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?' Il;

EXPERIMENTAL CHEMISTRY.

• S- «a9c & (Bo.e €bnrational §ttit0.

EXPERIMENTAL CHEMISTRY

FOR

JUNIOR STUDENTS

J. EMEBSON BEYNCLDS, M.D, F.R.S^

VICB-PRBSIDBNT CUmiCAL SOCIETY OP WXdON

PaomsoB OF camsTav. wnivemitt or dublut.

ce:4P. /. TO xvL

limed to cover work in IL Form of Sigh School

Course*

TORONTO:
^' J. GAGE & COMPAI^Y,
1886.

Entered according: to Act of Parliament in the oflSce of the Minister of
Agriculture, iu the year of our Lord, 1886, by W. J. Qaqi St Co.

PREFACE

THE SECOND EDITION,

The necessity for the issue of a Second Edition of '

Parts I. and II. has given me the opportunity to

make a few verbal corrections, and some addition,

required by our advancing knowledge. Otherwise

the work retains the form in which I am glad to

know ,t has proved acceptable to teachers and
Students.

November, 1882,

J. E. R

PREFACE

THE FIRST EDITION.

This work ,s identical in plan with my Six Ledum on
Expenmental Chemistry, but different in style and
much extended in ^ge, so as to include the
amount of knowledge of fact and principle usually
expected from junior Arts, Medical and Pharma-
ceufcal StuJents, as well as from the higher classes in
Intermediate Schools.

The system pursued in this book is designed to

pelts r' """^'^ ^ ^'' "" --ecffe !
h.mT r ^""'-'i"^'"'^ ■•" -m-and to assist

1 ^ wterpreution of his results, and in devi-

drawn from them. Thus while acquiring a tolerably
amomuTf ■°''^'^^ ''^ ^'"''^ '-eifes a cenat

rZ. / '"^'" "'^ P"^^'y 'experimental
method of mveshgating Nature. If this trainin.. be

mea"ns' of' ^'""^V^/'^^-'-y "-t prove a valu^ab^
means of mental education. How far the particular
P^ pursued in the following pages is liketyto con
tribute to such a result, I must leave «th<..= L .•,.^-. .

• ••

VI 11

Preface,

I !

but a reviewer of my Lectures was so good as to
say : — * In these Lectures the author departs widely
from the usual routine of elementary treatises. . . .
We believe that he. is right in the plan he has
adopted, and that instruction of this nature
would greatly facilitate the acquisition of clear and
distinct ideas of the leading facts and laws of
Chemistrjr.' (Chemical News, vol. xxix. page 227.)
This work is divided into four parts, each one being,
as far as practicable, complete in itself. Part I. is
introductory, and deals with first principles, and
with the chemistry of the typical elements, hydro-
gen and oxygan, and their compounds; Part II.,
with the rest of the non-metals ; Part III., with the
metals ; and Part IV., with organic chemistry.
The experiments described are, Whenever possible,
those easily performed ; in some cases, however,
methods are necessarily detailed which the student
may not have either the skill or the means to cany
out, but he should endeavour to see these operations
carefully conducted. It is assumed throughout that
the reader can obtain some practical instruction in
glass working and the construction of apparatus.

It is only necessary to add that the complete work
will contain the solutions of all the problems in my
Lecture Niote Book,

J. E, R.

CHERflCAL Laboratory,
Trinity College, Dublin i
Xvovember, 1880.

CONTENTS.

-•o*-

CHAPTER r.
Prenminary experiments-Difference between physical '^""

change Che .^'f^^-^^^- ^f effecting TeS
Change-Chemical attraction -Mechanical mixtures
and chemical compounds . . «iixtures

CHAPTER II

Experiments with Silver Nitrate and Magnesium-The

:Ste";-:r^ot^-^^^^^^^^

CHAPTER III.

^'kS'^w^^ ""^^^^""^ -^ Hydrogen-Equiva-
lents-^Chief characters of Jlydrogen gas . . .

CHAPTER IV.

Experiments with Hydrogen and Oxygen gascs-Con^n •
tion of water-Electrolvsis rhI5 ^^'^^^'"'^P^si-

_ ^*c^ifOl> sis — Chief Drnnpwioc ^c r\

gen-uombustion of candle in air ^"-"-'"^" "' '"^^■

Contents,

CHAPTER V.

Experiments with Hydrogen and Oxysen continued-
Specific gravities of gases— Effects of changes of tern-
perature and pressure on gases— Avogadro's law —
Dual character of elementary molecule — Gay-Lussac's
laws — Atoms — Atomic weights of gaseous elements
determined — Atomic Theory

PAGB

CHAPTER VI.

Experiments with Silver, Copper, and Magnesium— Capa-
city for heat— Specific heat— Dulong and Pedt's law-
Atomic heat ••••....

CHAPTER VII.

Table of Atomic weights— Distinction of metals and non-
metals — Electro-cht nical changes — Chemical for-
mulae, how deduced — Empirical and rational formulse
—Atomicity or quantivalence — Equations • • •

CHAPTER VIII.

Experiments with Acids, Alkalies, nnd Salts— Bases —
Classes of acids — Radicles of salts — Simple and com-
pound radicles .•••••••

CHAPTER IX.

Farther experiments with Hydrogen — Preparation — I ro-
perties- /lame tests — Hydrogen as a reducing agent —
i^er riduit ••••••••

Cofttents.

CHAPTER X.

Experimental determination of the volume occupied by
one centigram of Hydrogen gas -Correction of gaseous
volumes— The VoL-Calculations— Absolute tempera-
ture— Law of Charles ....

PACK

CHAPTER XL

Further experiments with Oxygen gas- Preparation -Pro-
perties— Oxides— Acid producing and basic Oxides or
Anhydrides-Indifferent Oxides -Oxyhydrogen flame
—Ozone— Preparation — Characters— AUotropism—
Isomerism • , . .

io8

CHAPTER XIL

Experiments with water-Purification of water bydistilla-
tidn-Latent heat of steam-Effects of cold on water
—Maximum density of water- Latent heat of water-
Solvent action on solids, liquids and gases-Water
supply-Hardness of water-Mineral springs-S°a
water-Peroxide of Hydrogen -Preparation-Proper-

fA7P'?'^'°" °^~'^'^'' ^^^ ^/^^^-Hydroxyl-Law
of Multiple Proportions . . / ;' 'iw

125

APPENDIX.
Modes of chemical change-Laws of Berthollet

143

PART IL

CHAPTER XIII.

Experiments with nitrogen — Atmospheric air — Its an-
alysis — Composition by volume and weight — A
mechanical mixturje— Effects of animals and plants
upon— Changes in, caused by burning candles, gas, or
coal— Causes of uniform composition — Graham's law
of diffusion of gases — Impurities in air, how detected •

rAGB

CHAPTER XIV.

Experiments with compounds of nitrogen— Nitric acid
— Its preparation, properties, and tests — Nitre— Gun-
powder —Nitrogen peroxide — Preparation and pro-
perties—Nitrogen sesquioxide and nitrous acid —
Preparation and properties —Nitric oxide— Preparation
and characters— Nitrogen monoxide — Laughing gas —
Preparation and properties— Physiological effects —
Ammonia — Prep-^'-ation and properties — Ammonium
hydrate — Salts a., -erivatives . • • • .

167

CHAPTER XV.

Experimsnts with hydrochloric acid — i reparation and
characters— Analysis oi—Aqua regiu—QYiXoxvat — Pre-
paration and properties — Synthesis of hydrochloric

Contents.

xin

acid-Chlorine water-Bleaching action of chlorine '''°"

~?ertr'r ^'"^'"^ li-e-Potassiu.n c

rests for chlorates-Potassium perchlorate- Pr.
paration and tests^Series of chlorine'acids " ,^^

CHAPTER XVI.
Experi„,ents with iodine- Separation of iodine- Manu
facture from kelp-Its characters -Hydriodl acid
Preparation and properties - Iodides - T sU for odiT
acid and anhydride . -resistor iodic

232.

!: il'

INTRODUCTION

EXPERIMENTAL CHEMISTRY.

PART I.

CHAPTER I.

PRELIMINARY EXPERIMENTS.

ChemVry has for its object the discovery of the laws
which govern the composition of all material things
and the action of one kind of matter upon another in
all cases mvolving change in composition. This
knowledge is acquired by experiment, accurate obser-
vation of the phenomena presented during an experi-
ment, and careful reasoning upon the result. The
lollowing pages contain numerous illustrations of the
application of this experimental method of inquiry in
the study of chemistry. ^

Experiment l.-Let us commence our course with
a simple experiment.

Hold by means of a small pincers or tongs a piece
ot thin wire of the metal njntinM

• «• \tt.i\. xitmiv \jk ((

li'

Fig. I.

2 Introduction to Experimental Chemistry.

spirit lamp, as in fig. i, or in that of a Bunsen gas<
burner. Observe that the wire soon becomes red-hot
and glows as long as it is held in the flame ; but,
when removed and allowed to cool, it resumes its

original appearance, and if
weighed before and after the
experiment, no difference is
observed. Therefore the
change from cold to red-hot
platinum is but a temporary
one, the metal remaining un-
changed in form and sub-
stance.

Experiment 2. — Now
make an identical experi-
ment with a piece of mag-
nesium wire or ribbon. Ob-
serve that the metal # soon
begins to burn and emits much light, even when
removed from the source of heat. It also gives out
white fumes .and leaves a white substance behind
which, though retaining some of the form of the
original wire or ribbon, can be easily powdered when
cold, and is seen to be utterly unlike the metal
which produced it. Moreover, the white substance
is found to iveigh more than the magnesium originally
taken. In this case, a change has taken place on
heating, and it is per ma?ient.

The temporary alteration of the platinum wire is
not accompanied by any difference in composition,
aftd IS spoken of as a pJiysial change ; that of the
magnesium, as a chemical ^nange, and the action, as

Prehminary Experiments.

^//«W«^//i,„, because a material alteration in com-
position has taken place, as shown l,y the gain in
weight; and a new body has been produced, evidently
possessing characters which serve to distinguish it
completely from the metal magnesium, and, indeed.
Irom all other known substances.

All observed changes in matter can be placed in
one or othe' of the above classes, but it is with
chemical change and chemical acti.m that we are
principally concerned.

.h /?u"'^ experiment with magnesium it was sho«n
that the application of heat served to bring about
chemica change, but we shall find as we proceed that
chemical action can be determined by other agents—
namely, \>j Mechanical Mce, Light, £/eetricit_y, and a
peculiar force called Chemcat attraction, or 'affinity '
which acts on ly at excessively minute distances.

Expenment a-Place two or three small crystals
(not more) of the salt called potassium chlorate in a
stone-ware mortar, powder the substance and add half
as much sulphur, also in powder. Mix gently and then
give the mixture a sharp blow with the peslle. A
report follows, indicating that chemical action has
jaken place, in this instance determined by mechamcat

Experiment l-Again, dissolve a few crystals of
s^ver nitrate in half a test tube of water and paint
the liquid over some ordinary writing paper in a
darkened room. Then divide the paper into two
parts : preserve one in a .irawer, and immediately ex-
pose the other to full sunlight or diffused daylight.
.^,._„ ^^^^, ,,,,, s.^ortiy aiscoiour and assume

4 lutrodiiciion to Experimental Chemistry,

a cliocolato ])rown tint, or even a bronzy black colour
--the result of chemical change brou^Mit iibout by the
ac;ency of j//////i^///, lor the paper preserved from light
does not suffer any api)areni. change in the same time.
The art of photography depends upon similar changes
brought ab(yijt h\ light.

Experiment *). ^ rrw take the little galvanic cell

described isl pugc 6 ^ ee fig. 2, a; and attach a small

slip of sheet platinum to the end of the wire from Z;/,

F,o. 9. and connect a slip

of copper with C«;
dip bo'h in a strong
solution of copper
sulphate contained in
B. Remove the slips
after a few minutes
and observe that a
reddish deposit has
formed on the slip
connected by wire
with tlie zinc plate Zn, of the cell. If the action be
continued for some hours, a considerable layer of red
tfieta ic copper is obtained on the slip as the result
of chemical change determined by electricity in the
solution of copper sulphate. The art of electro-
typi)-ig de):)ends on this power exerted by electricity.

Experiment 6.— Finally, if we add to a small
globule of the liquid metal mercury, or quick-
silver, contained in a mortar, a few fragments of iodine,
and mix them together with the pestle, the metal
and iodine gi .dually disappear and a powder is
formed. If the proportion of iodine used ht-. larfyp

• * " CJ-7

Zn.

■Vv

Preliminary Expcrinients. 5

the resulting powder is red in colour ; if little iodine
be enij)loyed, the colour is a dull green. Here the two
bodies named produce a new substance when brought
near to each other, and this change is alone due to the
chemical attraction of one body for the other. The
exercise of this attractive forcp is facilitated bv tie
liquidity of the metal, and the c.ange is hastened ^y
the addition of a fc v drops of spirit of wine, which dis-
solves some of the iodine and thus enables the par-
ticles of the latter to move more freely. 1 nis chemical
attraction differs from other forces in the important
particular that it only acts at excessively minute dis-
tances. This may be further illustrated in the following
way : — ®

Experiraent 7.— Mix in any dry glass vessel, such
as a benker or a tumbler, a tea-.spoonful of 'bread
soda,' or sodium bicarbonate, and the same quantity
01 hnely powdered tartaric acid.' However closely
the solid particles are brought together by stirring or
rubbing, no action takes place, provided the mixture
is dry. Add now some water to the powder, and
violent effervescence ensues, indicative of chemical
action. Water added to die acid or the soda separately
does not cause any effervescence and merely dissolves
each body, the violent action observed on addition of
water to the mixed powders must therefore have been
due to the mutual attraction of the two solids leading
to chemical action ; but that action could only take
place v,rhen, by solution in water, the particles of each
body were endued with greater mobility than in the

'Or the contents of the two papers sold as
powder • may be mixed instead of the above.

■ Seidlitz

6 Introduction to Experimental Chemistry,

solid state, and were thus enabled to get within the
sphere of each other's attraction.

We thus learn that chemical action is greatly facili-
tated by the solution or liquidity of one or all of the
bodies engaged. We shall find later on, Experiment
53, that a fine state of division of a solid tends to a
similar result.

In some of the experiments already cited, the
student will have observed the evolution of heat
and light during chemical action. Thus, when the
magnesium wire burned in air, much heat and an
intense light were proauced. But electricity is also
freely developed in certain chemical actions, and in
fact the source of electricity in an ordinary galvanic
cell is chemical action.

Experiment 8.— The simplest form of galvanic
cell may be easily made thus : — Take a glass vessel,

such as a tumbler (a,
fig. 3), and fill it about
two-thirds with water, to
which one-tenth part of
A oil of vitriol (sulphuric
y acid) has been added.
Next cut a slip of clean
sheet zinc, Zn^ a little
longer than the glass ;
its width may be equal
to half the diameter of
tlie vessel. Make a hole
through one end of the
slip, pass a piece of bright copper wire through it

and fasten securelv hv twisfinor th^ wirp Prpnnr**
-" J -• ^o — _ .^^.-^^

Fig. 3.

Preliminary Experiments.

a similar slip of clean copper, Cu, with its wire, and
, he apparatus ,s complete. M'hen the two ^2
are connected, as shown, and the plates immer 7d
m the hquul, wuhout touching one another, ,he znc
a^one dissolves m the acid, the copper not being cTe!
n^ically acted on, while a current of electrici.yVows
^ong the w,re, and may be easily detected by bringin;

m of a toy compass. The needle tends to se

ction be"f ""f r "" ''"'' ""' -^ »•- 'hemi '
action be stopped, by taking the plates out of the

1-qu.d, and the connecting wire be brought over the
-leedle as before, no motion takes place! as°he JJe
no onger conveys electricity. The compass need e
therefore, serves as a detecter of electric cu^ents'
circulatmg through copper wires. '

as Z"\T^: T^ "' '""" =™P'« g-^'vanic cells
«ay that the zinc plate of one cell is coupled with
the copper plate of the next, a ^afyanu MttfJ of Z
simplest kind is obtained; but for details conceit n'

Again turning to the experiment with burning
magnesium, we rind that it is capable of afford"" uf
another Item of information. We pointed out fha
the white substance produced when the met^I bums

^Ue to Itself some' oth/r ITdy thS cTi^d'r ^^
derived from the air in wl^vi, .u , .^ ^^

The chemical action th^indu'c^aVh^.-ri

8 Introduction to Experimental Cheynistry.

\\\ •

ill I

combination^ or the union of unlike kinds of
matter.

Experiment 9. — The same agent — heat— is capable
of effecting the reverse change. If we take a small
quantity of the well-known white, crystalline and trans-
parent substance called silver nitrate^ and heat it gently
in a small dry test tube, the body is seen to melt to a
yellowish liquid, and, on continuing the heat, bubbles
rise through the liquid and ruddy fumes pour out of
the mouth of the tube. If we continue to heat until
all action is over, and brcalc the tube when cold, the
residue is seen to consist of pure white metallic silver.
In this case the chemical action brought about by
heat resulted in decomposition^ or resolution, of the
silver nitrate into the metal silvt ;, and some other
kind of matter seen to be driven off as coloured
vapour or gas.

Since chemical action may result either in com-
bifiation or decomposition, it follows ihat chemical
substances may be conveniently divided into two
great groups: first, those forms of matter which do
not suffer decomposition by the exercise of any force
at our command; and, secondly, those bodies capable
of resolution into some two or more members of the
first group. The forms of matter included in the
first group are called elements, and those in the second,
compowids. The decomposition of a compound into
its elements is spoken of as a process of analysis, and
the production of a chemical compound from its
elements is termed synthesis.

The researches of chemists up to the present time

Preliminary Experiments,

names of the most important of these are given in
the table, which will be found at page 64. But it is
necessary to guard carcrully against the idea that the
' elements ' so-called are certainly simple bodies- we
cannot at present prove them to be compounds -that
IS ail we can say.

All known chemical compounds are the result of
union bet^'een some two or more elements; but the
important question now arises whether this union is
m the nature of a mere mixture, or of sometlung
much more intimate. ^

Experiment lO.-Make a mixture of iron filings
with about two-thirds of their weight of sulphur (the
flour of sulphur ' of the druggists). A greemsh-grey
rowdei results, but distinct particles of iron and of
sulphui can be easily recognised in it, not only with '
the aid of a magnifying glass, but also by stirring
some of the powder into a considerable quantitv of
water, when the heavy particles of iron fall quickly to
the bottom of the vessel, while the lighter sulphur
more slowly subsides and collects as a distinct layer.
Or the iron can be still more easily separated from
the sulphur by means of a small horse-shoe magnet
If the latter be passed through some of the powder'
the particles of iron are attracted by the poles of the
magnet, and attach themselves so firmly that the
particles of sulphur-which are not attracted but
mechanically adherent-may be blown away, leaving
the metallic iron behind. ^

The constituents of this mixture can therefore be
separated by mechanical means. Moreover ,>. r..^_
perties partake of those of iron and sulphur. ' ^ '"

\
I

Introduction to Experimental Chemistry,

iii '

Experiment ll.-Nowheat very strongly a portion
of the original mixture in a tube of Bohemian or hard
glass ; note that the mixture becomes pasty and then
gloivs for a short time. Cool and remove the result-
ing dark substance from the tube. When examined
with a magnifying glass, no particles of iron or sul-
phur can be detected, if the mixture was sufficiently
heated ; moreover, it is noc attracted, or but slightly
by the magnet, and therefore does not any longer
contain/;r^ metallic iron. The iron and sulphur are
no longer separable by mechanical means, and the
properties of the body resulting from the fusion do
not partake of those of free iron or free sulphur. In
fact, the glowing observed on heating the mixture
was due to chemical combination between the two
^ elements, and the product of that union-a body
termed iron sulphide— possesses a definite group of
characters which not only serve to distinguish it from
the free elements iron and sulphur, or a mixture of
them, but from all other known bodies.

Experiment 12.— Mix twelve parts by weight of
finely-powdered charcoal (a form of the element
carbon) with sixty-four par^s of sulphur, also in a fine
state of division. The mixture is an opaque, almost in-
odorous, dull, yellowish powder that may be exposed
to the air for an indefinite time without loss of weight or
other alteration. Now obtain a specimen of the liquid
termed ' carbon bisulphide,' which is a chemical com-
pound of carbon and sulphur in exactly the same propor-
• A glass which fuses with great difficulty, and hence may
be suitably used in operations requiring a temperature so high
as to easily melt ordinary glass tubing.

Preliminary Experiments.

tions as the mixture of the two elements already made.
I his liquid IS perfectly transparent and colourless,
and has a most disagreeable smell, while it is so
volatile that a few drc . let fall upon a plate disappear
m a very short time. We thus learn still more clearly
that a w;de difference in properties may exist be-
tween a definite chemical compound and a mere
mechanical mixture of its constituents. The special
properties of the elements can be easily recognised in
the mixture, but not in the definite chemical com-
pound, unless we decompose the lattei and sever the
union of Its components.

.n J''"^^/'^"-"^ ""= "y"*^^''^ °f ^ "ew chemical
compound from its elements, the philosophic chemist
performs an operation which approaches more nearly
than any other to a creative act.

' For the preparation of this body see Part Tr „,™
It must be handled with c»re. » it is Zr^lZJ^^^ "^^

12 Introduction to Experimental Chemistry,

! 11

III

CHAPTER 11. .

EXPERIMENTS WITH SILVER NITRATE AND
MAGNESIUM.

A KNOWLEDGE of the chief Laws of Chemistry can be
more simply and naturally attained by the study of
chemical compounds in the first instance than by the
detailed examination of simple bodies or elements,

'I Fig. 4.

BininmiBiiuoiniiiinininiiminiinmBiinimnnimMiiiiufliifiiffiiniiufflirmiimniir^

and the most easily managed compound with which
the beginner can experiment is the silver nitrate.
It has been already proved by Experiment 9 that
Silver Ni crate is resolved into metallic silver and
coloured gas, when otrongly heated in a glass tube.

Silver Nitrate ami Magnesium. 13

Let us now examine this case of decomposition
with the aid of a balance or delicate scales, one of
the best forms of which valuable instrument is repre-
sented in fig. 4.1

Experiment 13.— Break up in a perfectly clean
mortar some clear and pure crystals of silver nitrate ; =»
then press the powder between folds of white blotting-
paper, in Older to remove any trace of moisture.
Next take a stout test tube of /lani glass, measuring
12 centimeters long and 12 millimeters in diameter ;
take care that it is clean and dry; then place it oti'
one pan of the balance and counterpoise by placing
a small pill box on the other pan, and adding grains
of shot or pieces of tinfoil until equilibrium is estai)-
lished. Next place in the pan, along with the shot
or foil, weights representing 170 centigrams (=17
grams), and now pour into the test tube on the other
pan the powdered siher nitrate until the weights
are balanced. The test tube then contains 170
centigrams of the silver compound; Now support the
tube in a slanting position in the wooden clip shown
in fig. I, and gently heat the bottom of the tube with
a spirit lamp, or a Bunsen gas-burner of the icjtm
shown in fig. 5. The silver nitrate melts quietly to a

' Much cheaper balances than that figured can now be ob-
tained, which will indicate less than i milligram when loaded
with 25 grams. When the student cannot obtain the use of
a balance, he should perform the experiments as described
without weighing the materials or products.

* The crystals are alone certain to give satisfactory results,
as the ' Lunar Caustic,* sold in sticks, is sometimes adulterated
and often ia.pure.

i m

M' '

14 Introduction to Experimental Chemistry.

clear liquid. If the temperature be now increased by
bringing the flame closer, sHght effervescence is ob-
served— due to the escape of bubbles of gas. Soon
reddish brown fumes appear, and these pass away
mto the atmosphere, while the residue in the tube
loses much of its transparency owing to evident
dep<)sition of solid matter. The heating must be
continued in such a way as to prevent any loss by
spirting solid particles out of the tube, , and until
the ruddy fumes are c<:>mpletely dissipated and pure
silver alone remains; finally, let the flame play on the
sides of tiie tube so as to ensure the decomposition
of any particles of the nitrate that may have yet
escaped the full action of the heat.» When cold,
replace the tube oii the pan of the balance and
adjust the weights in the other pan so as to restore
equilibrium ; the weights required represent the pure
silver thus obtained from 170 centigrams of silver
nitrate.

Two separate experiments made in the way de-
scribed afforded the following results :

•

Weight of metallic silver obtained from 170 centi-
grams of pure silver nitrate.

I St experiment
2nd

108*22 c.grs.
108-40 c. grs.

The second experiment was made by a young student
but little skilled in chemical manipulation.

' The ultimate decomposition may be thus represented :

AgNO.-Ag-tNOs + O.

f «

Silver Nitrate and Magnesium. j t

Now, it is found that the more carefully the experi-
ment IS .na.le, the nearer does the result approach to
io8; we may therefore say that 170 c. grs. of pure
s. vtr nurate contain 108 c. grs. of the n.etallic element
silver. W hatever may be the source of the .silver nitrate
taken, pMd it be pure, and whatever the quantity
employed m the experiment, provided the decompo-
smon be carefully conducte<l, the weight of metal left
after heatmg is always in the ratio of .08 to 170 of
the silver nitrate employed. Thus we learn

1st That pure silver nitrate is a compound body.

2nd. That 170 parts of it contain 108 of pure
elemental silver. ^

3rd. That it is constant in composition.

froJ!r''"'.f'': "'' '"^''^'"^^ ^'^-^^'y '° Redrawn
from them is that chemical compounds are constant in

composition. This inference is completely borne out

by further experiments in the same direction, for"

has been found that every chemical compound which

possesses a group of characters serving to define it

and so to distinguish it from all other forms of matter

de ecl'V'^r^'^''"^'^ ^°°^'^"^y of composition £
detected in the case of silver nitrate.

Upon this great principle, often termed the 'First
Law of Chemistry,' the science really rests

rh J''^^'^'"''''°".°' "'^ constanr-. in composition of
chemical compounds leads us to expect that chemical
combination takes place in definite proportions, else
It were impossible to obtain an adequate expla-
nation of the fact that the constituents of such a
compound ,s silver nitrate are always to be found
"i cne Doay m fixed proportions. We can put this '

* '

1 6 Tntroductiou to Expcnwcutal Chemistry,

inference to the test of experiment in the following
way : — °

Experiment H—Di.sMlve two or three meniu.n

crystals of silver nitrate m half a test Inbc of water,

nnd throw in a sir.nll slip of mngnesiiim ribbon. Now

observe that the ningnesiuin soon becomes coated with

a dirty grey material which can be readily detached on

shakmg and then ildls quickly to the bottom of the

tube. As the powdery substance is shaken off the

slip, a fresh coating forms which can be again detached

by shaking, leaving the magnesium thinner each time.

i his goes on until one of two things happens : either

the magnesnmi slip disappears altogether, leaving the

powdery deposit behind it if a relatively large ouantity

of silver nitrate ' was taken in the first instance ; or, if

the silver nitrate was used in a relatively small propor-

tion, the magnesium slip no longer becomes coated

and may bs allowed to remain in the liquid without

undergoing any further chani^e.

We have next to examine the grey substance.
Remove the magnesium slip, if any remains, and then
pour off the clear liquid and drain it away from the

• In this case the clear liquid should still contain some
unchanged silver nitrate in solution. To test for this, add to
some of the clear liquid, poured off into a test tube, a fen
drops of solution of connnon salt. If the fluid becomes milky
and lets fall a white precipitate, silver is present. This tett .
for silver depends upon the fact that silver easily unites with
another element, chlorine, and forms therewith the insoluble
body termed silver chloride, ^^■hich separates out. Common
salt contams the necessary chlorine, and thus acts as a nap-ent
. for Sliver. For an equation representing this change see page
143.

Silver Nitrate and Ma-nesium, ly

grey d^^osit as much ns possible. Now trike out
some ot the moist matter with a glass rod and place it
on white l)iottmo paper. Jfdrifd ne:.r a fire, the deposit
becomes hghter in colour and appears as a Tmc powder,
nhicl), when rul,l)ed with a polished knife blade as-
sumcs a silvery lustre. Ily this means, and by ( hemical
tests which will be described later on, this powder can
be shown to consist of pure metallic silver in a very fine
state of division. We conclude, then, that magnesium
acts chemically on the silver nitrate in solution and
decompo.ses it, precipitating metallic silver, while the
metal magnesumi disa/)pear.s, evidently owing to .solu-
tion in the liquid.

By a slight modification ofthe above experiment
we can easily find the weight of pure silver deposited
during the complete solution of a given weight of
jmre magnesium.

Experiment 15.-For this purpose, dissolve about
200 c. grs. (=2 grams) of pure silver nitrate (the pre-
cise quantity is immaterial) in about twenty cubic
centimeters of distilled water contained in a perfectly
clean porcelain crucible, which latter has been gently
heated over the lamp flame to dry it, and then, when
cool, counterpoised in the way already described in
the experiment with the glass tube. Now take a piece
of carefully cleaned and bright magnesium ribbon
weighing about lo centigrams-the exact weight must
be accurately ascertained— and add it to the con-
tents of the crucible, stirring the magnesium about
occasionally with a short piece of glass rod, which
latter must not be removed from \\^f^ rmriM^ „«.n

Fig. 5.

18 Introduction to Experimental Chemistry.

tlic experiment ends. Silver separates as before, and
after some time all traces of the magnesium disappear.
The mixture is now allowed to stand for a uhort time,
in order that all particles of the heavy silver may
settle to the bottom, as much as possible of the clear
liquid is then carefully poured away without disturbing
the precipitate of silver. Some 20 or 30 cs. of dis°
tilled water are now to be added to the deposit, the
latter well stirred up with the fresh water and then
again allowed to stand, when the clear liquid may be

decanted off as before without
loss of silver. This process of
* washing by dccantation' of the
silver must be repeated five or
six times in order to secure the
complete removal of all soluble
impurity from the metal.' The
crucible with its moist contents
is next placed in a warm place to
dry, and is then carefully heated
over the spirit or gas lamp, as
i" fig- 5» ^OJ* a few minutes, m
order to ensure the removal of
all traces of moisture. When
cold, the crucible with the silver
is replaced on the balance pan and the weight of the
metal accurately ascertained.

An experiment performed as described afforded
the following result :— to centigrams of magnesium
were added to 200 c. grs. of silver nitrate in solution,
and the silver collected after the magnesium had
wholly disappeared was found fn u-Pmh ss

revtf

Stiver mtrate afid Ma^tesium. 19

By the foll( ving simple calculation we can find the
wei^ It of migncsium required to precipitate 108 c. grs
of saver from 170 c. grs. of the silver nitrate, in orL
to I nng the statement of our result into harmony with
that of our former quantitative experiment:—

^^ ; 108. MO ; 12-2

However frequently we repeat and vary the form of the
above experiment, we Imd that for io8 c. grs. of pure siU
ver^..ov.dfromas,lu.ioncontaininga'exceis7f.he

Zwl ^'T: '"' " "■ «"■' '^ "^^ -""'trials are
ab o u,e,y pure) 01 metallic magnesium dissolve. I„
other words .2 c. grs. of magnesium exactly replace
108 c grs. of s,lver contained, as we have alreldy een!
m 70 c grs. of silver nitrate. There is therefore no
doubt that metallic magnesium and silver nittte act
upon one another, or interact, in d'/fni/e proiort/ons
A 1 sum ar expcrin.en. have led to precisefy the same
result hence the -Second law of chemistry;'-

A// cnemual substances interact in definite proior.
twns by nieig/tt.' i^upor.

The change on heating silver nitrate was one of
deeon,pos,t,on, for 170 c. grs. of the compound bX

"il'ttL^r I '"• °'^''^"'''"'^ '^ '■ ^- °f '^-o'-
term",! . f^""'^ P™visionally group under the

InTthl -?' ^" ''"">"'"''<'" -1^0. between the silver

defin t. ■""" ^^^^ °"g'"'"'y "^^^^ place in

aehnite proportions. r = m

Again, the change consequent unon the action of
and of combmation, for while the silver n,>r„. „J

• »«vtvu rros

Introduction to Experimental Chemistry.

decomposed And. its silver separated just as completely as
by heating the body alone, the 12 c. grs. of magnesium
W/;/../with the 62 c. grs. of Miitrate,' and in fact
the solution contained at the end of the experiment
magnesmm nitrate weighing 74 c. grs. (12 + 62 c. grs.),
and that weight of the new compound thus formed
could actually be separated from the litiuid.

I m

i :!

I 'i

■\ ■ i

j: f
\ 1

i
1

M
%

CHAPTER III.

EXPERIMENTS WITH MAGNESIUM AND HYDROGEN.

