be washed with a mixture of 2
measures of alcohol and 1 of water.
If the precipitate of malate of lead be treated with excess of
ammonia, dried on the water-bath, moistened and triturated with
alcoholic ammonia, and then treated with absolute alcohol, only
malate of ammonium dissolves; ammonium citrate, tartrate, oxalate,
&c., being insoluble in absolute alcohol. Malic acid may be separated
from other organic acids in solution by adding ammonia in slight
excess, and then 8 or 9 volumes of strong alcohol, which precipitates
all but the malate of ammonium. The method may be conveniently
applied to the solution of the free acids obtained by suspending the
lead salts in water and passing sulphuretted hydrogen through the
liquid.
If the alcoholic solution of ammonium malate be precipitated by
lead acetate, and the malate of lead obtained filtered off, washed with
alcohol, dried at 100 C. and weighed, the weight obtained, multiplied
by 0*3953, gives the quantity of malic acid present.
For the determination of malic acid in wine, 100 c.c. should be
precipitated with a slight excess of lime water; the filtrate is con-
centrated to one-half its bulk, and absolute alcohol added in excess ;
the precipitate, consisting of calcium malate and sulphate, is collected
512 ORGANIC ACIDS.
on a filter, washed with proof spirit, dried, and weighed. If the
calcium sulphate be next determined by dissolving the precipitate in
water, precipitating the solution by barium chloride, and multiplying
the weight of barium sulphate obtained by *5837, the difference may
be regarded as calcium malate, 172 parts of which correspond to 134
of malic acid.
K. Kayser evaporates 100 c.c. of the wine to one-half, supersatu-
rates with sodium carbonate, adds 10 c.c. of a strong solution of
barium chloride, dilutes to 100 c.c., agitates, and allows the whole to
stand for twenty-four hours. The liquid is then filtered, and an ali-
quot portion of the filtrate acidified moderately with hydrochloric
acid and evaporated to dryness at 100. Free hydrochloric and
acetic acids are volatilised, neutral chlorides and free malic acid
remaining. The latter can be determined in the residue by dissolving
it in water and titrating the solution with standard alkali.
TARTARIC ACID.
French Acide Tartarique. German Tartarsaure, Weinstein-
saure.
C 4 H 6 6 = H 2 C 4 H 4 O 6 .
Tartaric acid occurs, either free or combined, in various plants.
The grape is the only source from which it is commercially obtained.
The deposit formed on the sides and bottom of the vessels in which
wine is manufactured consists largely of calcium and potassium tar-
trates. After purification, it is treated with chalk and calcium sul-
phate, by which a nearly insoluble calcium tartrate is produced, and
this, when decomposed with sulphuric acid, yields free tartaric acid,
which is obtained in crystals by cooling the concentrated liquid.
Tartaric acid has the constitution of a dihydroxysuccinic acid
and has been formed synthetically by boiling silver dibromsuccinate
with water, or the corresponding calcium salt with lime water.
Ag 2 C 4 H 2 Br 2 O 4 -f 2H 2 O = 2AgBr -j- C 4 H 6 O 6 .
Five distinct modifications of tartaric acid exist. Their chief phys-
ical and chemical differences are as follow :
DEXTROTARTARIC, or ORDINARY TARTARIC ACID, forms anhy-
drous, hemihedral, rhombic crystals, the aqueous solution of which
turns the plane of polarisation of a luminous ray to the right, the value
for S D at 16 C. being 13'l for a 15 per cent., and 14'7 for a 2 per
cent, solution. The crystals fuse at 135 C., have a density of 1*74 to
T76, and are readily soluble in absolute and in aqueous alcohol.
ORGANIC ACIDS. 513
In the following article, ordinary tartaric acid and its salts are
always referred to unless some special prefix is employed.
LEVOTARTARIC, or ANTITARTARIC ACID, forms anhydrous, hemi-
hedral, rhombic crystals, the aqueous solution of which turns the
plane of polarisation of a luminous ray to the left, the rotation being
equal and opposite to that produced by dextrotartaric acid. It fer-
ments less readily than dextrotartaric acid, and forms no crystalline
compound with asparagine.
PARATARTARIC, or RACEMIC ACID, occurs with ordinary tartaric
acid in crude tartars. It forms hydrated, holohedral, triclinic crystals
containing 1 Aq., which are optically inactive, have a density of T69,
effloresce in the air, and become completely anhydrous at 100 ; the
resultant anhydrous acid melts at about 200 C. Racemic acid is
soluble in five parts of cold water, and with difficulty in cold alcohol.
The calcium racemate is less soluble in water than calcium dextro-
tartrate, and is also distinguished by its insolubility in acetic acid,
and in ammonium chloride solution. 1
INACTIVE, or MESOTARTARIC ACID, is produced by prolonged heat-
ing of dextro-tartaric acid to 165 with a small proportion of water.
It is optically inactive, but is not resolvable into two acids. Meso-
tartaric acid is very soluble in water, forms crystals containing 1 Aq.,
and yields calcium and hydrogen-potassium salts more soluble than
the corresponding salts of ordinary tartaric acid.
METATARTARIC ACID is produced by fusing ordinary tartaric acid
at 180 C. It is deliquescent and uncrystallisable. Its dilute solu-
tion and those of its salts are converted by boiling into those of the
ordinary modification of tartaric acid. The same change occurs
slowly in the cold. On the other hand, dextrotartaric acid undergoes
partial conversion into metatartaric acid by concentrating its solution
on the water-bath.
When heated to 205 C., tartaric acid loses the elements of water,
and is converted successively into substances of the formulae :
C 8 H 10 On ; C 4 H 4 O 5 ; and C 5 H 8 O 4 , and finally carbonises like burnt sugar.
Dextrotartaric acid is soluble in 0'7 parts of cold and 0'5 parts of
boiling water ; in 2'5 parts of rectified spirit or 3'6 of absolute alcohol ;
in 250 parts of absolute ether, and is nearly insoluble in chloroform,
benzene, and petroleum spirit.
i Racemic acid can be prepared by mixing dextro- and levotartaric acids, and can be
resolved into them by appropriate methods. According to Staedel, crystals of natural
racemic acid differ from the artificial product by not disintegrating on exposure to air.
Anhydrous artificial racemic acid is stated to fuse at 198, and the natural at 201 C.
33
514 ORGANIC ACIDS.
The following table by H. Schiff shows the density of aqueous solu-
tions of tartaric acid :
Percentage by weight of tartaric acid. Density aU5 C. ( =59 F.)
33 1-1654
22 1-1062
14-67 1-0690
11 1-0511
7-33 1-0337
3-67 1-0167
Aqueous solutions of tartaric acid (especially when dilute) gradually
decompose with growth of fungus. The change may be prevented by
the addition of a little carbolic acid. Cream of tartar and other tar-
trates decompose when kept in a moist state.
Most oxidising agents convert tartaric into formic acid. Ammonio-
silver nitrate is reduced with formation of carbonic and oxalic acids.
In dilute solution, tartaric acid reduces auric and platinic chlorides,
and converts mercuric chloride into calomel.
Detection and Determination of Tartaric Acid and Tar-
trates.
Tartaric acid and tartrates are charred when heated with concen-
trated sulphuric acid of T845 specific gravity. The reaction may be
used to distinguish a tartrate from a citrate, or to detect tartaric acid
in presence of citric acid. For this purpose, 1 grm. of the sample
should be treated with 10 c.c. of pure concentrated sulphuric acid (free
from nitrous compounds), and the mixture heated to 100 C. for forty
minutes. Citric acid gives only a yellow color when thus treated, but
if 1 per cent, of tartaric acid be present the liquid has a distinct brown
shade, and this becomes still more marked with larger proportions.
If a drop of ferrous sulphate solution be added to a solution of
tartaric acid or a soluble tartrate, then a few drops of hydrogen per-
oxide, and the mixture finally treated with excess of caustic soda, a
fine violet coloration is produced, which in strong solutions is so deep
as to appear almost black. The color is discharged by sulphurous
acid. If potassium ferrocyanide be added to the violet liquid, and
then sufficient dilute sulphuric acid to acidify the solution, the iron
may be filtered off and a colorless filtrate obtained which again gives
the violet color on addition of a ferrous salt. The colorless filtrate
reduces salts of silver and mercury, and bichromate of potassium, and
instantly decolorises permanganate. After adding excess of alkali it
precipitates cuprous oxide from Fehling's solution in the cold, and on
heating metallic copper is separated.
ORGANIC ACIDS. 515
Acidulated permanganate or sodium hypochlorite may be substi-
tuted for the hydrogen peroxide in the foregoing test, if care be taken
to avoid excess, but the result is not so good as with the peroxide.
Heavy metals and oxidising agents must be absent. Citric, malic,
succinic, oxalic, and acetic acids and sugar were found by H. J. H.
Fenton, the observer of the reaction, to give no similar coloration
(Chem. News, xxxiii. 190; xliii. 110).
Soluble tartrates in neutral solution give white calcium tartrate
on addition of chloride of calcium. The precipitate is nearly insoluble
in cold water; soluble in many aramoniacal salts; soluble (after wash-
ing) in a cold solution of sodium hydrate, but reprecipitated on boil-
ing; soluble in acids (including acetic); and converted by heating
with a neutral solution of cupric chloride into insoluble cupric tartrate.
(Citrate of calcium yields soluble cupric citrate.) Calcium tartrate
may also be conveniently examined by dissolving it in the smallest
possible quantity of acetic acid, adding excess of potassium chloride
solution, and stirring vigorously, when the acid tartrate of potassium
will be thrown down.
The reducing action of tartaric acid on solutions of silver is an
extremely delicate test when properly applied, but is remarkably liable
to failure if the proper conditions are not carefully observed. The
solution of tartaric acid, or the tartrate of alkali-metal (all other
metals being first removed), is rendered acid with nitric acid, excess of
silver nitrate added, and any precipitate filtered off. To the solution,
very dilute ammonia is added until the precipitate at first formed is
nearly redissolved. The solution is again filtered, and the filtrate
heated nearly to boiling for a few minutes, when a brilliant metallic
mirror will be deposited on the sides of the tube. Citric acid does not
reduce silver under similar circumstances, but gives a precipitate on
continued boiling.
Tartaric acid prevents the precipitation of many metallic solu-
tions by alkalies, stable double tartrates being formed. For the sepa-
ration of heavy metals from tartrates, sulphuretted hydrogen or
sulphide of sodium must be employed, according to the metals present.
The filtrate may be concentrated, and any barium, strontium, calcium,
or magnesium present thrown down by boiling with carbonate of
sodium. Aluminium is not separated by either of the above precipi-
tants, but the tartaric acid can be detected and estimated in the solu-
tion without removing it.
The best method of determining tartaric acid by direct estimation
is to precipitate it in the form of potassium-hydrogen tartrate, KHT.
516 ORGANIC ACIDS.
When the free acid is to be determined, either alone or mixed only with
citric acid, no better process can be employed than that described under
Citric Acid. For the determination of tartaric acid in tartrates, and in
the various natural and artificial products of tartaric acid manufac-
tories, the processes of Warington and Grosjean are by far the best.
Tartaric acid in wine may exist in the free state, and as calcium and
potassium hydrogen tartrates, and ethyl tartrate is probably often
present. Its determination is described on page 117.
Like the corresponding salts of other organic acids, the tartrates of
the light metals leave on gentle ignition a residue of carbonate or
oxide of the contained metal, and by dissolving this residue in stand-
ard acid and ascertaining the amount of acid neutralised by titrating
the excess with standard alkali, an accurate estimation of the metal
can be effected, and, if it be known whether the tartrate was originally
an acid or a neutral salt, a determination of the tartaric acid itself is
obtained.
Tartaric acid and acid tartrates neutralise alkalies completely, and
litmus affords a fairly sharp indication of the end of the reaction ;
but phenolphthalem is preferable (methyl orange is unsuitable).
Hence the ordinary processes of alkalimetry are applicable to tar-
taric acid and tartrates.
The tartaric acid in tartrates of organic bases may generally be de-
termined by precipitation as acid tartrate of potassium.
The tartrates of the alcohol radicles are unimportant. Tartrate of
ethyl may be decomposed by heating with alcoholic potash, and the
acid tartrate of potassium subsequently precipitated by adding excess
of acetic acid.
Commercial Tartaric Acid is liable to contain the same impuri-
ties as citric acid, and is examined in a similar manner. It is also said
to have been adulterated with alum and acid sulphate of potassium, the
presence of either of which would be indicated by the ash left on igni-
tion and the formation of a notable precipitate on addition of barium
chloride to the aqueous solution.
Tartaric Acid Liquors are the liquids resulting from the
decomposition of calcium tartrate by sulphuric acid. They are of a
very complex character, containing : free tartaric acid ; foreign
organic acids ; sulphuric acid, and sulphates of calcium, potassium,
iron, and aluminium ; phosphates; and bodies of an indefinite nature.
Their analytical examination is limited to the determination of the
tartaric and free sulphuric acid, with the additional estimation, in
some cases, of the total organic acids.
ORGANIC ACIDS. 517
The determination of the tartaric acid is best effected by precipita-
tion as the acid potassium salt. Acetate of potassium is the best
reagent for pure liquors, but it is inapplicable in presence of iron or
aluminium. Citrate of potassium is free from this objection, and is
best employed in the following manner:
A quantity of liquor, of 30 to 40 c.c. in volume, as cold as possible,
and containing from 2 to 4 grm. of tartaric acid, is treated with a
saturated aqueous solution of tripotassic citrate, 1 added drop by drop
with constant stirring. As soon as the free sulphuric acid is satisfied,
the precipitate begins to appear in streaks on the sides of the glass.
In presence of much sulphuric acid, a fine precipitate of potassium
sulphate will precede the formation of the acid tartrate, but is readily
distinguished therefrom. When the streaks begin to appear, 1 c.c. of
citrate solution is added for every gram of tartaric acid supposed to
be present. A great excess should be avoided. Should a gelatinous
precipitate be formed, the experiment is repeated with a previous addi-
tion of some citric acid. After stirring continuously for ten minutes,
the precipitate is washed two or three times with 25 c.c. of a 5 per
cent, solution of potassium chloride, saturated with potassium bitar-
trate. The precipitate is then collected on a small filter and washed
with the same solution, until the acidity of the filtrate is only slightly
in excess of that of the solution used for washing the precipitate. The
filter and precipitate are finally transferred to a beaker, and the
amount of tartaric acid present is determined by titration with
standard alkali set against bitartrate of potassium ; litmus or phenol-
phthalein being used as the indicator. The presence of potassium
sulphate in the precipitate is of no consequence, as it has no neutral-
ising power.
Sometimes, however, an acid citrate of potassium is dragged down
by the tartrate, and this is obstinately retained. It is best got rid of
by dissolving the precipitate in 50 c.c. of hot water, adding 5 grm. of
potassium chloride, and cooling the liquid quickly to 15, stirring
continually, and continuing the agitation for ten minutes. This puri-
fied precipitate may be washed with the ordinary washing fluid with
great ease, 2 but a correction of one- half per cent, on the tartaric acid
found must be made for unavoidable loss in the process of puri-
fication.
1 Obtained by neutralising citric acid by pure potash or potassium carbonate.
2 The filtrate may be tested for citric acid by neutralising it with soda, and adding
calcium chloride. After prolonged standing in the cold and filtration from a little calcium
tartrate, the solution is boiled, when any precipitate will consist of calcium citrate.