Experiment 16.-Half fill a test-tube with water to
which two or three drops of oil of vitriol (sulphuric
acid have been added. Now plunge into Ihe liquid
a shp of magnesium ribbon and note the result'
Brisk effervescence takes place, and the metal .peedily
tZlZ'- ^'^^t---"« ■»-' be due 'to Z

of he tube the gas takes fire and burns with slight
explosions, but emits very little light while it burns

silver fror "fSnesium, which displaces metallic

Silver trom silver nitrate

causes the evolution of an in-'

flammable gas from acidulated

water. The next step is to

collect some of this gas and

examine its properties.

Experiment 17.^Take a
glass tube closed at one end
and about 20 centimeters
long, and 2 centimeters in
diameter, /, fig. 6; fill it com-
pletely with water acidulated
withyjjth of its bulk of sul-
phuric acid; thennlacen mW^^r^ — au^.^j ._i

a ground glass plate, over the mouth of the tube and

Fm. 6.

hitrodttcHon to Experimental Chemistry,

invert it. Next bring the month under the surface of a
larger quantity of the acidulated water contained in the
wideglass beaker,^, and support by means of the stands.
So long as the mouth of the tube is under the
surface of the liquid no air can enter, as the water is
retained in the tube by atmospheric pressure. Now
take a piece of magnesium ribbon about 20 centi-
meters long, crumple it up and rapidly pass it through
the water and under the mouth of the inverted tube.
It will ascend into the tube and cause effervescence
as before, but the gas cannot escape into the air and
therefore collects in the upper part of the tube, while
It displaces a corresponding volume of water. As
the magnesium dissolves add fresh pieces until the
tube is filled with the gas.

Pass the plate under the water and close the
mouth of the tube, then detach the latter from the
stand, remove the tube, still closed with the plate,
from the water, and examine the contents.

a. Note that the gas is free from colour.

b. Turn the mouth of the tube up quickly and
apply it to the nose, No peculiar odour is perceived.

c. Refill 1 the tube with gas as before, and apply a

Fig. 6 b.

' Instead of refilling the large
tube, the charge of gas collected
in it in the first instance may be
transferred to three small test
tubes, if the latter are filled with
water in a large dish or trough,
inverted and held with the mouth
of each under the surface of the
liquid. 1 he large tube of gas is

carried lo the wat«»r- nn/l fKo i^^.,>u 1 1.. . - -

.-# ii._ «_i„, „„^ „,^ Mivuwi wiwu^iii unaer one oi the

Mag7icsium and Hydrogen.

flame to the mouth. The gas takes fire and burns
witli a pale l,lue flame.

c.fL ff '"f " "v "'' '"^" with gas, turn the mouth
of the tube up-.c.ards and remove the thumb. After a
few seconds brmg a flame to the ,ou,h of the tube
No combustible gas is found in the tube.

We are therefore, warranted in slating that the
g.as produced when metallic n.agnesium acts^on a idu!
lated water ,s colourless and inodorous. We may
further assert that it cannot be soluble in water to
any extent as we are able to collect it easily over hat

quite nsoluble m water. It is combustible and is
much hghter than atmospheric air, as evidenced by
he rapidity with which it escapes on holding the
tube wuh Its mouth directed upwards. The gas
possessing these properties chemists call RvbrogS
and regard it as an elementary body.

Although hydrogen is an extremely light bodv-
m fact the lightest ku<,w„ form of matter- t admits
of bemg weighe<i like all other material thi^

set to work in order to answer the important question
What weight of hydrogen do ..-, centigrams of mag
nesuim displace from acidulated water ? ^

ilTobtainy "" ^"^^^^^ '° "'^^ ^"-- - ^^

tube. Several tubes mavthus b^ fin.^ ,.,uu _-_^" ^^''. ^^'*
iarge vessel. , - ^ ~..v« rrxw* gua ixoia & siugie

'Hi

■I m^

ji
I'

Fig. 7

■ i

24 Iiitroductioti to Exptrinicntal Chemistry.

The flask a should be very light, and of about 50
cubic centimeters capacity; the little glass apparatus
a should also be very light, and its tubes c and d must

be fused into the glass. The
. tube e, like c and d, is open at
both ends, but tlut within the
apparatus need not ])roject into
the ilask as shown in fig. 7, but
may be cut off close to the cork.
In order to use the appa-
ratus, fill the small inner flask a
to the extent shown with strong
oil of vitriol by removing the
cork carrying the tubes and
dipping a under some oil of
vitriol, contained in a beaker,
until the mouth of d is be-
neath the surface of the liquid.
Suction applied at c causes the
acid to enter to the desired
extent, when the apparatus is
remove d from the acid, washed well externally with
water so as to remove all acid from the exterior of
a and fioiii the mouth of the tube d. Before re-
placing the cork in a, drop into the latter exactly 12-2
centigrams of clean bright magnesium ribbon, along
wiih ihe amount of water indicated in the sketch:
then fix the cork in its place, plug the opening of
e with a small piece of wax, dry the outside of the
flisk with a soft cloth, place it on one pan of the
balance and accurately counterpoise the apparatus.*

' The apparatus, when ready for experiment, should not
weigh more than 50 grams.

Magnesium and Hydrogen.

Next remove the flask to a shett of clean white
paper, slip a small piece of flexible tube over c and
force air very gently into a until a few drops of oil of
vitriol fall from d into the water in a containing
the magnesium. Gas will soon be evolved, and this
gas we already know to be hydrogen. It has no exit
save through the tube d, and after bubbling through
the oil of vitriol in a it escapes from c into the at-
mosphere. In its passage through the liquid the gas
loses any moisture that it may cany with it, as the
oil of vitriol possesses the convenient property of
absorbing water with great avidity: hence only pure
dry hydrogen, mixed at first with some air, escapes
from c. As the evolution of gas slackens, a litde
more oil of vitriol can be forced over, and diis opera-
tion repeated if necessary until the magnesium dis-
appears. When this point is reached, remove the wax
plug from e and place it on the balance pan, next
"apply suction to the flexible tube at c. Air is thus
drawn in at e and replaces the last traces of the
hydrogen thus sucked out and dried in its passage
through a. The flask is wiped carefully, and replaced
on the balance pan. It will now be found lighter
than the counterpoise, indicating that it has lost
matter during the experiment. The matter lost we
know consists of the pure dry hydrogen gas, and the
precise weight of it can be ascertained on restoring
equilibrium by addition of weights to the pan on which
the flask a rests.

When the experiment describe d is carefully con-
ducted, I CENTIGRAM almost exactly restores equili-
biiuiii; thereiure that is the weight of hydrogen

.:ajiii

fr m

§'

1 08
170

26 Introduction to Experimental Chemistry.

evolved during the solution of 12 centigrams of pure
magtiesium' in acidulated water.

The results of the quantitative experiments hitherto

performed may be stated thus, neglecting decimals :—

I centigram of Hydrogen was separated by

c. grs. „ pure ^^AGNES1UM, which also

displaced
„ „ pure Silver from

>, „ Silver nitrate.

The numbers so obtained are called equivahntSy
because they represent weights which are of equal
value in chemical changes. In all such changes
hitherto examined, hydrogen has never been found to
directly displace or combine with less than its own
weight of any other element or compound, or indeed
with less than three times its own weight of any other
form of matte hence it is properly taken as tlie unit
of a scale of equivalents, which really includes all the
simple and compound bodies known. On this scale,
magnesium, silver, and the compound silver nitrate
occupy the positions assigned to them above.

A familiar illustration will probably render the
meaning of the term 'equivalent' clear. A single
brilliant diamond of purest water, weighing but one
grain, has approximately the same purchasing power
as the weight of

Gold represented by . '. 3 sovereigns.
Silver „ „ . . 60 shillings.

Bronze (an alloy of tin and copjier), by 720 pence.
A diamond of a certain quality will purchase more

iv.3 \jv!:i.i. wci^lit

^" of any uthcr substance s the

Magnesitim and Hydrogen. 27

economic value oidi unit weight of diamond in exchange
is therefore greater than that of any other material
found in commerce. Similarly the chemical value of
a unit weight of hydrogen in exchange is gieater
than that of any other element known to chemists.

As 170 c. grs. of silver nitrate are equivalent to i c
gr. of hydrogen, the student will now understand our
reason for selecting the weight of the silver compound
that we operated upon in the first quantitative experi-
ment.

Experiment 19. — The mo«it convenient method for .
the preparation of considerable quantities of hydrogen

Fig. 8.

gas for experiment is the following. Take a glass bottle
of the form shown in fig. 8, place in it some clippings of
sheet zinc and sufficient waterlo occupy about one-third
of the bottle Replace the cork and pour some oil of
vitriol — about a teaspoonful— down the thistle funnel.
Chemical action quickly commences and hydrogen gas
is freely evolved ; for zinc, like magnesium, easily dis-

28 Introduction to Experimental Chemistry,

places hydrogen from acidulated water— i centi-
gram of the gas being set free by 32-5 c. grs. or
one equivalent taf pure zinc. Tne gas is conducted by
means of the glass delivery tube under the water in
the ' pneumatic trough,' and it is there collected in
glass jars or bottles previously filled with water and
inverted, keeping the mouths under the liquid in the
trough. A small shelf supports the jars over the
delivery tube. It is advisable to allow the gas to
bubble through the water for some time before collect-
ing it in jars, or uniil the air is judged to be expelled
from the gas bottle and its place taken by hydrogen,
as the latter forms an explosive mixture with atmo-'
spheric air.

a. Remove a jar full of hydrogen from the water,
keepmg its mouth downwards. Take a piece of

Fig, 9.

Fig. io.

lighted taper attached to a wire and pass it rapidly up
into the jar, as shown in f^g. 9. The gas takes fire at

the month c\^ fJio fnK^ „.^^ 1 ^1

' "* ^"'- ■'"'-■^ «ii^ uuiiib there Willi a paie

Magnesium and Hydrogen. 29

blue flame, but ihe taper is extinguished ; on brinmntj
It down to the moutli of the tube again, it can be re!
kindled there. Therefore hydrogen, tliough a com-
bustible gas, does not support the combustwfi of a taper
which burns readily in air.

b. Take a dry glass jar, hold it with its mouth
downwards and V^ring under it a jar full of hydrogen
carried from the trough with its mouth downwards!
Now invert the jar of hydrogen, bringing its mouth
under that of the dry jar, as shown in fig. 10. After ten
or fifteen seconds remove the lower jar and bring the
lighted taper under the upper one :^a slight explosion
occurs, and fl^me is observed, indicative of the pr^^-
sence of hydrogen ; therefore the latter body is so
much lighter than air that it can be poured up through
the latter, and will nccumulate in the upper part of any
vessel previously fuli of air.

c. The same point can be elegantly demonstrated
by removmg the gas delivery tube from the water
drying u, and introducing the end into the neck of a
small collodion balloon. If any zinc remains undis^
solved in the generating flask, a few drops of fresh acid
added through the funnel will hasten the evolution of
gas, and the latter passing into the ballon will expand
It. When fully distended, detach the balloon from the
tube and set it free. It will ascend rapidly through
the air of the room until arrested by the ceiling, and
will remain there untii much of the gas escapes and the
residual hydrogen is no longer sufficient to buoy up
the balloon. The latter then falls and may be re-
served for another experiment

3© Introauction to Experimental Chemistry.

Fig. it.

CHAPTER IV

EXPERIMENTS WITH HYDROGEN AND OXYGEN GASES.

Experiment 20.— As we have already proved that
hydrogen gas bums in air, we may evidently .construct
a small apparatus which can afford us a stream of the
gas for combustion at a jet. 'i'he most convenient
form is that rcpr^ented in fig. ii. The gas delivery

tube of fig. 8 is replaced by a short
piece of straight tube, which passes
through the cork of the generating
bottle and through the cork of the
wide tube, /, which latter is filled
with fragments of calcium chloride,
a powerful absorbent of moisture.
Through the second cork of /
there passes a small glass tube,
drawn out so as to form a rather
fine jet. The flask contains strips
of zinc, and water, as before, and
on pouring oil of vitriol down the
funnel tube, hydrogen is evolved. Let the stream of
gas issue freely from the jet for some time before a
light is applied,^ else an explosion will occur; then
kindle the gas.

' It is well to cover the jet with an inverted test tube, and
to remove the latter, mouth downwards, when it is desired to
test the gas, and then to apply a flame to the test tube. If

Hydrogen and Oxygen Gases. 3 1

a. Note that the hydrogen flame is of a pale

bhnsh colour, and emits very little light ; but it is

intensely hot, for if we introduce a Hne platinum wire

into the flame it becomes nearly white hot, and emits

much light.

l>- It we take a glass ti;be, oi)en at both ends,
about one centimeter wide and 30 centimeters long
and pass the jet up into it, the flame is seen to sud-
denly elongate and a musical note results. The note
emitted by ihis chcmual Imrwonicum depends on the
dwmetcr and length of the tube; consequently tubes
varying m these particulars may be used to produce
diflerent sounds.

c. It will be observed in these experiments that
the glass tubes are bedewe,i when they approach the
hydrogen flame. Next place the flame under a large

W /""■' n-, '"'^"■' °'^' " ^ '"g'^ ^'y wide-mouthed
bottle. The inner surface of the bottle is quicklv

bedewed with moisture, and presently drops of liquid
rickle down thfe sides and collect at the shoulder.
When some drops of the liquid have been collected
It can be examined, and is then found to possess all
the properties of water. Now, since the calcium
'Chloride m the drjing tube completely removes
moisture from the nnbumed ,as, and the latter does
not bedew a coKl surface against which we may allow
U to impmge, the liquid we observe to be deposited
from the flame must be a product of the combustion
of hydrogen in air, just as the white substance, see
the gas burns quietly, it may be safely kindled at the jet ; but
rf with explosion, it is still unsafe, and the testing must be re-
i^vaicu uucr a icw minutes.

32 Introduction to Experimental CItemistry,

Kxpcriment 2, is a product of tlic combustion of mag-
nesium in air. • By means of the next experiment we
can prove that the water prcduced in the combustion of
hydrogen weighs more tlian the gas l)urned, and there-
fore that the process is one of chemical combination
in progress between hydrogen and some constituent
or constituents of atmospheric air; the resultant water
is consecpiently a compound of hydrogen, or of the
water generator (l^cwp, water; yeriuw, I generate), with
some other kind of matter.

Experiment 21.— Take aU tube of the form of ^,
fig. 12, fill the wide limb very loosely with fragments

Fig. 13.

of zinc and insert the cork b whicli serves to prevent
the zinc falling out when the tube is inverted, but
which should be perforated so as to allow liquid to
flow freely in and out. Pass the narrow limb of the
U tub«i ihrou£;h a good cork c which fits a test tube

Hydrogen and Oxygen Gases,

about 2 centimeters in diameter. The cork also
carries the glass tube s provided with a fine glass
stopcock which can regulate the supply of gas to the
jet in which the ti;be terminates ; the wide end of this
tube is sufficiently large to pass through the cork c to
the bottom of the test tube /. The latter is now filled
with fragments about the size of a pea of dry and
porous calcium chloride, and by turning the tube
nearly on its side and tapping, the tube of s can be
passed down along the glass and the cork inserted as
shown. Now pass the wide limb of a through the
neck of a light flask of about 80 or 100 centimeters'
capacity, containing diluted sulphuric acid, and secure
the tube a in the neck by means of slices of rubber
cork, but without interfering with access of air. On
turning the stopcock s the acid rises in a and acts
upon the zinc, hydrogen is evolved and passes through
the drying tube / before it can escape from the jet.
The evolution of gas is allowed to continue until all
air has been expelled, then the hydrogen can be
kindled at the jet, and once it is found to burn freely,
the stopcock is turned off, the evolution of gas ceases,
because the latter has now no exit through s^ and
accumulates in a, forcing out the acid through the
perforated cork b, and therefore away from contact
with the zinc.

Before the experiment, th*" appaiatus is accurately
counterpoised, and a quantity of dry gas is then burned
at the jet, under conditions to be presently described,
and the stopcock again closed. If, when cold, the
apparatus be replaced in the balance it will, of course,

U I

Introduction to Exftrmenial Chemistry.

weigh less than before, and the weight lost is the
weight of dry. hydrogen burned. ' '°'' " «"«

Another piece of apparatus is now to be prepared"
This consists of a small paraffin lamp . himney "fig
..connected by means of a corl, as shown, « th tht
U tube V filled with calcium chloride. This is our
water collector, and is to be attached by the w" e
hook to the arm of a balance and carefully counTer!
poised before an experiment. counter-

Diec« "nf"'' "" ^''P^"™^" f'us : counterpoise both
flexible tube w.th an aspirator^ p, as shown, so that a
stream of air may be drawn slowly through the water
collector during the combustion of thf hydroTeT
Now turn the stopcock .. immediately kindl7"e
hydrogen, and pass the flume well up into the tube i

chiefly m v. When the hydrogen has burned for
some mmutes. dose the tap ., and stop the current of
a.r through i.; allow both pieces of apparatus to cool

—r'T^l' *^".'''— « -1 weigh each
separately. The gam m weight of the dryins in
paratus represents the weight of water prXfd t

tJe jet"! ° "' ""*'"' °' ''^^^"e- burned at

When the experiment just described is conducted

Hydrogen and Oxygen Gases.

with great care, it has been found that for every centi-
gram of hydrogen burned almost exactly 9 centigrams
of water are obtained in the drying apparatus ; thus it
can be proved that the hydrogen gains in weight •
on undergoing combustion in air; and, further, that
the product of combustion weighs 9 times as much
as the hydrogen burned.

The next step clearly is to resolve water into its
constituents, or to decompose it, in order to isolate
the matter which hydrogen must have obtained from

air.

The conipound water, whether in the liquid con-
dition, or when gaseous (as steam), withstands a com-
paratively high temperature without decomposition;
similarly light alone is without action upon it, but
electricity is found to decompose it with facility, and
the current derived from a Grove's or Bunsen's gal-
vanic battery consisting of two cells is sufficient for

the purpose.

Experiment 22.— If we attach to the copper
connecting wires of such a battery small slips of
platinum (taking care that the connections are per-
fectly clean and bright), and then plunge the platinum
terminals or * poles' into some water acidulated with
a few drops of oil of vitriol, in order to make it a
good conductor for electricity, bubbles of gas are
seen to rise from each pole. Note that more gas
seems to be evolved at the pole connected with the
zinc end of the battery than at the other. In order
to collect the gas it is only necessary to arrange the
apparatus shown in fig. 13. The vessel v contains
the acidulated water. The two test tubes are tilled

D 2

• i

36 Introduction Jo Experimental Cliemistry.

Fig. 13.

with some of the same water and then inverted with
the mouth of each below the level of the water in the

vessel V, and supported close
together by clamps. The
platinum poles are now
arranged as shown, their
wires being attached to the
binding screws s, s, which
latter are also connected
with the battery. The wires
are dried and then com-
Pletely coated with sealing
wax, from the platinum slip to the point c, so as to pre-
vent any escape of electricity, except through the plates
when they are immersed in the water. Each platinum'
pole IS then brought under the mouth of a test tube and
secured m position. Gas bubbles arise from the pole,
as before but mstead of escaping into the atmosphere
they collect m the tubes placed to receive them
A marked difference is observed in the amount of
gas g.ven off at each pole, and it .s presently seen

TO fuT"' ' ' " "'" '"" °' ^^ "^^ ""'«''' "^"^
In order to examine the gas in each tube, remove
the wires, then close the mouth of the tube containing
the largest volunie of gas with the thumb passed under
the surface of the water in the vessel v. Invert the
tube shp as.de the thumb, and quickly apply a flame
o the mouth of the vessel ; the gas takes fae.nd '
burns with a pale blue flame, and this gas is hydrogen
A similar experiment is made with the contents of
the second tube, but the gas it contains does nnf tot.

Hydrogiii and Oxygen Gases,

fire. If, however, we dip into the gas a splinter of
wood with a glowing tip, the wood bursts into flame,
and active combustion ensues. This gas is, therefore,
incombustible in air, but is a supporter of combustion.
This body, like hydrogen, is an element and is called
Oxygen.

The process of analysis by electricity just used is
termed electrolysis, and is often employed in effecting
the decomposition of chemical compounds. During
the electrolysis of water we have already observed
that twice as much hydrogen is evolved as oxygen,
and the presumption is that those are the proportions
by volume in which the two gases unite to form water.*
But we have not yet proved that water consists of
hydrogen and oxygen ofily. If, then, we take the
mixture of gases evolved from water, consisting, as we
know, of two volumes of hydrogen and one volume
of oxygen, such a mixture must be capable of repro-
ducing water // the latter consists exclusively of these
two elements in tl proportions stated.

Experiment 23.— Take a stout wide-mouthed
phial of about loo c.c. capacity. Fit it with a
caoutchouc - -zk and, having bored a hole axially
through it, a.^^ert the short limb of the narrow but
strong delivery tube bent in the form shown at d, fi'g. 14.
The wider tube shown can be filled with fragments
of calcium chloride when a supply of the dry gaseous

' 100 cubic centimeter-, of water dissolve only 2 989 c. cs. of
oxygen at mean temperature and pressure, and 1 -93 of hydrogen
gas under the same conditions ; the solubility of each gas is
therefore so low and so nearly the same, that the above in-
ference may be faiiiy drawn.

38 Introduction to Experimental Chemistry.

mixture is reouired. Then pass two stout wires of
platinum through the cork on each side of, and close
to the glass tube, and attach small slips of platinum
ton to the ends of the wires that project within the
bo tie. Nearly fill the vessel with water containing a
little sulphuric acid arid insert the cork, connect the
wires projecting from the cork with the terminals of
the battery, as shown, and a steady supply of an
electrolytic mixture of hydrogen and oxygen will be

Fig. 24.

Fig. 15.

obtened When .t ,s judged that all air has been
expelled from the bottle and tubes, collect some of
he mixed gases m a small test tube over the liquid
meta mercury, contained in a small and strong plass
rough, as m fig ,5. This mechanical mixture^? he
two gases may be kept for an indefinite time without
comb,„at,o„ taking place, but if we remove the tes
tube from the trough and apply a flame to the momh
-a flash of hght, and a rather violent exolosion

i;jiiniv. irini.-Mfirirr ♦u ,k -.i = ... -

follow, u

-iojcuting that chemical union has taken place.'

Hydrogen and Oxygen Gases. 39

We thu", learn that combination of the gases can be
determined by heating them sufficientlj.^

Experiment 24.--A stout glass tube closed atone
end IS now taken ; it should be about 50 centimeters
long and i centimeter in diameter. Two thin
platinum wires pass through the sides and are sealed
mio the glass near to the closed end, and opposite
to each other ; but their extremities within the tube
must be kept at a very short distance apart. The
object of this arrangement is to leave a gap so that an
electric spark may be sent between the wires within
the tube, and thus, by heating the mixture of gases,
determine their combination. Such a tube is called
a eudiometer, and must be stout so as to resist the
force of the explosion that ensues ; it is shown at b,
fig- 15-

Fill the tube with mercury, and when quite full,
close the mouth with the thumb, and bring it under
the surface of some more mercury, contained in the
small trough /, fig. 15. Now half fill the tube with
electrolytic gases from the apparatus shown in fig 14.
Then remove the generator and pass a pad of india-
rubber under the mercury and under the mouth of the
tube. Press the pad against the bottom of the trough
with the tube grasped firmly by the hand. When
the tube is in this position, pass a spark from a coil,
a Leyden jir, or a small electrophorus, through the
gases by means of the wires sealed into the glass, one
of them being connected with the earth by means of
wire, the other with the apparatus that is to afford the

1 Qaa r'linnf.av TV t^ : » f.1 ..

en name*

\i'

11 '

40 Introduction to Experimental C/iewistry.

spark. A flash of light passes down the gas in the
tube and a jerkT is felt by the hand, and then all is over
On relaxing the pressure and moving the moutli of the
tube from the pad, but keeping it under the surface of
the mercury, the latter rushes up so as to fill the closed
end almost completely ; the gases have therefore been
condensed,' or rather, the product of their union is not
a gas, but must b. either a liquid or a solid occupying
an exceedmgly sniall space as compared with that
previously filled by the generating elements. If we
examme the upper part of the tube carefully with a
lens, we can detect between the mercury and the glass
mmute drops of liquid. This liquid can be proved
to be water. It is therefore certain that water con-
sists only of hydrogen and oxygen, and that those
elements combine to form water in the proportions
by volume mdicated by the results oi electrolysis.

Experiment 25.— A similar experiment to that
just described may be performed with the apparatus
shown mfig. 16, termed a 'Cavendish eudiometer'
because itw.swith such a vessel that the Hon. Henr^
Cavendish demonstrated the composition of water in
the year 1781. The strong glass vessel, fig. ,6
IS provided with a glass stopcock c and a stopper
through which wires of platinum p p pass, and th.s
stopper IS retained in the neck of the vessel by means

' As a matter of fact a small bubble of hydrogen remains
after explosion ; this is chiefly due to the loss of a little oxvtren
by solution in the water of the bottle d, fig. 14. and further bv
conversion of a very small proportion of the element into a body
called 'ozone.' If all the oxygen wore evolved as gas there
would not be any free hvdiofri>n a(t^r th» «».,x!» .:-.-

Hydrogen and Oxygen Gases.

of the damp a. The brass stopcock b allows the

apparatus to be screwed to the plate of a good air-

I)iimp, and when exhausted of air,

B and c are closed, and not opened

until the tube is screwed to the brass

stopcock of a bdl jar similar to

that shown in fig. i8, but containing

some of the electrolytic gases. On

opening the taps the mixiure of

gases rushes in to fill the vacuum.

The stopcocks are again closed,

the eudiometer screwed to its stand,

and a spark passed through the

mixture. A brilliant flash of light

accompinies combmation, and the

sides of the glass vessel are bedewed

with the water resulting from the combination of the

gases.

The experiments hitherto made have led directly
to the conclusions we have already drawn from them
respecting the composition of water, but they also
afford complete proof that atmospheric air contains
oxygen ; and we thus learn in addition that the great
heat evolved "during the combustion of hydrogen in
air is due to the chemical union of hydrogen with the
oxygen of the air. Finally, we are led to suspect that
all ordinary cases of combustion which come under
our notice are due to ihe rapid chemical combination
of atmospheric oxygen with the body burned. Under
Experiment 2 1 a method was described by which the ^
Wcigut Oi water produced during the combustion of
I c. gr. of hydrogen was determined, and it was stated

m.v'*,%:m\

if:

iili

42 Introduction to Experimental Chemistry,

that 9 c. grs. of water resulted. Since we now know
that the gam in weight could only be oxygen derived
from the air in which the gas burned, the equivalent of
Oxygen must be 9-1=8.

When the metal magnesium burns in air, a white
solid only IS produ. _d, and it is found that 12 centi-
grams of. the metal afford 20 c. grs. of the white
body, that IS to say an equivalent of the element
magnesium (12 parts) unites with an equivalent of the
element oxygen (8 parts), and produces an equivalent
(20 parts) of the compound body termed magnesium
oxide or * magnesia '—for

12 + 8=20.

The truth of the statement is not so evident in
the case of a candle, for when the latter burns per-
fectly m air, the matter of the candle is apparently
destro3^ed. But since we know that matter is inde-
structible, we conclude that the candle is resolved bv
combination with oxygen into invisible products.
These products we can actually collect if we burn a
candle m the apparatus, fig. 17.

Experiment a'J.-Attach the small paraffin candle
c to the peiforated cork, and insert in the lamp

through which a bent tube passes which serves to
connect the lamp glass with the U tube. The limb

t^L T\ ''.^'''^V *^^ ^^"^P g'ass is filled with
lumps of calcium chloride, and the second limb with
fragments of caustic soda When the cork c is placed
m position, the apparatus, with the rp.nH!- ic amch-d
to one arm of the balance and carefully' counte'rpoi'sed.

Hydrogen and Oxygen Gases.

The tube / is then connected by means of a flexible
tube with the aspirator a, and a current of air gently

Fiu. 17.

\ '

VaI

\ ^

c^^

(

[]

^£±11^

yf 4

M\ •

drawn through the apparatus. The candle is removed,
lighted and replaced, and then burned within the lamp
glass, while the products of combustion are obliged
to pass over the absorbent materials in the U tube.
When the candle has burned for five minutes or so,
put it out and allow the whole apparatus to cool down
to the ordinary temperature. Then replace in the
balance and observe that the weight has increased.
Therefore, not only has no matter been lost during
the combustion of the candle, but it has actually
gained, and, as we shall see at a later stage of our
study, the gain represents oxygen derived from
atmosnheric air, and chemically combined with the
matter of the candle during combustion.

l!i

44 Introduction to Expetimental Chemist.

ry.

\\m\

CHAPTER V.

EXPERIMENTS WITH HYDROGEN AND OXYGEN G/.SES

{continued).

11^7 ^T ''?"-'''^ "^" ""^S^" S^^ '■' - con-
stituent of atmospheric a.r-though it is not the only

one-and of water The study of the composition o^
he latter has further made kno.vn the curious fact
that oxygen requires twice its volume of hydrogen
gas to forni water, and only i„ this proportion does
a,rect combmation take place between those elements
Iherefore the two gases unite in as definite propor-"
tions by volume as by weight, and it is evidemlv
probable that an intimate connection exists between
weight and volume combination in this case- hence
we must investigate the point more closely '

Experiment 27.-The first step in this direction
ts to select a globe of about ,l literi' capacity Z^Z
with a stopcock, and to exhaust it of air a' com
P ete ly as possible, by means of a good aTr pi >To'
the plate of which it can be screwed ; then cTo e' 'th^
tap securely, remove and counterpoise carefully on
the balance. The globe is next taken from the balance
and connected, as shown, with a vessel containing
pure hydrogen gas, and the stopcock opened, hy
_- -^_„ . ....„€. „, auu uiib tnc giobe. The stopcock is

Hydrogen and Oxygen Gases.

Flu. 18.

again closed, after the levels of licjuid within and
without the jar have been equalised, and the vessel
re-weighed. The increase in weight
is that of the hydrogen which has
entered. The globe is again ex-
hausted to the original point as
determined by the gauge attached
to the pump, and again filled with
gas, but this time with pure oxygen,
whose weight is then determined.
Now if care be taken to exhaust as
completely as possible each time —
certainly to the same extent — and
that the bodies are pure, and the
temperature does not vary so as to
unequally expand or contract the
gases, the weights obtained are those of equal volumes
of the two gases. In a particular experiment con-
ducted in this way the hydrogen weighed 11 centi-
grams, and the oxygen gas 1 74 centigrams. The specific
gravity of oxygen as compared with hydrogen, or the
ratio of the weights of equal volumes of the two bodies ^
when hydrogen is taken as the standard, and =1, is

or as nearly in the ratio of i : 15-96 — the true ratio
• — as can be expected in a rather rough experiment.
Therefore oxygen gas may be said to be 16 times
heavier than hydrogen. Now since one volume of
oxygen requires two volumes of hydrcgen for the
production of water, it follows that 8 centigrams

i:i

46 Introduction to Experimental Chcmislry,

by weight of oxygen must unite with i centigram
of hydrogen to form 9 cc.uigrams of water- -a result
Identical w.th tluit ol)tained by the direct weighing
of the water produced in the combustion of a mven
we-ght of hydrogen. Therefore, a very close connec
tion exists between combination by weight and hw
vohime. ^

It may be added that the specific gravities of all
gases can be determined by the method just described,
and smce hydrogen .s the hghtest gas known, it is
taken as the standard for reference.
' The experiments already made with the two gases
hydrogen and oxygen, place beyond doubt the fact
that they are perfec Jy distinct forms of matter as far is

chemical characters are concerned,
but they evidently resemble each
other in certain physical cluu
racters, for they are both colour-
less, invisible, and inodorous.
Let us now see whether this re-
semblance extends farther.

Experiment 28.— Take two
tubes of as nearly as possible the
same diameter and length. Close
each at one end and bend to the
form shown in a and b, fig. 19.
The short limb may be about
20 centimeters, and the longer i
meter, in length, lake one of

\ . A -1. ,M ^^^ *"^^^' ^^* ^^'^^^ water acidu-

iated with dilute sulphuric acid and invert over the
po.e ^iig. 13) froi-a which electrolytic hydrogen is

Fig. 19.

Hydrogen anU Oxygen Gases.

being evolved ; collect enough of the gas to about
half fill the shorter limb of the U tube, then close the
njouth with the thumb, remove aiul make the gas pass'
completely into^he closed limb: this can easily be done
by bringing the tube to a horizontal position while the
shorter limb is uppermost. When the gas has been
transferred, bring the a|)paratus into the position shown,
and adjust the level of the liquid in both limbs ot the
u by sucking out the water in the long limb by means
of a pipette wi»h a flexible tube attached, which latter
should be of sufficient length to reach nearly to the
bend. Fill the second tube to the same extent and
in the same manner with electrolytic oxygen, and tie
the two tubes securely together as shown.