518 ORGANIC ACIDS.
Under favorable circumstances, determinations by the above method
show from 99 to 100 per cent, of the tartaric acid present, but much
greater variations occur if the proper proportion of citrate is departed
from. Grosjean concluded that, when an accurate assay of factory
tartaric acid liquors was required, a preliminary series of experiments
was necessary to ascertain what volume of citrate solution gave a pre-
cipitate of maximum acidity. This having been ascertained, a final
experiment should be made, using the proper quantity of citrate solu-
tion, and washing the precipitate very thoroughly. In presence of
much sulphuric acid, the results have a tendency to be in excess of the
truth. From very old bad liquors, potassium alum may be precipi-
tated on adding the citrate solution, owing to the formation of potas-
sium sulphate and the sparing solubility of alum in solutions of that
salt. When alum has been precipitated the results will be below the
truth, as on washing with the potassium chloride solution a fluid is
formed in which potassium bitartrate is readily soluble. If, on the
other hand, an alcoholic washing liquid be substituted, the alum is re-
tained in the precipitate, and increases the final acidity. The difficulty
may be avoided by adding phosphoric acid before the citrate solution,
but the filtration must be effected immediately after the stirring, or a
gelatinous precipitate of aluminium phosphate may be thrown down.
Racemic add, if present, will be estimated as tartaric acid by the
above method. Inactive and meta-tartaric acids are only imperfectly
precipitated, owing to the greater solubility of their potassium salts.
Oxalic acid has been detected in old liquors, but does not interfere with
the results.
The determination of the free sulphuric acid in tartaric acid liquors
is troublesome, owing to the insolubility of potassium and calcium tar-
trates in alcohol, and to the occasional presence of alum. Thus, if
mixed solutions of potash-alum and tartaric acid are treated with alco-
hol, potassium hydrogen tartrate and alum are precipitated, and the
liquid contains free sulphuric acid, which was not present originally.
A similar reaction occurs if sulphate of calcium be substituted for the
alum. These errors are removed when the quantity of free sulphuric
acid in the liquor is sufficiently great, and will occur in practice merely
in the case of new liquors of bad quality. The following process is the
best for the determination of the free sulphuric acid : From 5 to 20
c.c. of the liquor is slowly dropped into 100 c.c. of 90 per cent, alcohol,
with continual stirring. (If the liquor be concentrated and of bad
quality, it should be previously diluted with an equal bulk of water.)
The precipitate contains sulphates, aluminium phosphate, &c. The
ORGANIC ACIDS. 519
solution is filtered after twenty-four hours, the precipitate washed with
alcohol, and the filtrate precipitated with an alcoholic solution of cal-
cium chloride. The precipitate is filtered off, slightly washed with
alcohol, and ignited to destroy the tartrate. The ash is treated with
strong nitric acid, the excess evaporated off, the residue treated with
alcohol, and the insoluble calcium sulphate collected, ignited, and
weighed (Jour. Soc. Chem. Ind., ii. 340).
A useful indication of the presence of free sulphuric acid in tartaric
acid liquors is obtained by treating the liquid with half its measure of
a saturated aqueous solution of calcium chloride. A turbidity due to
the formation of gypsum occurs immediately in a liquor containing
sulphuric acid equivalent to 0'8 per cent, of brown oil of vitriol, and in
five minutes when only O'l per cent, of oil of vitriol is present (Gros-
jeau, Jour. Soe. Chem. Ind., ii. 340).
For the determination of the total organic acids in tartaric acid
liquors, R. Warington recommends the following method (Jour. Chem.
Soc., xxviii. 982) : Exactly neutralise a known measure of the liquor
with standard caustic alkali, evaporate to dryness, and ignite the resi-
due at a very low temperature till the carbon is nearly consumed.
Treat the ash with a known quantity of standard sulphuric acid, heat
and decant, and treat the insoluble residue with more standard acid,
concentrating, if necessary, to effect solution of the phosphates.
Treat the mixed cold concentrated solutions with sufficient Rochelle
salt (KNaT) to keep any alumina in permanent solution, and then
titrate the solution with standard alkali and litmus. The amount of
standard sulphuric acid neutralised by the ash is the exact equivalent
of the total organic acid in the liquor taken, and each c.c. of normal
acid neutralised represents '075 grm. of organic acid, expressed in
terms of tartaric acid.
Lees ; Argol ; Tartar. These are products of the fermentation
of grape-juice; they consist largely of bitartrate of potassium, and are
the materials from which tartaric acid and tartrates are extracted.
Their formation is due to the diminished solubility of the tartrates in
the alcoholic liquid produced by the fermentation.
LEES is the solid matter collected from the bottom of the vessels in
which the grape-juice is fermented.
Its composition is greatly altered by "plastering" the wine. This
process consists in adding to the wine some " Yeso," which is essen-
tially an impure calcium sulphate containing some carbonate. " Span-
ish earth," a kind of readily decomposed clay, is sometimes employed.
The result is, that in plastered lees the tartrate exists chiefly as the
520 ORGANIC ACIDS.
neutral calcium, instead of the acid potassium salt. The total tartaric
acid in lees is usually from 24 to 32 per cent. Lees contain from 30
to 40 per cent, of indefinite vegetable matter, the remainder being
tartrates, sulphates (in plastered lees), oxide of iron, alumina, phos-
phoric acid, and sometimes lumps of plaster, water, &c.
ARGOL, or CRUDE TARTAR, is the crystalline crust deposited on the
sides of the vessels used for the fermentation. It exhibits some variety
of composition, the tartaric acid ranging from 40 to 70 per cent., and
being always present chiefly as acid potassium tartrate. Very low
argols resemble superior lees, while first-class argols are equal to ordi-
nary refined tartar. The term " argol " is also applied loosely to both
tartar and lees. In argol, globules of sulphur are sometimes found ;
they are due to the sulphur burnt in the casks before introducing the
wine.
CREAM OF TARTAR, or REFINED TARTAR, is prepared by boiling
crude tartar (argol) with water, filtering, and crystallising the salt
from the clear liquid. The term " cream " of tartar is derived from
the fact that during the evaporation of the liquid the salt is deposited
in white crystalline crusts on the surface of the solution. Cream of
tartar thus obtained consists chiefly of potassium hydrogen tartrate,
KHC^HiOe, but it always contains more or less calcium tartrate,
which, though nearly insoluble in pure water, dissolves with moderate
facility in a hot solution of the acid tartrate of potassium. The pro-
portion of calcium tartrate normally present in commercial cream of
tartar varies from 2 to 9 per cent., and any proportion present in
excess of 10 per cent, may be considered as an adulterant (see a paper
by the Author, Analyst, v. 114). In addition to containing calcium
tartrate, commercial cream of tartar is sometimes adulterated to a
considerable extent, the sulphates of potassium and calcium being
occasionally used, in addition to marble, alum, and barium sulphate.
Potassium hydrogen sulphate, KHSO 4 , is sold under the name of
" tartaline," and employed as a substitute for cream of tartar in
baking powders, &c. It has a higher neutralising power than real
cream of tartar, and hence is sometimes diluted with potato-starch,
the mixture being sold as " cream of tartaraline."
ASSAY OF TARTAR, ARGOL, &c. For the detection of adulterants
in cream of tartar, the following tests may be applied :
The sample should be ignited, the residue boiled with water, filtered
off, washed, ignited, moistened with ammonium carbonate, gently re-
ignited, and weighed. The " insoluble ash " thus obtained from genu-
ine cream of tartar consists of the calcium carbonate corresponding
ORGANIC ACIDS. 521
to the calcium tartrate originally present, and its weight may be calcu-
lated to its equivalent of the latter by multiplying the CaCO 3 by the
factor T88. The calcium tartrate thus found should not exceed 10
per cent., or 12 per cent, at the outside. Any higher proportion is
usually due to adulteration with compounds of calcium. Sophistica-
tion with chloride of calcium is said to have occurred, though very
improbable, but there are authentic cases of adulteration by chalk and
marble. The author has found 20 per cent, of calcium sulphate (anhy-
drous), 1 probably added as plaster of Paris. In the case of adulterated
samples, the proportion of calcium tartrate cannot be deduced with
accuracy from the percentage of " insoluble ash." 2
The sample is boiled with a moderate excess of pure sodium car-
bonate and the liquid filtered. A portion of the filtrate is tested for
sulphates (e.g., calcium sulphate, potassium sulphate, and alum) by
acidulating slightly with hydrochloric acid and adding barium chlo-
ride, and another for chlorides by rendering it acid with nitric acid,
and adding silver nitrate ; traces of sulphates and chlorides may be
neglected. The precipitate produced by sodium carbonate should be
rinsed off the filter and treated with dilute hydrochloric acid. Any
insoluble residue may consist of sand or barium sulphate. Both the
chemical and microscopical characters may be employed to distinguish
these, and to determine whether the latter adulterant is crystalline or
amorphous.
The presence of alum is indicated by the detection of a notable
quantity of sulphates, with simultaneous presence of alumina in the
insoluble ash. The alumina cannot be precipitated by adding ammo-
nia to the original solution of the substance, owing to the presence of
tartrate ; but it may be detected by neutralising the hot solution of
the sample with soda, and boiling the liquid with a little acetic acid
and excess of sodium phosphate. Any aluminium present will be
thrown down as phosphate, tartrates having scarcely any solvent
action on the precipitate at the temperature of ebullition, and in
presence of excess of phosphoric acid. Alum may be dissolved out
of cream of tartar by treating the finely powdered sample with a
1 This was calculated from the weight of BaS0 4 obtained. The total calcium was con-
siderably in excess of the proportion corresponding to 20 per cent, of CaS0 4 .
2 Dr. E. Gr. Love, in a Report to the New York State Board of Health, gives the results
of his examination of twenty-seven samples of " cream of tartar." Of these, sixteen
were adulterated, and from some cream of tartar was entirely absent. Starch, terra alba,
and acid phosphate of calcium were among the adulterants found. Five samples con-
tained upwards of 70 per cent, of terra alba, and in one case it reached 93 per cent.
522 ORGANIC ACIDS.
cold, saturated, aqueous solution of potassium-hydrogen tartrate, con-
taining 5 per cent, of potassium chloride.
The determination of the tartaric acid in tartar, lees, and argol may
be effected by various methods, but the following processes of assay,
due to R. Warington, are the most generally accurate and reliable:
The tartaric acid existing as KHT is determined by titrating a hot
aqueous solution of 5 grm. of the sample with standard alkali and lit-
mus or phenolphthalein. Each c.c. of normal alkali required corre-
sponds to '150 grm. of H 2 f or '188 of KHT.
Another portion of the sample (2 grm.) is calcined in platinum at
a very low red heat. 1 The ash is dissolved in hot water, and the
liquid, without filtration, treated with a moderate excess of standard
acid, and the solution boiled. The excess of acid is then ascertained
by titrating back with standard alkali. From the alkalinity of the
tartar after ignition is subtracted the alkali required to neutralise an
equal weight of the original tartar, both expressed in terms of normal
alkali, when the difference is the neutralising power of the bases exist-
ing as neutral tartrates. 1 c.c. of normal alkali is equivalent to
0-1131 grm. of K 2 T, 0'094 grm. of CaT, or 0'075 grm. of H 2 T as a
neutral tartrate.
A preferable but somewhat more tedious method, for the assay of
lees and argol, is the direct estimation of the total tartaric acid by
precipitation as KHT, after previous decomposition of the calcium
tartrate by oxalate of potassium. An amount of the powdered
sample, containing about 2 grm. of tartaric acid, is placed in a
beaker, and heated with a small quantity of water till thoroughly
softened. A strong solution of neutral potassium oxalate is next
added, in quantity sufficient to react with all the calcium salts present,
and yet leave an excess of about 1? grm. of the salt. The mixture is
heated, with frequent stirring, for some time longer. The solution,
which will generally be strongly acid, is now cautiously treated with
solution of pure potash till almost neutral. After a little further
heating, the liquid (which should not occupy more than 40 c.c.) is
filtered on to a small filter. The residue is well washed, and the
washings concentrated on the water-bath and added to the main solu-
tion, which is made up to about 50 c.c. A strong solution of about 2
grm. of citric acid is next added, and the solution stirred continuously
during ten minutes, to facilitate precipitation of the KHT. The pre-
1 Complete combustion of the carbon is not to be expected. If the sample contained
sulphates, 5 c.c. of solution of hydrogen dioxide should be added to the solution of the
ash immediately prior to the standard acid.
ORGANIC ACIDS. 523
cipitate is then washed in the manner described on p. 517, and finally
dissolved and titrated with standard alkali. Each c.c. of normal
alkali equals '150 grm. of H 2 T.
This direct method of determining tartaric acid in tartars, &c.,
gives figures somewhat lower than those obtained by the indirect alka-
limetric method, but they are accurate and more consistent with the
practical results of the factory.
Mr. Allen has recently (Jour. Soc. Chem. Ind., 1896, 681) published the fol-
lowing methods for examination of commercial cream of tartar :
1. 1'881 grain of the sample, free from moisture, is dissolved in hot water and
titrated with caustic alkali, phenolphthalein being used as an indicator. In the
absence of potassium hydrogen sulphate and free tartaric acid, each cubic centi-
metre of alkali represents 1 per cent, of potassium hydrogen tartrate.
2. Ignite 1*881 grain for ten minutes, boil with water, filter, and wash the
residue.
(a) Titrate the filtrate with decinormal hydrochloric acid and methyl orange.
With pure tartar, the quantity of acid used will equal that consumed in the
previous titration with alkali. Each cubic centimetre of the deficiency of acid
equals 0'36 per cent, of calcium sulphate, or 0'72 per cent, of potassium acid
sulphate. Any excess of acid added points to the presence of normal potas-
sium tartrate, each cubic centimetre representing 0'6 per cent, thereof. If the
titrated liquid be treated with barium chloride, the barium sulphate will be
a measure of the calcium sulphate or potassium sulphate present.
(b) The carbonaceous residue is ignited, dissolved in 20 c.c. of decinormal acid,
filtered from any insoluble residue, and the filtrate titrated with decmormal
alkali. Each cubic centimetre corresponds to 0'50 per cent, of calcium tartrate,
or 0*36 per cent, of calcium sulphate (anhydrous). L.
METALLIC TARTRATES.
Tartaric acid contains two atoms of hydrogen replaceable by metals,
and hence forms two classes of metallic salts, viz., the neutral tar-
trates, and the acid- or bi-tartrates. Two additional atoms of hydro-
gen are replaceable by alcoholic or acid radicles. Few of the metallic
tartrates are readily soluble in water, and all are insoluble in alcohol.
The greater number of the metallic tartrates, except tartrate of mer-
cury, are soluble in ammonia. The tartrates of the heavy metals
unite with the tartrates of the alkali metals to form stable double
tartrates not decomposed on adding either a fixed alkali or ammonia.
Owing to the formation of these stable double tartrates, soda and
ammonia produce no precipitate in solutions of iron, copper, &c., to
which a sufficiency of tartaric acid or a tartrate of alkali- metal has
been previously added. The method of analysing these double tar-
trates, and the metallic tartrates generally, is described on p. 514.
524
ORGANIC ACIDS.
Potassium Tartrates.
The roost important of these salts is the POTASSIUM HYDROGEN
TARTRATE, Acid Potassium Tartrate, or Bitartrate of Potassium.
KH,C 4 H 4 O 6 = KHT. This substance is the principal constituent of
tartar, argol, and wine-lees, and is of importance in the free state as
a source of tartaric acid, and as a form for the determination of that
body.
Pure bitartrate of potassium may be conveniently prepared by
dividing a solution of tartaric acid into two equal parts, neutralising
one portion with potassium carbonate, and adding the other. The
product may be purified by recrystallisation from hot water.