When the apparatus is plunged up to the point a
in a large beaker nearly filled with water at the boiling
temperature, the gases in the tubes are found to expand
considerably. The expansion cf tho hydrogen is
seen to be the same in amount t^ that c^'the oxygen.
Simi-arly in cooling down again tO he te nperature of
the air they contract equally.

We learn from this experiment that the two gnses
resemble each other in another particular, namely,
that they are eff"ected to the same extent by equal al-
terations of temperature^ when observed under the
same conditions.

Now replace the hot water in the beaker by some
at the temperature of the room, and leave the tubes
undisturbed for several minutes, in order that the gases
may acquire the temperature of the water in the large
vessel ; then pour mercury into each wide tube until
nearly full, and the column in each is of equal length.

--^i

4? Introduction to Experimental Chemistry.

Wd InH "' n' '°'"'"'"' °f "'^•^"'y rise to the same

lrl!i 1"' "^ P'"'''""* ">^°" ">« g^^es equally in-
creases, they contract to the same extent

If we remove the mercury, the gases expand equally
and regam their original volume when the pressure is
reduced to that at which we commenced

Therefore hydrogen and oxygen gases, when com-
pared under the same conditions, are affected in the
same way and to the same extent Oy cjual alterations
0/ pressure. When the same n,ode of investigation is
applied to other gases, whether elementary or com-
pound, they are found to sufTer very nearly equal
changes of volume when subjected to equal variations
of temperature and of pressure.
_ The conclusion to be drawn from all the data
before us ,s that all gases ^«<^t\n physical constitution,
however niuch they may differ in chemical composition.
This conclusion is independent of any hypothesis that
may be founded upon the facts, but a most impor-
tent one has been based on them by the distinguished
physicist Avogadro. He assumed that all gases (as
wel as solid and liquid forms of matter) are made up
of almost numberless, separate little particles, termed
molecules (from molecula, a little mass), and that
e^ual volumes of gases ontain the same number of mole-
euies, when compared at the same temperature and pres-

ol'; \TT '^ '1""""""' "f Avogadro's, or, as it is
often called. Ampere's law, for to the last-named
philosopher IS due the credit of having specially drawn
he attention of scientific men to .he importance of
the principle enunciated by Avogadro, when the
t!at«m'>t<r rif \, ~„,i. u.. .u_ . . ' "*

Hydroj^en and Oxygen Gases.

: \'^-^

completely overlooked. It follows from Avogadro's
law that the ratio of the weights of equal volumes (con-
taining equal numbers of molecules) of hydrogen and
oxygen gases, compared at the same temperature and
pressure, must represent the relative weights of the
free molecules, or ultimate particles, of the two
bodies. We have already found (Experiment 27)
that a given volume of oxygen is sixteen times
heavier than an equal volume of hydrogen under the
same conditions : therefore the molecule of oxygen is
sixteen times the weight of the molecule of hydrogen.

Let us proceed a step farther. We know already
that one volume of oxygen and two volumes of hydro-
gen gas unite to form the compound water. We may
now express the same thing in the following state-
ment : — One molecule of oxygen unites with two
molecules of hydrogen to form the compound wpter.
But the question then arises whether one or more
molecules of the compound water result from their
union. We can obtain an experimental answer to
this question in the following way : —

Experiment 29. — Take a eudiometer tube similar
to that already employed in Experiment 15, 6 milli-
meters in diameter, and 80 centimeters in length, and
fill it not more than one-third with the electrolytic mix-
ture of oxygen and hydrogen as before ; now place over
the tube the glass jacket/ as shown, which is connected
above by a cork with a flask/ in which water is boiled
and by means of which the jacket can be filled with
steam- The lower end of the jacket is also closed by a

1$ I

50 Introduction to Experimental Chemistry.

tube /which serves to convey away the excess of
steam. *

When the gaseous mixture in the eudiometer is

Fig.

20.

-■K\

heated, it expands
until it acquires the
same temperature as
the steam. When
the mercury ceases
to fall, mark its posi-
tion in the tube by
means of a flexible
ring slipped over
the jacket, and also
measure as accur-
ately as possible the
height of the mercury
in the tube over the
surface of that in the
trough w, then nress
the mouth 01 the
tube firmly down on an india-rubber pad, /, passed
under tht mercury for the purpose, arid explode the
mixed gases as in the former exper ment. This can
readily be done if the wires fused into the glass sides
of the eudiometer are connected with short wires which
pass between the cork and the glass jacket, as at w
and Uf\

When the pad is removed from the mouth of the
tube after the explosion, the mercury is seen to rise
in the eudiometer ; but, before measuring the amount
of contraction that has taken nlace in the ^as it is
necessary to restore the original pressure by de°pressing

Hydrogen and Oxygen Gases,

the eudiometer in the well b, of the pneumatic trough,
until the dififcrence of level between the surface of
mercury in the tube and in the trough is the same as
before explosion ; it will then be found on measuring
the gas (water-gas) remaining in the tube that the
contraction amounts to one-third of the original bulk
of the mixed gases, while the temperature has through-
out been maintained by the current of steam.

After explosion we can have but water-gas, or
steam, in the eudiometer ; but the steam is prevented
by the high temperature and low pressure from con-
densing to the liquid form. We have therefore
measured water-gas under the same conditions as the
mixture of two volumes of hydrogen and one of
oxygen before explosion, and found that the water-gas
OQ.c\y^\Q.%\}[\^ same space as the hydrogen which generated
it* Now if, as we have seen, the two volumes of
hydrogen represent two molecules of that body, the
two volumes of the compound water-gas must, accord-
ing to Avogadro's law, represent tivo molectdes of that
body. The result may be stated thus in the form of
an equation : —

Hydrogen -f Oxygen = Water-gas -|- Water-gas.
2 molecules i molecule i molecule i molecule.

* The comparison of the results of a large number of experi-
ments of this order led the illustrious French chemist Gay-
Lussac to the following generalisations : —

1. Gases and vapours combine in simple proportions by
volume.

2. The volume of a compound gas or vapour always I fars
a aimpic n>ropoiiiun lu tne vuiuuica oi gases or vapours from
which it has been formed.

£3

in*

52 Introduction to Experimental Chemistry,

Reasoning upon this result, it is perfectly clear
that each molecule of wa.er-gas so produced must
contam oxygen, and, if the law of definite proportions
be true, as we know it is, each molecule of water-gas
must contain the same quantity of oxygen, conse-
quently a semi-moleciile of that body. Hence*,
though the free molecule of oxygen is not divisible by
any known physical means, it divides under the in-
fluence of chemical attraction into t^vo parts. Now the
weight of oxygen corresponding to the semi-molecule
of that body is the smallest quantity of it that takes
part m chemiral change, and as it cannot be further
divided, even by chemical means, it is called the atom^
O! oxygen.

Later on we shill find that the molecule of hydro-
gen IS also chemically divisible in two parts or atoms

Now, \{ the weight of the molecule of hydrogen
be taken as = i, the weight of the atom of hydrog-n
must be represented = \, but since less than i part
by weight of hydrogen is not known to act in chemical
change, it is convenient to take i as the atomic 7vei^ht,
or vveight of the semi-molecule, of hydrogen. The
weight of the molecule of hydrogen is therefore =rr 2.

As we have already seen from Experiment 27, the
oxygen molecule is sixteen times heavier than tliat
of Hydrogen ; therefore, since the molecular weight
of hydrogen=2, that of oxygen must=32, while the
atomic weight of oxygen is 16.

If, then, we desire to know the atomic iveight of an
elementary gas, it is only necessary to find its specific
gravity, /.^,, to weija:h it as in ExDerimpnt '>n affainc* ««

' &ro/ios, indivisible.

Hydrogen and Oxygen Gases. 53

equal volume of pure hydrogen under the same con-
ditions. The weight obtained, referred to hydrogen
as the unit, is the atomic weight of the body.

But the information that our experiment affords us
does not end here, for we can deduce from it the
specific gravity of water-gas, referred to hydrogen as
our standard.

We have already learned that two molecules of
water-gas, which must contam the hydrogen in two
molecules (i.e., 4 atoms) of that body, and the oxygen
in one molecule {i.e., 2 atoms) of that element, occupy
the same volume as two molecules of hydrof^en.
Therefore one molecule of water-gas occupies the
same volume as one molecule of hydrogen. Now,
one molecule of water-gas must have the relative
weight 18 (16, weight of the semi-molecule of oxygen
+ 2, weight of the molecule of hydrogen) referred to
the hydrogen molecule=2 ; this gives the ratio of
9:1; therefore 9 is the S[)ecific gravity of water-gas
compared with hydrogen gas as the unit.

It may be useful to add the following definitions ; —
A molecule of an element or compound is the
smallest portion of a body that can exist in the free
state.

An atom of a chemical element ' is the smallest
portion of it that is known to take part in chemical
change, and is almost invariably the semi-molecule.

An (quivalent of an element or compound is its
replacing or combining value compared with an unit
weight of hydrogen.

liiv, sn.vjf.j.iix. liic-wiy \}i uic ujiistn.r'"^ pniiosopner^
* A chemical compound has not atomic weight.

If et

ij n-

S4 Introduction to Experimental Chemistry,

Dr. John Dalton, of Manchester, was one of the first
substantial attempts ' to account for the law of definite
proportions t^iat we have seen to so remarkably govern
chemical changes, and we may now state the theory
and the differ eiice ;n form between it as enunciated
by Dalton (in 1804-8), i lid as adapted to the present
state of our knowledge. Dalton supposed, as Avogadro
did, that with all matter a point c^ i be reached at
which further mecbmical subdivisoa is impossible,
and it was to tliese ..timate particles he applied the
tetm atom— the atomic weight being a constant for
each element. The molecules of the present day are
the representatives of the atoms of Dalton, and we
have already learned from our expei iments that the
molecule of an element, though physically indivisible
as we suppose, can divide under the influence of
chemical attraction into two— but rarely laore or less
than two— pa»ts, and to each part we now apply the
term atom. Dalton further ass-med tAat chemical
action takes plact only beu^h^-n the .doms of matter, and
in proportions by weight -^^kic^ are determined by the
relative atomic tvei;:his of the detnmts.

In the Daltonian tlieorv- as tl us modified ^±
have an explaiiation of the law of definite proportions,
but it is necessary to guard against the supposition
that tie law of definite proportions depefids on this
hypothesis. As we have seen, the theory is founded
on two assumptions, both reasonable, it is true, but
which are not at present capable of direct proof. We

' The fundamental conception in the • Atomic Theory » was
distinctly enunciated by two Dublin chemists—Kirwan in 178.1.
and Hiji-lns s.i 1789. ' ""

Hydrogot and Oxygen Gases.

may, therefore, use the theory as an important help
in our inquiries, but not as a support on which we
may rest in full confidence. If, however, we desire
to go still farther, and to enqui-e how it is that these
elementary atoms possess the power of uniting with
each other, we must simply confess that this is one oi
the many mysteries that still lie hidden from the view
of man.

56 Introduction to ExperimSttal Chemistry.

CHAPTER VL

EXPERIMENTS WITH TdE METALS, SILVER, COPPER,

AND MAGNESIUM.

It is obvious that the method of weighing an element
in the form of gas against the same volume of hydro,
gen, when we desire to determine atomic weight, is
only apphcable in those cases in which the element
IS either a gas at ordinary temperature and pressure
or in which it can be converted into gas, or vapour, at
a moderate and manageable degree of heat. Neither
Sliver nor magnesium can be vaporised at even
moderately low temperatures: hence we must seek for
some other mode than that above referred to of
hxing their atomic weights. The equivalent, or re-
placing value of silver stated in terms of the hydrog'^n
unit, we have already proved to be io8, and that of
magnesium 12. Now it is evident that the atomic
weight in each case cannot be less than those values
but It may be more, for we have already seen that in
the case of oxygen the least weight of that body that
takes part as a whole in chemical change (the atom)
IS twice the equivalent. '

^ Experiment 30.-Make the following curious and
mstructive experiment. Take a five shilling piece »

^ ' Although the coin is not pure silver, it is sufficiently nur-
ior liiiit lough experiment. ' *"

Stiver, Copper, and Magnesium. 57

and fasten it securely to a piece of fine binding wire,
lake a piece of copper of the same ^veiirht and thick-
ness, and attach it to wire. Now, while holding the
wires dip the two pieces of metal into some water
boihng in a kettle, or other vessel. After ten minutes
or so remove the pieces, let them drain for a few
seconds and attach the wires to a rod. At first the
metals arc equally hot to the fingers, for they-Iiave
evidently been heated to the same extent; soon,
however, the silver will be cool enough to be held
between the fingers, and to be pressed against a
piece of phosphorus without igniting it, while the
copper will be still too hot to hold, and will easily
kmdle a test of the same kind. The silver, there-
fore, cools more rapidly than the same weight of
copper under the same conditions. As the two
metals do not differ materially in conducting power
we infer from this experiment that silver at koo° c'
(the tempcnmire of boiling water) contains less heat
than the same weight of copper at the same tempera-
ture---in other words, a less quantity of heat is re-
quired to raise the temperature of a given weight of
silver to the same extent as an equal weight of copper,
hence the eapacity of copper for heat is greater than
that of silver. » If we could conveniently replace the

th.t'o?siL'' *°w ^ '^! '^'"^' ^''' "^ ^^Pf^^^ '' greater than
hat of silver Water has the greatest capacity for heat of any

reftrred to that of an c.^mi .vei^rht of water as unity : thus the
capacuy of sUver for heat is about ,Vth that of an e'ual weight

ih.Z7.'r"7 T^Tl '""^ """^ '^5701 : I. This ratio is
the spa^fic heai of silver. The a^oruu; heat of aa, element U

^•}

\ '

i, ■

A ..t

ii'" 'i

J* I- -i

58 Introduction to Experimental Chemistry,

copper by the same weight of magnesium, the dif-
ference in rate of cooling would be still more marked.
This dirterctice amongst solid bodies in capacity foi
heat has long been known, but it remained for two
eminent French phyncists, MM. Dulong and Petit,
to point out the fact that the elements luiving the
highest eciuivalents are those of the lowest capacity
for Jjeat, and vice irrsCi, and they showed from
numerous observations that the heat capacity of an
element is inversely as its equivalent. This 'law of
Dulong and Petit' attracted comparatively little
notice until Professor ( 'annizz led the state-

ment of it, and drew attei ,,v . great value as
serving to aid the determin ition of the atomic weights
of many of the solid elements. The law, as it now
stands^ may l>e stated thus: -77/^ atoms of elementary
mat*er have the same capacity for heat.

If this law be true, toS centigrams of pure silver
and 12 centigrams of pure magnesium when heated to
100° C— the tempf.)ature of boiling water— and then
allowed to cool, ought to give out on cooling to the
same extent the .ame quantity of heat^ if the above
numbers represent tl e relative weights of their atoms.

Experiment 31. — By the method now to be de-
scribed we can apply this test to the two mttals.

The atometer, fig. 21, is really a large spirit ther-
mometer with a test tube inserted in the bulb, as
shown, and hermetically sealed therein. The shaded
portion is full 9f alcohol, coloured red in order to

the product of the specific heat by the atomic ^veight, and if
about 60. Thus '05701 x 108 =»6i S7.

Fig. ai.

Silver and Magnesium. 59

make its motions in the stem more evident. Tlie stem
s should be about 30 centimeters long, graduated
clearly in milli-
meters. The in-
strument ought to
be so constructed
that the t^read of
liquid should ad-
vance through a
length of fully 30
millimeters for an
increase in tem-
perature of one
degree centigrade.
The bulb of the
atometer is bed-
ded, as shown, in cotton uool contained in any con-
venient beaker, or better still, a heavy tumbler. A
small piece of cotton wool is passed down to the
bottom of the test tube /, and ont ubic
centimeter of water accurately delivered into
the previously dry tube from a measuring
pipette, or dropping tube, fig. 22. The whole
apparatus is left in a cool place until the thread
of liquid i the stem becomes steady, i.e.
until the ii. 'ument acquires the same lem-
peratiire.

Now taker ^jiece of pure metallic silver
weighing exactly j centigrams, and of
such a shape that it cau easily pass mto the
*^ -. xxxvsx, -. v: Liis. aiuincic,. i'iace tile centigram
atOLi of silv r in the test tube //, which passes rather

Fig. 2a.
ee

Tftirodndion to ExpcrimcnUtl Oicmistrv,

II '

\\r-.\

Fiu. aj.

loosely through the cork of the flask / fig 23 The
test tube sho^uld be closed by a small stopper of cork

or vulcanit»\ Throu^jh
the cork of the fla>k
another tube passes
which is open at both
ends, and which gives
exit to the current of
steam produced when
the water in the flask is
boiled vigorously. The
test tube and the con-
tained silver are thus
heated to the tempera-
ture ot steam, i.e. 100°
C. if the pressure be
760""". After ten minutes heating in the steam bath
the metal will have acqirred the tiesired temperature:
then remove the tube // quickly, bring its mouth near
to the mouth of the tube / of the aiometer, withdraw
the cork /, and so invert h that the lump of silver s
may ciuickly drop into the water in /, where it parts
with its heat. The little piece of cotton wool prevents
the lump of silver from breaking the glass.

If the temperature, as indicated on the stem s, be
noted just before the introduction of the silver, the
thread of liquid will be seen to. rise almost immediately
after the silver has been dropped in, and will continue
to rise imtil it reaches a maximum.

In an exj^eriment made in this way the thread
of liquid in the atometer rose from 10 to 30 (20

divi'clrknc\ qft-Av »ka t,*o ,. ./••i _«_•> 7\y

'■ "-'^-- ■•"■- •-■« ^. ©la. oi siivci iiau ueen mtro-

duced.

Silver and Mag.Hsium. 5|

luIt.Z^f'^^^ centigra>ns of pure >„a«ne.ium i,>

JTrooo r ?,"' '•'•■''"^ ■' '" '•'' '"'»-• '> ""'' heat

u,i •? ^' ""•' ''"'"^ '^■•■'y ''s 'he silver.
. h.„r . u "'"Snesium is heating, pass a wire with
a hook a the en.l nuo the tube of the atomcter and

Z:^ '° ''^" T •\°'' ""= ■-- '" ™"- woot
1 er h H ^ ;""' " "'" '"■"" "' ^'l^*^^- After the

silver with a force,« and push the cotton Lack under
the water then remove the wire. At this time the
liqutd m the stem . will be still above the point fro.u
whtch It started in the experiment with si ver tl er"
ore remove the bulb . and blow upon it, or o cool

l"rlou;:l''''"''r'""'^'^'"'''°-'n-inttl"an
we re,,u,re; now replace in the wool, an.l allow the
temperature to gradually rise, until the silver starting,
pomt .s reached. By this time the magnesium wm
have been heated to .00° C, and it is now to be
plunged into /. as in the former experiment, and the
nse in temperature noted. t

In the particular experiment above referred to. the
.quid expanded from .0 to only aj (,5 division ) or

as o ,oT" "/'f ""^ '=«'■""' """ " ^^ -the
case 01 108 c. gis. of silver.

The conclusion we draw from this result is that
l» c. grs. of magnesium at .00° C, contain but half
the quam.ty of heat that 108 c. grs. of silver do at the
same temperature. We therefore infer that the weigh of
magnesium that would contain the same quantL of
heat at loo" C. as ,08 c. grs. of silver is 24 c. grs and

Z^T^l^.^^^-^ 'his larger'weight.
- «:..;.; uic 5an.c conuitions as betore, we get an

: til
III

% I

62 Tiitroduction to Experimental Chemistry,

expansion winch is nearly equal to that caused by the
silver. Now, according to our definition of the term
e<iuivalent, silver cannot have a le^s atomic weight
than 108; neither ca.: it be greater, because the pro-
duct of the equivalent into the specific heat of silver
(see foot-note, page 57.) gives the number 6-157, which
accords, within narrow limits, with the highest product
similarly obtained with any element whose atomic
weight can be independently fixed* by means of Avo-
gadro's principle. Hence the weight of a solid ele-
ment that contains at 100° C. the sam«' quantity of
heat as 108 parts of pure silver at ioo« C. is the
atomic weight of the body.

Therefore, according to Cannizzaro's modification
of Oulong and Petit's law, 24 is the atomic as distin-
guished from the equivalent weight of magnesium.

It is right to add here that several exceptions are
known to this and the preceding law, but these will be
dealt with in tlie proper place.

CHAPTER VII.

TABLE OF ATOMIC WE.GHTS-EXPER.MENTS WITH
METALS AND NON-METALS.

The annexed table contains a list of the principal

^:ri:'ri-t-sci£r

nyarogen. O for Oxygen, N for Nitrogen A^ for

the nil r ""^ ''"" '"""''^ « "'^ beginning of
tLZ °f '""re elements than one, /L letlrs

i^Jt^TiL^ iTt "" '°'°"' "^ ^^
Beryllinm ' °' ''™'""'«> '""^ '^ for

Aun^mf and ekht c ur^ ^e\? f ' ^^' ^''^

/-c. grs. Of ACsit": ?hrz;::i!!«:/---:

m aiph.bet.cal order in the .ablerbu t ilTs ^I^

64 Introduction to Experimental Chemistry.

Name

I i

Aluminium
Antimony {SfiNiim)
Arsenic
Barium
Beryllium .
Bismuth .

BOROV

Hromink .
Cadmium .
Calciuri!
Carhon

CHl-ORFNii .

Chromium .

Cobalt

Copper {Cuprum)

Fluorine .

Grold {Anntut)

Hydrogen.

Iodine

Iron (t'enitm)

Lead {Plumbum)

Lithium

Mag^nesium

Manjg^aness

Mercury \ llyiirar^yntm)

Nickel

Nitrogen .

Oxygen

Phosphorus

Platinum .

Potassium {Kalium)

Selenium .

Silicon

Silver {Argentum)

Sodium {Natrium)

Strontium .

Sulphur .

Tri.i-urium

Tin {SUxnnum) .

Zinc .

Symbol Atomic Weiijht

Al''

Sb'

As'

Ha"

«e"

Hi'"

Br'

Cd"

Ca"

Cr"

Co"

Cu'

Au'"

Fe"'

Plj"

Li'

Mg"

Mn»'

Ilg"

Ni"

Pt"

Se«'

Si"

Ag'

Na'

Sr"

Te"
Sn"

Zn"

27.3
122.0

750
1370

9.2
210.0

II. o

80.0

112.0

40.0

12.0

35.5
524
58.6
63.0
19.0
196.2

I.O

127.0

56.0

207.0

7.0

24.0

SS.o
200.0
58.8
14.0
16.0
31.0
196.7

39.1

79.0

28.0

108.0

23.0

87.2

320

128.0

1 18.0

6;.o

Experiments with Metals and Non^ Metals. 65

divide them in two great groups, of metals and non-
metals, respectively. The names of tiie former are
printed m the table in strong Egyptian type, and those
of the latter m capitals, in order to facihtate reference.

J he most strongly marked members of each class
admit of easy distinction.

Experiment 32.^Take a slip of copper, about
ten centnneters long, and a roll of *cane brimstone'
or sulphur, of the same length. Compare them and
note:—

ti. That the red-coloured copper exhibits that
peculiar lustre termed metallic, while the yellow sul-
phur has a greasy lustre of a perfectly distinct kind.

Fic. 94.

^^-^^^SS^

b. That when one end of each specimen touches
the surface of some boiling water, the fingers which
grasp the other end quickly feel the heat conducted hy
the copper, while those holding the sulphur have not
any sensation of warmth conveyed to them.

c. That the copper, O/, fig. 24, when used to
connect the terminal wires of the galvanic battery
B With the galvanometer o in the circuit, conducts
the electricity along it, as shown by the ctrnn« d--.
flection of the needle. When the copper is removed,

m L

66 Introduction to Exi^erimental Chemistry,

and the wires connected by sulphur, the needle is not
affected.

I'he metal copper is therefore distinguished from
the non-metal hulphur— by the metallic lustre, and by
conducting heat and electricity freely. These broad
distmctions are sufficient for the present, but it must
be stated that the members of each group cannot all
be so sharply defined, and in some few cases it is by
tio means easy to determine whether in the free ele-
ment-arsenic, for example— we have to deal with a
metal or wiih a non-metal.

Experiment 33.--Again, take some crystals of
blue vitriol,' or copper sulphate, and dissolve them
in some hot water; now plunge into the solution two
platmuin slips attached to the terminal wires of a
strong galvanic Imttery. Immerse for a minute or
80, and observe that bubbles of gas separate from
one of the plates; withdraw the slips, and note that
a red deposit of metallic copper is obtained on the
slip connected with the zinc end (the negative pole)
of the battery. No deposit takes place at the other-
pole, but It was from this that bubbles of gas were
separated, and this gas could be shown to be oxygen
if collected and tested.

We learn, then, that when a compound of copper
with a body which certainly contains oxygen is elec-
trolysed, the metal makes its appearance at the negative
pole, /.^ that connected with the zinc end of the bat-
tery The reason commonly assigned for this selection
of the negative pole by the metal is, that the latter
t»etng electro-positive is most strongly attracted by the
unhkepole, while the non-metal, oxygen, being elecint.

Experiments tvifh Metals and Non-Metals, 6y

negative, makes Us appearance at the unlike, in this
case the positive pole. This is true, not only of the
copper compound, but of other compounds of a metal
with a non-metal, when subjected to electrolysis ; thu«.
while the metals are electro-positive elements, non^
metals are electro-negative.

Experiment 34.-Make a fresh solution of copper
sulphate and place it in a phial; suspend a clean strip
of iron wire mthe liquid by means of a string fastened
o the cork of the bottleJ A deposit soon forms upon
the iron, and if the bottle be shaken it falls to the
bottom ; when the iron is taken out of the liquid it is
seen to be coatea with copper, and the deposit in

.nni n .J' """''"•' "^PP"'- '^^'^ ^^''^^ SO^^ on
until all the copper has been separated from the

solution by the iron, the latter metal dissolving in the
liquid. Metallic iron therefore displaces copper from
solution without the assistance of a battery

Experiment 35.-Next dissolve a small quantity
of the poisonous 'corrosive sublimate,' or mercuric
chloride m hot water in a test tube, and plunge into
the liquid a clean strip of copper. The latter soon
becomes coated with a greyish deposit, and if we
remove the copper, wash it with water and rub it. a
bright silvery surface is obtained due to the separation
of the nietal mercury, or quicksilver, from the solu-
tion by the copper— the latter metal dissolving

Experiment 36.-Again, dissolve a few crystals of
silver nitrate in some water in a small phial, and pour
a few drops of pure liquid mercury, or quicksilver, into

i- - «.*can oieKi kuiic

6S Introduction to Experimental Chemistry.

Fic.

»s-

the solution, and allow the latter to stand for a day
or so. At the end of that time beautiful needle-like
crystals of metallic silver will be seen in the liquid,
separated out from the solution by the mercury.

We thus learn that the metals are not equally
electro-positive, thus iron being more tlectro-positive
than copper displaced the latter from the solution •,
for a similar reason copper displaced mercury, and
mercury the silver.

Experiment 37. — The displacement of silver by
magnesium already effected in Experiment 14, is
another case in point, and the well-
known ' lead tree ' is a further illustra-
tion. In order to prepare the latter,
dissolve about twenty grams of * sugar
of lead,' or lead acetate, in half a liter
of water and place the solution in a
white glass flask. Seaire a piece of
dean zinc to a string and suspend the
metal in the solution as shown (fig. 25).
The metallic lead separates from the solution after
some hours in beautiful plates or leaves, while the
«inc slowly dissoWes.

From the results of experiments of the kind just
described, we can draw up the following table of four-
teen metallic elements arranged in electro chf»mical
order. Each metal is electro-positive to those above,
and electro-negative to those below it in the list.

Chemical Formul<e.

Ehctro-negativ*,

Gold.

Platinum.

Silver.
Mercuiy.
Copper.
Bismuth.
Tin. •

Lead.

Iron.

Zinc.

Magnesium.
Calcium.
Sodium.
Potassium.

BUctro-fiositivi,

nature of the liqu.d m which the experiments are

andlir?"''""™ '" '^^ ^y^l^o's of the elements,
and have to mqu.re to what uses they are put in ex-
pressmg chemical changes.

of a^v'^n'^rt ■r'^u'' ^-^ '■"" "^""'^ "P ">= ''■°"nula,'
exnr^i T "'"'"'"'"' '=°"'P°'"'«I. and such an
expression mforms us of what kinds of matter the
body ,s composed, and in what proportions the several
constuuents are present. Thus 'the formula NaC
expresses the composition of rommon salt, H,0 tha
of water, and AgNO, that of silver nitrate

If we desire to find the formula by which the
composmon of common salt is to be expres ed, we
have to ascertain in the first instance o/'what e^!
mentary forms of matter it con.sists. With the aid of
Je methods of ,uaUt,Uive a^alysn we can pH
that .t consists of the two elements, sodium and
^onn^ Our next step is to find the proportion of
e«h element pre^^t, and this is accomplished by

; Si

fO Introduction to Experimental Chemistry,

the methods of quantitative analysis^ and the results
are stated below in percentages.

100 parts of common salt afforded on analysis : —

Chlorine . • • , 60*62
Sodium ..... 39-38

1 0000

These are facts, quite apart from any hypothesis ;
but in order to fin' I the relative number of atoms of
each element present in the compound, we divide
the percentage of each constituent by its atomic
weight, thus—

6o'62

35"5»

:i7 and

39*18
----1=17

Hence there is an equal number of atoms of each
element in the compound, aiitl the ratio of Na to CI
is I : I. The formula of the body ij, therefore —

iNa : iCl, or, more simply, NaCl,

for each symbol represents one atom of the element,
and the approximation of the symbols without any sign
between indicates that the definite compound, called
common salt, is the product of the chemical union of
the two elements sodium and chlorine. .The chemical
name ofihis compound is sodium chloride.

Again, 100 parts of water afforded on analysis —

Hydrogen . , . irir-f- ix=ii«iiora.
Oxygen . . . _88^ -4-16= 5-55 or i.

1 00 00

• The atomic weight of chlorine.
t The atomic weight of sodium.

"f^

Chemical Formulce.

formula - ^^ ' ^ ^^'^ '^ expressed by the

analysis- ^ °^ "'*'" ""^"e aflorded on

Silver ,
Nitrogen
Oxygen

^3'5»- 08=: 588, or I.
f'^-^ 14= -5878 „ X.
28^25^ '6=17656 „ 3.
100.00

The quotients, •c88i and -eft^a
equal that we n,ayVa.rly set Ij h'e 'sliX d^"'"'"

luent ; it is therefore a miH«,. ,.r • i- ^ cxperi-

tennwe employ to divide rUlr'"''""^' ''•'''^''
the quotient is a's ne^;' pLs'sS , h'""'' Tf
we have the same numl.er'^f ato„, 0^!",'' "h

nrnfonrn-tTtr-?"-'^^^^^^^^
expressed by the foSl '••"" "'°"'"= ^*"°-'' *«»

AgNO,.

cal ro^i ^Tfb^ran^ r «'■"" °"'^ *"■'-'•
its percentage compo L:!." be^'^I^h '" >"' "'"l
this problem is exceedinX i^l i^;/"'"""" °'

m &,i steg k to find the mo/auMr weigJU <rf the

^■i.\

||L 72 Tntroduction to Experimental Chemistry.

body, i>. the sum of the atomic weights of its consti-
tuents—thus : —

Ag . . . .
N . . . .

03(16x3)
Weight ot molecule

Three sums in simple proportion then obtain the
desired information.

«=io8.
= 14.
« 48.
= 170.

170 : IOC.-. 108 : 63 52 the percentage of Ag.
170 : IOC.-. 14 : &.23 „ „ N.
170 : 100/. 4S : 28-25 „ n O.

lOO'OO

The symI)ol AgNO., is called an empirical formula,
because it ex|)resses only the atomic ratios of the con-
stituents, ;ind iJoes not convey any idea as to the way in
which the elements are grouped within the molecule.
Jf however wc write silver nitrate thus,

Ag-O-NOa,

we seek to convey the idea that the atom of silver is
united by means of one oxygen atom to an oxygenated
group, NC)^, and this is termed a rational formula.
We shall presently meet with -mmy such expressions.
If we examine lists of cIh mnal formuije, we can
easily select a number oi ^ .mplet;, such as the
following : —

Fonnuloe. Names.

^ j HCl • , • Hydrogen Chloride.

(HF , , Hydrogen Fluoride.

«. HjO • , Hydrogen Monoxide.

f'h

Atomiciths of Elements,

Forniultv.

3. AuCI,

4. CCI4

5. PCI.

^5 MnF.

Gold Trii hloride.
Ca bon Tctratl, ride.
I'hosphorus Pentachlo-

ride.
Manganese Hexafluoridp

All these compounds are binary ronpounds or .K«...
Con,amn,g only t«o ki, ,1, of nfatter Tn ,'.,rce dis
met elen.ents unite, they forma /-«„n.c!,", o 'd «,'
B.H er nura.e, AgNU It is to be no,e.l that "re ter

this o-Turs only m the names of bijry eompo.m".
Aga,n the syml.ol written ,0 the left han.l fn S
formula ,3 , at of the ..ost .l^tro-posiUr. J " w
and th.s ., also a general rule, Ihou.h there a rZ
excepttons ,0 it. Lastly, the mm.I.er „f a^om. , the
bX^er " '=°"^"r "' '" ""^ -'-"'euLiii
i!.l the consideration of these formula; leads u.

H and CI, as well as H and F, comhine atom (or atom
(anu as a matter of fact, in no other prop.-rtiS Ind
are therefore .said to be e,,ual in chen.i^al po," r B« a
s-ngle atom of oxygen can a.tntct and a'tach'o itself
t^oo, but not more than two, atoms of hydrogen Ist
water. Again, one atom of the metal^on U!
Cham as u were three, but not more than three atom

.ton. LT'"\" " «."" '"'^"'"'''^^■- «in.ilarly one
atom of ca bon can fix the maximum number of four

atoms of chlonne, as in carbon tetrachloride . .h. ..IT

pno^piiorus atom, five of chlorine, as in 'the "pento!

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74 Introdjtction to Experimental ChemUry.

chloride ; and the manganese atom, six of the element
fluorine.

We thus learn that the atoms of the elements
differ widely in chemical power. The atom of man-
ganese resembles in this respect an open chain of six
hnks, each one of which can attract and hold strongly
one atom of the element fluorine ; phosphorus, a five
hnk Cham ; carbon, one of four links ; gold, one of
three ; oxygen, one of two ; while the hydrogen,
chlonne, and fluorine atoms are represented by single
Imks. °

We can thus divide all the known elements into
those whose atoms are

I link, or Monad, like Hydrogen.

Diad „ Oxygen.

Triad „ Gold.

Tetrad „ Carbon.

Pentad „ Phosphorus.

Hexad „ Manganese.
This hydrogen or chlorine fixing power of an ele-
ment IS often spoken of as the ' atomicity,' ' quantiva-
lence,' or 'valence,' of its chemical atom, and is thus
mdicated m the symbols by the marks shown •— H'
0",Au^Ov,pv, Mnvi.i '

But the atom of an element does not always act
with Its full chemical effect : thus nitrogen acts as a
pentad m sal ammoniac, NH.Cl, as a triad in am-
monia, NH3, and as a monad in nitrous oxide, N,0
or laughing gas. Returning to our simile of the'chain]

» The atomicity of each element is marked in the Table of
Atomic Weights.

5
6

Atomicities of Elements. 75

we say that the five link nitrogen atom may also act
with but three hnks or one, the other links {i.e. centresof
attraction, ' bonds,' ' equivalents,' or 'atomicities ') be-
com,ng.atem or inactive in pairs, owing to mutual sa-
tisfaction. If we regard the atom of nitrogen as a chain
of five equivalents or links, we can easily illustrate
the suppression of links in pairs.

Let the following diagram represent the nitrogen
atom, acting as a pentad, by an open chain of five
l.nk« each one having but a single free point of
attachment, i.e., at a bend or angle ; the chain should
therefore consist of oval and triangular links.

Fig 26.

thus

Ifwe close the chain by connecting the oval links,

Fig. 27.

three points of attachment are still free, and we have
a representation of the atom of nitrogen acting as an
apparent triad. s » ^n

The next diagram represents the monad condition

ot the nitrogen chain, in whiVh hn* rsr.^ k^^j •

free for attachment.

J i\

il:

76 Introduction to Experimental Chemistry,

The. disappearance of the points of attachment in
Fig. 28. pairs is thus seen to be a mechanical ne-
cessity in the case of the hnks of the
chain.

A triad clement, such as gold, would
be represented as a chain of three links
—one triangular and two oval, and this
chain when closed would represent a seem-
ingly monad gold atom, thus—

Fig. 29.

I' '1'

We are acquainted with a number of compounds, in
which the gold atom acts as a monad elem/int.

An ekment which is never more than a monad,
such as hydrogen, is best represerced as a single
circular \v[i\., as if^has but a single centre of attrac-
tion.

In this way we can symbolise the elements of
uneven atomicity, or pcrissads. The atoms of elements
of even atomicity, or ajtiads, may be represented in a
similar way. Thus the manganese atom acting as a
hexad —

Fig. 30.

-yvvv\-

Atomicities of Elements,

as a tetrad—

Fig. 31.

as a diad —

Fio.

3»

The element carbon is a good example of a tetrad
atom, and may be represented by a chain of two
tnangular and two oval Imks ; the closed chain corre-
sponds to the carbon atom acting as a diad

An element which is always diad can be best
representeu by a chain of two oval links, as in the
next figure, in this we represent the composition
of the molecule of water, which, as we have already

ZTr:. ''Tn """"^ ^'^"^ oio^yg^x, in union widi two
aioms of hydrogea *

Fig. 33.

78 Introduction to Experimental Cltemistry.

The circular links are atoms of liydrogen while
the pa.r of oval links represent the .torn of oxygen"
Such representations of monad, diad triad i^.
elements may be easily made in a h;rr^me b^
cuttmg some stout copper wire into equaT e gThs o'f
about lo centnneters, and bending each inf^
or other of the forms of hnk JTIZ Z^
can then be permanently coupled np into chai s so a'
to represent .uoms ; and the latter can be employed '
m ,lh,stratmg chemical combinations in Zlt
already pointed out. ^

In using these aids to study the hpamn«.
carefully ayoid regarding them as tpr^f " LT'ol

Sciairr"^^' "'' ■" ^^^'' - -'- ''^^ -e
The student will do well to attach the 'atomicity'
marks, as ,n the table, to all chemical symbol t
w.ll thus be<:ome soon familiar with the relcL and
combining values of the atoms. ^ ^ ^

SrequSn-"""""'^ '' ''""'"' ^^''^-'"-

2H' + 0"*=H'20".
is intended to represent that two atoms of H and one

.hat every „„k of e.ch cha,„ is'.llv e^d. ' " """"■

lhe//«jsign + signifies 'added to 'or ««,i,o« j

II 4-

Chemical Equations, yg

of O, when brought together under the proper con-
l^'tions, unite and produce the compound water.
The number of atoms of each kind of matter on one
side of an equation must evidently be equal to that
on the other hence we say-//,. .,,,4./,,, o/lAepro^.a
or products of a gtven change, must be equal to the sum
of the weights of the bodies taking part in the reaction.
Again —

indicates that the compound water has suffered de-
composition, and that the products are cne atom of O
and two atoms of H. In other words, 18 c. grs of
water can afford on decomposition 2 c. 2xs of H
and i6c.grs. ofO. fc> • ^^^ xi,

These examples are sufficient for the present, but
many otners will be given as we proceed. It mu^t be
added, however, that the student should not look
upon every equation that complies with the above
me as bemg necessarily a correct one ; it must not
only equate, but represent the facts as accurately as
possible: therefore the quantitative experimental test
IS the only true one of the accuracy of an equation.

i '

' 1

f .

«0 Introduction to Expr. imental Chemistry.

Ill m

CHAPTER VIII.

EXPF.niMRN-TS WITH ACIDS, ALI'.AI.,ES, AND SALTS.

Experiment 37 A-Take some common hydrochloric
or 'muriauCaad, dilute it with about twenty bes'

tnste and that a piece of blue litmus paper is red-
dened when dipped into the liquid. Then add a small
quantity of common • bread soda,' and note that brisk
effervescence takes place, much gas being evolved.

acid and Tf ^^■~'^t^ '°'"' '^"'' -f"''"' °' """c
ac.d, and dilute it to the same extent as the former

acid with water. Note that it also tastes swir

^^T Tf' '"^^ ^^"'"^ effervescence when bread
soda is added to it.

Experiment 39.-Again, take some ' oil of vit iol •
or sulphunc acid, and dilute it with twenty times it's
bulk of water, adding the strong acid to the water
arjjp by drop, and stirring witli a glass rod. This
solution is also sour, reddens litmus, and sets up ef-
fervescence when bread soda is added to it
...H T^ ^^"'^"ded our experiments to all known
ac ds which are soUible in, or can be easily mixIS
with, water, we should find them to possess in a
greater or less degree the characters detected in the

All!,''"" ''•?'^'' "''■''''' '=''"'*'"' " '""'y <=al'=d acetic acid
^l^su™gac,dsm„Mbcca„,io„s1yha„med,«.hey«ege„e:r,t

i t

\ I

Adds, Alkalies, and Salts. gj

HCI .
HNO3
H,S04

. HydrocI'loric acid.
. Nitric acid.
. Suiphuric acid.

tasu ; that it does not redden blue litmus Daner hm
../^^^the colour of the paper .Xr.^C^X

cause anv Iff' "'°" °^ " ^""'^'"^ ^^"^ ^^^s "Ot
Ss appl;""^"^^""' °^ ''•" '^ -^ ^- -bb.es of

Experiment 41.-DissoIve in a similar way a small

t'st t r/ r"'" P"'^^"'' °^ potassium hydrLe,an1
test It in the same way.

calle?'thr,''!f !j"rfP'^"'"^"'^'''^«h are often
caJied the l.^ed alkalies,' or ' bases,' the latter term
being generally applied to bodies which posset
characters opposed to those of an acid. The foraute
of the two bases are the following-

NaOH . Sodium hydrate, or caustic soda.
*^UH . Potassium hydrate, or car tic potash.

canSlTlX';'''''""'' ^'"''^ ^'' '" ^h^^^«-^^ 'hey
can easily netiirahse one another

Experiment 4a.-Take a piece of caustic soda

.1 '

l\^

j . ^jg Iv

■ ■*

82 Intf-odnction to Experimcutnl Chemist}'}'.

about the size of a bean, dissolve it in about 30 c cs
of water. Pour the liquid into an evaporatin- basin'
f>^ fig. 34, and throw into the liquid a strip of blue
litmus paper. Now. add, drop by drop, colourless
hydrochloric acid, stirring the liquid in the basin after
each addition until the litmus parser begins to assume
a reddish colour. Tf we now taste the solution it has
a salt taste, the action of it on litmus paper is neither
acid nor alkaline, and the solution is said to be
;/^///r.//; the acid character of the hydrochloric acid
iias been exactly counter-balanced by the alkaline
Fig. 34. property of the caustic soda, and a

salt is the product. If now we place
the basin on the ring of the retort
stand and apply heat, as shown in
fig- 34, the solution soon boils, and
the water is gradually converted into
steam or vapour, and is driven oflf,
or evaporated. When the liquid has
been thus reduced to a very small
bulk, little granular crystals separate.
Pour off the liquid and allow the
crystals to dry. They will then be
found to possess the familiar characters of common salt.
Therefore that body is produced when we neutralise
hydrochloric acid by caustic soda. The formula of
common salt is NaCl.

The following equation expresses the change :»—

' If 'bread soda' instead of caustic soda be treated with

hydrochloric, or other soluble acid, a gas- carbon dioxide, or

Carbonic acid '— is evolved, as in Experiments 37, 38, and 39,

AciJs, Alkalies, and Salts.
Na^03 + «'C1' = Na'Cr

Sodium hy.

drate, or
caustic soda.

Hydro-
chloric
acid.

Sodium
chloride, or
common
salt

a-, or H in HC, b^he'Z"?:::™' "^""^
is con,n,on ni"e. ' "'"" '""^ '"^ "^"'''" »°'"tion

£53 + g-No, = K,V0, + n^

Water.

Potassium

hydrate, or

caustic potash.

Nitric
acid.

Potassium

nitrate, or

* nitre.*

the solution and hard crystal nf .1! , ^^^^"''^^
sulphate, K,SO., separate"': in Ims Ta';!!'-'-

y^'OH) + H^^SO, = K.SO. + .„,o.
^•""^ ^SSr- ^ ^

requires for neutrahsation twice as

^!!!3 *Ji2L ■ NaCl . H,0 . CO.

B-d^a. Hv.^ co;;;^„ ^^ ^-^^

'**"• add gas"

Hydro-
chloric
acid.

■1:

t !

■J

I 11

m- i

S4 Intyoduction to Experimental Chemistry.

much (/>., two molecules) caustic potash as the
mo ecule of nitric acid did. The reason for this is
that the molecule of sulphuric acid contains two
atoms of H, and, as we have already seen, each atom
of H requires an atom of monad metal such as K to
replace it .-. two molecules of KOH were required
because the necessary number of atoms of K could
not be obiamed in any less quantity.

But, as we shall find later on,*it is possible to
displace only half the hydrogen by K in such an acid
as sulphuric and to form an acid salt, KHSO,, or acid
potassium sulphate-a body which still contains
hydrogen capable of replacement by a metal The
compound, K,SO„ is the neutral or 'normal' salt »

^ Although It is not desirable to go much further in
this direction at present, we can evidently draw the
following conclusions from the foregoing experiments
aad statements.

1st. That acids do not necessarily contain oxygen
else the undoubted acid HCl could not belong to that
class of bodies. ^

2nd. That the acids used contain H replaceable
by a metal, with the production of a salt This is
true of «// acids.

^rd. That all acids do not contain the same number
of atoms of replaceable H within their molecules.

1 hose acids containing one atom of replaceable H,

' A group of bodies termed * double salt. ' is known ; com-
Z^^lT IS a good example of such a salt, for in it we have
suTohate''%rr '^^''>f\^'^^^^^ sulphate and aluminium
K ^n A . Tc^^?'"""'^ °^ anhydrous alum may be thus writtea-

Acids, Alkalies, and Salts.

or.bas,c hydrogen; as it is sometimes called are
. ™ed mouobosic acids, and those containing two

t^'acids^ir'-'^'""^^'''^- ^'*'- -d''-^-
"a, ac ds, likewise exist, containing respectivelv

three and four atoms of basic hydrogen. General '
monobasic acids are the only members of the clas '
which do not form acid salts.

It may be added that we can recognise in all salt,
an electro-positive constituent-the metal Vltl

tld S/r"!"" f ^'-"-%'ative constituent or
actd,a,/Hlc When the latter ,s an element such a,

™o J?' " '^ " '"'"' """'■' ""' '^ -^ "" •«
KNO,, or SO, m K,SO,. it is called a cou^ln^

I Ji;!

86 Introduction to Experimental Chemistry.

CHAPTER IX

FURTHER EXPERIMENTS WITH HYDROGEN.
HvDROGEN. Symbol H'— r T l^.t

«^«^/if^ _-.2. — ihis element, which wae
discovered by Cavendish in X766, has already bl^
expenmented with, and we have found it to be "
colourless modorous, and extremely light gas which

s.af rL^vsnrirweZhr^ ^'- ^--•^

een'SrIt''* ^ ''■'''^' terrestriarstorehouse of hydro-
fart'h « ^ ^ °'''" '" "'^ fr«« ^'^te upon the

volcanoes. It is a constituent of animal and veeetable
tissues, and of all true adds. vegetable

The hydrogen can be liberated from water as we
Which case the compound is resolved into its consti-

H20=2H + 0.

wate^'^whl"*"'* ^'•rH>''J^°gen is also separated from

.Te s ze o " 7eZ?"' " ^'''' °' "^^ ■"''-' ^odinm
dish Th/ K^ i°™^ '=°''^ '^^'^^ contained in a

a<! rt,,. „vi, 1 \r "-"""'1'"='™ witn a his
as the g,obule of metal rolls abo.it nn ,1,

Further Experiments with Hydrogen, ^7

and if a flame be brought near to it, the hydrogen
gas evolved is ignited, and burns with a yellow
flame, until the sodium disappears. If we do not
Ignite the gas, the metal also disappears, dissolving in

Na + H,0 =

Sodium,

NaOH

Water.

Caustic soda

or so ium

hydrate.

The caustic soda can be recognised in the water
by Its property of turning reddened litmus paper blue
bee Experiment 40. •

atom of H m the water molecule and a mtallu
hydrate .s formed, or sodium waler, i.e. water in which
the hydrogen rdle is played in part by the Na '

«'0"H' • . . . Water '

• • • • Sodium hydrate.

53.periment 46.~If we substitute a pellet of the

t^e nfp^Tr Z '^' '"^^""^ ^" '^' ^''' experiment,

hydraTe ""' "'^^ ^'^^"^^^ P°^^^^i"™

H2O"
Water.

Potassium.

= K'O'^H'

Caustic

potash or

potassium

hydrate.

But in this case the temperature of the evolved

' It is possible to displace the second atom of H in water

by another atom of Na. h„t «nt ,« «^ r . " " ^^^^'

ft« in »»,- - • ' ' '" *'**'°^"^'= w* m«cn iicc water

as m the experiment.

■'fl;

■iff

'A !

i i

Fio. 35.

88 Introdiktion to Experimental Chemistry.

hydrogen is raised by the heat of chemical action to
such a point that it takes fire in the air, and burns

Experiment 47.-As we have ah-eady seen, the
colour of the pure hydrogen flame is
a very faint blue, but the yellow
flame observed in Experiment 45 is
due to the presence of a little sodium
vapour, which communicates to the
flame the characteristic tint ob-
served.. Any compound of sodium,
such as common salt, NaCl, will
also communicate a strong yellow
tint to an otherwise colourless
spirit or gas flame, if we introduce
a little of the solid supported on
a loop of platinum wire, as in fig. 35. TWri^here
fore a flame tat for sodium. ^'

c^!Tnt^ r'^f '"" ""^ ''" compounds communi-
flame ^ ^ characteristic reddish violet colour to

•Experiment 48.-Hydrogen can also be displaced
from water by the action of red hot iron on steam
Take an old gun barrel, fig. 36, and fill it to with!n a
few centimeters of each end with bright iron turningsor
furn^f^ V "P^'S^ 'he tube through the little charcoal
!nT f i^ and connect one end b by means of a cork
and leaden tube ,/with the flask ., in which some

steam. Attach a cork a and gas delivery tube , of
lead or glass to the other end. and let^L ..„^

AVfcWA

Further Experiments with Hydrogen. 89

the surface of the vater in the pneumatic trough/
When the iron tube has been heated to full redness,

Fig. 36.

boil the water in c and pass in the steam. Gas will
issue from the delivery tube, but most of it is air at
fir^t, and may be allowed to escape; a few tubes
full are then collected, and may be tested as in Ex-
periment 19. The following equation represents the
change.

3Fe + 4H2O
Iron. Water.

^ — , — --

Magnetic

oxide of

iron.

In this case a metallic hydrate is not formed, but
a metalhc oxide is produced. It has been found by
careful experiment, that three atoms of the iron' or
168 c. grs. (56 X 3), liberate eight atoms, i.e. 8 c. grs'. of
H by weight, and these data enable us to calnjlate ^K«
weight of H which can be evolved by any given

;t i

•^

n t .

90 Introduction to Experimental Chemistry.

OJ steam. Thus m the case supposed :—

168 : IO.-.8 : X ( X = -476 c. grs'._^«..).

acid bv^Tf ° .""" t° ^' '^'"'^^^""^ *''°'" ^"'Ph^ric
acid by the act.on of magnesium, as in Experiment

17, a J by iron or zinc, Experiment 19. Zinc is the
metal most commonly used

Experiment 49.-Fit „p ,he apparatus as in
Exper^ent 19. Having introduced .he zinc, and
filled the bottle one-third with water, replace the cork
and pour two or three cubic centinfeters of T^Td

Mual ;„ t !J°'"'"' °^ ^''' J"''g^<l '° b« about
equal to tw.ce the capacity of the bottle, to escaoe

and then collect in jars for experiment a^ before'
^ + H',SO, = Zn"SO, + ^H
Zinc. "rr — ^7- — -

^'oc sulphate.
In this case, the single atom of diad zinc displaces the

ubhT^h ^'"°"'' " *°'" *^ ^"'' -d form i
sulphate which remains in solution

Experment 50,-When all evolution of gas

Sf ehrboti"™"«^ '=°^'' '"•" f °"^ *^ <^-'«"
of the bottle on a filter, supported by a funnel as in

%._37,'any undissolved zinc, and particles of carbo!,

A.filterislhusmad<!. Cut a circular piece of whu. k.-k 1
paper about a decimeter in diameter doX hVs^o a,.' r "'
a semicircle, and do :ble again so as totla , °™

conve.,.hisi„toa paper -n^ ^^^r.^SsX ''Xer Z
one side, and one fold or thickness on the other pK,!,-
™o.„wards. in .he funnel, as shown, a^d lis^^:^;

Fia 37.

Further Experiments with Hydrogen. 91

lead, and other impurities not dissolved by the di-
luted acid are left behind on the filter, while a clear
liquid passes through, and the latter
when evaporated (as in Experiment
42), until a pellicle or crust begins
to form on the surface of the solu-
tion, deposits fine needie-shaped
crystals of the salt, zinc sulphate—
a body having the composition
ZnS04,7HjO. The water included
in the formula is termed ' water of
crystallisation,' as its presence is
essential to the existence of the
crynals as such, but not to that of the compound zinc
sulphate, as almost every trace of the waCcan be
driven off m the form of steam when the crysmls are
carefully heated to a temperature of 26o» C

Experiment 51.-After repeating former exner!
ments take a gas jar standing over wato i^Z'
trough, half fill with hydrogen an'd the rema nd „i h
air. remove and quickly apply a flame, and an ex

o a,r:'r ?"''• '/ P"-"^ °^yS^" "^ "=ed instead
of atmospheric air, the tube should be two-thirds
filled with hydrogen and the rest with oxygen in
the latter case the explosion is more violent and i"
.s^well to wrap the jar in cloth before applying 'the

. Hydrogen gas, when inhaled into the lungs of
animals, causes death by excluding air

Hydrogen forms two compounds with oxvgen-

Zr::i".5 *^'^ --P-*- - have ILdy
— c...„„^^, «,,cl a uuay lermecl peroxide of hydrogen,

Jli

92 Introduction to Experimental Chemistry.

or oxygenated water, H,0,, whose preparation and
properties will be referred to later on

Experiment 62.-The ease with which hydrogen
combines w,th oxygen renders it a useful 'reducing' or
^W»w^.agent, especially when heated. Take a tube
about I centimeter in diameter, and 20 centimeters long!
Place midway m ,t, at a, fig. 38, a small quantity of
black ox.de of copper, C«0, and connect the tube as
shown wuh the hydrogen bottle b, taking care to

Fig. 38.

interpose the drying tube d filled with calcium chloride,
so as to remove moisture from the gas. Generate
hydrogen as usual and keep up a steady current
^•igh the apparatus. When all air has been ex-
pelled, but not till then, apply heat to the tube so as
to raise the temperature of the copper oxide at a-, the
latter soon begins to glow and steam issues freely
from the end of the tube. The lamp may be re-
moved, and when the glowing ceases the tube is seen
to contam a red body, easily identified as metallic
copper. The change is expressed by the equation—

Further Experiments with Hydrogen. 93

Qm"0" 4- 2H =

Copper
oxide.

Cu + H2O.

Metallic
copper.

This reaction was employed by MM. Dnmas and
Bouss,ngault m order to determine with extrem" pTe
cision the composition of water by weight Thev
heated to redness a carefully weighed fuantity of
pure copper oxi<le in a current of perfectlj pure and
dry hydrogen gas, and collected and weigl^d The
water produced.. I„ one of their experLentt le
cupric ox.de lost 59789 grams of oxygen, and he

tion of this weight of water is, therefore—
Hydrogen . . . ^
^"^8^" 59789

Calculate the peranta^^e composition of LL and
deduce the formula from these data by the method
given at page 70. ^ metnod

Experiment 53._Substitute for the copper oxide
in Experiment 52 some iron rust in fine powder The
red rust-consisting chiefly of a sesquiox'^de^ of iron!!
Aen becomes greyish black when heated to rXlI
m hydrogen, and water is produced. The Wack

weighed quantity of hydrogen e^ih/Jlh/r" '" ^""""^ »
being collected and weight ^ °' water produced

I to'.fT/"'"'"""' ""'' * ^^' f"' *e ratio of Fe to O i.
I to l|; but since an atom is inHivic'Ki^ ♦!. • "* ^'= ^o v^ is

for the oxide i. Fe.O " '^'"^^^> *« amplest expn^ssion

If I

I * i

94 Introduction to Experimental Chemistry.

body left in the tube chiefly consists of metnllic iron
in a very fine state of division, in which condition the
meta eastly takes fire, if the warm powder be poured
out through the air.'- In this condition the metal is
said to \i& pyrophoric.

Fej03+6H=2Fe + 3H20.

Thus prepared from pure oxide, the metal ronsti-
tutes the Ferreduit, or Fenum rcdactum of the British
Pharmacopoeia.

Hydrogen gas is absorbed by water in very small
proportions, loo cubic centimeters of the latter dis-
solve only 1-9,^ c. cs. But some soli.i metals absorb
hydrogen, noiably the metals platinum » and palladium.
The atter take up no less than 370 volumes of the
gas at ordinary temperatures.

M ^lt?7r^^" ''"' ''"'" '■'•^^""y condensed by
M P ctet of Geneva to a liquid, exhibiting steel-blue
metallic \^,r^, under the enormous pressure of 650
atmospheres, and at a temperature of 140° C. below

v^o: 1 ^t' u'f' *''"■'*''""'• *° ^ ^^Sarded as the
vapour of a highly volatile metal.

' The same weight of iron in the form of wire would but
slowly rust or oxidise when exposed ,0 the air, the Ibove ex
penment therefore well illustrate., the effect of a fine s,I!e";
division in determining rapid chemical changes

For a descripUon of the Dobereiner lamp see Platinum.

CHAPTER X.

EXPERIMENTAL DETERMINATION OF THE VOLUME
OCCUPIED BY ONE CENTIGRAM OF HYDROGEN.

Tlt^r ^^"'^^^ ^'^'""^ ^'^"^ Experiment i8 that

ac d"^&:r' H '' '^'^^^^" ''' '^ -^1-d from
aciauiated water dunng the solution of 122 c grs

of pure metalhc magnesium; we, therefore know h^w

to get our unit weight of hydrogen. In he exnen

ment cited we allowed the gas to escape we 3,l"i

now collect the gas and measure it.

Experiment 54.-Obtain a tube about 40 c ms

long and 2 c. ms. internal ^ ^•

c'lameter, graduated into 130

cubic centimeter divisions, a,

% 39- Dilute 50 c. cs. of
oil of vitriol with about a liter
of water in a jug, and throw
into the liquid a few scraps of
metallic zinc. Hydrogen will
be developed and the liquid

will have nearly or quite satu-
rated itself with the gas in a
few minutes. Next pour some
of the diluted acid into a tall
-ffow „ea.er i, a„u, naving filled the graduated tube

Fig. 39.

.1'

111! • .

11 ,t

96 Introduction to Experimental Chemistry.

completely with the same liquid, invert it in the acid
in the bjaker and support it as shown.

Now weigh out 12-2 c. grs. of pure and clean
metallic n)agnesium— the weight of the metal that we
know will liberate i c. gr. of hydrogen—and place it
in the bottom of a narrow test tube, c, to the middle
of which a wire is attached to serve as a handle. The
tube is then filled with water and plunged under the
surface of the acid in b, and the upturned mouth of
tiie test tube rapidly brought under the mouth of the
graduated tube, and even passed up into the latter.
•Very soon the acid liquid displaces the water in the
test tube and th6 metal is attacked ; the hydrogen gas
evolved passes into the inverted tube and there collects.
When the last trace of magnesium disappears the
action is at an end, and we have confined in the
tube the volume of pure hydrogen gas that weighs i
centigram. Now depress the tube in the acidulated
water until the liquid within and without the tube
stands at the same level, and read off the volume of
the enclosed gas. Immediately afterwards read the
tewpmitiire as indicated by a thermometer in the
neighbourhood of the apparatus, and the pressure as
indicated by a barometer.

A more precise experiment can be made with the
apparatus, fig. 40. The stand a supports a tall glass
cylinder, r. Through the large india-rubber cork
which closes the lower opening of the cylinder the
U tube c is passed, great care being taken to avoid
breaking the small t connector c. The outer limb
of the U tube is provided with a glass tap t. The
limb within the tall glass cylinder is sufficientlv wide

t^o/ume of I c. gr. of Hydrogen.

to contain 150 cubic
centimeters in the ex-
panded portion, which,
in our apjmratus,
measures sixty centi-
meters in lent^th. The
graduation cannot be
conveniently carried
beyond fiftlis of a cubic
centimeter. At the
point shown an india-
rubber tube ,g is at-
tached, whicli can be
closed at will either
by a good clip or by
a stopper of glass rod.
The glass side tube c
serves to connect the
measuring apparatus,
filled to o with water,
with the generating
vessel D, which is a
long and wide glass
tube placed within the
cylinder. The glass t
tube E is connected
by means of rubber

tubing with r, while one
limb passes through the
india-rubber cork of d,
and the other is con-
nected by another

Fig.

98 Introduction to Experimental Chemistry.

piece of rul)bcr tubing with a fine tube of the long
pipette F (of about 20 c.cs. capacity), which {)rojects
through the cork. .This connection must be suffi-
ciently long to admit of the clip being applied as

rhe large glnss cylinder b is filled with water, in
ordei a maintain a steady tcmpeniuire, the value of
which can be known by means of a thermometer
immersed in the water.

A determiiiation is made with this apparatus in
lie following way: — H.vjng disconnected the T tube E
from c and removed the clip, the tube d is taken
out of the water of the cylinder, the cork carrying the
pipette, &c., withdrawn, and then 12*2 c. grs. of
magnesium introduced into the tube d. Before re-
placing the cork the pipette f is filled with diluted
sulphuric acid by suction at e, while the small
glass tube opening on the under side of the cork is
closed by a finger: the clip is then applied. The
exterior of the pipette is now washed with a little
water, and the cork, with the apparatus attached, is
then replaced in position; the tube d again immersed
in the water of the large cylinder, and the joint
between e and c securely made. Before making the
connection the water in the graduated tube should
stand at the zero of the scale, but after securing the
joint the pressure within the apparatus is usually
greater than that without. As the air in the tube D
cools down to the temperature of the surrounding
water, contraction takes place; but should the water
not return to the zero, equilibrium is at once restored

hv nnpninor the finp ir: '!a-r!ihh*»r fnK*

• t (^K^^TA VVtl,^^

^' I a few S

Volume of I c. gr. of Hydrogen. 99

seconds, and then closing in such a manner as to
prcyciu any imssible escapf of gas.

The acid is brouglu in contact with the mai^ntsinm
by removmg the chp fron. the india-rubl,;, ,2
connected wuh the p.pette; the r .. nt then fa
upon the metal at the bottom of the tuOe D. Hydro
gen >s volved and .1 .places water from ., the Ikp °d

the U tube by a!lo«i„g the water displaced to run off
by means of the tap t. When the evolution of gaf

tt ?r • '. r'"" '"'^' '^ "^^"■^''^'1 by .neans of

r!!-t '' T^ '^\ '°'"'"^ °f S^^ P™fl"<^"l "> the
reacfon then read off on the graduated tube ; the

tet.perature of the water in the cylinder . i, ,1 en
thTti'r '/' '"'!,'' **^ '"-"'S'^' °f "^^' baron,cterat

cIlcuTatS'™^^"""^-^"'*'^---''--''/

A student obtained, as the result of an exi eriment
madetn this way, xai cubic cemimeters of "c bu
moist hydrogen, measured at 16° C. and 7s= milli
meters pressure, during the solution of 12-2 c l s ■ of
magnesium in acidulated water. • fc • "i

So far for our experiment : we now have to find

he volume this gas would occupy if dry and measured

at o C. and 760 millimeters-the ' standard temp, ra-

corrected, for reasons that will presently appear

The corrections are three in number-namely: fo,
temwn of aqueous vapour, iox pnssure, and iox tem.

r . ^, .xxi^^uiiiy m rne saiupie of metal.

H 2

S t

* I

! ,J

100 Introduction to Experimental Chemistry,

perature, and we shall deal with each in some detail
in order to illustrate the method of solving such
problems.

I. Correction for tension of aqueous vapour.^ — We
find from the annexed table of tensions for different
temperatures that at i6° C. the pressure exerted by
vapour of water =13-5 mm., that is to say, the
pressure exerted by the aqueous vapour within the
tube tended to balance the atmospheric pressure to
the exter.t of a column of mercury of 13*5 millimeters
in height ; therefore the actual pressure under which
we measured the confined gas was

755 — 1 3 "5 =74 1 "5 millimeters of mercury.

Tensions of Aqueous Vapour.