Acid tartrate of potassium is a white substance forming hard, trimet-
ric crystals. It is soluble in 240 parts of water at 10 C. (= 50 F.),
180 at 20 C., and in about 15 parts of boiling water. In alcoholic
liquors it is much less soluble. Thus it requires (at 15 C.) 400 parts
of a spirit containing 10'5 per cent, of alcohol, and 2000 parts of proof
spirit (49*24 per cent, alcohol) for solution. In still stronger spirit
it is practically insoluble. The presence of glucose does not affect
its solubility in water or weak spirit ; but the presence of certain salts
and acids has great influence. This is shown by the following table
by Warington, in which the effect of water containing equivalent 1
quantities of various acids is given. For comparison with them, ex-
periments were also made with solutions containing equivalent amounts
of acetic and citric acids neutralised by potash. All the experiments
were made at 14 C. :
Solvent.
Grams of Acid or
Salt in 100 c.c. of
Solvent.
Grams of KHT
Dissolved bv 100 c.c.
of Solvent.
Water
422
'8106
422
Tartaric acid . .
1-0331
'322
Citric acid
8448
546
Sulphuric acid . .
'6853
1'701
Hydrochloric acid,
Nitric acid,
Potassium acetate
5037
8445
1'3875
1-949
1-969
'744
Potassium citrate
1'3966
'843
These results are of importance in the estimation of tartaric acid as
KHT. Clearly free mineral acids should not be present, nor any
1 Not equal weights, but amounts of acid requiring equal quantities of alkali for their
neutralisation.
ORGANIC ACIDS. 525
large excess of potassium acetate or citrate. On the other hand, solu-
tions of the sulphate, nitrate, and especially the chloride of potassium
have very little solvent action on the precipitated acid tartrate. Thus
the solubility of the acid potassium tartrate at 12 C. is 1 part in 3213
of a 5 per cent, solution of potassium chloride, and only 1 in 4401 of a
10 per cent, solution of the same salt.
Acid tartrate of potassium dissolves many metallic oxides, forming
double tartrates ; tartar-emetic, K(SbO)T, is a compound of this
character.
Cream of tartar consists chiefly of bitartrate of potassium. Its com-
position and the mode of assaying it are considered on p. 520.
When acid tartrate of potassium is treated with solution of potas-
sium carbonate or hydrate until the liquid ceases to redden litmus
paper, there results :
DIPOTASSIUM TARTRATE ; Neutral Tartrate of Potassium, K 2 CJJ. 4 O 6
= K 2 T. This salt forms very soluble monoclinic prisms. When its
solution is treated with an acid, KHT is precipitated.*
POTASSIUM-SODIUM TARTRATE, or ROCHELLE SALT, KNaT is pro-
duced by neutralising cream of tartar with soda or sodium carbonate.
It forms large rhombic prisms, containing four atoms of water, and is
very readily soluble. Addition of acetic acid precipitates crystalline
KHT. This reaction distinguishes it from the neutral sodium tar-
trate, Na 2 T -f- 2H 2 O.
Seidlitz Powders are largely composed of Rochelle salt. There is no
preparation of the sort in the British Pharmacopoeia, but the dispen-
saries of other nations have powders of the following compositions :
Tartaric Rochelle Sodium Hydrogen
Acid. Salt. Carbonate.
French, 31 grains. 93 grains. 31 grains.
German, 31 116 38
United States. . . 35 120 40
The preparations commonly sold in England as Seidlitz powders are
of very varied composition. A normal preparation may be regarded
as containing 120 grains of Rochelle salt in admixture with 40 of
bicarbonate of sodium, while the white paper contains 35 grains of
tartaric acid. "Double Seidlitz powders" contain about the same
amounts of acid and sodium bicarbonate, together with a considerably
larger quantity of Rochelle salt. Sometimes the Rochelle salt is
largely, and occasionally entirely, replaced by sodium bicarbonate.
Such a preparation would be of a strongly alkaline character, and
notably different from Seidlitz powder of the normal composition. On
526 ORGANIC ACIDS.
the other hand, if the acid be in excess, the powder is apt to produce
a turbid solution with water, owing to formation of cream of tartar.
In examining so-called Seidlitz powders, the absence of notable pro-
portions of sulphates should be proved, as a substitution of acid potas-
sium sulphate for tartaricacid is not unlikely to occur. Some powders
receive an addition of magnesium sulphate, or a minute quantity (y^
grain) of tartar emetic, while others are flavored with lemon or ginger,
and sweetened with sugar. Potassium chlorate is a constituent of cer-
tain patent remedies of the nature of Seidlitz powders.
POTASSIUM- FERRIC TARTRATE. Potassio-tartrate of iron. K 3 FeT 3 .
Prepared by adding precipitated ferric hydrate to cream of tartar,
and then treating with cold water. It constitutes the Ferrum Tarta-
ratum of Pharmacy. The solution acidulated with hydrochloric acid
should give a copious blue precipitate with the ferrocyanide, but none
with the ferricyanide of potassium. It should contain 30 per cent, of
Fe 2 O 3 , as estimated from the weight of the ash insoluble in water.
POTASSIUM ANTIMONYL TARTRATE ; Tartarised Antimony ; Tartar-
emetic. French Tartre Stibie. K(SbO)C 4 H 4 O 6 - This important
remedy is prepared by mixing antimonious oxide (Sb 2 O 3 ) with cream
of tartar, and subsequently adding water, boiling, filtering, and crystal-
lising. The crystals contain half a molecule of water. Cold water
dissolves 7 per cent., and boiling water 53 per cent, of the salt ; the
solution has an acid reaction. Antimonial ivine is an official solution
of 40 grains of tartar-emetic in a pint of sherry.
Tartar-emetic is now extensively employed for fixing certain coal-
tar colors on cotton, its value for this purpose depending on the
content of antimony. It is frequently largely adulterated, the per-
centage of antimony being sometimes scarcely one-half of that present
in the pure substance.
The antimony may be conveniently determined volumetrically, in a
manner described by W. B, Hart (Jour. Soc. Chem. Ind., iii. 294).
The sample is dissolved in water, and bicarbonate of sodium added to
the solution. Excess of a standard solution of calcium hypochlorite
is then added. The excess is found by titrating back with a deci-
normal solution of arsenite of sodium, until a drop of the liquid
ceases to give a blue color with iodide of potassium and starch. The
strength of the hypochlorite solution is found by taking a measure
equal to that added to the antimony solution and titrating with
arsenite as before. 1 c.c. of a solution containing 4'95 grm. of pure
arsenious oxide per litre has the same reducing power as *0060 grm.
of Sb or -0072 of Sb,O 3 .
ORGANIC ACIDS.
Potassium Antimonium Oxalate, SbK 3 (C 2 O 4 ) 3 + 6H 2 O, is now used
as an adulterant of, and substitute for, tartar-emetic. It is readily
soluble, does not blacken on ignition or on heating with sulphuric acid,
and gives a white precipitate on adding calcium chloride to the solu-
tion previously acidified with acetic acid. The salt contains only 23'7
per cent, of Sb 2 O 3 .
The Tartrates of Ammonium closely resemble the correspond-
ing potassium salts, but are wholly volatile on ignition.
Calcium Tartrates. The neutral tartrate, CaC 4 H 4 O 6 = CaT, is
a natural constituent of the tartarous deposit from wine, the propor-
tion contained being much increased if the wine has been " plastered."
It also constitutes the greater part of the residue obtained on treat-
ing commercial tartars with hot water. Tartrate of calcium is like-
wise precipitated as a crystalline powder containing 4 Aq., by adding
excess of calcium chloride to a solution of neutral tartrate. It is
soluble in 6265 parts of water at 15 C. (= 59 F.), and in 352 parts
of boiling water. Free acids and cream of tartar dissolve it readily ;
and hence it is frequently present in notable quantity even in purified
tartars. These solutions are precipitated by ammonia, either imme-
diately or after some time. Calcium tartrate is soluble in ammonium
chloride and in cold caustic alkali, the latter solution being repre-
cipitated on boiling. By digestion with a hot neutral solution of cupric
chloride it is converted into insoluble cupric tartrate. This reaction
distinguishes it from calcium citrate, but the reaction fails with mix-
tures containing a large proportion of citrate. The tartrate differs
from the racemate and oxalate of calcium by its solubility in acetic
acid.
Moist tartrate of calcium, if kept warm, undergoes fermentation
and forms butyracetate of calcium.
The acid tartrate of calcium is sparingly soluble ; in solution it is
unstable, the liquid gradually depositing crystals of the neutral salt.
CALCIUM RACEMATE, CaC^HAj -j- 4H 2 O, is even less soluble in
water than calcium dextro-tartrate, and is precipitated in fine needles
on adding calcium sulphate to a soluble racemate, or even to a solu-
tion of free racemic acid. Calcium racemate resembles the oxalate in
being insoluble in acetic acid. It dissolves in hydrochloric acid to
form a solution which is at once precipitated on adding ammonia,
whilst the dextro-tartrate is not precipitated till after some hours.
CALCIUM MESOTARTRATE, CaC 4 H 4 O 6 + 3H 2 O, forms bright, glis-
tening crystals which dissolve in 600 parts of boiling water, and
separate very gradually on cooling. Like the racemate, calcium
528 ORGANIC ACIDS.
mesotartrate is insoluble in acetic acid, but is not precipitated by
adding calcium sulphate to a solution of free mesotartaric acid.
The assay of crude calcium tartrate is best conducted, according to
L. Weigert (Zeits. Anal. Chem., 1884, 357), by heating 5 grm. of the
sample for an hour or two at 100 C. with 30 c.c. of a 10 per cent,
solution of potassium carbonate. The liquid is then filtered, and the
residue thoroughly washed with hot water. The filtrate is concen-
trated to 5 c.c. and treated with 5 c.c. of strong acetic acid, the
mixture being thoroughly agitated. 100 c.c. of rectified spirit
should next be added, and the whole allowed to rest for several
hours, when the liquid is filtered and the precipitate of tartar washed
With about 100 c.c. of rectified spirit, or until 10 c.c. of the wash-
ings, after dilution with 20 c.c. of water, requires, for neutralisation,
only one or two drops of standard alkali, of which 1 c.c. corre-
sponds to O'OIO grm. of tartaric acid, or 0'02508 of KHT. The
precipitate of tartar is dissolved in hot water and titrated with this
solution, and to the quantity found 0'0165 grm. is added as a correc-
tion for solubility in the above quantities of solutions ; or, if 5 grm. of
the sample be employed, 0*33 per cent, of KHT must be added to the
amount found.
The carbonate in crude calcium tartrate cannot be estimated by titra-
tion. It is best ascertained from the amount of carbon dioxide gas
evolved on treatment with acid.
For further information on tartrate of calcium and the methods of
determining it in tartarous deposits see p. 520 et seq.-
Cupric Tartrate, Cu"T, is a nearly insoluble, blue, crystalline
powder, obtained by precipitating a neutral soluble tartrate by a neu-
tral solution of cupric sulphate or chloride, or by digesting calcium
tartrate with a hot neutral solution of cupric chloride. Cupric tartrate
is soluble in ammonia, soda, and potash. The copper in the solutions
so obtained is readily reduced to the cuprous condition when heated
with glucose or other reducing agents, and hence alkaline solutions of
cupric tartrate afford a valuable test for such bodies. Various meth-
ods of preparing such solutions have been proposed, but the reagent
most generally employed is that known as Fehling's solution.
For the detection of a reducing substance by Fehling's solution, it
is merely necessary to heat the clear and neutralised solution of the
body to the boiling point with twice its measure of the cupric solution.
In some cases, the reduction occurs in the cold, or on very gently
warming the liquid. If a yellow or orange precipitate or turbidity of
cuprous oxide, Cu 2 O, be produced, a reducing substance is present.
ORGANIC ACIDS.
529
The following table shows the behavior of various substances when
their neutralised solutions are heated to boiling with Fehling's solu-
tion :
The Cupric Sohition is
KEDUCED by
Carbohydrates, &c. Dextrose, levu-
lose, maltose, mannitose, milk-
sugar, galactose, arabinose, gallisin.
Alcohols, Phenols, &c. Aldehyde,
chloral, chloroform, valeraldehyde,
resorcinol.
Organic Acids. Pyrogallic, gallotan-
nic, trichloracetic.
Inorganic Acids. Arsenous.
The Cupric Solution is
NOT REDUCED by
Carbohydrates, &c. Maunite, dulcite,
sucrose, inosite, cellulose, dextrin,
arabin.
Alcohols, Phenols, &c. Alcohol, glyc-
erin, phenol, benzoic aldehyde,
salicylic aldehyde.
Organic Acids. Acetic, lactic, suc-
cinic, oxalic, tartaric, citric, gallic,
saccharic, mucic, gluconic, lactonic,
benzoic, salicylic.
Inorganic Acids. Sulphurous.
CITRIC ACID.
French Acide Citrique. German Citronsaure.
Citric acid occurs in a free state in the juices of all the plants of the
genus of Citrus (order, Aurantiacece), and also in the gooseberry, cran-
berry, currant, tamarind, and many other fruits. The lemon, lime,
and bergamot are the fruits from which it is extracted. It has also
been manufactured from unripe gooseberries, which yield about 1 per
cent, of their weight of citric acid, besides containing malic acid.
Good lemons yield about 5 per cent, of crystallised citric acid.
Citrates of calcium and potassium are also widely distributed 'in the
vegetable kingdom.
Citric acid is prepared from lime, lemon, or bergamot juice, by neu-
tralising the liquid with chalk, decomposing the resultant calcium
citrate by an equivalent amount of sulphuric acid, and evaporating
the liquid to the crystallising point.
Citric acid usually occurs as a crystalline powder, or in transparent
colorless prisms belonging to the trimetric system. In the trade, the
crystals are always assumed to have the composition 2C 6 H 8 O 7 +
H 2 O, but seventeen samples from various makers were found by War-
ington to contain from 8'46 to 9'35 per cent, of water, the average
being 8'72 per cent. 1 This result agrees with the formula C 6 H 8 O 7 +
H 2 O, which requires 8'57 per cent, of water.
1 In determining the water in citric acid, it is necessary to dry the powdered sample for
34
530 ORGANIC ACIDS.
Crystallised citric acid melts at 100 C., but the previously dehy-
drated acid fuses at 153, and on further heating to about 175 de-
composes into water and aconitic acid, CeHgOe. 1 On dry distillation,
citric acid yields carbon dioxide, acetone, and the two isomeric acids,
itaconic and citraconic, C 5 H 6 O 4 , which bodies are also produced by
heating citric acid under pressure with water or a dilute acid.
Citric acid has a strong, but pleasant acid taste. Four parts of
citric acid dissolve in three parts of cold, or two of boiling water, the
hot saturated solution readily depositing crystals of the acid on cool-
ing. The solution of citric acid has no rotatory action on a ray of
polarised light.
Aqueous solutions of citric acid readily turn mouldy. When mixed
with chalk and yeast, and exposed to a temperature of about 25 C.,
the solution ferments, with formation of acetate and butyrate of
calcium.
Citric acid is very soluble in aqueous and in absolute alcohol, but is
nearly insoluble in ether, chloroform, benzene, or petroleum spirit.
When heated with syrupy phosphoric acid, citric acid gives off car-
bonic oxide, carbonic acid, acetone, and other products. A similar
some hours at 50 to 60 C., and then gradually to raise the temperature to 100 C. Some
samples lose their water much more readily than others; many samples effloresce in
warm dry air.