Degrees
Centigrade

5
10

15
16

17
18

Degrees
Centigrade

M i

riitii

Tensions in
millimeters
ot mercury

4'6o 19

6*53 20
9-16 30

979 40

10-45 50

iit6 60

II "90 70

1 2 '69 80

13*53 90
I4'42 100

15-35

2. Correction for pressure. — We learned from Ex-
periment 28 that when a confined mass of gas was

' The student must refer to a work on Physics for full
details of corrections of ffasos^

Tensions in
millimeters
of mercury

i6'34

i7'39

31*54

54-90
91-90

14870

23300

354'6o

525-40
76o'oo

Correction of Gases, loi

compressed, its volume or bulk diminished with in*
crease of pressure, and conversely, increased in volume
as the pressure diminished Thus, if the pressure on
a given mass of gas be doubled, the volume is reduced
to one-half, and if trebled, to one-third, and so on.
When the original pressure is restored the gas returns
to its original volume. If now we reduce the pressure
to^ one-half, the volume of gas is doubled-, if to one-
third, the volume is trebled, and so on. These facts'
find expression in the law of Boyle or Mariotte :
* The volume 7c>hich a gas occupies is inversely propor>.
tional to the pressure to which it is subjected: Now
741-5 mm. being a lower pressure than the standard
760 mm., our gas would occupy a less volume at the
greater pressure ; how much less we find thus—
760 : 741-5 /. 121 : X (>,; =118-5 CCS.).

3. Correction for temperature.— Eyi^&x\m^\\\. 28 also
showed us that gases expand equally when heated,
and contract when cooled. If we begin with a given
volume of gas at the temperature of melting ice, i.e.
0° C, and measure the gas as we raise its tem-
perature at a definite rate, we find that for each rise
m temperature by 1° C. the gas expands ^|,rd of its
volume at 0° C. That is to say, 273 c.cs. at o°-C. expand
to 274 c.cs. if the temperature be raised to 1° C. ; or
to 280 c.cs. if heated to ')° C. ror to 289 ccs. if heated
to 16° C. ; the pressure throughout being constant. •
Similarly, 289 c. cs., cooled too° C. contract to 273 c.
cs. Hence we can easily find the volume that
118-54 ccs of gas at 16° C. would occupy if cooled

tilUb-

289 : 273 ••. 1185 : X (K=iti-9c.cs.).

I' f

iff

i'"- *

102 Introduction to Experimental Chemistry.

The final result is that i centigram of pure dry hy-
drogen, when measured at o° C. and 760 mm. pressure,
occupies as nearly as possible 112 ccs. As we have
already adopted the centigram as our unit of
weight, we may conveniently take the bulk of i c.gr.
of hydrogen, measured under standard conditions, as
our unit of volume, and call it briefly a vol. Thus
when we speak of i vol of any gas, we mean 112 ccs.
of it measured at 0° C. and 760 mm.'

The zW as thus defined is a small and convenient
quantity of a gas, which is well within the capacity of
the ordinary measuring vessels used in laboratories ;
moreover it possesses the great advantage over the
liter as a unit of gaseous volumes, that its weight in
hydrogen is identical with the atomic weight of that
body in centigrams; consequently a vol of any
other elementary gas weighs the number of centi-
grams indicated by the atomic weight of the element.
Thus —

Name of gas

Hydrogen
Oxygen .
Nitrogen
Chlorine

Atomic
weight

I.O
16.0
14.0

35-5

Weight in centigrams

of I 7W(at o°C. and 760

mm.) or 112 c. cs.

1.0 c. gr.
16.0 „
14 o

35-5

A number of^/^/ tubes may be prepared by cuttin- a good
cylmdncal glass tube 4.2 centimeters diameter into lengths of
7.8 centimeters, one end of each tube is then close 1 by a glass
plate which is cemented on. Each tube or jar should hold 112 c
cs of water We have a number of these jars prepared and
hlled with different coloured wool, in order to illustrate the
volume reiauons of elementary and compound gases.

Chemical Calculations. 103

Hence in order to find the weight of a given bulk
of gas, for instance, of 900 cos. of hydrogen at stan-
dard temperature and pressure, it is merely necessary
to proceed as under :-^ ^

112:900/.! : X(X=8o3c.grs.}.
But if the gas were oxygen—

ii2:9oo.M6: K(K = 128-57 c.grs.) ^.
n X at. wt.

Generally —

K =

112

Smce the w/ of hydrogen represents the semi-
molecule of that element, the molecular weight being

renrZn, T ^'''''''' '"'" '^''^ ^'^^ 5^)' ">^ ^'"^"'^o
represents the sem.-molecule of any compound gas-
water gas for example-consequently the weight of
one po/ of a compound gas is half the molecular
weight m centigrams. Thus—

Name of gas

Molecular Molecular
I roimula i weight

Hydrogen
"Water gas

Hydrochloric
gas .

Ammonia ,
Marsh gas
Carbon dioxide
Carbon monoxide

acid

ii:o

HCl

NH3
CII,
CO.,
CO"

2
18

36.5

17
16

44
28

Weight in centi-
grams of one 7JoI
(at o"C. and 760) or

112 C. CS-

18.25

8.5

c. gr.
>>
I)

>i
if
tt
it

The numbers in the fourth column are identical
kMI Tl''".. S^^^''!- °/ the gases referred To

111

S ffll

104 Introduction to Experimental Chemistry,

in centigrams of a given hulk of a compound gas—^ox
instance, of 1200 c. cs. (=i'2 liters) of ammonia gas

at standard temperature and pressure— we say

112 : I200.-.8-5 : K iX=9i c. grs.).
If the gas were hydrochloric acid gas—

112 : I200.M8-25 : x (X = i95-5 c. grs.).
Generally —

«_x sp. gr.
112

when n = the number given in cubic centimeters of
dry gas at 0° C. and 760 mm.

Instead of the' z/^/, we may use the liter as our unit
of volume. The weight of a liter of pure dry hydrogen
at o°C. and 760 mm. is -08936 (this weight is called by
Dr. Hofmann a crith), A liter of oxygen weighs 16
criths, of chlorine 35-5 criths, of nitrogen 14 criths, &c.
A liter of water-gas weighs 9 criths, of ammonia 8-5
criths, of hydrochloric acid gas 18*25 criths, &c.

We have already learned from Experiment 29 that
the specific gravity of the compound water gas is half
its molecular, weight; and the above table tells us the
same thing for other compound gases. If then we have
presented to us a gas of unknown composition, we can
determine its molecular weighthy first taking its specific
gravity, as in Experiment 27, and that vakn, when
doubled, should give the molecular weight of the com-
pound. Thus, ammonia gas has the specific gravity
Z'^, its molecular weight is therefore 8-5x2= 17.
^ Hydrochloric acid gas has the specific gravity
i8-2^ ; the molecular weight of the compound is
therefore 18-25x2= 36-5.

Absolute Temperature.

Fig. 4t.

There are a few exceptions to this important rule,
Which u'lU be noticed in the proper place

^ ExperimentSS.-TnkeaUtubeoftheformshown

m lig. 41, with Innbs 60 centimeters long. Let one

Jimb be hermetically sealed at

the top and the other open.

A stopcock is provided near

to the bend of the open linib-

Now fill both limbs completely

with mercury so as to expel

all air, then insert the cork u

through which passes the end
of a small tube open at both
ends, and filled with fragments
of calcium chloride. Now open
the stopcock s, and allow about '
half the mercury to flow out,
while //ryair enters through the
drying tube c. Next transfer
this dry air to the closed lirub
by inclining the tube suffi-
ciently. Then bring the mer-
cury in both limbs to the same
level by drawing off some
through the stopcock. Should
the volume of air in the closed
limb be less than half the tube
full, after levelling, transfer

sufficient to make up the de-

sired volume, and level again, but this time by remov-

ingf the cork and nnnrinrr ;«f^ 4.1 !• , ^ .

---— r --o "^«-^ i"c open iimo suJiicient
mercury. T he cork and tube c need not be replaced

i>, ' .

I-

« • I

iiiii

106 Introduction to Experime?ital Chemistry,

We have now a confined xnass of dry air in the
closed limb. Place over this tube a glass jacket/,
which IS stopped below by (he cork /, through which
the closed limb passes, and the small side tube m.
Fill up the space between the exterior of the U
tube and the jacket with pounded ice. This will soon
cool down the air in the tube, and the gas will con-
tract m volume. When no further contraction takes
place, again adjust the level of the mercury in the
two hmbs, and mark off as accurately as possible in
the outer tube the position of the mercury in the
closed hmb. This iparks on the tube the volume
occupied by the dry air at the temperature Ox melting
•• ^, i.e. at 0° C.

Now pour tepid water into the jacket/ ; this will
melt the remaining ice,' and the water will flow off
through the side tube m, which is opened or closed at
pleasure by the pinchcock or clip/, that compresses a
piece of india-rubber tubing attached to m. When the
ice has melted, and the water been drawn off, remove
the pmchcock/, and connect the tube h, by means of
vulcanised tubing, with a flask from which a good cur-
rent of steam can be obtained by rapidly boiling
water contained in it ; the steam rushes through the
jacket and the excess may be allowed to pass off into
the air through the tube in. As the air n the clos'id
hmb becomes heated it expands until it has acquired
the temperature of the steam. When it ceases to ex-
pand, adjust the level of the mercury as before, and
mark on the tube the volume occupied by the dry air
9X the particular temperature.

Now divide iha interval between the two points

Laiv of Charles. xty

marked into loo equal parts, by transferring the
length to cardboard, and plotting ofif the intervals
With the scale thus obtained, measure the distance
from the position occupied by the mercury when the
gas was cooled to the temperature of melting ice, to
the sealed top of the tube, and it will be found that
the end of the tube is reached, as nearly as possible at
273 DIVISIONS of the scale. This point is termed the
absolute zero, for it is evident that the contraction of
the gas could not go beyond this point, even {{ it con-
tracted with regularity nearly to its limit. U then we
represent the top of the tube as absolute zero, or
00°, the enclosed air at the temperature of melting
ice will occupy the position 273°, and that of free
steam the position of 373°, on such a scale of absolute
temperature ; hence the ' law ' enunciated bv Charles
that the volume of a given mass of gas, under constant
pressure, ts directly as its absolute temperature, i.e.,
as Its temperature measured from absolute zero. This
IS 273+/, t being the number of degrees above the
freezmg-pomt on the scale of the centigrade ther-
mometer.

f f

X08 httroduction to Experimental Chemistry

ill

i
I
I t

CHAPTER XI.

EXPERIMENTS WITH OXYGEN AND OZONE.

OxYGEN-«5>w^^/, 0"=i6. I F^/ wei^r/is i6 e. grs.
Molecular wei^ht=^2,—\N(t have already proved
conclusively that oxygen is not only a constituent of
water, and that it forms |ths of that body by vei-ht, but
also that it is present in atmospheric air. Later on, we
shall find that it is met with in most of the chemical
compounds of which the solid crust of our globe is
composed, but in the air alone do we find the element
m a free state (/. e. not in chemical combination),
though mixed with four times its volume of another
gas called nitrogen. We do not possess a convenient
process for the direct separation of oxygen from air,
hence we always prepare it from one or other of its
compounds. Oxygen can be '• prepared from water
by electrolysis, as already described, Experiment 22,

H,0=2H + 0,

or more conveniently by heating certain bodies which
easily yield oxygen— ior example— mercuric oxide,
or the salt called potassium chlorate.

Experiment 56.— take a tube of hard glass, /,
fig.^ 42, closed at one end, and fitted with a cork and
delivery tube as shown. Place in the tube about 200

Fig. 42.

Experiments zvith Oxygen, 109

c. grs. of red oxide of mercury, the * red precipitate '
of ihe druggists. Heat gently at first, and then
increase the temperature. Gas will soon escape from
the delivery tube and
bubble through the
water in the pneu-
matic trough. After
expulsion of the air,
the gas collected is
found to have the
property of rekindling
a match with a gib wing
tip, and is oxygen ; at
thesametimeitwillbe
observed that bright
metallic globules con-
dense on the sides of the tube /, and, if the heat be
contmued long enough, the pure mercuric oxide is
wholly resolved into oxygen gas, and globules of the
liquid metal mercury or quicksilver. Thus :—

Hg" O" =

^-^ ,

Mercuric oxide.

Mercury.

Oxygen.'

This process is not an advantageous one for the
preparation of oxygen in quantity, but it possesses
special interest, since it is the method by which the
element was first prepared by its discoverer, Dr.
Priesttey, in'1774.

Oxygen can also be obtained by heating manga-

. o.e ^xw ^. i;.a. ui ngu anord i6 c. grs. of O, the
weight of one vol at o°C. and 760 mm.

, .;: \.:.

1 1 o Introduction to Experimental Chemistry,

nese dioxide, in which case the following decom-
position takes place—

3MnO,=:Mn3 04-f2 0.

Barium dioxide and other similar bodies also afford
the gas, and the processes will be described under
the respective compounds; but the most convenient
method is the following : —

Experiment 57.— Fit a flask— a clean Florence
oil flask answers well— with a cork and delivery tube

Fig. 43.

as shown in fig. 43. Break up some crystals of the
salt potassium chlorate (KC102)in a mo.tar, then mix
with about one-third of its weight of black oxde of
mang:anese (manganese dioxide), and pour the mix-
ture into the flask, but resen'e a small portion and
heat the latter strongly in a test tube before applying
heat to the contents of the flask. If no violent action
takes place when the small quantity is heated, the
manganese used may be considered free from any
dangerous impurity, such as charcoal, soot, or lamp
th which it is sometimes accidentallv mixed

KIm.I

ui.13.-^ n., TV 1

Preparation of Oxygen,

III

or even adulterated ; ' then heat the flask. After
expulsion of the air, the gas can be collected \\ several
jars or in w'"de.mouthcd bottles over the
water )n the pneumatic trough, as ico ^

CCS. of water dissolve but 2*989 ccs. of \

wimmm

gas at 15° C. If it be desired to store
a (]uantity of the gas for a number of
experiments, the gas-holder shown in
section, fig. 44, is to be emi)loyed.

The heat resolves the potassium
chlorate into oxygen gas and potas-
sium chloride, which latter remains in the flask at
the end of the operation along with the black oxide
of manganese ; for the latter body is not known to
undergo any chemical change during the operation,
though its presence undoubtedly enables the oxygen
to separate at a lower temperature than it other-
wise would. The following equation represents the
ultimate change : —

K'C1'0"3 = K'Cl' + 3O

Potassiijm
chlorate.

Potassium
chloride.

The potassium chloride left is easily soluble in water,
whereas the black oxide of manganese is insoluble ;
we can take advantage of these facts in order to sepa-
rate the two bodies. Add some warm water to the
contents of the flask, allow the mixture to stand for
half an hour or so, and thf n throw the dirty black
mixture on a paper filter. The clear liquid passes

' Several fatal accidents have resulted from such admix-
ture.

I¥

'..fl

.S&.i

112 Introduction to Experimental Chemistry,

through and is collected in a l)eaker, while the solid
pnrticles of the insoluble manganese dioxide are
retained by the filter and thus separated. When aH
the liquid has passed through the filter, place the dish
on a ring of a retort stand, and evaporate (as in
Expeninent 50) until all the water is removed, and a

i!ridf '""^ ^"""^^ ''"''''"'• '^^''' '' '^^ potassium
With the aid of the equation just given we can
easily calculate the weight and the volume of pure
oxygen gas, at 0° C. and 760 mm. that a given weight
say 100 cgrs., of the pure potassium chlorate can aficrd

T J°"?^^^^^ '^^''^^P^^'tio"- '^he molecular weight
of K UO3 is 122-6, and this is found by the general
method of adding together the weights of the con-
stuuent atoms, /.. K=39T, 0=35-5, 3 0=48
^10 X 3}. bince all the oxygen is evolved when the
salt is strongly heated for a suflicient time, it follows
that 122-6 cgrs. of K CI O3 can afford 48 cgrs. of O.
Hence the weight of gas 100 cgrs. can yield is—

122-6 : ICO.-. 48 . K ( K =39-15 cgrs. Arts.).

We have now to find the volume:- 16 cgrs. of oxygen
at 0° C. and 760 mm. measure 1 z'^/( = ii2 c cs ) •
now ' 'I >

16 : 39-I5.MI2 : K (X=274 ccs. Am.).

The general answer therefore is- 100 cgrs. of pure
potassium chlorate afford 39-15 cgrs. of oxygen gas,
which occupies the volume of 274 ccs. at 0° C and
760 mm. The same method is employed in all similar
calculations, as for instance in the calculation of the

Experitiieiits toit/i Oxygen.

»I3

volume of oxygen that can be collc< ,cd on heatins a
given weight of red oxide of mere ury '

VVe already kno^v that oxygen gas is colourless, in-
o< orous. and a powerful supporter of .omhustion.

th^l '' '•■"■' °' °"' -^fsas already collected n,ake
tne lollowino experiments -^

Experiment 58 -Take a small Unnp of charcoal
and tw,st a piece of copper wire round it. Hold the
char, oal m the spirit or gas flame tmtil it is kindled,
and then plunge it into a jar of oxygen. The char
co^ burns energetically in the pu'fe gas, enii fng
much hght and heat. In this and si.„ilar experf
men s it is well to provide a cover for the jar of
cardboard, through a hole in which the wire passes.
VVhen the combustion is at an end remove the char-
coal ami pour into the jar some clear lime water-
no e that the latter becomes milky when the mouth

shaken. The reason is that the product of the com-
bustion of charcoal (carbon) in oxygen is a gas called
carbon dioxide, this forms insoluble a,/i, or calcium
carbonate, when it meets with lime water (solution of
caelum hydrate); the latter is, therefore, a Ust for the
gas. 1 hese reactions are thus represented—

C + 2O = CO2

" ^ ' ^ , — '

Carbon. _ ^ Carbon

dioxide.

weight of a body required to afford a given volume of gas.

... , " '""" "^.^^^^ ^« '^^^<^^ in a jar of pureoxv^en it do.«
iiut Dccome lurbid. " '"

t li

'^1

1 14 Introduction to Experimental Chemistry.

Then—

CO2+ Ca"(0Hy2 = Ca^'COa + HgO.

Calcium
hydrate.

Calcium
carbonate.

Fig. 45.

The chalk is the calcium salt of an acid HXO3
formed by the action of water on the gas CO.,.

Experiment 59. — Place a small quantity of
sulphur in the iron spoo'.i, fig. 45, and
kindle it, when feebly burning plunge
it into a jar of oxygen. The sulphur
burns with a beautiful blue flame,
and )\ gas — sulphur dioxide— havi. g
"N-' A a suffocating oclour, is the product.
Remove the spoon, pour some water
into the jar, close the mouth with
the hand and shake. Now test the
water in the jar with some blue litmus
paper. It ill be found to redden the
paper, and to have a sour taste. In
the first instance —
S +20= SO2.

Sulphur.

Sulphur
dioxide.

The sulphur dioxide gas when dissolved in water
pioduees sulphurous acid, thus —

SO2 +H20=^ H.SO.,.

Sulphur
dioxide.

Sulphiircus
acid.

Experiment 60.— Clean the spoon used in the

last exnerilYient nnd nlnrp in if n vprt/ email Ar^r .^."^

Experiments with Oxygen. 1 1 5

of phosphorus.' Kindle and plunge into a jar of
oxygen. It burns with great brilliancy and produces
white fumes in abundance; these deposit a. a white
l)owcler on the sides of the jar, if the latter be nearly
dry. Remove the spoon and pour some cold water
into the jar and shake as before. The white sub-
stance disappears, dissolving in the water; this solution
also is found to contain an acid. The first change is'
thus expressed —

2P- ,+ 50"=

Then—

Phos-
ohorus.

Phosphorus
pentoxide.

P2O5 +H20= 2(HP03).

Phosphorous
pentoxide.

Metaphos-
phoric acid

In each of these experiments, then, an oxide was
the product of combustion in oxygen, and the oxide
produced an acid when added to water. The name
of the element^ signifying 'acid producer' was given
m allusion to this property, but it is now known to be
only one amongst several elements which can give
rise to compounds exhibiting acid characters.

Experiment 61.— Take a piece of thin iron wire
and coil it into a spiral, twist one end of the spiral
round a small sfjJinter of wood coated with sulphur.
Now set fire to the latter and plunge the coil into a

^ ' Take care to cut this under water, as phosphorus is easily
Ignited by friction, and it burns with great violence

Fig. 46.

316 Introdtiction to Experimental Chemistry.

large jar of oxygen, as shown in fig. 46. The sulphur
and the match burn and soon raise the temperature
of the iron to such a point that it
undergoes strong combustion, molten
drops falling from the point of wire
into the water covering the bottom
of the jar. When the combustion is
ended, the jar is removed and the
solidified drops examined. They con-
sist of an oxide of iron, but they do
no^ produce an acid with water under
any conditions, nor do they exhibit any
alkaline or basic characters.

3Fe + 40=Fe304.

Again, when hydrogen burns in air or in oxygen,
it produces 7vater, which we already know to be a
liquid that does not present the ordinary characters of
an acid or of a base.

We thus learn that all oxides do not produce acids,
though some do; further that some oxides do not
produce either acids or bases, and may be classed as
indifferent oxides.

Experiment 62. — Place a small piece of the metal
sodium in the little spoon, shown in fig. 45, heat the
metal until it fuses and begins to burn, plunge then
into a jar of oxygen. The sodium produces a white
or nearly white body (NajO) which dissolves in water
with a hissing noise and produces a liquid which ia
strongly alkaline to test paper. Thus —

2Na' +0"= Na'oO". •

Sodium.

Sodium
oxide.

Then —

Experiments with Oxygen. ny

Na^O +H20= 2(NaOH).

Sodium
oxide.

Sodium hy
drate, or
caustic soda.

A similar experiment can be made with the metal
potassmm.

Experiment 63.~Finally, burn a piece of mag-
nesium wire or ribbon in air or oxygen, and throw
the white sohd produced (magnesium oxide, or
magnesia, ) into a small quantity of water. » Although
he body does not seem to dissolve in the water the
latter acquires an alkaline reaction if allowed to stand
for some time, and a piece of reddened litmus paper
left m the liquid becomes blue.

Mag-
nesium

Magnesium
oxide.

Then—

Mg'^O

:'0" +H20=Mg''(0H)V

Magnesium
oxide.

Magnesium
hydrate.

oxid'e-^'cao'''„l,'""'' "^ '""""°" * l'"^'''™^.' or calcium
oxide CaO-used in morlar, when added to water falls to

powder and dissolves to a small extent, uflording an a'ka ine ol ^

ovTr :L: t: X"\ '' .""^ ' '""''' "-"'"^ °f watt be poutd
over the lime, it is absorbed and the mass crumbles to a ^wder

zrVh :tri^.^'!-:.s^'"")c™-H hea.r:tg

Part III.) ""'"" " '"'' """^ """ ''^^^'- i^ee *""her

1 1 8 Introduction to Experimental Chemistry,

RwhIBSb i

■P?

Our results may be thus tabulated —
Acid producing Oxides —

Carbon dioxide
Sulphur dioxide
Phosphorus pentoxide

Indifferent Oxides —

Water

Iron oxide . • , .

Basic Oxides —

Sodium oxide ....
Potassium oxide
Magnesium oxide

CO2.
SO2.
P2O5.

'H,0.
Fe304.

Na20.

K2O

MgO.

The members of the first class are termed acid
anhydrides, and those of the third class, basic anhy-
drides, because the corresponding acids and bases can
yield these oxides when the elements of water are
abstracted from them.

Experiment 64.— Fill a stout gas jar with water,i
and invert in the^pneumatic trough in the usual way,
introduce oxygen until one-third of the water has
been displaced, and then hydrogen until the jar is
filled with gas. Slip a glass plate under the mouth of
the jar, remove the latter from the trough and apply
a flame. A violent explosion takes place, as in the
.similar Experiment 23, and water is produced, as we
nave already proved by Experiments 24 and 25,
when we exploded the mixture of "gases under such
conditions that the resulting water could be observed.

lA/P cV»oll -n/Mir «-Mol:r£> fU^-v ^,.^^^.._ l-.x. 1 • .1

Fig. 47.

Oxyhydrogen Flame. 1 19

Experiment 65.— Connect the tube h, fig. 47, with
a small rubber cloth bag full of hydrogen by means of
a flexible tube, and with a similar bag containing
oxygen gas, the stopcocks s and s' being closed. Apply
^^//.^/ pressure to the bags, and turn on a little hydro-
gen by cautiously opening the stopcock s ; the gas
passes through the meslies of the wire
gauze g, placed over th^ opening of
both tubes, and enters the little chamber
c, whence it passes by the narrow tube
t, to the jet at which it is to be kindled.
While the hydrogen burns, producing a
flame 3 or 4 centimeters long, turn on
tlie oxygen gradually by opening s'.

The flame shortens considerably as the

proportion of oxygen increases, up to a

certain point, but if too much oxygen

be introduced, it is extinguished with

a snap, then the stopcocks must be

turned off and the same plan of lighting

repeated. When burning properly, the

oxyhydrogen flame is of pale blue colour, and emits

little light, but it is intensely hot—in fact the hottest

Vxio^fxx flame.

a. Introduce into the flame the end of a piece of
platinum wire. The metal melts eae:ily to a globule,
though it is almost infusible in our most powerful
furnaces.

^ b. Introduce an iron or steel wire ; it also melts
quickly, and burns, emitting brilliant sparks.

- ^.^-.-^ ix. tii^ liaiiie a picLu 01 quickiiiiit;, or one
of the cylinders of the same material, commenly sold

120 Iniyoduction to Experimental Chemistry,

for the purpose, /, fig. 47. The lime does not m-It,
but it becomes intensely hot, ahnost white hot, and
emits a brilliant light. This is the oxyhydrogen, or
* limelight,' which is used for various illuminating^
purposes. **

Ozo^Y.— Symbol, O3. Molecular weight^^%.

Experiment 66.— Pour a layer of water on the
bottom of a tall and wide-mouthed bottle, and intro-
duce a stick of clean, freslily-scraped phosphorus,
takmg care that the latter shall not be immersed in
the water through more than one-third of its length.
Partiafly close the mouth of the vessel with a piece
of card-board, and let it stand for half an-hour or so.
i\1iitish fumes soon appear, and ultimately fill the
bottle : on opening the latter, a strong and peculiar
smell is perceived, and when a strip of moist starch
and potassium iodide paper » is plunged into the air of
the bottle, it is quickly discoloured, while pure air is
almost without action upon the paper. The peculiar
smell and the effect upon the test paper are alike due
to the presence of a small quantity of a body discovered
by Schonbein in 1840, and named by him Ozone?

The strong smell noticed when an electrical
machme is worked, or electric sparks are passed
through air, is due to the formation of a little ozone ;
and if the oxygen evolved on the electrolysis of water'
as m Experiment 22, be examined with the test-paper]

» Easily prepared by soaking pieces of white bibulous paper in

fodide"'' '^""''^ ^^''^' """^ ^'^"'''"' '°^"*^°" ^^ potassium

* ''O^w, I smeii.

Experiments with Ozone. 121

it will also give the colour change just observed. Dr
Andrews, of Belfast, has proved that ozone is nothing
but free oxygen in a remarkably active condition, for
pure, dry oxygen can be partially converted into
ozone by the silent electrical discharge, • and the oxygen
dunng conversion is found to contract in volume In
fact, It has been shown that three volumes of ordinary
oxygen form t^^ o volumes of ozone ; the molecule of
the latter therefore contains three atoms (unlike so

many other elementary molecules, which contain two) •
hence, ozone may be correctly spr^ken of as a chemi-
cally condensed and active modification of ordinary
oxygen, and its symbol written O3. On heating
ozone to 260^ C. it is reconverted into ordinary
oxygen, and the gas returns to its original volume,
while It loses the power of afiecting the test paper.

1 his remarkable instance ol" what is termed alhtro.
ptsm s not the only example of an element occurrinff
m two forms which differ in physical and chemical
characters, and yet consist of the same matter : for we
shall meet, later on, with analogous allotropic forms of
phosphorus, sulphur, and of carbon-the black and
dull charcoal and the colourless and brilliant diamond
being but allotropes of the element carbon.

Isomerism in compounds is the condition analo-
gous to allotropism of elements ; we are acquainted
with pairs of compounds which contain the same ele-
ments m the same proportions, but exhibit different

' - ^^7 '^'^^^-^ favourable circumstances the proportion
of ozone formed m a given volume of oxygen rarely exceeds
one-tenth of the whole, ev^n w>,«. „ c:„lT__. I '-^ceeas
electrical ozoniser is employed.

122 Introduction to Experimental Chemistry.

ill

physical and chemical characters ; for example, lactic
acid, met with in sour milk, and solid grape sugar.
But we have in two bodies, whose empirical formula is
in each case CON2H4, illustrations of a special kind
of isomerism. One of these substances, ammonium
cyanaie, is easily converted l)y heat into the second, a
jDody termed tirca, and the latter is identical with a
well-known product of the animal organism. (See
Appendix aud Part IV. for details.)

Experiment 67.— Pour a small quantity of per-
fectly bright c}ean mercury into a short wide test tube,
and lower the hitter by means of a string into the jar
containing ozone used in the last experiment. Note
that a very short exposure to the ozonised air suflices
to render the surface of the mercury dull, owing to
the production of a film of dca oxide of mercury. Pure
oxygen does not afifect pure mercury under the same
conditions, but the mo'e energetic ozone rapidly tar-

nishos or oxidises the metal.
A piece of rubber tubing
is also quickly attacked by
ozone.

Experiment 68. — Bend
a tube about 50 centi-
meters long and 1-5 cms.
diameter into U form. Fit
one opening with a cork
carrying the bent gas de-
livery tube, as shown, fig.
48, and through the cork
pass a stout platmum wire terminating within the tube

Before inserting

- - ^

Fig. 48.

in a strip of foil of the same metal

Experiments with Ozone. 123

the cork, coat it (but not the platinum) thoroughly
with moMtx, paraffin, as the latter is not affected by
ozone, and serves to prorect the cork from the in-
fluence of the gas. Let the end of the small gas de.
livery \ ibe dip under the surface of a small quantity of
ether contained in the phial p. Now connect the wire
w with the platinum end uf a small two-cell Grove's
battery, and insert the other pole in the open side of
and well down into the bend of the U tube, the
limbs ot which have been previously half filled with
water acidulated with chromic acid, or, if the latter
IS not available, with sulphuric acid (one volume of
strong acid to three of water). Oxygen containing a
little ozone will be evolved from the plate iv but
haying no exit save from the gas delivery tube, will
bubble through the ether. The latter dissolves the
ozone, and after some time becomes so charged with
that body that it instantly discolours the ozone
test paper when a strip is dipped into the liquid.
Moreover, when some of the ozonised ether i? shaken
up with water, coloured of a pale blue tint by * sul-
phate of indigo,' the colour is destroyed, and the
liquid thus bleached. Ozone is also soluble in
turpentine and several essential oils, but it is dissolved
to a very -mall extent by water : according to Carius
only o'5 c.c. in 100.

Experiment 69.-Expose a piece of ozone test
paper freely to the outer air for a few hours, shading
It, however, from sunshine. Even prolonged exposure
to the air of a large city rarely produces discolouration
of the paper, but pure country air usually causes a
uistmci browiiish colouration in a {q\j minutes. It

124 Introduction to Experimental Chemistry,

has been proved that ozone is present in pure air in
. mmule proportions, though other .bodies are occa-
sionally met with which hkewise discolour the paper.
It IS supposed that the bkie colour of the ' sky ' is due
to the presence of ozone.

It is not surprising that city air should contain
but httle ozone, as the organic and other impurities
destroy, and, we may add, at the same time are de>
stroyed by the ozone, which latter, therefore, acts as a
natural disinfectant by reason of its extremely energetic
oxidising power.

^ When highly 'ozonised oxygen or air is inhaled
into the lungs, much bronchial irritation results; but*
a small proportion does not produce any sensible
efifect

We have thus studied in some detail the two
strongly contrasted and typical elements hydrogen
and oxygen— the former a type of metals, the latfer of
non-metalsT The products of theifurfion irow require
further examination at our hands, in order that we
may complete the first stage of our inquiry.

lil

'try.

125

re air in
e occa-
' paper.
' is due

I ■

contain
purities
are ele-
cts as a
lergetic

inhaled
ts; buf
ensible

le two

drogen
itfer of
•eqiiife
lat we

CHAPTER XII.

EXPERIMENTS WITH WATER AND HYDROGEN

PEROXFDE.

Our previous experiments having placed beyond
doubt the composition of water by weight and vokime
and its molecular weight (H20=i8), we have now to
examme some of the more prominent characters of
this most important of all liquids.

Experiment 70.— Arrange the stoppered retort a.