1 ACONITIC ACID, H 3 C 6 H 3 6 , is an unimportant acid occurring as a calcium salt in Aconi-
tum napellus and other plants of the same genus. It also exists as a magnesium salt in
Equiaetum fluviatile. It is a product of the dehydration of citric acid, and is occasionally
found in citric acid liquors. Aconitic acid also occurs in the juices of the sugar-cane,
beet-root, and sorghum-cane.
Aconitic acid crystallises with difficulty in colorless, warty masses, or small four-sided
plates, and is resolved into liquid itaconic acid, C 5 H 6 4 , by heating to 187 C. Aconitic
acid is readily soluble in water, alcohol, and ether. Anhydrous ether may be employed to
separate it from citric acid. Aconitic acid crystallises more readily than maleic, and is
more soluble in water than fumaric acid. Its aqueous solution has a decided acid re-
action and a sour taste.
Many of the aconitates are insoluble. Mercurous aconitate is precipitated on adding
mercurous nitrate to a solution of free aconitic acid. Aconitate of calcium, Ca 3 (C 6 H 3 06) 2
+ 6H 0, forms small crystals which require 100 parts of cold water for solution, but are
much more soluble in boiling water. Hence aconitic acid gives no precipitate with lime
water either in the cold or in boiling, a behavior which distinguishes it from citric acid.
If the solution of calcium aconitate be treated with lead acetate, insoluble aconitate of lead
is precipitated, which, when decomposed by sulphuretted hydrogen, yields free aconitic
acid.
When perfectly free from citric acid, aconitic acid does not prevent the precipitation of
ferric solutions by ammonia. Citric acid may be detected in aconitic acid by converting the
acid into a barium salt, and examining the crystals microscopically ; barium citrate
assumes very characteristic forms.
ORGANIC ACIDS. 531
reaction occurs on heating with concentrated sulphuric acid, but sul-
phur dioxide is evolved in addition, and more or less coloring ensues.
Heated with an alkali, it yields an oxalate and acetate : C 6 H 8 O 7 -j-
4KHO = K 2 C 2 O 4 + 2KC 2 H 3 O 2 + 3H 2 O.
When citric acid is heated with dilute sulphuric acid and manga-
nese dioxide, or an acidulated solution of potassium permanganate, it
is oxidised with formation of carbon dioxide and acetone.
Bromine and chlorine act on a solution of sodium citrate in sunlight,
with formation of pentabrom- and pentachlor-acetone respectively.
Detection and Determination of Citric Acid and Citrates.
When 5 grm. of citric acid are heated with 30 c.c. of ammonia for
six hours in a sealed tube at a temperature of 120 C., 1 a yellow color-
ation is observed and small crystals are formed. If the cooled liquid
be poured into an evaporating basin, it becomes blue in the course of
some hours, the color becoming more intense on standing, and in a
few days turning to green, and ultimately disappearing. The change
of color goes on more slowly in the dark. Heating the liquid on the
water-bath hastens the production of the color. Malic, tartaric, and
oxalic acids do not interfere, even when present in large excess; but
itaconic acid must be absent. It is said that O'Ol grm. of citric acid
can be detected by this process (Zeits. Anal. Chem., xvii. 73).
Citrate of calcium is very sparingly soluble, and less soluble in hot
water than in cold. Hence, addition of excess of lime water to a
solution of citric acid produces but a slight precipitate in the cold,
but a somewhat more considerable precipitate of tricalcic citrate,
Ca 3 Ci. 2 , is obtained on boiling, the deposit redissolving as the solution
cools.
Precipitation as tricalcic citrate may be employed for the determi-
nation of citric acid, and serves to separate citrates from malates, ace-
tates, formates, butyrates, &e.; but the precipitate may contain tartrate,
oxalate, or racemate of calcium.
Citric acid may be roughly separated from tartaric acid by digesting
the mixed calcium salts with a hot and perfectly neutral solution of
cupric chloride, 2 when soluble cupric citrate is formed, and an insol-
uble tartrate remains. In the case of mixed tartrates and citrates
which can be converted into the calcium salts by precipitation with
1 This temperature is conveniently obtained by immersing the tube in a bath of
boiling saturated solution of nitrate of sodium.
2 This solution is best extemporised by precipitating a solution of cupric sulphate by
barium chloride, and filtering from the resultant sulphate of barium.
532 ORGANIC ACIDS.
calcium chloride or nitrate in perfectly neutral boiling solution, this
method of separation is occasionally convenient for qualitative pur-
poses, but it is greatly inferior to the precipitation of the tartaric acid
as an acid potassium salt, and fails wholly if the proportion of tar-
trate be small.
From tartaric acid, citric acid is best separated by the method de-
scribed on p. 534. In the filtrate from the precipitate of acid potas-
sium tartrate, the citric acid may be determined by boiling off the
alcohol, exactly neutralising with soda, and proceeding as directed on
p. 538, or by precipitation with barium acetate or lead acetate. If
the acids do not exist in the free state, the solution must be prepared
as directed under Tartaric Acid.
From oxalic acid citric acid is separated by neutralising the solution
with soda, acidifying with acetic acid, and adding calcium sulphate
or chloride. After filtering from the precipitated calcium oxalate,
the citric acid may be thrown down by adding lime water and boiling,
If moderately pure, citric acid may sometimes be conveniently con-
verted into barium citrate, Ba 3 Ci 2 , by precipitating the neutralised
solution with barium acetate, and adding two volumes of 95 per cent,
alcohol. After twenty-four hours, the precipitate is filtered off,
washed with alcohol of 63 per cent., ignited, moistened with sulphuric
acid, again ignited, and the weight multiplied by O'GOl. Alkaline
acetates do not interfere, so that the method is applicable to liquids
from which the tartaric acid has been separated as KELT.
In the absence of other free acids, citric acid may be titrated with
standard caustic alkali, but the end of the reaction is not very sharply
indicated with either logwood, cochineal, or litmus. Carefully made
litmus paper is preferable to the solution, and the alkali should be set
against pure citric acid. The best indicator in titrating citric acid is
phenolphthalein, the end-reaction being delicate and exact.
For the determination of citric acid in presence of heavy metals, the
latter should be first removed by sulphuretted hydrogen or sulphide
of sodium, and the filtered liquid rendered neutral and precipitated
with excess of lead acetate. The unfiltered liquid is mixed with an
equal volume of alcohol, filtered, the precipitate washed with proof
spirit and treated with ammonia. The filtrate may contain citric and
tartaric acids, but will be free from sulphates, phosphates, and
oxalates. When unmixed with other lead salts, citrate of lead may
be suspended in water, decomposed by sulphuretted hydrogen, the
liquid filtered, well boiled, and the free citric acid in the solution
titrated with standard alkali and phenolphthalein.
ORGANIC ACIDS. 533
Full descriptions of the methods of determining citric acid in lemon
juice, citric acid liquors, &c., will be found in subsequent paragraphs.
Commercial Citric Acid frequently contains small quantities of
calcium salts, due to imperfect manufacture, and traces of iron, lead,
and copper are also met with these last being derived from the
vessels used for the crystallisation and evaporation of the acid liquids.
The presence of all these impurities is indicated by igniting 5 or
10 grm. of the sample in a porcelain crucible. The ash usually
varies from 0'05 to 0*25 per cent. When the proportion of ash does
not exceed the latter amount, it is rarely of importance to examine it
further, except for poisonous metals. The presence of lead or copper
will be readily indicated by dissolving the ash in a few drops of nitric
acid, diluting largely, and passing sulphuretted hydrogen.
For the detection of smaller quantities of lead, &c., as much as
50 grm. of the sample should be dissolved in ten times the weight of
water, the solution nearly neutralised with ammonia, and sulphuretted
hydrogen passed through the liquid.
A very fair approximative determination of the lead or copper
present may be obtained by placing the solution of the ash in a tall
glass cylinder standing on a white surface, and comparing the depth
of tint produced by sulphuretted hydrogen with that obtained by
treating an equal bulk of a very weak standard solution of lead or
copper in a similar manner. .If the metal present be copper, a blue
color will be observed on treating the ash with nitric acid, and the
diluted solution will give a brown color with potassium ferrocyanide.
The presence of poisonous metals in citric acid is always accidental,
and the proportion present is usually extremely small (1 part in
10,000) ; but as lead and copper are occasionally present in dangerous
amount, it is necessary to take every precaution to avoid their intro-
duction.
Many samples of citric acid contain free sulphuric add, an impurity
which renders the crystals deliquescent. Sulphuric acid and sulphates
may be detected and estimated by acidifying rather strongly with
hydrochloric acid and adding barium chloride. 233 parts of the
white precipitate of BaSO* correspond to 98 of sulphuric acid
(H 2 S0 4 ).
Formerly citric acid was liable to adulteration with tartaric acid,
but of late the latter substance has been somewhat the more valuable,
so that the tendency to any such sophistication is reversed.
If present, tartaric acid may be conveniently detected by the
charring which occurs on heating the sample with concentrated sul-
534 ORGANIC ACIDS.
phuric acid, as described on p. 514. When the proportion of tartaric
acid in admixture with the citric acid is not too small, it may be de-
tected by the dark color produced, within five minutes, when 1 grm.
of the sample is dissolved in 10 c.c. of a cold saturated solution of
potassium bichromate.
For the detection of tartaric acid in citric acid, Vulpius dissolves
0'5 grm. of the sample in 10 c.c. of distilled water, and adds 5 drops
of the solution, drop by drop, to 15 c.c. of lime water. If the citric
acid contain mere traces of tartaric acid, a distinct turbidity will be
produced in a few moments, which increases on adding more of the
acid solution and stirring. In this manner the presence of 1 per cent,
of tartaric acid may be detected.
If present in admixture with citric acid, tartaric acid is best deter-
mined by converting it into the nearly insoluble acid tartrate of
potassium, in the following manner (A. H. Allen, Chem. News, xxxi.
277) : Two grm. of the sample of acid are dissolved in 20 c.c. of
proof spirit (made by diluting methylated spirit to a density of '920),
the solution filtered from any residue (consisting of tartrates of potas-
sium and calcium, &c.), and made up to 45 c.c. with proof spirit. 5
c.c. of a cold saturated solution of potassium acetate in proof spirit are
next added, the liquid well stirred for ten minutes. If any tartaric
acid be present it will be thrown down as a crystalline precipitate of
KHC 4 H 4 O 6 . When the proportion is very small there may be no
defined precipitate, but there will be white streaks on the sides of the
vessel, in the track of the glass rod used for stirring. Two per cent,
of tartaric acid in samples of citric acid can thus be detected. When
more than a trace of precipitate is obtained, it is filtered off* and
washed with proof spirit. Kinse the precipitate from the filter with a
saturated solution of potassium-hydrogen tartrate in cold water, 1 digest
in the cold for a few hours, with occasional stirring, filter and wash
once with proof spirit. The precipitate consists of potassium-hydrogen
tartrate. It may be rinsed off the filter with boiling water into a small
porcelain dish, and weighed after evaporating off the water at 100 C.
( = 212 F.). The weight multiplied by the factor 0'798 (or roughly,
0-8) gives the quantity of tartaric acid in 2 grra. of the sample taken.
Instead of weighing the precipitate, it may be dissolved in hot water
and titrated with standard alkali and litmus or phenolphthalein in the
1 This is necessary to get rid of any co-precipitated citrate, which in the concentrated
spirituous solutions employed has a great tendency to be dragged down with the tartrate.
In cold weather a very copious precipitation of an acid potassium citrate sometimes occurs,
but it dissolves with facility when digested with the solution of acid tartrate of potassium.
ORGANIC ACIDS. 535
ordinary manner, when each c.c. of normal alkali used equals 0150
grm. of tartaric acid in the 2 grm. of sample taken. In many respects
this method is preferable to the actual weighing of the precipitate.
When great accuracy is desired, a correction should be made for the
solubility of the precipitate in the mother-liquor. When the fore-
going directions are adhered to, an addition of 0'020 grm. to the
weight of tartaric acid actually found is sufficiently near the truth. If
desired, the citric acid maybe determined in the filtrate.
Citric Acid Liquors. This term is applied to the liquors result-
ing in citric acid works from the treatment of the citrate of calcium
with sulphuric acid. Their assay is limited to the determination of
the contained citric and sulphuric acids. For this purpose the total
acidity may be determined by titration with standard alkali and phe-
nolphthaleiu, and the free sulphuric acid then estimated. By sub-
tracting the acidity due to the latter from the total found by titration,
that due to the citric acid alone is ascertained. The free sulphuric
acid is determined by treating 10 or 20 c.c. of the liquor with five
times its volume of strong alcohol. After twelve hours, a portion of
the clear liquor is treated with more alcohol, and, if opalescence result
the whole is treated in the same way. The liquid is ultimately filtered,
the precipitated sulphates washed with spirit, and the filtrate precipi-
tated with an alcoholic solution of calcium chloride. The precipitated
calcium sulphate is allowed to settle completely, the supernatant
liquor poured off, and the precipitate and small quantity of remaining
liquor gently warmed. The alcohol is gradually displaced by cautious
additions of small quantities of water, and, when the precipitate has
become crystalline from its conversion into gypsum, alcohol is added,
and the precipitate collected on a filter, washed with spirit, ignited,
and weighed as CaSO 4 . The weight multiplied by "7206 gives the
sulphuric acid (H 2 SO 4 ) in the liquor taken.
Another method, which agrees well with the last, is to neutralise
exactly a known measure of the citric liquor with pure caustic soda,
evaporate to dryness, and ignite gently in platinum. The ash is
wholly dissolved in a known quantity of standard acid, and the excess
of acid ascertained by titration with alkali. (In presence of iron or
aluminium, some neutral sodium tartrate or Rochelle salt should be
added before titration.) The acid neutralised by the ash is equivalent
to the organic acid contained in the liquor used.
In old liquor, the citric acid should be precipitated as calcium salt,
as other organic acids will be present in serious amount. For this pur-
pose the liquor is treated exactly as directed for juice.
536
ORGANIC ACIDS.
Lemon-juice ; Bergamot-juice ; Lime-juice. These juices
contain free citric acid ; free acids other than citric ; citrates ; salts of
organic acids other than citric ; salts of inorganic acids ; and albumin-
ous, mucilaginous, saccharine, and other indifferent bodies. Spirit is
frequently added as a preservative, and mineral acids are not uncom-
monly employed as adulterants. Verjuice has also been used for the
purpose.
J. Macagno finds that the alcoholic fermentation which takes place
when freshly expressed lemon -juice is kept does not diminish the
amount of citric acid present, but that this is succeeded by another
fermentation during which bacteria make their appearance; this
causes the citric acid to diminish and the proportion of other acids
(chiefly acetic and propionic) to increase. Similarly, juice expressed
from rotten fruit contains acids other than citric, sometimes to the
extent of 10 per cent, of the whole.
A very pure preparation has been introduced by the Montserrat
Lime Juice Company. The producers grow their own limes on the
Island of Montserrat, and by care in the preparation of the juice,
and proper precautions to avoid fermentation, they obtain and export
a very superior product.
Citric acid juices lose some of their acidity by concentration.
Warington observed a loss of 3*5 per cent, of the total free acid on
concentrating English-pressed juice to one-sixth of its original bulk.
The loss is due, at least in part, to the presence of volatile organic
acids, which, of course, exist in much smaller amount in concentrated
juice. Warington found 1*25 per cent, of the total acidity of concen-
trated juice to be due to volatile acids. Among the latter were recog-
nised formic, acetic, and probably propionic acids.
Density.
Free Acid,
oz. per gallon.
Combined
Organic Acid,
oz. per gallon.
Lime-juice
Raw Sicilian,
6-9
0-85
,, English,
1'04 -1-05
11-13
0-3
Concentrated,
1'20 -1-25
56-72
6-8
Bergamot-juice
Concentrated,
Lemon-juice
Raw,
1-22 -1-25
1-035-1-040
47-55
10-6-13-5
7-8
0-4-0-7
Concentrated,
1-28 -1-38
82-112
8-6
The foregoing table, compiled from Warington's data, shows the
ORGANIC ACIDS.
537
density, free acid, and combined organic acid (the two last expressed
in terms of crystallised citric acid, H 3 CiH 2 0) of the various citric
juices commonly met with in commerce.
In the following table, due to Grosjean, are given determinations of
the free acid and precipitable organic acid (both calculated as citric
acid) in commercial samples of concentrated lemon and other juices :
Density.
Acid (reckoned as Citric
Acid)
oz. per gallon.
Proportion
of
Precipitable
to 100 of
Free Acid.
Free Acid.
Total Acid
Precipitable.
Lemon-juice
Average of 65 samples,
Sample A,
Sample B, ...
1-241
1-240
1-235
1-235
1-235
1-326
1-205
1-400
1-350
62-1
65-8
64-9
47-9
52-3
108-3
59-2
16-8
11-7
61-6
59-7
55-7
48-5
49-9
99-8
53-9
11-6
8-0
99-2
90-7
85-8
101-4
95-4
92-2
011
69-0
68-4
Bergamot-juice
Highest,
Lowest,
Lime-juice
Sample A, . . ...
Sample B,
Orange-juice
Sample A
Sample B
From the first of these tables it will be seen that English-pressed
juice contains more free and less combined acid than the raw Italian
and Sicilian juices. This is probably due to the fact that the finest and
ripest fruit is sent to England, while the windfalls and damaged fruit
are treated locally. Concentrated lemon-juice is considered of stand-
ard quality when it contains free acid equal to 66'87 of crystallised
citric acid (C 6 H 5 O 7 -f H 2 O) or 64 oz. of nominal acid (2H 3 Ci+H 2 O).
The Board of Trade standard for lemon -juice is a density of 1*030
(without spirit), and an acidity equivalent to 30 grains per ounce
( = 11 ounces per gallon) of citric acid.
According to the British Pharmacopoeia, lemon-juice should have a
density of T039, and should contain 32? grains of acid per ounce
( = 11 "9 ounces per gallon.) 1
Concentrated bergamot-juice is far less acid than lemon-juice, while
concentrated lime-juice is a thick viscid fluid far exceeding the others
both in density and acidity.
1 According to Stoddart this density is too high for the proportion of acid.
538 ORGANIC ACIDS.
Lemon- and lime-juices are extensively employed as antiscorbutics.
The ash of the lemon-juice has been found to contain 54 per cent, of
potash and 15 per cent, of phosphoric acid ; but as the proportion of
miueral matter is very small, it is difficult to attribute the effects of
lemon -juice to the constituents of the ash.
THE ASSAY OF GENUINE JUICE is practically confined to the deter-
mination of citric acid and citrates, and for this purpose the following
processes are employed :
Determination of the specific gravity. A special hydrometer is some-
times used. On this " citrometer," 60 degrees correspond to a specific
gravity of T240, so that each degree appears to be equal to 0'004
specific gravity above unity.
The valuation by specific gravity is open to many frauds. Berga-
mot-juice, which has a high gravity but low acidity, has been mixed
with lemon-juice, and sea-water has been added to the juice during
concentration. Of course the presence of alcohol materially affects
the density, but its influence may be got rid of by boiling the juice
and again taking the density after making up the volume to that
originally employed.
Determination of the free acid. This is effected by titration with
seminormal caustic soda, very pale and nearly neutral litmus paper
being used as an indicator. In the case of concentrated juice, 50 c.c.
should be diluted to 500, and 25 c.c. to 30 c.c. of the diluted liquid
employed for the titration. With unconcentrated juice, 10 c.c. or
20 c.c. may be measured out at once. In either case, the alkali is
added in quantity sufficient to neutralise about fths of the acid
present; the liquid is then boiled for a few minutes, and when quite
cold the titration is completed. The neutralising power of the alkali
should be known in terms of pure citric acid. The number of grams
of citric acid contained in each cubic centimetre of the juice, multi-
plied by 160, gives the ounces of free acid per gallon.
Determination of the citric and other organic acids in combination with
bases. This is effected by evaporating to dryness the portion of juice
which has been already neutralised by soda for the determination of
the free acid. The residue left on evaporation is heated gradually,
and charred at a low red heat. The ignited mass is treated with
water, a known volume of standard sulphuric acid added, the liquid
boiled and filtered, and the excess of sulphuric acid determined in the
filtrate by standard alkali. The amount of sulphuric acid neutralised
by the ash is equivalent to the total organic acid of the sample, for on
ignition all the salts of organic acids were converted into the corre-
ORGANIC ACIDS. 539
sponding carbonates. 49 parts of H 2 SO 4 neutralised = 40 of NaHO
= 70 of H 3 C 6 H 5 O 7 ,H 2 0, or 67 of 2H 3 C 6 H 5 O 7 ,H 2 O.
The result gives the total organic acid of the juice taken, calculated
as citric acid. By subtracting the amount of free citric acid, obtained
by titration of the acid juice, the amount of combined citric acid is
ascertained.
If the original acid juice be evaporated and ignited, and the com-
bined citric acid calculated from the neutralising power of the ash,
the results obtained are too high, owing to the decomposition of
chlorides, &c., by the citric acid during evaporation.
Determination of the real citric acid. Of the organic acids present
in genuine lemon and similar juices, the citric is the only one of
importance which forms an approximately insoluble calcium salt.
Malate and aconitate of calcium are pretty freely soluble, and the
same remark applies more v strongly to the acetate and butyrate of
calcium produced by the fermentation of citric acid juices. For the
determination of the amount of insoluble calcium salt obtainable from
a citric juice, R. Warington recommends the following method (Jour.
Chem. Soc., xxviii. 934): 15 to 20 c.c. of unconcentrated lemon-juice,
or about 3 c.c. of concentrated juice (previously diluted to facilitate
exact measurement), should be exactly neutralised with pure caustic
soda. The solution is brought to a bulk of about 50 c.c., and heated
to boiling in a salt or glycerin bath, and so much of a solution of
calcium chloride added as is known to be rather more than equivalent
to the total organic acids present. The whole is boiled for half an
hour, and the precipitate then collected and washed with hot water.
The filtrate and washings are concentrated to about 10 or 15 c.c., the
solution being finally neutralised with a drop of ammonia- if it has
become acid. The second precipitate thus obtained is collected on a
very small filter, the filtrate being employed to transfer it, and the
washing with hot water being reduced as much as possible. In very
accurate experiments the concentration should be repeated and any
further precipitate collected. The precipitates, with their filters,
are then burnt at a low red heat, and the neutralising power of the
ash ascertained by treatment with standard hydrochloric acid and
.alkali. Each cubic centimetre of normal add neutralised corresponds
to '070 grm. of crystallised citric acid (H 3 Ci -f H 2 O). The presence
of mineral acids does not interfere; oxalic or tartaric acid would
render the results inaccurate. It is desirable to add peroxide of
hydrogen to the solution of the ash and boil before titrating, other-
wise an error may occur from the presence of sulphides.
540 ORGANIC ACIDS.
In English-pressed lemon-juice the real citric acid is 99 per cent,
of the total organic acid, but in the concentrated Sicilian juice it
varies from 88 to 95 per cent, of the total. In a sample of concen-
trated bergamot-juice, Warington found the precipitable acid to be
about 88 per cent, of the total organic acid, but a more usual propor-
tion is 96 to 98 per cent. The method of determining the value of
juice by its acidity usually, but not invariably, gives tolerably accurate
results in the case of lemon- and bergamot-juice, but in lime-juice the
results are commonly in excess of the truth. Of course this state-
ment is only true of genuine juice.
Determination of alcohol can be effected by the usual methods.
ADULTERATED LIME- AND LEMON- JUICES are not uncommon. The
production of considerable precipitates with barium chloride and silver
nitrate sufficiently indicates the presence of sulphuric and hydrochloric
acids respectively, pure juices containing merely insignificant traces of
sulphates and chlorides. 1 Free sulphuric acid may also be deter-
mined as in citric acid liquors, and both that and free hydrochloric
acid by Hehner's method for the determination of mineral acids in
vinegar.
According to F. D. Scribani (Gaz. Chim. Ital., viii. 284, and Jour.
Chem. Soc.j xxxiv. 914) nitric acid has occasionally been used for the
adulteration of lemon-juice. On concentrating such juice the nitric
acid decomposes the citric acid, either wholly or partially, with forma-
tion of oxalic, acetic, and carbonic acids ; so that on neutralising the
juice with lime a mixture of calcium salts is obtained. To detect the
nitric acid, Scribani adds to the juice an aqueous solution of ferrous
chloride, strongly acidulated with pure hydrochloric acid and quite
free from* ferric salt. The liquid is then boiled for a few minutes, and,
after cooling, tested with a thiocyanate (sulphocyanide). If the liquid
contain nitric acid, a more or less deep-red color will be produced,
owing to the formation of a ferric salt. This test is said to answer
equally well in presence of common salt or sulphuric or tartaric acid. 2
In boiled and dark-colored juices dilution is necessary before the color
can be observed.
METALLIC CITRATES.
Citric acid contains three atoms of replaceable hydrogen, and there-
fore forms three classes of salts. It has a great tendency to produce
1 Sea water has been added to lemon-juice, and would, of course, react with silver nitrate.
2 A more satisfactory and direct test for nitric acid would be to boil the juice with
metallic copper, when red fumes would be produced if nitric acid were present.
ORGANIC ACIDS. 541
stable double citrates, and hence many metallic solutions are not pre-
cipitable by alkalies in presence of sufficient citric acid. This fact is
often utilised in analysis.
None of the metallic citrates is wholly insoluble in water. The
calcium salt is one of the least soluble and hence is employed in the
determination of citric acid. General reactions of the citrates are
described elsewhere, and the properties of the more important commer-
cial forms are given below.
Lithium Citrate. Li 3 Ci. As usually prepared, this is a white
powder, but it may be obtained in crystals with 4 Aq. The salt is
generally stated to be deliquescent, but this is an error. It should be
soluble without residue in twenty-five parts of cold water.
The pure salt, after being rendered anhydrous by drying at 115
C., on ignition leaves 52*9 per cent, of lithium carbonate, Li 2 CO 3 . The
residue should be treated with ammonium carbonate, and again
ignited very gently, as it is liable to lose carbonic acid. A higher ash
than the above indicates impurity or adulteration by (probably)
sodium citrate, which leaves 61*5 per cent, on ignition. One gram
of anhydrous lithium citrate leaves on ignition a residue which should
neutralise at least 14 c.c. of normal hydrochloric acid. The same
amount of sodium citrate (after ignition) would only neutralise 11'25
c.c. of acid. If the resultant solution be evaporated to dryness, lithium
chloride may be dissolved out of the residue by a mixture of equal
volumes of alcohol and ether, while any potassium or sodium chloride
will remain undissolved.
Much of the commercial lithium citrate contains lithium carbonate.
This gives it an alkaline reaction, and increases its ash and its saturat-
ing power. Excess of citric acid gives the salt an acid reaction, and
reduces. the percentage of ash and the saturating power. Hence these
impurities can be distinguished from sodium citrate, which raises the
ash and diminishes the saturating power of the sample.
Potassium Salts may be detected by adding tartaric acid to the con-
centrated solution of the sample and stirring, when a white crystalline
precipitate of acid tartrate of potassium will be produced.
Insoluble matters, such as powdered petalite or lepidolite, will be left
undissolved on dissolving the sample in hot water, and calcium com-
pounds may be estimated in the solution by adding ammonium oxalate.
Calcium Citrate. Ca 3 C 12 H 10 Ou = Ca 3 Ci 2 . This is a white sub-
stance, very sparingly soluble in cold, and still less in hot water. It
is produced, in an impure state, by the citric acid manufacturer by
boiling the juice with chalk, and is sometimes offered in the market as
542 ORGANIC ACIDS.
a convenient source of citric acid. The product consists essentially of
citrate mixed with other salts of calcium, and excess of chalk or lime.
In Sicily, dolomitic lime is sometimes used for neutralising the juice,
in which case magnesium salts will be present. It is particularly
liable to decompose if the percentage of moisture is considerable (more
than 10 or 12 per cent), and therefore some samples contain scarcely
any real citrate.
For the analytical examination of commercial citrate of calcium,
it is sufficient to determine the citric acid and the excess of chalk or
lime. For the latter purpose, 5 grm. of the sample should be dis-
solved in a known quantity of weak standard hydrochloric acid kept
gently boiling, and, when the solution is quite cold, the amount of
acid neutralised is ascertained by titration with standard alkali as
described on p. 531. Each cubic centimetre of normal acid neutral-
ised by the sample corresponds to 0'050 grm. of chalk in the portion
taken. To determine the organic acids, 2 grm. of the sample should
be ignited, the ash boiled with standard acid, the liquid filtered and
titrated with alkali. The acid neutralised by the ash is due to the
chalk existing as such in the sample, plus the calcium carbonate pro-
duced by the ignition of the citrate and other organic salts. By sub-
tracting the neutralisation due to the chalk proper, the equivalent of
the organic acids is found ; each cubic centimetre of normal acid
neutralised being equivalent to '070 grm. of H 3 Ci,H 2 0. This
method gives all the organic acids as citric acid, a result which is
misleading in decomposed citrate. In such samples, the real citric
acid should be determined by dissolving a known weight in hydro-
chloric acid, exactly neutralising with caustic soda, and treating the
precipitated citrate of calcium as described on p. 539. Citrate of
magnesium, or citrate prepared with dolomitic lime, can be correctly
analysed by the titratiou method ; but if precipitation be desired, the
sample must be decomposed by boiling with carbonate of sodium, the
carbonate of magnesium filtered off, the filtrate neutralised with
hydrochloric acid, and precipitated with calcium chloride.
Magnesium Citrate is an intermediate form into which the
citric acid of lemon-juice is sometimes converted. The popular medi-
cine known as " Effervescent Citrate of Magnesia " is a mixture of
citric and tartaric acids with acid carbonate of sodium, loaf-sugar, and
about 3 per cent, of crystallised magnesium sulphate. The last con-
stituent and the citric acid are frequently omitted. A solution sold
as " citrate of magnesia" by a New York manufacturer was found by
A. Claasen to contain only sodium tartrate (Analyst, vi. 202).
ORGANIC ACIDS. 543
Ferric Citrate, Fe (C 6 H 5 O 7 ), is obtained by dissolving ferric
oxide in citric acid and evaporating the solution in thin layers. It is
thus obtained in transparent garnet-red scales, which are permanent
in the air. It is insoluble in alcohol, but dissolves slowly in water to
form a solution of a faintly ferruginous taste, not precipitated by
ammonia, but yielding ferric hydrate on boiling with a fixed alkali.
After drying at 100 C M the scaled should leave from 29 to 30 per
cent, of residue on ignition.
CITRATE OF IRON AND AMMONIUM is a preparation of the British
Pharmacopoeia made by dissolving precipitated ferric hydrate in a
solution of citric acid and adding ammonia. It occurs in thin trans-
parent scales of a deep red color and slightly sweetish and astringent
taste. When heated with caustic potash (not soda) its solution evolves
ammonia and deposits ferric hydrate. The alkaline liquid filtered
from the precipitate should not give any crystalline precipitate or
streaks of acid tartrate of potassium when acidulated with acetic acid
and vigorously stirred. When ignited in the air, the ammonio-citrate
of iron of the British Pharmacopoeia should leave not less than 27 per
cent, of FeaOs, 1 which should be free from alkaline reaction when
moistened. Citrate of iron and ammonium is readily soluble in water,
forming a faintly acid solution, but is almost insoluble in rectified
spirit. A solution of 160 grains in one pint of orange wine forms the
Vinum Ferri Citras of the British Pharmacopoeia.