Fig. 49.

fig. 49, Liebig's condenser, b, and receiver c, as

™^

Siiown. iiitroduce some rain or river water into a,

ii^

ll<< »

126 lutroductm, to Expenmcnlal C/ia,nstrj, .

s,tf '„!"""<=''""' "^'-' P'-n-ose, a„.I apply „,e heat of a
s mt or gas flame, taking care to n.ove >he la.ier
about at l.rst an.] to wipe off drops of moisture 1
form on the bottom of the retort VV|,en t he v te
has l,een ,l,u, warn.ed at first, the hu,.p flam , Uy
allowed to play steadily on the retort. After a hort
time the water ^w/.i vigorouslv and ,h. !
into fh,. i,„.i, r .1 "^'t'"'""'*'/' and the steam passes
nto the beak of the retort, and idtimately in o the
■n'^^r glass tnhe ^, of the condenser ; here il is cl ed

[he in nhf t '">"=' I"««i"g water-tight through
the tin plate jackety.hs cooled by a current of rolH

::L?of tT "-'""^ '''""'' ''"^ f'-nel/arthe 10 2
poin of the apparatus, whUe the warmer and there-

most of Its heat, is carried away by the tube t it ,h^
"pper part of the condenser. "iL first po toin of e
condensed steam, or &////„/ „,„,,,., ^ J ,„ "f^^ ' n
away and the rest collected in the receiver b Tt^^
not advisable to continue the distillat L" 'aSr 1 e
quid in the retort has been reduced to one fifth of
1^ original volume. The water thus colleaed is
almost chemically pure. "'■cttea is

,nH^^'"'''j'"" "'"' P'""' '' ^ C"Io"rless,« inodorous
and msipid „c,md, which at ordinary iemperIrS

.he .„nosp„er^ a. the .! IfH:':::':?;':"",:' '" """ °'
ture is ico° C at -76-. n, '"i,"^ ^'^^^ «fwatc this tempera-

.iscs .™„ fans With increased I J:^^^^^:^"' """'
Great ,«as.,e. of pure water have a distinct bluish co,„,ar.

Experiments with Water.

127

gives off invisible vajraur, and diffuses into the sur-
roundms air ; hence, water can be slmvly but whoilv
evaporated by, simple exposure to the air. When
heat IS applied it can be rapidly and completely
converted into steam-one volume of water affordiuR
nearly 1,700 volumes of steam at 100° C and a
pressiire of 760 mm. One gram of steam at 100° C
passed into ice-cold water can raise the temperature
of S37 grams of the latter i» C. The ' latent heat
of steam is, therefore, 537 thermal units. Water
. becomes solid when sufficiently cooled, either by its
own rapid evaporation, or by the application of external

in ,^Ti,*"f°* "-I''^^« '^ f-^w drops of pure water
in a watch-glass and suspend the latter over a basin
containing strong oil of vitriol, standing on the plate
of an air-pump. Now cover the whole with a small
bell jar and exhaust the air. As the pressure
diminishes, rapid evaporation of the water takes place
while the vapour is absorbed by the oil of vitriol'
The quantity of heat abslricted by rapid conversion
mto vapour is sufficient to cool the water down to he
freezing point in a. very short time, and a small piece
of ice IS qu.cKly produced. Several ingenious ice-

prkciple."'" ' ''''' ''''" ^°"^'™^<^d o" this
Exneriment 72.-Take a tube about 30 c ms
long and 4 ,„m. internal diameter. One end musi
be closed and expanded into a bulb. Pour in water

the bulb and half the stem in a beilcpr nf ,.„.„ ;..
cold and containing ke. The water in the stm fir«

i ;

t St

f "f"

Si^.j'

il^

128 Introduction to J'.xperivtcntal Chemistry

rises, owing to the contraction of the glass on cooling
diminishing the c ijucity of the vessel and pushing up
the column of water ; as the water cools, however it
contracts more rapidly than the glass, and the level
of liquid sinks below the starting point until it be-
comes stationary and, if the external water be really
ice cold, then rises acr(mi in the tube. If a thermometer
could be plunged in thc^ water within the bulb it
would be found to mark about 4° C when the liquid
commenced to rise. Now remove the bulb and plunge
It into a 'freezing mixture'' of ^Glauber's salt' and
common ' muriatic acid/-the salt just covered with
acid. The expansion of the liquid goes on until a
sudden check is observed ; if the bulb be then re-
moved, it will probably be found cracked and con-
tainmg ice.2 l^hus water, when cooled down, contracts
until the temperature of 4° C. is reached; then it ex~
pands axain up to the soluiifying point, and still greater
expansion at that point suffices to burst the containing
vessel, if it offers any obstacle to the free motion of
the ice, for the latter occupies, ^weight for weight,
more space than water at 0° C. The temperature of
maximum density of water is 4° C, or that temperature
at which one cubic centimeter of water has the greatest
weight, i.e., one gram.

' Poumled ice mixed will, half its weight of common salt
may be used instead, but the mixture given above ii convenient
and eflective.

« This sudden expansion on freezing aids materially in the
d.smtegration of rocks, as the water contained in the cavities
and hssures, wlien converted into ice, expands with great force,
and breaks up successive layers of the material. The same
Cause Ifii ' • ■ ' •

kIc i,-\ »K<

ig of Watcr-pi

pes.

Solution of Solids. , j.

If similar experiments are made with alcohol oil,

.and other hqu.ds, they will be found to contract £

not to expand again as the temperature >s r^du Id

hus water .s the great exception to this gene^lTat'

and m thts respect stands alone amongst the hautl'

hitherto examined. "quids

seem toTT' ""'"^'' "''^ P^P^"^ "^ "«'« may
seem to be, its consequences are of ereat mnm-.„. .

mankind Thus, if water obeyed L^ZC^

^ nvers and lakes would s,K,n become mCeT of Lud

.ce, their fish would be destroyed, anftte heaTt^

summer would be unable to undo the effm rfth^

ioTlXbir" ''"^ -'' equatorial regiL ai-
We thus have 'evidence of design ' in this excen
honal property of water, which exceeds in im~t'
any a orded by the animal or vegetable ki gdC

When .ce at o°C. melts, it absorbs without el J^tion
of temperature ^^ much heat as would raise thHet
perature of an equal weight of water from o»C to L-C ^

Lm STr '"; "' "^"^'^^ ^° ^"^"^e '"/L^e
irom solid to liquid water, and is spoken of as its

latent heat, ,>, hidden (insensible) heat

place m each ,00 c. cs. of cold water. Weigh out

"noer" sH ^T °[ ' "'"^ ^■''™' ' ^"y»''"""d
copper sulphate), and introduce into one of the'

a2l;'°fr'' °' "' P"'^"'"'" ^'•'•"-"'^e, into
anoUier ; and 50 grams of common salt into the

Of 79 tinicfc Its weight ol water i^C,

*!'

i'llf

1 30 Inirodticiion to Exp^imental Chemistry,

third. Now boil the contents of each flask : note
that the copper and bichromate alike dissolve com-
pletely on boiling, each body communicating its
colour to the liquid. But even long continued
boiling fails to dissolve all the common salt There-
fore common salt is less soluble than the other two
bodies in boiling water. As a mitter of fact, bodies
vary greatly in solubility : some dissolve to such a
small extent that they are commonly spoken of as
insoluble, for example, chalk and glass ; others so
freely that they are almost indefinitely soluble, for
example, caustic ptotash and calcium chloride.

When the contents of the three flasks are quite
cold, it will be found that beautiful crystals have
separated in the copper and the bichromate solutions,
and these crystals can be made to disappear and re-
appear by alternate heating and slow cooling of each
liquid. It is therefore evident that heat increases
the solubility of both solids in water, and that the ex-
cess of solid ' over and above that which the cold
liquid can dissolve separates out, thus leaving a
solution which cannot dissolve more of the particular
body at the given temperature, and is therefore said to
be a cold saturated solution. A hot saturated solution
is obtained by adding the desired substance to boil-
ing water until the solid ceases to dissolve. The

• When decomposition does not accompany the act of solu-
tion, the crystals which separate from the hot sohition h-we the
same composition as the body originally dissolved. If d« com-
position precedes solution, as when sodium and potassium
dissolve in water. Experiments 45 and 46, the body in solution
must be different from thar intrrMhirnd.

Solids and Liquids. x\\

solubility of a non-volatile solid is usually determined

saturated a a known temperature, until the solven
IS completely expelled ; the dry solid residuum ,s then
accurately weighed and the ratio ol the solid to the
solvent l,q«,d thus directly determined. '

Experiment 74.-Pour off into a large test tube
some o the cold and clear saturated soluL of com!
mon salt prepared m the last experiment, now boil
dol'no.''^"^'''^'^'"""'"" ^^"' the latter evidemy
the solubility of common salt in water is nmrly the
^««.ath,ghand low temperatures, and in this respec

S ' i ,M ''■""''^'''^ ^^<^^Ption to the general ?ule
that solids are more soluble in hot than cold liquids.

I.m. ^vater (seepage 117) in a flask, and note that the

ome of T" '"'''• , '"''= '^ '"^ '° "-^ separationbf
some of the previously dissolved lime, its solubility
. ; boiling water being little more than hllf that nea to

on to the general rule, as it is las soluble at h.gh
than at low temperature. ''

.,.K^''-l'^*°* 7e.-Take four test tubes and half fil'
each with water. A.Id a k^ drops of alcohol to one,
of chlorofor,n to another, of oil to a third, and o
g ycenne to a fourth. Note that the alcohol and
glycerine read.ly dissolve in, or mix with, the wa.e"
«he„ the contents of the tubes are shaken up, and
«,..' ^"'" "fU'^'ed with one salt can dissolve others • thus .

rrrrlr.^"^ -""•.--■'- stilldis^tveeithercoi:
r- •-. "i i^u turoinaic oi potasoium.

K3 '

III

i
s

'"^^

132 Introduction to Experimental Chemistry,

t1>e water can take up an indefinite quantity of each.
On the other hand, agiiati.on fails to make the chloro-
form or oil disappear, but when the clear water is
poured off from the layer of heavy chloroform, it has
the odour and sweetish taste of the latter : therefore
chloroform is shghtly soluble in water. The oil, on
the other hand, fails to dissolve to any sensible ex-
tent

Hence water is a good solvent for some liquids as
well as for solids.

Experiment 77.— Obtain a bottle of* soda water.' *
On removing the ffressure of the cork, a rush of gas
takes place. Whtin effervescence has subsided, pour
some of the liquid into a flask anc^heat : effervescence
recurs, and a cork lightly inserted in the neck of
the flask is quickly blown out, owing to the es-
cape of much gas. If the liquid be boiled and then
allowed to cool, it will be found to have lost its brisk
taste, due to the presence of the gas, for the latter has
been wholly expelled by heat.

Place another portion in a beaker or tumbler, and
the latter on the plate of an air-pump, cover with the
bell-jar and exhaust. As the pressure within the
receiver diminishes, strong effervescence commences in
'fhe liquid and continues as the exhaustion proceeds,
until all but the most minute traces of gas are
removed from the liquid.' It is clear, then, that the

' The amount of ' soda ' present is usually so small that we
may regard it as a solution of carbonic acid gas in water.

' Although the weight of any gas dissolved does not, gene-
rally speaking, diminish regularly with increase of temperature,

{■Va/er Supply. jj^

gas present in this solution-called 'carbonic acid
gas -i« rather freely soluble in water, unlike hydro-
gen and oxygen,' which we have already found to
d^lve to an almost insensible extent; an.l later on
a art II ) we shall meet with much wider differences
n solubihty; but the fact is that all gu.es are n.ore or
Jess soluble in water^

.nd „1 our experience proves it to be the most general
solvent known. °

Owing to the general solvent power of wate. it is

from ,r r «r°"'''"d ^ven solid impurities
from the air through which it passes, and from the
soil on which it falls.

The prime source of all water supply is ua-
doubtedly, the ocean, since in nature thirl is a c^
ttnuous circulation from the sea to the air, then frol
air to rivers, and, finally, to sea again. The air a
contact with the ocean becomes quickly .saturated with
the vapour of water, and then, bemg carried by
currents over the earth and suddenly cooled, lets faU
^e, u.kiU ,H. ../„„,. ,v M. sam^M all fr^^ura (Henry-.

H„.?° IT'"''!."''' °' 2" '" *•■"" "" ^ determined by „p,a.
tiogtogelher known volumes of gas unci wa.er i„ a graduTced
tube elosed by :nercury, and „, ii„g the volun.e abLbei it
constant l.mpcrature and pressure. •■'■'«)ri«j at

• At„,osph..ric air is soluble to a very small e.v:e:,t in water
loo CCS. of the latter dissolvin,; only ,., c es of .|p 1 ' '
te;nperature. Small ,h„„g„ .bis amoL. L",: to be it sTrl"
^.s source that «sh obtain the air neces^rv for thl Ml*!;™

fiil

u -

134 Tntroduction to Experimental Chemistry,

much of the aqueous vapour in the form of rain.*
If the soil be not very porous, small streams are
formed (which wash out soluble impurities from the
surface soil), and these flowing into a common channel
produce a river. If the soil be porous, the water
percolates through it, and may drain away again at a
lower level and form rivulets and/ivers, or it sinks into
the subjacent permeable strata, thus serving to main-
tain the supply of wells and of natural springs, often
situated at a great distance from the place of rainfall.
If the permeable strata are not overlaid by those only
slightly pervious, \ land-springs not rising above the
surface are obtained over the district ; but if the strata
dip between two impermeable beds, an Artesian spring
is obtained on boring, at a lower level, through the
upper bed to the water-bearing strata. Water in its
passage through the rock strata, often under con-
siderable pressure, dissolves out more or less of the
soluble constituents of the strata, and makes its
appearance in land-springs and natural or artificial
Artesian wells or springs as a mineralised water. If
the rocks, through whose substance cr fissures it
passes in its downward course to find its level, happen
to be the older metamorphic, granitic, or quartzose
rocks, or green-sand beds, but little impurity is taken
up, and the springs usually yield a supply of very
pure water. If the rocks are cretaceous, or magnesian,
or both, the water is then charged with lime and
other salts, to an extent dependent on the particular

* If the rainfall of a district be known, the calculation^ for the
catchment area can be easily made, if it be remembered that a
fall of lo inches of rain yields 226, 170 gallons per acre.

Mineral Wafers.

135

of the latter inhelinnln K ''"^ '^''^°'^'^^ l'"' ""'e
acid, since tie ami of chalr^f' -"-""onic
taken up bears a dire rehtfon J H "'"" '"'""^"=>
ciis.solve(l carbonic !"] I ''"''"'''^ °'" ''"^

of the Cnrara snrin!« I ^°""'™«' as in the case

probably Tder fs Ire LT'" '"",""' '^''"^=^^.
acid and with chalkln!; " """'"'■'' ^^"^n' ""1'

loses much of its f ko"f °"r"':« '"™'" 'he sot.rce

is the depos,°[o^oT.t°"chal\ oL"' 'T\ "' ""^ '°-
tion by the acid in !! ? •' P'«^'°"sly hel.l in solu-

Mme, '2Z^t:'T^. '"-"gh stmta containing
with carboni :'c°; ^^iTin't' !'' "^.'" '''^'^^^

Posable ferruginous ~th°Cr Ten'"""-
portion of their iron as ll.^ I ^^''' "I' *

dissolves in the excess of IT- ^"'^°"''"^. 'vhich
the water of a chaj:! IpT Tt "''' ''"'^ ^°™'
meet with in volcanl dttr Cj aJd aT "^"^T" °'''"
bourhood of the coal measTres' In .h T '" '^ ""'s''-
-e rarely fai, to „,eet not oX' ^Uh st""' '"^'""''^^
less worthy of the name rh, , '^'"'springs, more or
> ot tne name chalybeate, but we also find

carbonate dissolved by carboni, \°\ "" ''''"'' "'••'gncsi,,,,,)
water, and is called ■ ,emD„;m' " ""'"""=^ "J' •»"i"S 'he
boiling is . perma en, h"Ie7. and T ' ' """ ""' '""»'='' by
or sulphate of calcinn. ll" 1!'! '"'' " ''"* '° *»«"'«! chlorid;
Calcium, and I'art IV ,' Soap'^""'"'"' '^'' ''""""• P"' "I-,

lu'

h I'.

h :

136 Introduction to Experimental Chemistry,

the sulphur spas, the sulphuretted compounds of which
have been ctuctly derived iroui the decomposition of
SI piiidcs, always present in the shales and true coal
beds, by infiltrating water charged with carbonic acid.

The most celebrated of tnese rnmeraiised waters
of medicmal value may be thus grouped, accordmg to
their chief constitueiits : —

Carbonated ami Alkaline^ as those of Vichy, Bilin,
Ems, and Malvern.

Sulp/iatcdi^o(X\\va\\ Carlsbad, Cheltenham, PuUna
(Magnesium), Epsom, Sedlitz.

Sulphuretted, iJarrogate, Aix-la-Chapelle, Lucan,
Lisdoonvarna

Chlorinated^ Leamington, Harrogate, Clielteaham,
Wiesbaden, Homburg, Kissmgtn.

ChalyOeate, iSpa, Tunbndge, Harrogate, &c.

In addition to these, we meet with special pro-
ducts of the action of volcanic gases and steam in
the —

Siliceous waters of the Icelandic Geysers.

Boracic waters ot the Tuscan lagoons.

Sea water is the product ot continual land wash*
ing, and m it enormous quantities of saime matter
are stored.-* An analysis ot the water ot the Iristi
Channel, made by Messrs. 'I'horpe and Moreton,
afforded the following results ; —

> Sea water is easily rende,red potable by Dr. Normandy's
process for providing pure water lor ships at sea. Salt water i$
distilled, as iii Experiment 70, but in l.ri;e iron reiuiis (or
ttiUs), the salt- are Icli in tiie retort, and uit condensed and
pure water, wl. Ji is flat and insipid at hrst, is rendere ^ bri:,k and
agreeable by .rcing it to di .solve ome atmospheric au m «
i>|)cciai apparatus.

Peroxide of Hydrogen,

137

n
n

looo parts gave —
Sodium chloride
Potassium „
Magnesium chloride
bromide
sulpliate
>» nitrate .

Calcium sulphate ,

V carbonate
Lithium chloride .
Ammonium „
Iron carbonate ,
Silica ,
Water .

• «

26.459
0.-/46

0.070
.'^.066
0.002

^•331
0.047

traces

>»

0.005

traces
966.144

volumes) of the water .s 1024.8, if pure water =,000
the Dead Sea is so large that the specific cravitv of a
AsX:r'? ''''■'' '° '' "'*■ (-'- = oooj

foil" tt^'" ■'''•''"'''• '^ '"^'y ^-'Sh^rlLn xroo. if
follows that an average man wouM be buoyed ud

!h n' r''' f '^' ''^"^ Sen, and could not sink
wholly beneath its surface without some effort

Peroxide OF HvDRoGEM (Oxygenated WaterW^,«.

Experiment 78.-Add, with frequent agitation
about 5 grams of barium peroxide (liSTbi

^u"'"!_' ^- <^- ."'^ '"-""g a-:"! ; filter, and add som.
"..=1 to a portion of the filtered liquid and a fe^

H-

I'^I

138 Introduction to Experimctttal Chemistry,

drops of solution of red potassium bichromate, and
shake. Note that the ether (which is but little miscible
with water) rises coloured of a magnificent blue tint,
which is evanescent. .

Barium peroxide and sulphuric acid afford hydro-
gen peroxide (or oxygenated water) and barium
sulphate. The latter body being insoluble is filtered
off.

BaOa + H2S04=EaSO4 + HjOa.

The chromic compound serves to detect the pre-
sence of the peroxide of hydrogen formed in this re-
action,* as it is characteristic of that body to produce
an unstable and highly oxidised blue chromic com-
pound which is soluble in ether, and less quickly
changes in that liquid than in any other. The solu-
tion of H2O2 made as above is dilute; when carefully
prepared in the first instance, and then evaporated
oyer oil of vitriol in the exhausted receiver of the
air pump, a syrupy liquid of specific gravity 1452
(water =1000) is obtained, which is colourless and
inodorous, but has a strong somewhat metallic taste,
and can be cooled down to — 3o°C. without freezing!
This is the pure peroxide, but so unstable is it that
a slight heat suffices for its decomposition into water
and oxygen, and even the dilute solutions of the body
sold are easily decomposed in the same way.

Experiment 79.— Take a long and moderately

A'7^^ peroxide, like ozone, sets free iodine fr-rm potassium
iodide, and therefore colours the ozone test paper This
colouration by the peroxide takes place even in presence of
•green vitriol ' or ferrous sulphate, unlike that due to o.nn«

Peroxide of Hydrogen, j 39

thin glass tube, scaled at one end, tliree-fourths fill
It with mercury, and the remainder with as stromr 1 a
solution of the peroxide as can be obtained : then in-

Z% "!. """TT' ^' '''°^^'"' ^S 50. If the tube be
inchned, and the portion occupied

by the peroxide gently heated by f.c 50.

means of a spirit or gas flame,

bubbles of gas will quickly make
their appearance. When sufficient
gas has been collected, pass the
thumb under the mercury, close the
mouth of the tube, remove from the
- mercury, invert, and test for oxyiren
by plunging a match with a glowing
. tip into the gas.

HaC^HgO + O.

This decomposition of peroxide of h3'drogen into

aTd of reir^"" ^"' ^^" '^ ^^^---^^^ -t'out h:
aid ot heat by mere contact with—

and^arf f rrf"'"''''-.''° ""' "'''"^^'^<='' '''«^' -change
and are therefore said to act catalytically Mox exaunt

-gold sUver, platin.™, charcoal and fibrin o b ood
b. Bodies wh,ch lose oxygen at :he same time ^

give a substanfi'al *.vr^I-,„»..•„• _r ., . i''^"^"^ unable to

Tha. brings aSuTc^eS^han' "in'Xerit °' "^"^
itself suffering sensible alteration ^ ""' *"^<""

140

Iniroduction to Experimental Ckanistry,

Experiment 80. —Moisten a sheet of writing paper
with a solution of lead acetate, and expose it to the
fumes arising from a few drui).s of ammonium sulphide
sprmkled over the bottom of a shalluw dish. The
paper becomes quickly chscoloured, owing to the
production of the dark-coloured lead sulphide (PbS).
When stained a dark brown, remove the pai)er and
dry It, then charge a brush with a solution of peroxide
of hydrogen, and draw a design on the stained surface.
The (lark lead sulpiide will be rai)idly bleaclud by the
perox'de, and the^ design will appear in white on a
dark ground. In this case, the peroxide actsas a power-
ful t?.r/^/>///<,r agent, converting the dark lead sulp///^^
into white lead sulp/z^/^, (PbSO^), thus—

PbS + 4HaOa=PbS04 +4H2O.

In a similar way, discoloured oil paintings and
engravmgs can be bleached by careful treatment with
dilute solutions of the peroxide. The latter has also
been largely used to bleach dark hair, and change it
to the golden colour, lately fashionable.

The chromic test, described under Experiment 78,
is another example of oxidation effected by the per-
oxide, but in that case cdlour is developed not
destroyed.' *

' Another case of oxidation by the neroxide accompnnied by
a colour change is the following :-Add a {tsv drops .of a fresh
alcoholic solution of guiacum nsin to a few c.cs. of water, then
a few drops of solution of the peroxide to the turbid liquid If
to the mixture a little colouring matter of blood be added a
beautiful turquois blue tint is soon develo; ed. In this case
the blood determines the decomposition of the peroxide whose

^ Hydroxy!, 1^,

Although the peroxide cannot be converte(! into
gas, and have its specific gravity taken in that con-
dition so as to determine its molecular weight its
analysis, and the reactions already cited, leave no
doubt that its formula is H^O,. Its relation to water
may be thus shown —

Water.
H-O-H

Peroxide.

In the peroxide we assume that the two double-
link oxygen atoms are united, and form a chain, to each
end of which IS attached a single-link hydrogen atom.
If we break this chain at the dotted line, it is evident
that we get two -r'..ups, each containing one atom of
oxygen and of lydrogon, and each group is expressed
by the symbol III. Ve should not expect, and do
not find, these i m..j,s to exist in the free state,
because each wouid have one link of oxygen free, and
that is contrary to the general rule ; but we might
look for OH in combination. As a matter of fact we
meet with the group OH in an immense variety of
oxygenated compounds, and this group acts like a
single atom of a monad or uni-link element, and is
commonly spoken of as the * compound radicle,'
hydroxy!. The molecule of the peroxide of hydrogen
contains two hydroxyl groups, and therefore is to be
regarded as the free molecule of that body.

The study of water and peroxide of hydrogen
—two distinct compounds of the same elements— l^ds

atom of available oxygen at once oxidises the finely divided resin
into the blue coloured body. This is Dr. Day's, of r^dnn.,
test for biood. ' ' "*'

J •

f '
. i

J42 Introduction to Experimental Chemistry

ot fcis *.;;:■ "'"'« «i>™"> ««,.««:

I' i

11 '

'" f '

l^.<' I

APPENDIX.

may be referred to one or other of the following divisions
As one or „,ore examples of each kind of changroccur

ofe eacrcaTe^KT""™'^' '"^ '^'"^^ '' ""vised o
rcier each case he has met with to its proper division

In order to acilitate this process of general isa^n a
smgle exan,p,e. with its reference, is Jven uXTach

I. Cases 0/ direct combination of elements,

(Experiment a.)

Mg + ^ - MgO

Magnesium. Oxygen. Magneslu^xid..

2. Cases oj simple decomposition,

(ExPBrtlMBNT aa.)

H^ - 2H + o
Water. Hydrogen. Oxyien.

3- ^<^e5 of double decomposition,

(Experiment 14.)

AgNO, + NaCl »

AgCl

ver nitrate.

NaNO,

^L"r„*'.°n?« Sllv.rclUor.d.. Sodiun.'

Jit 1

lit/-.

mumtaw

Js!

144

Appendix.
4. Cases of decomposition by substitution.

(EXPERIMUNT 19.)

Zn + H,SO, - ZnSO

Zinc.

Sulphuric
acid.

^ ^ + 2H

Zinc sulphate. Hydrogen.

5. Cases qf decomposition by reduction.

(EXHEKIMBNT SaX

CuO + 2H - Cu +

W.iter.

Copper oxide. Hydrogen. Co^cr.

6. Cases of rearrangement, or isomeric change.

J (Pack laa.)
Ammonium cyanate. Urea.

Two conditions tend so materially to determine double

fng Ta^.T "' *""'" *"" '"""""'"=" '"« fo""-
I. Two bodies in solution will always decomoose
each other, .f it be possible, by double declmposiS, :
produce a new body to soluble than either of the two
original substances. **

• ''<•'■ e'"»n>Ple-silver nitrate and common salt orodur*
insoluble silver chloride. (Experiment ,4.)

alwnv. 7 "^'^ *''*" """^ "■■ heated together will
^-Tm j'"^'""f«''« ^^-^h other, if i, be possible bv
double decomposition, to produce a n^w k!S ^
^olaHU than either of the tw^o :^;"arsubsTanc:s.'' '""'"

car^It rd'K.^^t-c^td' "/""r ''^''™«-
-lo.de at ordinJir;::,-;^. ''t^^Z\T''

PART IL

Fic. SI,

CHAPTER xm.

EXPERIMENTS WITH AIR AND NITROGEN.

abn.^r^*''*/^-^"' " P'^^^ °^ phosphorus

Swlf z. V as ' '' -'^ ^-'^ ^~

paper, and place it in the

small porcelain capsule r,

fig- 5i» which floats on the

water in the pneumatic

trough. Fire the phosphorus

by the touch of a hot wire,

and immediately invert over

it the bell-jar, which is at

first full of air. The mouth

of this jar must be under

the surface of the water so

as to completely inclose the

gas it contains. Bubbi*a ^f «•- ^s.-^^-^ ^^ i:_

* " '^ "''■ i''- «*i msi, Owing

4 ,■
1 i

1 :
f ■
■1

146

Experimental Chemistry.

to expansion by the heat, hut soon contraction takes
place and the water rises in the jar. The white fumes
produced during the cornbustion of the phosphorus
are the same in composition as those formed in Ex-
periment 60, i.e. P2O5, and we already know that they
dissolve in water and form phosphoric acid ; thus the
oxygen of the confined mass of air is removed in the
form of solid oxide of phosphorus, and the latter is
washed away by the water \ the gas in the jar there-
fore contracts in volume. Now it is obvious that if air
consisted only of oxygen, and we used sufficient phos-
phorus in our experiment, all the gas would disappear
and water would completely fill the jar ; but, as a
matter of fact, the phosphorus soon ceases to burn,
and then, on allowing the jar to stand over water until
the white fumes disappear, we find that a consider-
able volume of colourless gas remains behind.

Now transfer this gas to smaller tubes in the
manner directed in Experiment 17, and make the
following,' observations : —

a, A tube full of gas when turned up is found to
be free from smell, if it has been washed ihoroughly
from all fumes.

b. A burning taper plunged into another tube full
of the gas is immediately extinguished.

c A little Mime-water' shaken into another jar
of gas is not rendered milky, unlike the result ob-
tained with the carbon dioxide gas formed in Ex-
periment 58.

Therefore air from which oxygen has been re-
moved is colourless and inodorous ; it is incom-
bustible, does not support the combustion of a taper,

Experiments with Nitrosen. 147

and does not render lime-water turbid. This gas

Nitrogen' — Svml>ol fi^ — t . , rr t ••
Molauiaru'ei<;/itz=2S.
Nitrogen does not support anima! life, and is
sometimes called azote » in con5Pn„„n tI •
^li<.l-.l« .„i, ki consequen ;. It is very

sligl.tly soluble m water ; i cc. of water dissolves
only 001478 cc. at 15° C. ais.olves

Free nitrogen is one of the most indifferent gases
<ve are acquainted with m its chemical relations !nd
hus contracts strongly with the energetic oxygc^ Pure

K^7 wT:'%'T '°"'"^ °^ t'-e.wo''dissi,u
gasts. We.next have to determine the proportions
m which these bodies are present in air. The r"u "h

result, for when we measure the maximum height to
which the w^ter rises in the jar after removaf of he
oxygen by phosphorus, we find that about o>Mof
Indf.orf '"'"P"^"^'^- A similar, but muchlwe

f^foCrw:;™' '''^'""'"" -^ '^ -"^^ - ^^

Experiment 82.-Fill the gra.'uated tube a, fig. ,3
wuh .00 CCS. of air, taking care that the vo nme s'
measured when the water stands at the same height

confin.? '".'r.'- ""*' P"^' ''•Sh up into, the

confined air a small stick of phosphorus at arhed to a
stout copper wire Secure the wire in its place ^d

' From ►iT(>w, nilie, and y,n«,, I generate.

J-

•fc.

f r

lj i

148

Experimental Chemistry,

leave t^e whole for twenty-four ^ ours. The phos-
phorus slowly combines with and removes the oxygen,
and leaves onlv nitrogea In order to measure the

Fig. 53.

PtG. 5«.

' \~<$

latter, withdraw the phosphorus, adjust the water,
level again, and read the graduation. If the temjjera-
ture and pressure are unchanged, the residual nitrrj^f^n

— ■ a- —

Anafysis of Air. ,_j„

th,,^d.ference. or oxygen absorbed, is, thcr.forl! nearly'
Or another, and very rapid, method of anilvsis hv

S.orpyro.UoU.sorJ::eCnrs:rS

IcJ^^fT""^ 83.-Take a cylindrical tube, , meter
tong and about i6 millimeters diameter nL j

h "corLdl,'"'''^'^ r '"^ '"•-• ^- -o e

drops to rail into the J^Z d7„ t 'I ai ra^r
a1> rau rj' a?;' ^^ T^c °T ^^ '""^ ■"-" ^'^

tX back .„°h ' '"•°" "^ "'^ ""''"■'^ Bring the

riXThumbCnT.lr'"';' 'I' ""'^™-'-
liquid rapidly runs rfr™;Th.TT"''*' "l^"-'" ^^ "'«
tion h-« fl-nn 1 . ^ '^""' "°«'- as absorp.

before Re" ^!T ^'''''" ^'°'^ ^ ""^ P^°<^eed is

-Uthi;.;^^e;;;;rh'lbr:brb.f'^b

— ^. «ii the bulb co«,ple,ely with waterrdos^^;

p ';
* ^

I., I

5#i

I '

1 50 Experimental Chemistry.

• with the thumb, and invert in a tall vessel of water
On opening 5 the heavier dark liquid flows out, and is
soon replaced by pure water. Adjust the liquid to
the same level within and without by depressing the
tube to the reciuisite extent The water should'then
stand above the second ring, or, on a graduated tube,
at 209 divisions out of too of air.