CITRATE OF IRON AND QUININE will be more conveniently de-
scribed under " Quinine."
Bismuth Citrate, Bi (C 6 H 5 O 7 ), is a white, amorphous, insolu-
ble powder, obtained by boiling bismuth oxynitrate with a solution of
citric acid. It is soluble in ammonia with production of the
CITRATE OF BISMUTH AND AMMONIUM, which occurs in small,
pearly scales, very soluble in water, forming a solution which is not
precipitated on dilution. The "Liquor" of the British Pharmaco-
poeia has a density of 1/122, and contains 24 grains of Bi 2 O 3 to the fluid
ounce. The bismuth is best determined by precipitating the diluted
liquid with sulphuretted hydrogen, when 1 fluid ounce should yield
26-48 grains of Bi. 2 S 3 .
1 Six samples, prepared by large manufacturers of scale preparations, were found by
R. Wright to yield from 31'7 to 44'0 per cent, of oxide of iron on ignition (Pharm. Jour.,
[3] xv. 731), while a specimen occurring in greenish-golden scales left only 22 per cent.
The United States Pharmacopeia requires 25 per cent, of residue on ignition.
ADDENDA.
DETECTION OF GALLISIN IN BEER.
Addendum to Page 133.
Schridowitz and Rosenheim's method is as follows : The beer is
evaporated to thin syrup containing from 20 to 30 grm. of water ; 200
c.c. of alcohol, 90 per cent, (by volume), are added, and then alcohol
95 per cent, (by volume) until no further precipitation occurs. About
500 c.c. will be required, and the product will measure about 750 c.c.,
and contain about 98 grm. of water. The liquid will, therefore, be
a solution of gallisin in alcohol of 85 per cent, (by weight).
Haar stick's Process. One litre of beer is evaporated to a thin syrup,
and 300 c.c. of 90 per cent, alcohol gradually added in quantities of
1 to 2 c.c., and finally 95 per cent, alcohol until the filtrate gives not
the slightest turbidity with 95 per cent, alcohol. The liquid is filtered
after standing for twelve hours, most of the alcohol distilled off, and
the remainder evaporated. The residue is dissolved in water, diluted
to 1 litre, and then fermented at 20 C. with well-washed beer-yeast.
After two or three days a little fresh yeast is added, and on the fourth
day fermentation is complete. The concentrated liquor should show
no dextro-rotation.
Addendum to Page 37 4>
The gallisin of commercial glucose is quite a different substance
from that designated " other matter " in the analyses of invert-sugar
quoted from Moritz & Morris' " Text-Book of Brewing." These sub-
stances originate from the action of the acid on the sugar, and occur
in small quantities in the best samples. Prolonged boiling with acid
reduces the levulose to humin bodies, which, if not harmful, are cer-
tainly valueless. These will be especially formed when the material is
stubborn in inversion, and the boiling has to be protracted, or more
acid used. This is the case when low-class syrups and beet-sugars are
the raw material ; the existence of these humin bodies is, therefore, a
reflection on the quality of the raw material used for the manufacture
of the invert-sugar.
544
ADDENDA.
545
Moritz and Morris also give a number of analyses of cane- and beet-
sugars, which do not show the presence of the humin and other unfer-
mentable matters present in commercial invert sugars.
INVERT SUGAR.
Addendum to Page 357.
ANALYSES OF INVERT-SUGAR (TYPICAL). From Moritz and Morris'
"Text-Book of the Science of Brewing."
Good.
Invert-sugar, 75 '23
Cane sugar, 0"95
Ash, 1-16
Albuminoids, 0'78
Water, 19'23
Other matter, 2'65
100-00
In ferior.
60-53
8-56
5;53
1-89
13-77
9-72
100-00
OUTLINE PROCESS FOR THE DETECTION OF BITTER PRINCIPLES IN BEER.
Addendum to Page 135.
One litre of beer is evaporated to half its bulk and precipitated boiling with neutral lead
acetate, the liquid boiled for fifteen minutes and filtered hot. If any precipitate occur on
cooling, the liquid is again filtered.
PRECIPITATE
con tains hop-
bitter, car-
amel - bitter,
Ophelia acid
(from chir-
etta), phos-
phates, albu-
minous mat-
ters, Ac., &c.
FILTRATE. The excess of lead is removed by passing H 2 S, and the filtered
liquid concentrated to about 150 c.c. and tasted. If any bitter taste is per-
ceived, the liquid is then slightly acidulated with dilute sulphuric acid, and
shaken repeatedly with chloroform.
CHLOROFORM LAYER, on
evaporation, leaves a bitter
extract in the case of gen-
tian, calumba, quassia, and
old hops (only slightly or
doubtfully bitter in the case
The residue is dissolved in a
bot water added, and the hot
d with ammoniacal basic lead
tered.
AQUEOUS LIQUID is shaken with ether.
ETHEREAL LAYKR leaves a bit-
ter residue in the case of chir-
etfa, gentian, or calumba. It is
dissolved in a little alcohol, hot
water added, and the hot solu-
tion treated with ammoniacal
basic lead acetate and filtered.
AQUEOU-" LI-
QUID, if still
bitter, is
rendered al-
kaline and
shaken with
ether- chlor-
oform. A
bitter ex-
tract may be
due to ber-
berine (cal-
umba) or
strychnine.
The aqueous
liquid, sepa-
rated from
the ether-
chloroform,
may contain
caramel -bit-
ter or choline
(somewhat
bitter).
of chiretta).
little alcohol,
solution treate
acetate and fil
PRECIPITATE contains old
hops, gentian, and traces of
caramel products. It is
suspended in water, de-
composed by H 2 S, and the
solution agita'ted with
chloroform.
FILTRATE is
boiled to re-
move am-
monia, and
treated with
a slight excess
of sulphuric
acid filtered
and tasted.
If bitter, it is
agitated with
chloroform,
and the resi-
dueexamined
for calvmba
and quassia.
PRECIPITATE
is treated with
water and de-
composed by
H 2 S. The fil-
tered liquid is
bitter in pres-
ence of gen-
tian.
FILTRATE is
treated with
a slight ex-
cess of dilute
sulphuric
acid, filtered
and tasted. A
bitter taste
indicates cal-
umba or chir-
etta, which
may be re-ex-
tracted with
ether and fur-
ther exam-
ined.
CHLOROFORM
LAYER is ex-
amined by
special tests
for gentian
and old hop-
bitter.
AQUEOUS
LIQUID
contains
traces of
caram,el-
bitter.
35
546 ADDENDA.
SPECIAL PROCESSES FROM BULLETIN OF A. O. A. C.
Method for Estimating Galactan. Bring 3 grm. of the substance into a
beaker about 5 '5 cm. in diameter and 7 cm. deep, together with 60 c.c. of
nitric acid of I'lo specific gravity and evaporate the solution to exactly one-
third of its volume on a water-bath at a temperature of 94 to 96. After
standing twenty-four hours, add 10 c.c. of water to the precipitate, and allow it to
stand another twenty-four hours. The mucic acid has in the meantime crystal-
lised, but is mixed with considerable material only partially oxidised by the
nitric acid. The solution is therefore filtered through filter paper, washed with
30 c.c. of water, to remove as much of the nitric acid as possible, and the filter
and contents brought back into the beaker. Thirty c.c. of ammonium carbonate
solution, consisting of one part ammonium carbonate, nineteen parts water, and
one part strong ammonium hydroxide, are added, and the beaker heated gently
on a water-bath for fifteen minutes. The ammonium carbonate takes up the
mucic acid, forming the soluble ammonium mucate. The solution is filtered
into a platinum or porcelain dish, and the residue thoroughly washed with
water to remove all the ammonium mucate. The filtrate is evaporated to dry-
ness over a water bath, 5 c.c. of nitric acid of 1*15 specific gravity are added, and
the mixture thoroughly stirred and allowed to stand for thirty minutes. The
nitric acid jdecomposes the ammonium mucate, precipitating the mucic acid,
which is collected on a tared filter or Gooch crucible, washed with from 10 to
15 c.c. of water, then with 60 c.c. of alcohol and quite a number of times with
ether, dried at 100 for a short time, and weighed. The mucic acid multiplied
by 1 33 gives galactose, and the product multiplied by 0'9 gives galactan.
Determination of Pentosans by Means of Phloroglucol . Three grm. of the
material are brought into a ten-ounce flask, together with 100 c.c. of 12 per cent,
hydrochloric acid (sp. gr. 1*06) and several pieces of recently heated pumice
stone. The flask, placed upon wire gauze, is connected with a Liebig condenser,
and heat applied, rather gently at first, using a gauze top to distribute the flame,
and so regulated as to distill over 30 c.c. in about ten minutes. The 30 c.c.
driven over are replaced by a like quantity of the dilute acid by means of a sepa-
ratory funnel, and the process continued as long as the distillate gives a pro-
nounced reaction with aniline acetate on filter paper. To the completed distillate
is gradually added a quantity of phloroglucol dissolved in 12 per cent, hydro-
chloric acid, and the resulting mixture thoroughly stirred. The amount of
phloroglucol used should be about double that of the furfural expected. The
solution first turns yellow, then green ; and very soon an amorphous greenish
precipitate appears, which grows rapidly darker, till it finally becomes almost
black. The solution is made up to 500 c.c. with 12 per cent, hydrochloric acid,
and allowed to stand over night. In case there is very little furfural in the sub-
stance tested, and the resulting distillate consequently small, it is best to add
sufficient 12 per cent, hydrochloric acid to the distillate before adding the
phloroglucol solution, so that, upon the addition of the latter solution, the
resulting mixture will contain approximately 500 c.c.
The amorphous black precipitate is filtered into a tared Gooch crucible
through asbestos felt, washed with 100 c.c. of water, dried to constant weight
by heating from three to four hours at 100, cooled and weighed, the increase in
ADDENDA.
547
weight being reckoned as phloroglucid.
phloroglucid, use the following table :
Weight of phloroglucid :
To calculate the furfural from the
' '20 gn
n. 1
820 ]
22
:
839
24
856
26
871
28
884
30
L'895
32
L'904 i
34
1-911
36
L'916 |
38
L'919
40
1-920
45
L'927
I '50+
.
.
L'930 J
furfural.
INDEX.
ABSINTHE, 161
Absinthiu, 134
Absorption spectra, 33
Acarus of sugar, 308
Acetal, 159, 225
Acetaldehyde, 222
Acetate of aluminium, 481
ammonium, 476
amyl, 210
calcium, 476
commercial, 477
copper, 484
ethyl, 215
- iron, 481, 482
tincture of, 483
magnesium, 481
methyl, 215
lead, 483
lime, 476
basic, solution of, 484
potassium, 476
sodium, 476
Acetates, detection of, 459
determination of, 460
metallic, 475
reactions of, 456
Acetic acid, 457
commercial, 463
density of, 458
detection of, 459
determination of, 460
fusing point of, 457
furfural in, 462
glacial, 457, 458, 464
homologues of, 485
Acetic aldehyde, 222
Acetic ether, 186
Acetone, 75
Acetylene, use of, 38
Achrodextrin, 420
Acids, vegetable, 454
fatty, 485
Aconitates, reactions of, 530
Aconitic acid, 530
Acrolein, 218
Acrylic acid, 495
Albuminoids of cereals, 435
Alcohol, 69
absolute, 85
allyl, 78
amyl, 165
calculations, 87
commercial, 88
definition of, 69
density of, 84
density of diluted, 93
detection of, 90
' fusel oil in, 154
methyl compounds in, 79
determination of, 92
by color test, 101
by density, 93_
by oxidation, 102
in tinctures, 162
ethyl, 84
methyl, 69
production of, 107
proportion of, in wine, 112
Alcoholic fermentation, 107
liquors, 107
Alcohols, 69
acid derivatives of, 454
hexatomic, 243
in fusel oil, 168
primary, secondary, &c., 168
Aldehyde, 222
acetic, 222
acrylic, 218
formic, 218
resin, 216
trichlor-, 225
valeric, 212
Aldehydes, 216
general reactions, 216
Ale, 127
Aleurometer, 443
Algin, 423
Allyl alcohol, 78
Allyleue dichloride, 231
Alum, in bread, 449
in flour, 447
Alumina cream, 257
Amidoglutaric acid, 314
Aniidulin, 404
549
550
INDEX.
Amyl acetate, 210
alcohol, 165
hydrate, 165
nitrate, 214
nitrite, 211
commercial, 212
Amylsulphuric acid, 166
Amylan, 387
Amyl alcohol, 165
deleterious effects of, 153
detection of, 166
in spirits, 169
determination of, 166, 170
separation of, 167
Amylin, 387
Amylocellulose, 405
Amyloid, 390
Analysis, definition of, 17
elementary or ultimate, 41
Arabic acid, 424
gum-, 424
Arabin, 422
properties of, 425
Arabinose, 247
Arabinosic acids, 425
Argol, 519
Arrack, 140
Arrowroot, 411
Arsenic in organic bodies, 53
Artificial fruit essences, 214
Assay, definition of, 17
Ash, determination of, 64
of cereals, 446
Asparagine, 313, 448
Aspartic acid, 313
Attenuation, 136
BALLING'S hydrometer, 269
Barley, composition of, 434
sugar, 295
Bassorin, 423, 428
Bastose, 397
Bates' saccharometer, 269, 329
Baume's hydrometer, 23
Beck's hydrometer, 25
Beer, 127
bitter substances in, 133, 545
composition of, 127, 129
definition of, 127
extract in, 127
glycerin in, 109
picric acid in, 135
preservatives in, ,132
Beer-wort, original gravity of, 135
maltose and dextrin in, 330
solids in, 329
specific gravity of, 328
strength of standard, 328
Beet products, valuation of, 317
Beet-root, composition of, 316
juice, 316
molasses, 313
sugar, 301
( Bergamot-juice, 536
Bi-rotation of sugars, 264
Black liquor, 481
Boiling point, 29
Brandy, 141
Bread, 447
Brewing sugar, 375
British gum, 421
Brix hydrometer, 269
Bromethane, 210
Bromide of ethyl, 210
Bromine in organic bodies, 53
Bromoform, 241
Butyl alcohol, 168
- chloral, 231
Butyrate of calcium, 496
copper, 496
ethyl, 215
Butyric acid, 495
determination of, in wine, 491
Butyric chloral, 231
hydrate, 231
CALCIUM acetate, 476
Camphor, compound tincture of, 163
spirit of, 163
Candy, 311
Cane products, valuation of, 317
Cane-sugar, 248, 294
adulterations of, 307
ash of, 302
assay of commercial, 301, 306
composition of commercial, 301
detection of, 298
determination of, 255
in milk, 342
fermentation of, 108, 274
inversion of, 263
manufacture of, 300
optical determination of, 255
specific rotation of, 250
Camose, 294
Capric acid, 488
Caproic acid, 488,
Caprylic acid, 488
Caramel, 296
in spirits, 145
Carbinol, 69
Carbohydrates, 386
density of solutions, 265
Carbon, determination of, in organic
bodies, 43
tetrachloride, 240
INDEX.
551
Carbon trichloride, 209
Carragheenin, 423
Carrier's hydrometer, 25
Celluloid, 401
Cellulose, 387, 388
determination of, 391
- nitro-, 399
varieties of, 389
Cerasin, 423
Cerealin, 445
Cereals, albuminoids of, 435
composition of, 434
mineral constituents of, 446
Chloracetic acid, 459
Chloral, 225
alcoholate, 227
butyric or butyl, 231
detection and estimation of, 229
hydrate, 227
assay of, 229
tests for purity of, 228
meta-, 226
preparation of, 225
Chlorethane, 209, 210
Chlorethylene, 209
Chloride of carbon, 209, 240
ethyl, 199, 208
ethyl ene, 209
ethyl idene, 209
metheuyl, 232
methyl, 182, 184
methyleue, 240
Chlorine in organic bodies, 53
Chlormethane, 182, 240
Chloroform, 232
commercial, 234
detection and estimation of, 233
methylated, 235
spirit of, 239
Cider, 125
Citrate of barium, 530, 532
bismuth, 543
calcium, 541
iron, 543
lithium, 541
magnesium, 542
Citrates, properties of, 540
reactions of, 456, 540
Citric acid, 529
commercial, 533
- determination of, 531, 532, 538
liquors, assay of, 535
Clean spirit, 147
Clerget's sugar method, 260
Cocculus indicus, 135
Cognac, 149
Collodion, 400
Compound ethers, 181
analysis of, 183
Compound ethers, formation of, 181
in wine, 120
physical properties of, 182
Confectionery, sugar-, 311
Copper, in food, 67
Cordials, 160
Cork, composition of, 394, 396
Corn-cockle, in flour, 454
Cotton fibre, recognition of, 397
Cream of tartar, 524
Croton chloral, 231
Crotonic acid, 231
Crystalline form, 19
Cutose, 394
DAMBOSE, 246
Densities, determination of, 20
of sugar solutions, 266, 268
Dephlegmators, 32
Dextran, 423
Dextrin, 387, 419
commercial, 421
in beer, 131
rotatory power of, 420
syrup, 348
Dextro-glucose, 246
Dextrose, 246, 351
estimation, 246, 346, 375
specific rotatory power of, 353
Diabetic urine, examination of, 344
Diastase, preparation of, 415
Diastasic power of malt, 333, 335
Dichlorethane, 209
Dimethyl-acetal, 75, 225
Dispersion, 33
Distillation, 29
fractional, 30
Draff, in malt, 327
Dulcite, 245
Dutch liquid, 209, 235
EBULLIOSCOPE, 105
Edestin, 436
Elementary analysis, 41
Erythro-dextrin, 414
mannite, 245
Essences, artificial fruit, 182, 214
Esters, 181
Ether, 176
acetic, 186
assay of, 178
chlorinated, 226
chloro-carbonic, 234
commercial, 177
methylated, 181
methylic, 181
nitrous, 192
552
INDEX.
Ether, nitrous, spirit of, 181
production of, 176
Ethers, compound, 181
Ethyl acetate, 186
alcohol, 84
bromide, 210
butyrate, 182
chloride, 199, 208
chlorinated, 209
disulphocarbonates, 190
ether, 176
iodide, 182
nitrate, 182
nitrite, 191
determination of, 197
oxalate, 86
oxide, 176
pelargonate, 182
sulphates, 189
sulphuric acid, 190
Ethylates, 86
Ethylene chloride, 209
dichloride, 209
Ethylideue chloride, 209
Eucalyn or eucalyptose, 247
Eucalypton, 249
Examination, preliminary, 19
Extract, estimation of, in beer, 127
in wine, 113
of malt, 332
diastatic power of, 333
FATS, constitution of, 183
Fatty acids, 485
Fehling's solution, 281
action on different sugars, 283
behavior with organic bodies, 529
influence on reducing power of,
287
mode of employing, 281, 283, 529
preparation of, 281
titration of glucose by, 282
Feints, 147
Fermentation, acetic, 109
alcoholic, 107, 274
lactous, 107, 276
of sugar, 107, 274
Fermentative power of malt, 333
Fibres, vegetable, recognition of, 397
Fibrin, vegetable, 436
Finish, methylated, 79
Fixed oils, constitution of, 183
Flax fibre, 398
Flour, adulterations of, 447
alum in, 451
ash of, 446
gluten in, 436
Fluorescence, 33
Foreshots, H7
Formates, reactions of, 456, 493
Formic acid, 493
aldehyde, 218
Formulae, empirical, 42
Fruit essences, artificial , 182, 214
Fumaric acid, 510
Fungin, 389
Furfural, 159, 546
in acetic acid, 462, 464
Fusel oil, 150, 167
assay of, 154
constituents of, 150
detection of, in spirits, 154, 170
determination of, in spirits, 154,
171
GALACTAN, 546
Galactose, 247, 357
Gallic acid, reactions of, 456
Gallisin, 115, 360, 544
Gallotanic acid, reactions of, 456
Gelose, 423
Gentianin, 134
Gin, 141
Gliadin, 436
Gloy, 421
Glucolignose, 393
Glucoses, 246, 343, 358
dextro-, 246, 351
levo-, 246
syrup, 358, 370, 383
in honey, 384
Glucosides, 384
Glutaminic acid, 314
Gluten, 436
assay of flour for, 436
casein, 437
fibrin, 437
Glutenin, 437
Glutin or gliadin, 436
Glycerol, formation of, 108
determination of, in beer, 133
in wine, 114
Glycocine, formation of, 279
Glycogen, 387
Glycyl ethers, 183
Granulose, 405
Grape-juice, composition of, 111
Grape sugar, 246
Grog, 160
Gum arabic, 424
assay of, 426
tragacanth, 423, 428
- wood, 423
Gums, 387, 422
Gun-cotton, 401
nitric peroxide in, 403
INDEX.
553
HEMP fibre, recognition of, 398
Hesperidin sugar, 245
Hollands, 141
Homologues of acetic acid, 485
physical properties of, 485
Honey, 379
examination of commercial, 381
Hop resin, 133
substitutes, 545
Hydrocellulose, 389
Hydrochloric ether, 208
Hydrogen, determination of, inorganic
bodies, 43
Hydrometers, graduation of, 23
Hydrostatic balance, 22
IMMISCIBLE solvents, 57
Inorganic matters, 64
Inosite, 247
Inosol, 247
Inulin, 387
Inversion of sugar, 263, 544
Invertase, 108, 300
Invert sugar, 356, 545
Iodine in organic bodies, 53
lodoform, 241
Iron liquor, 481
Iso-butyl alcohol, 168
Iso-butyric acid, 491, 496
Iso-dulcite, 245
Iso-maltose, 373
Iso-valeric acid, 496, 497
Itaconic acid, 530
JUICES, bergamot, lemon, and lime,
536
cane and beet, 315
Jute fibre, composition of, 396
recognition of, 398
KlRSCHWASSEE, 141
Kjeldahl method, 45
Gunning method, 49
Knapp's solution, 286
LACTIC acid, see Vol. IV
fermentation, 107, 276
Lactose, 248, 336
Lead in food, 67
Leucosin, 436
Levo-glucose, 246
Levulan, 423
Levulin, 387
Levulpse, 246, 354
Lees, 147, 519
Lemon juice, 535
adulterated, 540
composition of, 535
Lichenin, 387
Lignin, 393
Lignose, 393
Lime juice, 535
Linen, recognition of, 397
Liqueurs, 160
Low wine, 147
Lupulin, 134
MALATE of ammonium, 510
barium, 510
calcium, 510
lead, 510
Malates, reactions of, 456, 510
Maleic acid, 510
Malic acid, 509
in wine, 511
Malt, 322
density of solutions, 266, 325
examination of, 324
extract, 332
liquors, 127
sugar, 248
worts, 136, 328
Mai ton, 319
Maltose, 247, 319
Mannite, 245, 380
Mannitol, 245
Mannitose, 247
Maraschino, 161
Marc, 141
Meconates, reactions of, 456
Melitose, 249
Melizitose, 249
Melting point, 27
Mercuric nitrate solution, 339
salts, action on sugars, 286
Metals in organic bodies, 53
detection of, 67
Metacellulose, 389
Metacetonic acid, 494
Metachloral, 226
Metaldehyde, 225
Metarabin, 423
Methaldehyde, 218
Methyl acetate, 74, 182
alcohol. 69
carbinol, 84
chloride, 182
chloroform, 210
compounds, detection of, 79
ether, 181
iodide, 182
oxalate, 70
salicylate, 182
554
INDEX.
Methylated chloroform, 235
ether, 181
finish, 79
spirit, 78
of nitre, 207
Methylene dichloride, 240
Methylic alcohol, 69
density of, 71
detection of, 79
determination of, 73
preparation of pure, 70
Milk-sugar, 248
detection of, 338
determination of, 338
Mohr's balance, 22
Molasses, 312
Mucedin, 437
Mucic acid, 270, 422
Mucilages, 423
Mucoid sugar, 246
Mucous fermentation, 109
Must, constituents of, 110
Mycose, 249
NEUTRAL alcoholic derivatives, 176
Nitrate of amyl, 212, 214
cellulose, 401
ethyl, 182
sucrose, 297
Nitric acid, action of, on sugars, 270
Nitrite of amyl, 182, 211
ethyl, 182, 191
spirit of, 181
Nitrocellulose, 400
Nitrogen bodies, 44
Nitropentane, 213
Nitrosucrose, 297
Nitrous ether, 192
determination of, 197
spirit of, 192
assay of, 197
Normal solutions, 63
Noyeau, 161, 162
OAT-MEAL, examination of, 412
CEnanthylic acid, 486, 488
Oils, constitution of fixed, 183
Opium in tinctures, 164
Optical properties of orgauic bodies, 33
rotation, 34
of sugars, 250
saccharimetry, 255
Optically active bodies, 38
Orange juice, 537
Original gravity of worts, 135
Oxalate of antimony, 526
calcium, 506
Oxalates, properties of, 502
reactions of, 456, 502
Oxalic acid, 500
commercial, 505
determination of, 503
reactions of, 456, 502
toxicological examination for,
504
Oxycellulose, 390
Oxygen, determination of, 54
PAKACELLULOSE, 389
Paraldehyde, 224
Pararabin, 423
Parchment paper, 390
Paregoric elixir, 163
Pavy's solution, 285
Pectates, 395
Pectin, 423
Pectinose, 247
Pectose, 350
Pelargonates, 182, 488, 489
Pentoic acid, 496
Pentyl acetate, 210
alcohol, 165
Perry, 125
Persitol, 245
Phaseomannite, 247
Phenylhydrazine test, 349
Phosphorus in organic bodies, 53
Physics, 140
Picrotoxin, detection of, in beer, 135
Finite, 245
Pith, composition of, 395
Plants, proximate analysis of, 429
Poisonous metals, examination for, 66
Polarimeters, construction of, 34
employment of, 255
Polarisation, circular, 34
of sugars, 250
Potato-spirit, 165, 167
Potatoes, assay of, for starch, 418
Porter, 128, 130
Pot ale, 147
Pot-still whisky, 147
Preliminary examination, 19
Proof spirit, 87
Propionic acid, 486, 494
determination of, in wine, 491
Propyl alcohol, 151
Proximate analysis of plants, 429
of woody tissues, 395
Pyrocatechol, 482
Pyrogallic acid, reactions of, 456
Pyrogallol, 456
Pyroligneous acid, 462
Pyrolignite of iron, 481
lead, 483
INDEX.
555
Pyrolignite of lime, 477
Pyroxylin, 400
QUASSIA, detection of, in beer, 133
Quercitol, 245
RACEMIC acid, 513
Raffinose, 245
Reactions of vegetable acids, 456
Rectified spirit, 87, 140
Red liquor, 482
Reducing action of sugars, 279
on Fehling's solution, 280
Refraction, 33
double, 34
Rhiuanthrine, 454
Robur, 161
Rochelle salt, 525
Rotary power of sugars, 250
Rotatory power of organic bodies, 34
Rum, 142
bay, 143
essence of, 182
SACCHARIC acid, 270
Saccharimetry, optical, 255
Saccharin, 278
Saccharine solutions, density of, 266,
268
Saccharinic acid, 278
Saccharoids, 245
Saccharometers, 269
Saccharoses, 248, 294
Saccharum, 358
Sachsse's mercurial solution, 286
Salicylate of methyl, 182
Salicylic acid in beer, 132
in wine, 118
Saponifieation, 183
Schnapps, 141
Schweitzer's reagent, 388
Scyllite, 247
Seidlitz powders, 525
Sinodor, 481
Sizal, 398
Solidifying points of organic bodies, 27
Solvents, action of, 54
immiscible, 57
Sorbin, 247
Sorbinose, 247
Sorbite, 245
Soxhlet's tube, 55
solution, 288
Specific gravity, 20
bottle, 21
of saccharine solutions, 266
Specific rotatory power, 38
of sugars, 250
tables of, 254, 353
of cane sugar, 254
of dextrose, 254
of maltose, 254
Spectra, absorption, 33
Spectroscope, 33
Spirit indication, 136
of camphor, 164
of nitrous ether, 192
analysis of, 197
of wine, 84
methylated, 78
proof, 87
Spirits, 140
examination of, 143
flavoring substances in, 146
Sprengel's tube, 22
Standard solutions, 63
Squibb's acetone process, 76
hydrometer, 21
specific gravity bottle, 21
Starch, 403
commercial, 403
corpuscles, structure of, 405
detection of, in coffee, 413
determination of, 414
in potatoes, 418
isomers of, 387
microscopic characters of, 408
reaction of, with iodine, 413
soluble, 404
sugar, 351, 358
detection of, in cane sugar,
309
in honey, 381
subliming point, 28
Succinates, reactions of, 456, 507
Succinic acid, 506
commercial, 508
determination of, 117, 508
formation of, 109
reactions of, 456, 507
Succinic anhydride, 507
Sucrates, 297
Sucro-dextrose, 246
Sucro-levnlose, 246
Sucrose, 248, 294
Sugar, adulterations of, 307
beet, 304
brewing, 375
cane, 248, 294
commercial, 300
crystallisable in raw, 306
fermentation of, 274
grape, 246
inversion of, 271
invert, 356
556
INDEX.
Sugar malt, 248, 319
- maple, 301
milk, 336
rnucoid, 246
- palm, 300
purity, co-efficient of, 318
solutions, clarification of, 256
density of, 266, 268
sorghum, 301
Sugar-acarus, 308
Sugar-beet, composition, 316
Sugar-cane, composition, 315
Sugar-confectionery, 311
Sugars, 243
action of acids on, 270
alkalies on, 277
as reducing agents, 279
assay of commercial, 306, 317
bi-rotation of, 264
classification of, 243
density of solutions of, 266, 268
inversion of, 263
isolation of, 263
non-fermentable, 245
reaction with Fehling's solution,
280
recognition of various, 291
- relations of, to polarised light, 250
specific rotation of, 250
table of, 254
Sulphates in wine, 119
Sulphites, 119
Sulphovinic acid, 190
Sulphur in organic bodies, 53
Sulphuric acid, action on sugars, 270
Sweet spirit of nitre, 164
Synanthrose, 249
TABARIE'S method, 103
Tartar, 519
assay of, 520
cream of, 526
emetic, 526
Tartaline, 520
Tartaric acid, 512
commercial, 516
determination of, 514
in citric acid, 534
in wine, 117
liquors, assay of, 516
reactions of, 514
varieties of, 513
Tartrate of ammonium, 527
antimony, 526
calcium, 527
copper, 528
potassium, 524, 525
and antimony, 526
Tartrate, potassium, and hydrogen, 524
and iron, 526
and sodium, 525
Tartrates, 523
reactions of, 456, 523
Tea spirit, 161
Tetrachloride of carbon, 240
Tinctures, 162
deposits from, 164
Tragacanth gum, 428
Tragacanthin, 423, 428
Transition tint, 35
Treacle, 312
Trehalose, 249
Trichloracetic acid, 230
Trichloraldehyde, 225
Trinitrocellulose, 401
Twaddell's hydrometer, 23
ULMIC acid, 393
Ultimate analysis, 41
Urine, sugar in diabetic, 344
VALERAL, or valeraldehyde, 218
Valerates, 497
Valerianic acid, 497
Valeric acid, 496
commercial, 498
reactions of, 497
Vanillin in molasses, 314
Vapor densities, 261
Vasculose, 393
Vegetable acids, reactions of, 456
fibres, recognition of, 397
mucilages, 423
Verdigris, 484
Viuasse, 314
Vinegar, 465
acetic acid in, 466
aromatic, 472
ash of, 471
cider, 467, 471
eels, 475
factitious, 468
flies in, 475
glucose, 468
malt, 467
mineral acids in, 472
perry, 467
proof, 466
sugar, 468
sulphuric acid in, 473
tartaric acid in, 475
wine, 467
wood, 472
Vinous fermentation, 110
Viscose, 423
INDEX.