Experiment 84.--Fill the eudiometer used in
Experiment 23 with water in the large pneumatic
trough, and allow about one-third the water to be
displaced by air ; adjust the water to the same level
withm and without the tube, and note the volume.
Now pass in half the volumo of pure hydrogen gas,
level again, and read the total volume. The hydro-en
^n be easily obtained from the apparatus used'' in
Experiment 68 if dilute sulphuric acid be employed
m It and the wire w be connected with the zinc end
of the battery ; gas should not be collected in the
eudiometer until sufficient has been separated by
electrolysis to expel all traces of air from the apparatus.
1 he tube instead of passing into the bottle, as shown,
should, of course, dip under the surface of the
water m the pneumatic trough. Press the mouth of
the eudiometer on an india-rubber pad placed between
It and the bottom of the trough ; now grasp the
tube, hold It firmly against the pad, and pass a spark
between the internal wires. After explosion rela. the
pressure on the tube and allow water to enter ; adjust
levels again and read. One-third of the total contrac
Uon observed represents oxygen present in the air.
for we already know from Experiment 23 that two
volumes of hydrogen and one volume of oxygen unite

Analysis of Air.

'Sr

to form water, which latter condenses at ordinary tem-
perature.

If, in a particular experiment, loo parts of air are
mixed with 50 of pure hydrogen, and after explosion
the residual gas measures 87-3 parts, the pressure and
temperature being the same at the beginning and end
of the operation, we can calculate the composition of
air by volume thus :~The contraction after explosion
IS 150 - 87 '3 ^627 parts. Then «^ = 20-9 - the

Tie. 54.

proportion of oxygen gas in the original 100 parts >-
volume of pure air. The difference, or 100-20-9
— 79"i, IS the percentage of nitrogen gas.

Experiment 85.-FiIl the tube of hard glass, a,
fig. 54, with bright copper turnings, support it 'as
shown, and heat with a large gas or spirit flame •
connect the end by rnean^ of an india-rubber tube
with a glass delivery tube, /, which latter dip under
the water in the pneumatic trough. The flask/ s. yii^
onlv contain water efQUf^* ^'^ r>^..«.- ^u^ .^ j _/• ..

;«i

; 1

i <

' ^L^^

'Hi

i
i

t$2 Experimental Chemistry.

funnel tube. Now apply heat to the tube contalnine
the copper turninss and when a red heat is reached
pour water into the limnel tube of the flask ; air is
thus mnde to pass over the calcium chloride in </,
and then over the hot copper, which latter combines
with th.- oxygen and forms dark copper oxide, CuO
while nitrogen gas bubbles from the delivery tube'
through ; he water!- 1 trough, and should be col-

Scribed ' " ''^ *" "'^ ■""""" '''^'^^y

This experiment illustrates the principle of the
method adopted by Dumas and Boussingault in their
precise determination of th<- cc,iui>..,itiop of air by
weight. They caused pure dry air to pass over red-
hot coj.ptr contained in a glass tube, and thence into
an exi;.- psted glass globe ; each portion of the appa-
ratus w^^ accurately weighed before an ex|,eriment
itie Pbe and globe were separately weighed after an
exper,n,ent. The former gained in weiglit, owing to
the combination of the copper and oxygen, and the
gam of the globe was due to nitrogen ; the sum of
«iese quantities was the weight of air operated upon.
The mean of a number of Laborious experiments of
this kmd, m vhich every possible precaution against
error was adopted, gave the following results, which
for convenience, we compare with those of the volu-
metric analysis of air already de'^cribed ;—

Percenlage of By w. ,h. By volume

Nitrogen . . 76-995 . . \^.^
Oxygen. . , ,3.00. . , j^.^

If nitrogen and oxygen were of the same specifio

AiraMixtun. 153

gravity the percentage composition of air by weinht
and volume would be the same; but we have already

O- r /u"" '''^"' ''"■"'"y °^ N = i4 and of

, ^"7'^' '"="■= "S oxygen is, volume for

volmne, a lutle heavier than nitrogen, it follows

In" fi'J!!! ^fT^ °' *'''>*'^" """ «<='K'^ """•' than
one-fifth of the total weight of five volumes of air

although oxygen forms but one-fifth by volume of the
gas.

m ^^\ '^^n?^" ^'^'''^y ^^ P"*-^ ^^y ^'r is 1447
1447 cgrs.''^'"'"' ''"' ^'^ ^''- "' "•"'•> ^^^'Shs
Atmospheric air is ^..^r/^ constant in composition,
ihe results of numerous precise analyses of pure
air collected at various and widely-separated points
of the earth's surface, and at considerable heights
above sea-level during balloon and mountain ascents,
prove that the variations in the proportion of oxygen
are well wuhiu one-fifth per cent, by volume In
tropical countries, however, the oxygen has been ob-
served to drop suddenly as low as 20-3 per cent
owing to some hitherto undetermined cause.

^f//*^^ air were a definite chemical compound of
nitrogen and oxygen it shuuld be absolutelv constant
in omposition, and we know that it is not quite on-

8U ^>^^^^^ox^ it is not a definite chemical cow tound.
Again, oxygen and nitrogen are not present in sim-
pie atomic proportions in pure air, the ratio b. mg ro
atoms of nitiogen to i of oxygen. If the inclusion
just stated be true, a mere mixture of the v..o gases
in the proportions indicated' by analysis ought to
fwsic^ -Oi the propertit ii of air. To test this, make—

if i

'S4 Experimental Chemistry.

>n ert ,t ,„ ,he pncu.na„o .rouf,h : introducr as nn.ch
n.trogon gas (prepared as in Kxperimcnt 8,)\r will
d>sph,re four-nrths of „,e „,ter, and a, m„c ^ vgl

fill llie jar. I his .» an evi.lfnt mixture of the two
gases, and no heat i. develo,,ed, nor .:an «c find . nt

ease, M„„ ''''■"'-' l>^«>»«-'en the two

Tand ,f '^™°''-' "" ■"•" '" ""^ "'"='' «-.-.v, invert

t TnotT? "..T" "•'"' '"°*'"e .ip into the j.ar1
■t .8 not rekindled as it would be in pure ox>4a

to bTn^ "r?/"'"' '"'° '"^ «^^- ^"'' " -«^"-

lo Durn a.^ it did in air In fart .« «n

.his mixture or the two galL at lljXo!

t o,e of"o "' •■"' ".^ '^•'"•■'^'=" '^f "^« '=•«--«

ndfferent h'T" '""'=' ,''"""•■'' *'"' J"« ^"^h an
ndiflerent body as we know nitrogen to be We

.M,^ have ,,.«M./,. evidence in favour of the mix.i:

rath!''^'*^T *''-T'"<e » "■'''k capable of holding
rather more than one liter, fit u with an india-rubbl?

S 71X: "'"' '"^^ "' ««• 55. but the short
tube of the latter must not pass quite through the
cork. CompUMy fill the flask with clean and fresh
ram water, and the bulb tube also ; insert thecok
carryng the latter in the ne, k of the flask in such a
«ay as to have the flask and tube quite full of wat r!
Let the delivery tube, d, dip under some of the same

rturmf d '" .r"'^" '™"^''- """ -vert-"™

a test-tube filled with water. Apply heat to the flask

Air dissolved by Water. ij.

and gradually raise the water to the boilinR point •
bubbles of gas «i|l |,e evolved all the time and col-
cct in the bulb b ; this is air previously dissolved l.y
^nM ' T. '^l """"^P''^''- When the boiling
^11 r f """ '"=•'"" '''^"'^"'^•^ P"*hes the air

recuve it If the boilmg be continued for some time,
expelled and collected with little loss in the test-tube.

Flo. 55.

should afford ,7-95 c.cs., but this volume is rarely
obtamed.' If the test-tube be removed from he
<^ater, then inverted, and a burning match be now
plunged mto the air extracted from the water thi
comU,st,on of the wood will be n.uch more a^t ve
for a feAv seconds than in air We are thus led to

oXn' thf ^':,.^'"^^'"^'' fr-" -a'er contains more
oxygen than ordmary air, .nd when analysed by any

' The residiial water is quite flat aixl insipid.

. !|

'56 Ex/icrimental Chemistry,

of the methods aheady given, it is found to
in loo volumes:—

contain

Nitrogen
Oxygen

65-

TOO*

more sohiF.)^ tk- '^ ' utcause the forn^er s
for .f U was a chemical compound the t ^^u^^lk

Sniall though the proportion of air dissolved in
wa^er ., u makes all the di/Tercnc. betwS 1 e Ind
death to fish, as the oxygen they can withdraw from

water by their respiratory organs-
the gills-is essential to their ex-
istence. Hence it is necessary to
secure the due aeration of water
m a^juana, either by frequently
changing or by making a number
of fme streams of air-bubbles pass
through the licjiiid.

Experiment 88.~-Arrange a
bottle as shown in fig. 56. Put

.he cork carrying Z^l^:::::: ^^ ^^ ^^^
'hrou« Ihe ime :.rru.' i.™';"' ' """ ''"''"«''

H.uia..^ijj-;rLX;"r,?;.;^-

^ 'iL

Ana/jysis of Hxptnd Air, ix^y

mdexhaie air from the lungs through the tube- ih.

a.r from the lungs bubbles through the lil'^^^

and the latter soon becomes turbid '""^-"^^^'•'

We have already learned from Fx '*'*'• ^^•

penment 58 Uiat the lime-water acts

•as a detector' of carbon dioxide or

carbonic acid in a gas ; therefore the

expired air differs from that inspired

by containing much carbonic acid

gas.

Experiment 89.-^Expired air is
analysed by collecting it in a gra-
duated tube • over mercury. A few
drops of strong solution of caustic
potash are then passed up through
the mercury into the confined gas
from a curved pipette, as shown in
H' 57. Thecarl>on dioxide is (piickly
absorbed by the alkali in the pro-
duction 01 potassium carbonate, thus :—
£0a + 2KOH = K.COa

Carbon

diuxide.

Caustic
I^tash.

Potassium
carbonate.

mg for ievcJ, gives tlie proportion of carbon dioxida

Inve'r.Il'in'^h'"'""'"','"'". ''"''' """' "'"' "•""^'''X ""d then
rr he „'LT'« ''""*■ .'^ '"'" "f 8la»». curve,] a, one end

nnJintoTTK « '-'• "•""'^ '" """'r ">« «ir from >h.
hinp. mo / I he hm ,k„.,o„s of air expelled from the mouth

forcing it tlirouah the ae"".". L-u- . " """"™' '•J'

' 58 Experimental Cfiemistiy.

If a small quantity of strong solution of pyrowllic
pi^,:"" '"f-t"^--d, a further conirJZ S

™ thi"' '" ^''''«""'<="' «3, to absorption of
ox)gtn , th.s ,s measured, and the residual .as is
nurosen, whose volume is then deter.nined In h ,
way the com,K>sition of a sample of air exuirel h! ,
man was foun-i to be. in too volumes- ' '

Nitrogen
Oxygen .
Carbon dioxide

79-58
16-04

^4-38

lOO'OO

evwinlv in i T" •' '°"'""'"^'* '" 'he proces^
evidently m the combustion of tarbomsed n ateriaL

evolved. An adult man thus expires about 450 liters
of COj in twenty-four hours.

Experiment 90. -Pour 30 or 40 cc^ of lime-water
>nto a w.de-mouthed bottle ; now plunce a burinl

burn for a short tm,e ; then remove the tauer do,!
the mouth with the hand, and shake. The lime-w tl
becomes very turbid, therefore carbon diSe w^l
produred durmg the combustion of the taper

A snfljlar experiu,ent may be m.ide with the flame
of a small i^etroleum lan.p or of roal-c^s o w , h
Pjece of red-hot coal. In' all these ,^es carl o„
dmuie .s a product "f the combustion, and the r
tec on of tins particular nro.luc, proves he pescnce
of the element carbpn in ne br^y burned. '

We have thus detected several sources 0/ con-

Fig. 58.

^cf^on 0/ Plants on Carbon Dio:ade. ,59

We knoi that y^'r . i!r f""""^ '° '"-•
process of purification mth^ "' *'''"' "'""'"'

■i-|.e next e!y.ri„,enrwm Lp '"0'""'^ •'' "■°^''-
nature of this process. ^ understand the

Experiment 91._vVe tair» t^.
other of the following JZV- °" ^"''^^^ °"= °'
the common .4««./}<,„i, /j,,^;,^.

5f ; ""'''""• to te found in our
ditches and rivers, Ehdea cana-
1'nus, OratophyUum, if.uoma,
Sp,rogyra, or any whose leaves
have large stomata

% 5«) with water saturated
wKh carbon dioxide by the
method described later' oa
Attach a ,^„,on of the p,ant,
*'th as many fresh leaves as
Pos'-ble. ,0 a piece of ^Z f„

order .0 sink it in the water ,n " -

and secure Tin d^1o„ h ' '" "^^'"^"^ ^^^^<
Fill a test-tube wi,r«a° ^ '"'""■"' °^ *"^ ^'^J'*
over the tube ofX ^n '..rir 'S '""^ '"-"^
'hat no change takes pla;e in 7^1, r'? T
c^'I'ose the whole arranceml. . ./ ^^ '*'"• ''"«
»ome houi. =^-. ..,;!''''""*"* •" ''"Kht sunshine Mr
""•' """"'«* "f Ijas will J,e evolved, and

i6o

Experimental Chemistry.

will rise through the funnel and collect in the test
tube. When a sufficient quantity has been collected,
remove the tube in the usual way, invert it, and
plunge into the gas a match with a glowing tip ; note
that it is rekindled. The gas can be easily identified
as pure oxygen thus evolved from the plant. A care-
ful examination of this process of separation of oxygen
has shown that the latter is a product of the decom-
position of CO, in the green or chlorophyll cells of
the leaves ; in these cells the carbon is fixed and em-
ployed in the production of various carbonised bodies,
starch, woody fibre, &c, while any oxygen not re-
quired for similar purposes in the plant -organism is
returned to the atmosphere in the gaseous form,
as we have seen.' We learn, thus, that the carbon
dioxide which issues from the lungs of a man or other
animal, from the burning candle, the factory fire, and
many other sources, and that would, if allowed to
accumulate, soon render the atmosphere deadly to the
higher animals, is rapidly decomposed by vegetation
under the influence of the solar rays. Thus man is
saved from slow poisoning by the depurating action of
vegetation on impure air, and this action is, moreover,
the chief cause of the nearly constant composition of

' In additifjn to this decomposition of cariion dioxide, which
hi only eflfecttd in the chlorophyll cells under the influence of
light and chiefly of the yellow rays a process of nsptration
analogo' ."^ to that of animals takes place in all parrs of the
pian», and is not dependent on the action of light ; but this ah-
«<».ption of oxygen and evolution of carbon dioxide is so very
/eeble that the loss of carlxjn involved is insignificant when
ciimpofeil with the enormous gain of carlx»ii l»ydecuuipoiU»ono/
its dioxide in the chlorophyll cells.

the test
)llected,
it, and
p ; note
lentified
A care-
oxygen
decom-
cells cf
nd em-
bodies,
not r«-
nism is
» form,
carbon
»r other
re, and
wed to
f to the
;etation
man is
:tion of
•reover,
ition of

B, which
lence t)f
pimiion
i of the
this ah-
«o very
It when
mXMM of

Fk;. 5^

Diffusion of Gases. i6i

the air, aided as it is by the action of atmospheric
currents arismg from alterations of temperature, and
the operation of a curious physical law in virtue of
which the constituents of a gaseous mixture tend to
diffuse or distribute themselves eciually throughout
the mass. This principle can be easily illustrated by
the following experiment.

Experiment 92.-Fit the doublc-riecked bottle h
as shown in fig. 59. The tube / passes through the
cork nearly to the bottom of the bottle,
where it dips just under the surface of
some water coloured with litmus or co-
chineal ; this tube is drawn out to a rather
fine jet at the end c Both corks are best
of india-rubber ; through the second passes
the long tube m ; this, hke /, should just
dip under the surface of the water in h.
The end outside the bottle passes airtight
through the cork c, which closes the porous
earthenware cell s. The latter is one of
the small porous cells used for galvanic
batteries, and should be new md clean.
AH the corks, if not of rubber and very
tight, must be coated with paraffin. Having
prei)ared the api^aratus, fill a rather large
jar with hydrogen, and bring it mouth
downwards over s. Almost immediately gas bubbles
from m through the liquid in the bottle, and as it has
no exit It w confined in h and exerts considerable
pressure upon the surface of the coloured water,
whu b latter is, in consecpience, driven up through /
?.nd ia^ucs from <, iarawng a temporary fountain. On

3^ I

'^,

162 Experimental Chemistry,

withdrawing the jar the reverse action takes place—air
enters through /, and the liquid rises in ;//.

The reason for the accumulation of gas within the
apparatus at first, and consequent increase of pressure
IS that the hydrogen rapidly diffuses itself through the
air m the cell and vice versd, while the porous cell
walls do not oi)pcise material obstacles to mis process
of diffusion, though sufficient to intercept mere currents.
But hydrogen gas, Jx^ing so much lighter than air (in
the ratio of i to 14-47), rushes through the pores at a
higher rate than the heavier air can pass in the oppo-
site direction-corisequently gas accumulates in the
cell and the evidence of this is the increased pressure
withm the apparatus, which suffices to raise a column
of liquid to a considerable height. If oxv^rcn wer^
present at first in the cell, the pressure would he still
higher, owm^j to the greater specific gravity ot that
gas^ The law regulating this diffusion of gases is
allied 'Graham's law,' as it was di3covered by the late
Professor Graham, the last scientific Master of the
British Mint, and its statement is that Mv diffmion
rates of two misses of gas in contact are inversely pro^
pomonal to the spmre roots of their spmfic gravities,
1 hus, comparing hydkogen and oxygen, the specific
gravity of the latter is 16, and the square root of 16 is
4-therefore, according to the faw, four times as much
hydrogen as oxygen will pass through i\xt cell wall in
a given time.

In the case of air the two constituents do not diffuse
out into the external hydrogen at the same rate the
heavier oxygen passing out in the above proportiorL
una the somewhat lighter nitrogen nt « hii/iu-- ^-^-^

■Q-.NM. ««*tp4M

Carbon Dioxide in Air.
iMruRiTiEs IN Air.

"5.^

The impurifics commonly met with in air are
the noatmg solid parti,:lcs~the 'motes in the sun-
beam beautifully seen when a beam of sunlieht
passe, through the air-and the gaseous or vaporous
bodies we should expect to find, viz., ,arlm.. dioxide
water, ammonia, and ozone; while we , «:casionallv
meet with carbon monoxide, marsh gas. and other
hydrocarbides, sulphur dioxide, sulphuretted hydrogen

t^T.^ t-'™^'"; ,''"°"""' ""'^ "^^""''^ emanations
fron the skms and lungs of men and other animals.

Experiment 93.-Exposc in a dish a quantity of lime

water to the air of some open space for a few hours •

the water will soon be covered with a white pellicle'

owing to the formation of chalk arising from the

action of the carbon dioxide, always present in ordi-

nary a,r, upon the hme in the water (see Experiment

50;.

The usual proportion of CO, in good fresli air is
from C-033 to 004 percent, i.e. 3t0 4partsm ,0,000,
bm tJie a.r of confined and ill-ventilated sp.tces ,s
often much less pure, as it is rapidly alie.red by animaj
respiration and burning illuminating material

An adult man exjnres about sixteen cubic feet
of a|r per hour and about ,«,th of this 1. carbon
dioxide. A single gas-jet which consumes three cubic
feet of coa gas per hour (equal to about ,50 grams
of oil or mt) uses up more air th^m two men.

When the proportion of carbon dioxide reaches
0-C9 to 01 per cent, the air is clogft and * fu=tv ' £0 — -
senses, and is unwholesome. The late Dr! VmhL

I *?

1 1

164 Experimental Chemistry.

held, and we think rightly, that air should be con-
sidered unwholesome for" human beings when the
carbon dioxide present exceeds 006 |)er rent., or 6
volumes in iq,ooo, the carbon dioxide being in this
case taken as a measure of the general purity of the
atmosphere. • Good ventilation aims at keeping the
atmosphere of a room well under this standard, and
for this purpose 3,000 cubic feet of fresh air must be
introduced per head every hour, and about twice
this volume of fresh air per hour for each gas-burner
that hourly consumctJ three cubic feet of coal gas, un-
less the products of combustion arc removed by
special means.*

Experiment 94. —Take two plates ; expose to the
air on one some lumps of calcium chloride, and on
the other some common pearlash— impure potassium
carbonate. After a time both substances will [)e found
in a moist condition, having absorbed aqueous vapour
from the atmosphere and dissolved in it, or deli-
quesced ; if exposed long enough each will become
completely liquid, and a strong solution of calcium
chlorfde be formed in one case and of potassium car-
bonate in the other. Both substances are spoken of
as hy^roscopii\ or moisture-imbibing bodies, and thus
serve to prove the presence of water in the air.

' Two methods will t)e found in Chapter XX. for the esti-
mation of CO., in air.

» The amount of air-space required for healthy adults in a
foom is at least 300 cubic feet per head \ hut it is well to aim at
a hijiher proportion. A room la feet long, lo feet wide, and
10 feet high contains, when free from furniture and inhabitants,
I.aoo cubic feet of air, and mil therefore accommodate four
Sviiithy udutis if uu^ajuaic veniiiaiion be provided.

Moisture and Ammonia in Air. 1 65

Experiment 95._Piace a few pieces of .ce in a
N-.st..ube ; the sides of ,l,e lat.cr are soon cookd
down nearly ,0 the .em,,era.ure of m.hing ice. and m
tun ,hcy cool the a,r immediately m contact wnh the
exte nor of .l,e tube : moisture is then seen to be de
posited on the glass, because a,r nearly saturated
wuh aqueous ■ .our at a comparatively h,..h tem
perature deposits much of its water when cooled neaHy
th. !, \'^'r« P"'"'- " '° ''ny temperature k-low

would suffi ■ """""" °^ ^■"'""' """•'•"y P^'"^"'

salumtion point is passed, the excess semrates in
he form of dew, cloud, or rain. Therefo e. by the
atracuon of deliquescent bod.es and by the method
of coohng, we learn that ordinary air contain,
aqueous vapour , the amount of this is. however
extremely variable. "uwcver,

of h^owr"^'"* °''-: ''"' " '^^8^ S'-^^' beaker capable
of holding two or three liters with fresh and clean
am w^ter ; add to the water about ,0 c.cs. TnI^Z
/«/ solution,' and let the mixture stand after mixinr
Few samples of rain water fail ,0 show a pale yel ot
colour when treated with the test, which lit, r is hi

moisitirp in nJr « .u '-naptir A\. for estimation of

1 Ti t»'^"«'»i iiufyect of liyi^rometry.

io<,i„i'"sr,i;r;z. °' "" "'"""" " ""^^-^ ""'"

' *>0 delicate Is this tt^t fW •'♦ »':" J-Js • __

I part of .mrnonia 1„ io.ooo:couorwa.e;r"" "' '"""""' "*

166

Exfierimem, Chemistry.

Jht animoma (NH,) in air rarely exceeds one

^^en c tnH A T ^- ■"'""' "f ''""• ''"'°""'» '° be-
tween 5 and 6 lbs. per acre annu illy, and from this

source vegetation on uncultivated soils derives some
Of the nitrogen necessary for healthy dew! mment.
though ao the elaborate experiments of Mess,.. Lawej
and Gilbert at Rothamstead have shown, the agrirul-
tural importance of this aerial ammonia has probably
been exaggerated. ""luiy

VVe have already (Experiment 69) learned how to
test for ozone in air, and the characters of the other
accidental constituents of the atmosphere already
enumerated will best be dealt with under the severi
compounds. >- waj

Exftrimtt

CHAPTER xrv.

«XPEH,ME.T. W,T„ COMPO^NOS OP K.TROCEN.

f IS. io.

nitrogen, potassium, and oxvirpn in n,<.

indicated by the iorrc^Z^Zl' '''°''°«'°"'

NtTRic Ac.n= HNO,.-J/,w^^ „^,i^,= 6,
_ Experiment 97.— Plar^ in , ...i...i-._. .
% 60. about 30 gran, of nitr^ and ;:;;'';" e7hwit;'

W' •

k-»1t*'j

MICROCOPY RESOLUTION TEST CHART

(ANSI and ISO TEST CHART No. 2)

1.0

I.I

1.25

15.0 ""

■■1 yy 3 A

■■ 1 4.0

•A u

■iUU

11111=
|2.2

2.0
1.8

1.4

1.6

^ /APPLIED \^J\A\3E Inc

S^. 1 653 East Main Street

r.,S Rochester. New York 14609 USA

SS: (716) 482 -0300 -Phone

SaS (716) 288 - 5989 - Fax

1 68

Experitnental Chemistry.

\ ' ■

strong sulphuric acid; connect the retort directly with
the receiver /, which latter is supported by the dish
d containing cold water ; gently heat the retort and
raise to the boiling point; a heavy fuming liquid of
a yellow colour distils over and collects in the receiver,
which latter should be occasionally cooled by pouring
water over it. When the distillation is at an end
allow the apparatus to cool, when the residue in the
retort will solidify to a crystaUine mass easily dissolved
out by water, and consisting of acid potassium sul-
phate, KHSO4. The contents of the receiver are
now to be examintJd.

a. Allow a drop of the liquid to fall on a piece of
blue litmus paper ; the latter is instantly coloured
red and then bleached, while the paper is soon de-
stroyed—therefore the liquid is a strong and corro-
sive add.

b. If a piece of white silk, some wool, or coVk be
immersed in the acid it is quickly coloured yellow,
and, in the case of the cork, soon destroyed. The
skin is likewise corroded and stained yellow by the
acid.

c. Add a few drops to a solution of indigo ; the
blue colour of the latter is instantly changed to a
dirty brown.

d. Place a few fragments of copper in a test-tube
and pour over the metal a small quantity of the acid.
Deep ruddy fumes are rapidly evolved, and a blue
liquid remains in the tube.

The acid possessing these characters is nitric acid,
or aquafortis, whose formula when pure is HNO.3.
A he foiiowmg equatioii represents the change liia-t

Experiments iviik Nitric Acid. i6g

takes place when nitre and sulphuric acid are heated
together —

J^NOa^ + £^J^ = ^NOa + KHSO4

Potassium Sulphuric Nitric Potassium and

nitrate. acid. acid. * hydrogen sulphate.

On the large scale the cheaper sodium nitrate
(NaNOg) or * Chill nitre' is used instead of the potas-
sium compound ; moreover, in order to avoid wa{;ve
of sulphuric acid, two molecules of the nitre for one
of acid are used, but the heat required to complete
the operation is much higher than that employed in
the Experiment 97, and the residue in the large
retorts used is neutral sodium sulphate, Na2S04—

2(NaN03) ^ H2SO4 = 2(HN03) + Na2S04.

Pure nitric acid has a specific gravity of 1-510
(water = i -ooo), ^

The best commercial acid is a colourless liquid of
specific gravity 1-420, and contains about 30 per cent
of water. When exposed to the air it emits an acrid
corrosive vapour, and begins to boil when heated to
121° C.

The acid is distinguished by the characters and
tests already observed, and we have in the copper
test (d) an experiment illustrating the fact that nitric
acid is a powerful oxidising agent, since it easily
suffers deoxidation to a low oxide of nitrogen, to-

• The colour of the ordinary acid is due to the presence in
solution of oxides of nitrogen ; these can "be removed by making
a stream of air bubble through the acid. Other impurities
OiiSn lOUHvi jn t«v eoinmercial acid arc sulphuric aod hydiO-
chloric acids ; for their tests see the respective acids.

ill;
Jill

170

Experimental Chei,nistry.

gether with loss of hydrogen. In the case of copper
the reaction in the strong acid may be thus written—

f.^ + ^J^3 = N2O3 + 2(Cu(NO,)2) + 3H2O.
Copper. Nitric 'Nitrogen Copper Water'

Nitric
acid.

'Nitrogen
sesquioxide.

Copper
nitrate.

The ruddy fumes observed in the experiments con-'
sist in part of the sesquioxide of nitrogen, and the blue
liquid formed contains in solution the blue-coloured
copper nitrate,* which latter can be separated by
evaporation and crystallisation.

Experiment 98.— Put a lump of red-hot charcoal
on any suitable support under a flue. Take up a few
drops of strong nitric acid in a long glass tube and
allow the acid to fall on the charcoal. Note that
violent action at once takes place, the charcoal burn-
ing rapidly in the oxygen of the acid.

Experiment 99.— Add some of the acid to a solu
tion of ferrous sulphate or 'green vitriol;' it at once
communicates a black colour, which is changed to
brown on boiling. 2 This is the iron test for nitric
acid.

Experiment 100.— Place a crystal of the alkaloid
Brucia on a white plate and let fall a drop of the
strong acid upon it Note that a fine orange redzoXom
is developed.

Experiment 101.— Place a few cubic centimeters
of nitric acid in a capsule, and add caustic potash
solution until the acid is neutralised ; then evaporate

^ For the action of tbe weaker acid on copper, see page 179.
* Foif the explanation of this, see page 180.

Experiments on the Basicity of Nitric Acid. i;i

until a peilicle forms and allow to stand On cooling
crystals oi nitre separate—

HNO3 + KOH = KNO3 + H^O.

The analyses of nitric acid and of nitre lead to
the formulae just given as the simplest expressions for
their composition ; but the discussion of the analytical
data cannot tell us whether nitric acid may not be
represented by the symbols ^ H^N^Oe, and nitre by
K2N2O6, or some multiples of these values. Moreover
the vapour of nitric acid is so easily decomposed by
a high temperature that Avogadro's law cannot help
us to decide between the above formulae. How then
are we to pro.-eed in order to determine which of the
formulae, HNO3 or H^N^Og, for example, is correct-
m other words, whether nitric acid is mono- ordt-basic}
(See Part I. page 84.) A little consideration will satisfy
us that if the acid be di-basic and its formula H,N,0, ,
It ought to be possible to form a second potassium
salt-one containing KHN^O^. We must, therefore,
make an expeiiment calculated to deiermine this
point.

Experiment 102.-Take two porcelain capsules
perfectly clean and dry, and place one on each pan of
the balance and counterpoise exactly; then mark one
capsule A and the other B, so as to know which pan it
belongs to. Remove the capsules and place In each
10 CCS. of the same strong solution of causti6 potash
coloured blue by the same quantity of solution of
litmus. Now neutralise the potash in A by nitric acid
added gradually, without loss, from any convenient
measanng vessel Note the quantity required for this

i-h

^72 Experimental Chemistry.

purpose. Next add to the caustic potash in B double
the quanuty of the nitric acd required to just neutra-
lise the first. Place the two capsules dose togetiier
on a small tray of sheet iron, the bottom of which is
covered w,th a layer of sand, and heat this 'sand bath'
ZZT\^ V ^"f """'P'"' "'^'"^ underneath, so as

l^Vh . K r """^ '" ^""""^ '^•'"'^"''^ »'°»''y evaporate
without boilmg or spirting. When the solutions have

been concentrated to the some extent small crystals
separa'^ ' "o difference is observed in the appearance
of these or m their apparent amount, but during
evaporation acid fumes are freely evolved froin

left ?r T \ ^'""' '^^'■' """• ^ dry mass is
left m each capsule and acid vapours are no longer
given off; then when cold, replace the capsules t
Aei respective balance-pans. If the operations have
been carefully conducted the capsules should still
counterpoise, proving that the same weight of matter
was produced in each case ; and when each residue
.s carefully examined it is found to possess all the

detected there by a great gain in weight and by
differences m the characters of the safts obtained
m the two capsules. No new salt is separated, but
merely a mixture of nitre and excess of nitric acid is
obtained, and the latter being volatile is dr ven off
during evaporation. Therefore nitric acid is a monr!
basic acid, and its formula must be written HNO,
?'.-.p,nment I03.-Introduce into a test-tube some

solve the latter, and heat No fumes will h^ <.v.i„„^

B double
t neutra-
together
which is
id bath'
\ so as
^^aporate
•ns have
crystals
earance
during
i from
mass is
» longer
ules in
IS have
Id still
matter
residue
all the
rm the
Band
nd by
•tained
:d, but
acid is
en off
mono-

tsome
o dis-
Dlved.

Gunpowder, its Composition, 1/3

Cool the liquid and add a cubic centimeter or so of
oil of vitriol ; violent action soon begins and ruddy
fumes are freely evolved, just as in Expernnent 97, d.
In this case the metallic nitrate is inactive ; but on
addition of the powerful sulphuric acid the salt is
decomposed as in Experiment 97, and the nitric acid
thus set free at once produces its characteristic effects.
For a similar reason a metallic nitrate reacts, as in
Experiments 99 and 100, only after the addition of^
sulphuric acid ; hence this addition cannot be neglected
in testing a salt of nitric acid.