557
WESTPHAL balance, 23
Whisky, 143
fusel oil in, 147
Wiley's extractor, 55
ebullioscope, 105
Wine, 110
alcohol in, 112
analysis of, 113
antimonial, 526
artificial, 125
- coloring matters in, 120
composition of, 112
ethers in, 85
extract in, 114
- gallisin in, 115
- glycerin in, 114
malic acid in, 118
organic acids in, 118
plastering of, 118
propionic acid in, 491
salicylic acid in, 118
spirit of, 84
succinic acid in, 118, 508
sugar in, 114, 123
tannin in, 116
Wine, tartaric acid in, 116
valeric acid in, 491
volatile acids in, 116, 490
Wood gum, 423
naphtha, 72
- spirit, 72
assay of, 73
Woody tissues, analysis of, 395
composition of, 31).'J
Wort, original gravity of, 135
strength of standard, 328
XANTHATES, 190
Xanthic acid, 191
X-ray, application of, 34
YEAST, action of, 149, 274
ZEIX, 440
Zinc in food, 67
Zymom, 437
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INDEX TO J. & A. CHURCHILL'S LIST.
Allen's Chemistry of Urine, 12
Commercial Organic Analysis, 13
Anderson's Deformities of Fingers and Toes, 9
Armatage's Veterinary Pocket Remembrancer, 14
Barnes (R.) on Obstetric Operations, 3
on Diseases of Women, 3
Beale (L. S.) on Liver, 6
Microscope in Medicine, 6
Slight Ailments, 6
>- Urinary and Renal Derangements, 12
Beale (P. T. B.) on Elementary Biology, 2
Beasley's Book of Prescriptions, 5
Druggists' General Receipt Book, 5
Pocket Formulary, 5
Kell on Sterility, 4
Bellamy's Surgical Anatomy, i
Bentley and Trimen's Medicinal Plants, 5
Bentley's Systematic Botany, 5
Berkart's Bronchial Asthma, 6
Bernard on Stammering, 7
Bernays' Notes on Analytical Chemistry, 13
Bigg's Short Manual of Orthopaedy, 9
Bloxam's Chemistry, 12
Laboratory Teaching, 12
Bousfield's Photo-Micrography, 14
Bowlby's Injuries and Diseases of Nerves, 9
Surgical Pathology and Morbid Anatomy, 9
Brockbank on Gallstones, 8
Brodhurst's Anchylosis, 9
Curvatures, &c. , of the Spine, 9
Talipes Equino-Varus, 9
Dislocation of Hip, 9
Brown's (Haydn) Midwifery, 3
(Campbell) Practical Chemistry, 13
Bryant's Practice of Surgery, 8
Burckhardt's (E.) and Fenwick's (E. H.) Atlas of
Cystoscopy, n
Burdett's Hospitals and Asylums of the World, 2
Butler-Smythe's Ovariotomies, 4
Butlin's Malignant Disease of the Larynx, 11
Operative Surgery of Malignant Disease, 1 1
Sarcoma and Carcinoma, n
Buzzard's Diseases of the Nervous System, 7
Peripheral Neuritis, 7
Simulation of Hysteria, 7
Cameron's Oils, Resins, and Varnishes, 14
Soaps and Candles, 14
Carpenter and Dallinger on the Microscope, 14
Carpenter's Human Physiology, 2
Cautley's Infant Feeding, 4
Charteris' Practice of Medicine, 6
Chauvean's Comparative Anatomy, 14
Chevers' Diseases of India, 5
Churchill's Face and Foot Deformities, 9
Clarke's Eyestrain, 10
Clouston's Lectures on Mental Diseases, 3
Clowes and Coleman's Quantitative Analysis, 13
Elmntry Practical Chemistry, 13
Clowes' Practical Chemistry, 13
Coles on Blood, 6
Cooley's Cyclopaedia of Practical Receipts, 13
Cooper on Syphilis, 12
Copper and Edwards' Diseases of the Rectum, 12
Cripps' (H.) Ovariotomy and Abdominal Surgery, 9
Cancer of the Rectum, 12
Diseases of the Rectum and Anus, 12
Air and Faeces in Urethra, 12
Cripps' (R. A.) Galenic Pharmacy, 4
Cuffs Lectures to Nurses, 4
Cullingworth's Manual of Nursing, 4
Short Manual for Monthly Nurses, 4
Dalby's Diseases and Injuries of the Ear, 10
Short Contributions, 10
Dana on Nervous Diseases, 7
Day on Diseases of Children, 4
on Headaches. 8
Domville's Manual for Nurses, 4
Doran's Gynaecological Operations, 3
Druitt's Surgeon's Vade-Mecum, 8
Duncan (A.), on Prevention of Disease in Tropics, 5
Dunglison's Dictionary of Medical Science, 12
Ellis's(T. S.) Human Foot, 9
Fagge's Principles and Practice of Medicine, 6
Fayrer's Climate and Fevers of India, 5
Natural History, &c., of Cholera, 5
Fenwick (E. H.), Electric Illumination of Bladder, u
Fenwick (E. H.) Tumours of Urinary Bladder, n
Fenwick's (S.) Medical Diagnosis, 6
Obscure Diseases of the Abdomen, 9.
Outlines of Medical Treatment, 6
The Saliva as a Test, 6
Fink's Operating for Cataract, 10
Flower's Diagrams of the Nerves, i
Fowler's Dictionary of Practical Medicine, 6
Fox (G. H.) on Skin Diseases of Childien, 10
Fox (Wilson), Atlas of Pathological Anatomy of Lungs, 6
Treatise on Diseases of the Lungs 6
Frankland and Japp's Inorganic Chemistry, 13
Fraser's Operations on the Brain, 8
Fresenius' Qualitative Analysis, 13
Quantitative Analysis, 13
Galabin's Diseases of Women, 3
Manual of Midwifery, 3
Gardner's Bleaching, Dyeing, and Calico Printing, 14
Brewing, Distilling, and Wine Manuf. IA
Gimlette on Myxcedema, 6
Glassington's Dental Materia Medica, 10
Godlee's Atlas of Human Anatomy, x
Goodhart's Diseases of Children, 4
Cowers' Diagnosis of Diseases of the Brain, 7
Manual of Diseases of Nervous System, 7
Clinical Lectures, 7
Medical Ophthalmoscopy, 7
Syphilis and the Nervous System, 7
Granville on Gout, 7
Green's Manual of Botany, 5
Groves' and Thorp's Chemical Technology, 14
Guy's Hospital Reports, 7
Habershon s Diseases of the Abdomen, 7
Haig's Uric Acid, 6
Diet and Food, 2
Harley on Diseases of the Liver, 7
Harris's (V. D.) Diseases of Chest, 6
Harrison's Urinary Organs, IT
Hartridge's Refraction of the Eye, 10
Ophthalmoscope, 10
Hawthorne's Galenical Preparations of B.P., 4
Heath's Certain Diseases of the Jaws, 8
Clinical Lectures on Surgical Subjects, &
Injuries and Diseases of the Jaws, 8
Minor Surgery and Bandaging, 8
Operative Surgery, 8
Practical Anatomy, i
^ Surgical Diagnosis, 8
Hellier's Notes on Gynaecological Nursing, 4
Hewlett's Bacteriology, 3
Higgens' Ophthalmic Out-patient Practice, 10
Hill on Cerebral Circulation, 2
Hillis" Leprosy in British Guiana, 10
Hirschfeld's Atlas of Central Nervous System, 2
Holden's Human Osteology, i
Landmarks, i
Holthouse on Strabismus, 9
Hooper's Physicians' Vade-Mecum, 5
Hovell's Diseases of the Ear, 10
Human Nature and Physiognomy, 14
Hyde's Diseases of the Skin, 10
Hyslop's Mental Physiology, 3
Impey on Leprosy, 10
Ireland on Mental Affections of Children, 3
Jacobson's Male Organs of Generation, 12
^ ^ Operations of Surgery, 8
Jellett's Practice of Midwifery, 3
Jessop's Diseases of the Eye, 9
Johnson's (Sir G.) Asphyxia, 6
Medical Lectures and Essays, 6
Cholera Controversy. 6
(A. E.) Analyst's Companion, 13
Journal of Mental Science. ?
Kellogg on Mental Diseases^ 3
Keyes' Genito-Urinary Organs and Syphilis, 12
Kohlrausch's Physical Measurements, 14
Lancereaux's Atlas of Pathological Anatomy, 2
Lane's Rheumatic Diseases, 7
Langdon -Down's Mental Affections of Childhood, 3-
Lazarus-Barlow's General Pathology, i
Lee's Microtomists* Vade Mecum, 14
Lescher's Recent Materia Medica, 4
Lewis (Bevan) on the Human Brain, 2
Liebreich's Atlas of Ophthalmoscopy, 10
Lucas's Practical Pharmacy, 4
[Continued on the next page.
LONDON: 7, GREAT MARLBOROUGH STREET.
INDEX TO J. & A. CHURCHILL'S LIST continued.
MacMunn's Clinical Chemistry of Urine, 12
Macnamara's Diseases and Refraction of the Eye, 9
-, . of Bones and Joints, 8
McNeill's Epidemics and Isolation Hospitals, 2
Malcolm's Physiology of Death, 9
Marcet on Respiration, 2
Martin's Ambulance Lectures, 8
Maxwell's Terminologia Medica Polyglotta, 12
Maylard's Surgery of Alimentary Canal, 9
Mayne's Medical Vocabulary, 12
Microscopical Journal, 14
Mills and Rowan's Fuel and its Applications, 14
Moore's (N.) Pathological Anatomy of Diseases, i
Moore's (Sir W. J.) Family Medicine for India, 5
Manual of the Diseases of India, 5
Morris's Human Anatomy, i
Moullin's(Mansell) Surgery, 8
Nettleship's Diseases of the Eye, 9
Notter and Firth's Hygiene, 2
Ogle on Tympanites, 8
Oliver's Abdominal Tumours, 3
Diseases of Women, 3
Ophthalmic (Royal London) Hospital Reports, 9
Ophthalmological Society's Transactions, 9
Ormerod's Diseases of the Nervous System, 7
Parkes" (E.A.) Practical Hygiene, 2
Parkes' (L.C.) Elements of Health, 2
Pavy's Carbohydrates, 6
Pereira's Selecta e Prescriptis. 5
Phillips' Materia Medica and Therapeutics, 4
Pitt-Lewis's Insane and the Law, 3
Pollock's Histology of the Eye and Eyelids, 9
Proctor's Practical Pharmacy, 4
Purcell on Cancer, n
Pye-Smith's Diseases of the Skin, n
Ramsay's Elementary Systematic Chemistry, 13
Inorganic Chemistry, 13
Richardson's Mechanical Dentistry, 10
Richmond's Antiseptic Principles for Nurses, 4
Roberts' (D. Lloyd) Practice of Midwifery, 3
Robinson's (Tom) Eczema, n
Illustrations of Skin Diseases, n
> Syphilis, n
Ross's Aphasia, 7
Diseases of the Nervous System,, 7.
Royle and Harley's Materia Medica, 5
St. Thomas's Hospital Reports, 7
Sansom's Valvular Disease of the Heart, 7
Shaw's Diseases of the Eye, o
Shaw- Mackenzie on Maternal Syphilis, 12
Short Dictionary of Medical Terms, 12
' Silk's Manual of Nitrous Oxide, 10
Smith's (Ernest A.) Dental Metallurgy, 10
Smith's (Eustace) Clinical Studies, 4
Disease in Children, 4
Wasting Diseases of Infants and Children, 4
Smith's (J. Greig) Abdominal Surgery, 8
Smith's (Priestley) Glaucoma, 10
Snow's Cancer and the Cancer Process, n
Palliative Treatment of Cancer, n
Reappearance of Cancer, n
Solly's Medical Climatology, 8
Southall's Materia Medica, 5
Squire's (P.) Companion to the Pharmacopoeia, 4
London Hospitals Pharmacopoeias, 4
Methods and Formulae^ 14
Starling's Elements of Human Physiology, 2
Sternberg's Bacteriology, 6
Stevenson and Murphy's Hygiene, a
Sutton's (J. B.), General Pathology, i
Sutton's (F.) Volumetric Analysis, 13
Swain's Surgical Emergencies, 8
Swayne's Obstetric Aphorisms, 3
Taylor's (A. S.) Medical Jurisprudence, 2
Taylor's (F.) Practice of Medicine, 6
Taylor's (J. C.), Canary Islands, 8
Thm's Cancerous Affections of the Skin, n
Pathology and Treatment of Ringworm, ir
on Psilosis or " Sprue," 5
Thomas's Diseases of Women, 3
Thompson's (Sir H.) Calculous Disease, n
Diseases of theUrinaryOrgans,n
Lithotomy and Lithotrity, n
Stricture of the Urethra, n
Suprapubic Operation, 1 1
Surgery of theUrinaryOrgan3.il
Tumours of the Bladder, n
Thome's Diseases of the Heart, 7
Thresh's Water Analysis, 2
Tilden's Manual of Chemistry, 12
Tomes' (C. S.) DentaJ Anatomy, 10
Tomes' (J. and C. S.) Dental Surgery, 10
Tooth's Spinal Cord, 7
Treves and Lang's German-English Dictionary, 12
Tuke's Dictionary of Psychological Medicine, 3
Tuson's Veterinary Pharmacopoeia, 14
Valentin and Hodgkinson's Qualitative Analysis, 13
Vintras on the Mineral Waters, &c., of France, 8
Wagner's Chemical Technology, 14
Walsham's Surgery : its Theory and Practice, 8
Waring's Indian Bazaar Medicines, 5
Practical Therapeutics, 5
Watts' Organic Chemistry, 12
West's (S.) How to Examine the Chest, 6
Westminster Hospital Reports, 7
White's (Hale) Materia Medica, Pharmacy, &c.
Wilks' Diseases of the Nervous System, 7
Wilson's (Sir E.) Anatomists' Vade-Mecum, i
Wilson's (G.) Handbook of Hygiene, 2
Wolfe's Diseases and Injuries of the Eye, 9
Wynter and Wethered's Practical Pathology, i
Year- Book of Pharmacy, 5
Yeo's (G. F.) Manual of Physiology, 2
N.B.J. fy A. Churchill's larger Catalogue of about 600 works on Anatomy,
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