Experiment 104.— Mix a very small quantity of
nitre with about one-third of its weight of powdered
charcoal in a small porcelain crucible, and apply heat
Violent action almost amounting to explosion takes
place ; the mxture is said to * deflagrate '—the carbon
or charcoal burning in the available oxygen of the
nitre. All nitrates » cause this deflagration. When
sulphur as well as charcoal is mixed with nitre, gun-
powder is produced The proportions of the ingre-
dients differ somewhat, according to the purpose for
which the powder is to be employed, but the per-
centage composition of good rifle powder is—

Nitre ..... 75
Sulphur . . . .10
Charcoal . , , .15

Such a powder when fired affords about 280
times its volume of gas, corrected to o" C. and 760
m.m. ; and this gas is found to be a somewhat
variable mixture of nitrogen, carbon dioxide, and

' For the characicrsi of particular nitrates, see Part 111,

m. :'

174 Experimental Chemistry.

carbon monoxide gases, with much smaller pro-
portions of other gaseous bodies. A solid residue
rich m potassmm sulphide, results from the decom'
position, and this, when blown out into the air from
the muzzle of a gun, quickly burns and forms potas-
smm sulphate, of which the white smoke chiefly

consists. v-'iiciiy

By the aotion of phosphoric anhydride on strong
nitnc acid colourless crystals can be obtained con
tammg N,0, This is nitrogen pentoxide, or nitric

SS'th^s-'^" '''''' '° -^- " «--

NsO, +*H20 = 2HN03.
The same anhydride is produced when dry chlo-'
rme gas is conducted over dry silver nitrate: silver
chloride and oxygen are likewise obtained-

2AgN03 + 2CI = 2 AgCH- N2O5 + O.
Poisonous action -Strong nitric acid is a powerful
corrosive, colouring the skin or mucous membrane
yellow, and destroying the tissues. When swallowed
It acts as a strong irritant poison and produces violent
vomiting, great pain, loss of voice, difficulty of breath,
ing, and ultimate death. When much diluted with
water the acid can be safely taken in small quanri ty
^«A^<,*..-Calcmed magnesia or dilute solution of
borax, followed by oily or mucilaginous- drinks.

Nitrogen PERoxiDE=NO,orN,0,.J/^/;K,«^/,/=46.

I^perLment lC5.-Take a tube of hard glass

closed at one end ip, fig. 6.). Having introduced

Experimefits with Nitrogen Peroxide. 175

about 10 grams of dry and powdered lead nitrate into
a, bend the tube in the form shown ; then apply heat
to the salt ; presently deep orange fumes are given
off, and these pass down the tube b\ if che bend r be
immersed in ^ freezing mixture of ice and salt, or a
mixture of hydrochloric acid and sodi'iru sulphate,

Fig 61.

the fumes condense and form drops of a blue liquid,
which solidifies to a white crystalline mass if cooled
to - 10° C. This body is an oxide of nitrogen whose
formula in the state of gas is NOg,* though often
written N2O4 for reasons that will be stated when con-
sidering another oxide of 'nitrogen.

• When electric sparks are passed for some time through dry

air, a mixture of oxides of nitrr»oron jc fx—v-r^,! . i. . ., .

body occurs.

176

Experimental Chemistry

prcsIL'r"'"""" ^' '''' '^^^ "'^-'^ - thus re.
?b;W03), = .NO, + PbO + o

Lead nitrate.

Nitrogen
peroxide.

Lead
oxid£.

Oxygen.

• oxid?' '''^'" ^'^ ^-^ "^'^'^^ "^^h the nitrogen per-

.> KnKM ' 'u^ ^""^ '''"^' ^'^'^ the delivery tube make
t bubble through .// ./ ,//././. Note that much of
the ruddy fumes dissolve in the acid th.T
escaping. ^^^^' the oxygen

Of n^^ietlTl'"^"'^ ^^^'^^ '° '- -'>-^"-
^NO, + H,0 = HNO3 + HNO,

Nitric
acid.

Nitrous
acid.

N,TK0GE._S.SQ„,0X^, OR N.TROUS AnhvorzoB

Nmous Acm=HNO, J/./,^/,,, ^.^^/^^^
blue hqu.d, or when passed into ice-cold waTekfbiue

ft*

thus re-

'e make
nuch of
oxygen

^assium

ed.

:e-cold

tained.

lixture

oxides

)US

3RIDE

vo of
^6i ;
ne of
rown
brda
blue

Experiments with Nitrous Add. ij^

solution is obtained. The formula of the body is N.O
The reaction ,^hich affords u .s thus expressed^: "

AS2O3 4- 2H.,0

^ -f- 2(H3AsO,)

Arsenic
acid.

2HNO3 +

Nitrogen
sesiiuioxicle.

The arsenic acid remains in the tube. We have'alre.rfv

anMride, ,i.e N^O,. and^SI dSrbut te"

events o?r:r '^''^ "'-^ -•-'' ^'^^^^^

N30a + H,0 = 2HNO,

Nil
acid.

rous

rt will be remembered that this is one of the two
aads^a^ady known to result from the action o/no:

b. Add a few drops of the solution of nitrous acid

° pot'i'umT' '^ ' ""'^ ^""'^^'^ """^ »n
whh wh chT P'™^"«'''"^'^' ^ body rich in oxygen
v.ith which ,t easily parts, and then loses its fine pu^l"

tc. ^ In the above case, nitrous contains less nwl' .L?^f J°

' 78 Experimental Chemistry.

HNO, + O = HNO,

mikfnU correTpondrJ:"''' ""^ Pe"nan,a„ate. by
^ '-urresponding experiment.

or Joo ci' of^wat"'' °' "" ""^""' "^'^ '° "°
i„jj "'"^'^ containing a little Doh«,„m

IJiuuucea Jt the so ution be vrrv Hi'ii,*^
'iodidrof s'ta'ch . 'fn th"'" ^^'^-g'y ^o'o-ed

hydrate. oxide

Nmic Ox,BK=NO or N,0. Mol. ..^,,=3, ,,,,.
Expenment 107.-Take the bottle, fig. 6.. used

water ihe ,.e,„ „„, beir^dt .'::;::" "''-*" '- -»

le nitrous

disinc: or
in dilute
nate, by

to 200
otassium
v^ colour
ite, or a
e to 'the
I of the
oloured
acts as

Nitric
oxide.

n atom

f nitro-

nitrous

in the

' or 60.
, used

5n, and
means,
in well

Experiments with Nitric Oxide. ,;g

'" tJie preparation ot hydroecn oas nn^ • . j
some copper turnings or v.refmo^r.. "•'"''"'*
with some warm water and in 1-t 'l "'"'' \ "'«••"
the thistle funnel. NoV ?i" 1 ^^°l^ ™^^>'"«
a liU>e strong nitn^Idr ct ^ a^'"''^' '"'-
commences and „n,<:h gas is evolved ?hl r '''°"

are allowed to escine m,l .^ ' '^'''■■" P"""'"^

usual i„ the ars As' 2 , ^'' " "'"" ^""""-•'ias
jars. As the evolutiot, of gas slackens, a

Fig. 6a.

little more acid will make it brisk arrafn Ti. • .
gas should be allowed to ^fJZ ^ i ^^ ^^'' ""^

short time in order Zf h T ""''' '^' ''''''' ^^^ ^
generally a^X ma^SSth^ ""^^^ '''''
leave the gas colourless. ^ ' '" '^' ^^^^^ ^"^

follcSli^JLnilii^r^^^ P^°^"-^ - the

g reaction with the somewhat if//u/e^ acid—

SCu'' + 8HNO3 == ^Cu'YNO ^ ^ ^Tr^

-» • IV

oxide.

:' S:

i8o

Experimental Chemistry.

iln

Fig 63

a. Remove a jar full of the colourless gas, covered
with itf glass plate as usual. Withdraw the plate and
note that brownish fumes are instantly produced when
the gas meets the air. This is the most characteristic
property of the gas, as it rapidly passes into one or
other of the higher oxides of nitrogen— N.Og or NO —
on meeting with a sufficient proportion oV>.. oxygen
This property is of the utmost importance in the
manufacture of ojI of vitriol.

A Place a piece of phosphorus in the spoon,
lig. 63, and touch it with a warm wire ; while it is
just kindling or burning feebly, plunge it
into a^jar of nitric oxide— the flame is almost
or quite extinguished. Now withdraw and
again kindle, but let the phosphorus burn
briskly, then plunge into another jar of the
gasj vivid combustion now takes place.
In the first case, the temperature was not
sufficiently raised to decompose the gas
and render its oxygen available; in the
second this decomposition occurred, phos-
phoric anhydride was produced, and free

sTnZrVt ^r ^'^ -^Pe^n^^ents may be made with
sulphur and wood.

c. Make a strong solution of ferrous sulphate
(green vitriol) m water and pour the solution into a
jar of the gas, close the mouth quickly with a glass
plate or the hand, and shake. Note that absorption
occurs, as the plate or hand is drawn tightly up to the
mouth of the jar, and the contents of the latter
become dark-coloured. Therefore the gas is easily
soluble in solution of ferrous sulnh.-.fp .j,„„„i, , /

Fig. 64.

Experiments -mtk Nitric Oxide. igj

of pure water dissolve only ? c r. nf ,1

definite comtwunrl i- f„ j • '''^ S^^' A

niula is no' FeSO ^ If'Th !," f ''"'°" ^^ose for-

the nitnc ox de ifdriven off' ''"''' ^' "'""^'^

brownish solution le Th f '' ""'^ " ^°'"^^^''«
compound is fo med in.^ 7 '. "^"^ dark coloured

the nitric acid and the rv'J f '" <^^°'<'d'ses
nitric oxide-then d«!>l '^1°'^"" "^ reduction-

ExpertaenJ "oa-F ;r: L'eVf^r f ^""*^'^-

%• 64, with mercury, and "n vert in ™ '^°""'

stout tumbler ; now in ™^'''^"y '" '^

troduce as much nitric

oxide gas as will about

half fill the tube. Pass

tip into the gas, through

the mercury, a pellet as

large as a pea of the

metal potassium (iiie ,at.

~y Jfth 'r fhS:,Tf -^^^^^

sium can be thrown ilth/"''."^ ' ^'"'' '"^^ P"'^^"
any mercury theT p T^ " ™'''°"t "saving

tube still uLer the furfur V'\""™''' ^''^^^ "^«'
end a depressed 1 1 f "'" "'^'■^"^y ^"d the

potassium the m!,^''°""' "'^" "PP'V heat to the

with the oi r/l'":L^lt1?^ ^°"''"^^
mtrogen gas. Allow the apmrntus t ' f"^. ^"^
that the mercury has r^^ZT. ^^'^L""'^ "°^«
Penment be properly co„du«,,Th;- ^^' -J-

ii'i

1 82

■■''

Experimental Chemistry,

.assuming that it contlt , "^S^^^"'"' Justified in
Heat the copper stronp^v = ^ Experiment 52.

Fig. 65.

nitrogen when co.,:ct;d'l1i:Ld^ 7^ '" °^
IS abstracted by the copper just TsTn ih ? °''^^'"

but to find the eXL tl ^ ''"°^"' *^ have

Cotnposiiion of Nitric Oxide,

specific grav r i! o„ ' °^'" t"'' '"'>'^^"' ""^ its
.4'99 X 2 -J:.'s f ; ' "■■'"^ ""^ conclusion, for

gasfor the ^ekhfof two /'"°'''"'" "^'^ht of the

and one ^/l erSrffrc 't-""''«^-^-
certainly NO. '^rmuia ol the gas is

But the nitrogen atom is pentad nr fi i- i
and that of oxveen H,-o^ Pentad, or five-hnk,
..^ -ui ^-xygen diad, or two-linV o«^

unatticJr/.''Ir:eTarrrer2^ ^"^ °"^ """^
the general rule that frle J.T } I ^^^^V^^ou to

links (i.e., centres of atacSnih"' '" *•=''
atoms enga-ed Som/ll ^ • ''^"" ^mponent

this ^^X-J:2:^z2^o'': " ^" °-'
weight acc:<;::;T: i::;s:r,r^ r'^^r

far above its conde„t^ ^f"^ ^' '^-"P^^^^^^
NO, whicl! sTrlTlkf^^^^^^ '° '"^^ ^"""""^
is cooled down 7fs t V / ' •'"" ''''''" '"^^ gas
^3 (H = r) t^nVr ;K cE Ir^"!: ^^'"^
Point-the latter number gvesth. °ot' 7"'^"^'"^
92 and the formula N„0.^ t,! .! l","'*^^"'" weight
assumed in the ca<ip of V;.'- "T '"" conibmation
case of nitric oxide can be distinctly

b I '

ill

I ^4 T^^xferimental Chemistry.

validate' rgnlrui": ."Tf °"' '^^ "°' '"-

show that the!:rcoi; rwh.c'h" ,£ 7:^

or * atomicities ' nc fk^ "'"xcn imjcs, 'bonds,'

Nitrogen Monoxide (M'/rous oxij, „ , ,■
weight =^^. o ■• ■'^99^-gn. Molecular

J^xperiment 110. _ Pour some
30 or 40 CCS. of strong nitric acid
'"'° "", evaporating basin (see fig
66) ; dilute with an equal volume of
water, and add gradually the strong
commercial 'solution of ammonia'
until the acid is neutralised; this

point ,s ascertained by ,est-paper
n the way already described. The

l.qmd in the dish is now a solution

ot ammonium nitrate—

HNO

+ NH4OH = NH,N03

* Solution of
ammonia.'

+ :i.o

Ammonium
nitrate.

"t:]r.-,sr,Ax- s.^

rtheless,
ich best
perature

^istence
not in-
?rve to
bonds,'
appear,

iighing
lecular

some
c acid
e fig.
ine of
trong
onia '

this
)aper

The
ition

by
ue

Experiments with Nitrous Oxide. , gj

when cold, is removed from th^ hn.- ^

'n a well-closed bottle ITw^a ^"" ^"'^ Preserved

Experiment 11 If t Vn o f ''^"''''"' ^y-
the preparation of oxyg n L 6,^'^ "'''' ""' '°'
the flask about 30 grams of fh ^'^^ "''°''"'" "«°
prepared as just descr L ^ ^^mmonmm nitrate,

corlc carr,ing\he dS^'^bfanHll '^T' '''
matic trough with /,^, . ' , '""^'^ 'he pseu-

The salt mf,„,?d etlr ^f' '^' ^^P'^ ''^^t.

the temperatur; Shes "o c" rf '"'•^'^''" ^^

-^30 u The gas is termed

Fig. 67.

cloudy at fir.f „, ^ ^ ^"'■^ "^ generally

carried oyer ^ .11"^ '° "'''''''' °^ =^""« "'«'er
c<ear,.„ot:thlti:t2r;'"''^°°"''---

- ..... uaocner jar of gas plunge burning phos-

i86

Expertmentac Chemistry.

nearly as vmd comDmtion ensues as in oxygen
but all the bodies, more especially sulphur, rjqmre
to be burning strongly in air before they are brought
into the gas, else they are extinguished ^

c. Transfer a jar of gas to a vessel of cold water •
allow about one-fourth of the gas to esc'ioe ThL'
firmly close the mouth of the jaf while unde 'water
w.th the hand, and shake up the gas with he wa te

tl™th" ft^^'" '''; ''^"'^ "'""^ drawn aS

waters ^'"■' ""f °" ''""«^'"g *^ '^«^^ under

water and removmg the hand the proportion of sas

iToVX'^ ^r'^T"^ ^^'^"-<^' '"dicating'tfa
some of the gas has dissolved. By reneatin^ tw,.

treatment several times, the gas, if fiLlm 2 S
be completely absorbed. Therefore this gTs unlike
oxygen, is tolerably soluble in cold watef in "act
i-oo cc. of water at 15° C. dissolves 07T78 ca oi
bom^g^prt" '^-"^'^-■ve inwate/nearto%hi
Experiment I12.-Heat some potassium in a tube

Experiment T''' '/ '""'''^'^ ^°^ ""™ ^^^f In
toper ment ic -md note that the gas does not

th?Z /" rT" ^''^^ ^^''^-' decompoSn by
the metal and the residual gas possesses the properties
of pure mtrogen. Therefore the n>olecule oi this g^
u«at of nitric oxide, contains ... ^. if^;

By the method adopted in Experiment 109 it can
be shown that this gas, like nitric oxide, contains hd"

3-.6/c".:nhf^""'""" '"^-^ '-perature abscbs

Physiological Effects of Nitrous Oxide, 187

its volume of oxygen. It therefore contains, for the
same volume of oxygen, twice as much nitrogen as
nitric oxide, and its formula is N^O.

The change that takes place on heating ammonium
nitrate is therefore represented by the equation—

NH4NO3 = N,0 + 2H,0

Ammonium
nitrate.

Nitrous
oxide.

The molecular weight of the body should be 44 =
(14 X 2) + 16, and its specific gravity (H = i) ought

to be —= 22. The experimental number is 21-99 ;

therefore the above formula is correct. Consequently
I vol weighs 21 '99 c.grs. at 0° C. and 760 m.ms.

Experiment 113.— Take a jar, that we may call A,
containing only air, and hold it mouth upward. Take
a jar, B, of NgO, and turn it mouth upward also and
remove its plate. Now slowly pour the gas from B
into A, just as you would pour a liquid from the
vessel, and test both jars with a taper having a
glowing wick. The taper is re-kindled in A, but not
in B, thus proving that the gas is so much heavier
than air (1-52 times) that in can displace the lighter
air just Hke liquid. The gas cannot be retained in
an open vessel for any length of time, as it escapes
by diffusion (see Experiment 92) into the atmosphere.
It is liquefied by a pressure of 30 atmospheres at 0° C.

The gas is often termed laughing gas, in allusion
to the curious property Sir Humphry Davy found it
to possess, when mixed with some air and inhaled
of causing temporary excitement and a sense of

i88

Experimental Chemistry.

PC!

exhilaration. When unmixed with air or oxygen, and
pure, nitrous oxide produces insensibihty if inhaled
tor a short time ; at first ringing noises are heard and a
general sense of pulsation ' is experienced, then sleep
supervenes, during which any short operation, such
as the extraction of a tooth, can be and frequently is
performed. A few full respirations of pure air restore
the patient, and no unpleasant after-effects follow the
administration. In the latter respect nitrous oxide
IS superior to ether and chloroform as an anesthetic
U.e., a body used tp procure insensibility to pain) but
the gas can completely suffocate if too long inhaled
Ringer says of it : ' It appears to me to produce its
anaesthetic effect by preventing oxidation of the ner-
vous centres, and this chieiiy by depriving the blood
of its supply of free oxygen from the air.' Although
there is more oxygen in nitrous oxide than in aiN
it IS chemically combined with nitrogen, and thu's
we have, m the comparative action of nitrous oxide
gas and air on the animal economy, a remarkable illus-
tration of the wide difference in characters that may
exist between a chemical compound and a mechanical
mixture of the same elements.

We have thus recognised the existence of five
oxides of nitrogen, two of which are anhydrides of
distinct acids. If we assume that the molecule of

n„rL^'^^"' '''''^^ ^'' '"^'"^'^ ^°^ '"^^1'-^^'°" should be
purified from ammonia and higher oxides of nitrogen by
Gb hging It to pass in succession thro«gh sulphuric acid and

uLkT . r? ^^"'P'^^^' "^ S'-^^" -^"°'' contained in
suitable wash -bottles.

• 53*$ pe? omU hy weight, as against 23 per cent, in air.

%'.

air,'

N2O

N2O2, or NO.

N2O3

N2O4, or NO2

NoOv

Experiments with Ammonia. 189

each oxide contains the same weight (i.e., 28 parts) of
nitrogen— althv u.jh we know this is not quite true
in one instance at least-it follows that the group of
known oxides of nitrogen is a complete series of com-
pounds resulting from successive additions of single
oxygen atoms to the lowest term-i.e., nitrous oxide.
Thus —

Nitrous oxide , ,
Nitric oxide ....
Nitrogen sesquioxide, ornitrous
anhydride ....
Nitrogen dioxide .
: Nitric anhydride .

In this group of bodies we therefore have additional
evidence in support of the law of multiple proportions
already deduced from the examination of the two
oxides of hydroi^en. ( Vide Part I. under Experiment
80.)

Ammonia = NH3. \ Vol iveighs ^-^ c.grs.
Molecular weight =-17.

Experiment 114.~Boil some metallic zinc with
strong caustic potash solution in a large test-tube •
the metal slbwly dissolves and a gas is evolved which
burns at the mouth of the tube, and can be easily
shown to be hydrogen, and zinc potassate is left—

Zn + 2KOH = Zn''(0K)2 + 2H.

On the addition of a few drops of nitric acid or a

little mtre to the solution anH ckn^\r^ i,^«*.«„ *u

"ft""' "^avijig, tiic pun-
gent smell of hartshorn is noticed, and a piece of

i: J

Itl

J 90 Experimental Chemistry.

pour We r ''"'• ''''''"'' °' "" """"'"' ^^-

the hydrogen, 'no'lo^^e^::;; ; Vufwh/nT "he'
«<,...«/ .state, quickly deoxid.ses , he nitre form „!

nitrogen of he nitre and forms ammonia gas which
lajter^ evo,.d^.hi,e potassium hydrateTiSt

KNO3 + ^H = mi^+ KOH + .H,0

Potassium
nitrate.

Ammonia. Potassium
hydrate.

Experiment 115.— Pass a rnrr^nf r
hydrogen through a hot aiic^iin^e sX To ofnitfe^d

ra e':/r 1? ''' "'* ^^'^'^-^'^ litmus-paper No
trace of allcahne ammonia can be detected if tZ

materials employed are pure, and care be Ikl t^
prevent any of the liquid reaching the paper '°

^^«.f fo experiments well illustrate the difference
rJ TJ .''"'"""" ""' comparatively stable free mole

condhL;'':rf "^ *^ "^^ ^■^"^"' - *~'

condmon-i.e., at the moment of liberation of its
atom from a compound, and, as some suggest before
It can meet with another atom in orderTform °he

^rb:r:-r,atey--'^-----='"^^^^^^

Experiment I16.-Take a tube of hard gia.s
closed at one end, and one-third fill it wirpites
of horn, bone, gelatine, feathers, wool, hair, or, if the

From naxrn^. l-rt K/» 1

y ■»--- s^« uvm.

Experiments with Ammonia.

Fic. f S.

191

Teat \L '"^' ""'• ^"^'"^"'^ °^ '°=^'. and apply
heat. The organic or carbonised matter soon ri7

voTErtt r '""'ir^^ °^ '"^ heatand variot

to bluu All the bodies mentioned agree in cnn
taming nitrogen-even coal contains from to 2Z

Wise present,ii^:;^:rmlT 7.1 '''-'-' "^^"

nitrogenised animal and vegetable

bodies afford more or less ammonia

m this way, not only at high but at
ordinary temperatures, when they
undergo slow putrefactive change or
decomposition in presence of mois-
ture-in fact, much of the atmo-
.spheric ammonia is derived from the-e
sources.

^ Most of the ammonia employed

in the arts is obtained from the tarry

ammoniacal liquors collected during

the manufacture of coal gas. The pre

paration of sa/-ammomac and similar ji^

TndSs oH '""'^^ .'^'-''^--^ will be referred to
unoer baits of Ammonia ' in Part III

aJo!^T' '^^-^---^y powder some ../.
with rather more than its own weight of slaked

'' Or distillation attended by decomposit

ion.

ig2

Experimental Chemistry.

hme in fine powder, quickly transfer the mixture
to the flask / fig. 68,. insert the cork carrying the
delivery tube d, -nd invert over the free end of the
latter the dry h tie On applying a very gentle

heat to clrr mixti, n , / abundnnre of ammonia Kas
fs evolved, \ht pungei.^ smell ot which is quickly
perceived, ^vhiie red litmus-paper passed up into the
gas is instantly rurned blue, .md white fumes are pro-
duced when a glass rod," moistciied with hydrochloric
or acetic acid, iff I'lfought to the mouth.' Note that
the pure gas is colourless.

2NH,C1 + Ca(0H)2 = 2NH3 + CaCl., + 2H,0

Ammonium
chloride.

Calcium
hydrate.

Ammonia.

Calcium
chloride.

Fig. 69,

a. Pass up a lighted taper into a jar full of am-
monia. The flam- is extinguished
without igniting the gas.

A Take a dry gas jar and at-
tach a piece of red litmus-paper
near the top inside by means of
gum. Invert the tube, and bring
under its mouth a rather larger
tube full of ammonia gas, as shown
in fig. 69, and slowly invert the
latter. The colour of the litmus
in the upper jar quickly changes,
proving the ascent of the ammonia,
and the flame of a taper is ex-
tinguished if passed up into the gas. Therefore am-
' Any other ammoniacal salt may be used instead of the
chloride, aad potassium or sodium hydrate instead of lime.

mixture
ying the
id of the
ry gentle
onia pjas

quickly
into the
are pro-
ochloric
fote that

f- 2HnO

I of am-
guished

and at-
is-paper
cans of
d bring
■ larger
5 shown
'ert the

litmus
hanges,
imonia,

is ex-
)re am-

d of the
ue.

Experiments with Ammonia. 193

monia {slighter than air, and displaces the latter from
the upper jar. Its specific gravity is 8-5 (H = i) or
but httlc more than half (0-586 if air = ,) as heavy rri
air. ^

c. Fill another stcit bottle with the gas, close with
a glass plate, and remove, still mouth downwards
to some water ; withdraw the pla! « when ti.e mouth

Fig. 7a

IS under water. Note that the water rapidly rushes
into the jar and nearly fills it ; therefore ammonia gas
IS very soluble m water-in fact, i c.c. of water at
15 C. and 760 m.ms. dissolves 783 ccs. of ammonia
gas, or 783 times its volume.

^^ SAperiment I18.-Prepare ammonia gas as be-
fore, .-ut wasli it from impurity by making it pass"

'94 Experimental Chemistry,

through the small quantity of water ' in the little wash-
bottle z£/, fig. 70, and then conduct the gas into a
measured quantity of water contained in the bottle
b, which latter is cooled by immersion in a beaker of
cold water, as heat is evolved during absorption of
the gas. Apply heat to the flask/ and pass the gas
through the water in b as long as it is absorbed, but
when bubbles pass through without sensibly diminish-
ing m size it may be concluded that all the gas has
been dissolved that the water can hold at the particular
temperature and pressure. Measure the bulk of the
liquid in b after Ijhe experiment, and it will be found
to have increased to the extent of about one-half its
volume.2 This 'solution of ammonia ' is colourless,
with a characteristic and very pungent smell, and
strong alkaline reaction to test-papers. The specific
gravity of the solution is about o-88 (water = i).

When the solution is heated, ammonia gas is
expelled, and after boiling for a short time almost
every trace of the gas is removed ; thus ' solution of
ammonia ' is a very convenient source of the gas, and
we shall use it presently for this purpose. Ammonia
gas is also easily soluble in alcohol.

The extraordinary solubility of ammonia gas in
water, accompanied as it is by considerable evolution
of heat, IS commonly regarded as due to true chemical
combination— a new body being formed which closely

' Rather more than 50 c.cs. of water should be used for
every 100 grams of sal-ammoniac.

''The process employed on the large scale in the manufacture
of liquor ammonia fortior-^ of the British Pharmacopoeia is
identical with that given above.

ExperimenU with Ammonia. 195

resembles potassium and sodium hydrates in its
h^hly alkalme character and power of neutralising
acids (e.g. „,tr,c acd, Experiment .10), and forming

hence the liquid may be fairly regarded as a hydrate
similar to those of the metals above named, in which
hydroxylis united to a monad compound radicle
NH „ which acts like a monad metal and is termed
ammonium.^ Thus— 'c.mcu

J^ + HjO = NH'.OH

Ammonia. ^T '"~ — ""

Ammonium

- ' hydrate.*

Water saturated with ammonia gas at o° C and
under the pressure of 760 m.ms., may be regarded as
nearly pure ammonium hydrate, since it contains a
weight of ammonia equivalent to about 96 per cent, of
JN II4OH. But a slight elevation of temperature suffices
to decompose this body, and nearly all the gas can
be expelled before the liquid reaches 100° C Thus-
NH,OH = NH3 + H20.
From the above experiments we learn how to pre-

J's'oLt. f"" "^"''^"^ ^^"'^^^^ ^"^' ^"d '^ obtain
solution of ammonia 'of the British Pharmacopoeia,
or ammonium hydrate.

Ammonia can be condensed to a colourless liquid
by cooling the gas to a temperature of - 40° C or F.

' See further, Experiment 124.
.Z ^"lf^\ compound is known, which is intermediate in
composition between NH, and NH.OH ; its composition is
represented by the formula NH..OH. and ,> i= ..^^TuTJ^

been replaced by the group OH or hydroxyl.

196 Experimental Chemistry,

(and, it may be stated, this particular temperature is
the only one indicated by exactly the same value on
the Centigrade and Fahrenheit thermometer scales) by
means of a freezing mixture of two parts of snow and
three parts of crystallised calcium chloride.

The comparative ease with which ammonia gas can
be liquefied by cold leads to the presumption that it
admits of liquefaction by very moderate compression
at ordinary temperatures. By means of the following

Fig. 71.

cheap and effective apparatus we can reduce the gas
to the liquid form. *

Experiment IW.-A species of U tube of stout
wrought uon is made of the form shown in fig. 71,
ALB. A IS about 40 centimeters long, B 30 centi
meters, and each is 2 centimeters internal diameter • C
is about 25 centimeters and 5 or 6 milhmeters internal

tubes. The whole is fastened to the wooden stand A

A is provided with

ucv^uw a;.icw-cup n^ tne joint

Liquefaction of Ammonia,

19;

being rendered gas-tight by a leather washer. B is
also fitted with a strong screw-cap with a deep head,
through which a conical hole is bored ; the long glass
tube t of the apparatus / passes through this hole to
the expansion c, which should fit into thg cone and
be there secured by any good cement. The screw-cap
m therefore carries the glass apparatus, which latter
is a form of pressure tube now easily obtained through
good instrument-makers. The liquefaction is to take
place within the glass tube /, which must of course be
very strong ; the length of this tube is about 25 centi-
meters, and at first it is open ; the wide reservoir o
must have at least ten times the capacity of / ; the
reservoir terminates below in a rather narrow curved
tube w, which is always open. The glass apparatus
must be filled with dry ammonia gas by connecting w
by means of a flexible tube with/ fig. 70, affording
a current of ammonia gas, but freed from moisture by
passing through a long tube packed with fragments of
fresh quicklime. When all air has been expelled—
and a good current maintained for ten minutes is
sufficient to effect this— the flow of gas is allowed to
slacken and the capillary end of / securely sealed at
the blowpipe ; the tube is removed from w and the
latter at once dipped in mercury, which enters and
prevents escape of ammonia.

Now remove the cap n, and • pour mercury into A
until the metal rises nearly to the top of B ; then
introduce mto B, allowing the mercury displaced to
overflow into a vessel placed to receive it, and screw

home thp rnn ttl l\u\\\r\\ r\f f^rxuraa.

uc piOViuec

with a good leather washer). We have, therefore^

'.nl

V Is

198 Experimental Chemistry.

nothing but mercury between the gas in and the sur-
face of the metal in A. Next remove enough mercury
from ^ by a pipette to leave a space of some 1 2 centi-
meters between the surface of the metal and the cap ;
then fill up to the top with the strongest 'solution of
ammonia,' and screw down the cap n, and the
apparatus is ready for experiment, which is performed
in the following way : —

Gradually heat the portion of A -containing the
solution of ammonia by a Bunsen flame occasionally
applied; as the temperature rises, ammonia is
expelled from thg solution, but since the gas has no
escape, considerable pressure is exerted in A on the
surface of the mercury, and the latter, acting as a
fluid piston, compresses the gas in 0, which steadily
diminishes in volume until at last the mercury rises
into view in / ; > and if the heating of A be now care-
fully managed, the compression proceeds until a layer
of colourless liquid is seen to form on the surface
of the mercury in /. This is the liquefied ammonia,
and IS obtained when the pressure reaches about 6-5
atmospheres at mean temperature.

If the joints are well made and the heating well
managed, it is easy to maintain a steady pressure for
a considerable time, but anything like violent heating
must at all times be carefully avoided. On allowing
the apparatus to cool, the mercury recedes in /, and
the liquefied ammonia disappears. This apparatus is
always ready for experiment, though it is desirable to

'It is well to cover / with a large cage of fine wire gauze,
lest the glass should give way when first subjected to consider-
Su»e pressure.

Covibustion of Ammonia. 199

unscrew the cap of J occasionally and change the

kSbV. '"""""'^ " ^""^ '^^"^^S^ ^^^ '^ i'
Experiment 120.-As we have already seen ^x-
penment 117, <.) ammonia does not burn when a light
.s appued to the cold gas. Now pass it through a
narrow glass tube heated to redness near to the point
at wh.ch gas issues, and it can be easily :gnit"d burn-

2' It :ror""'-^^"°" "^-"^ '" the'oxygen'ofX
Z^^ K i""^"'^^^ ""roge" gas and water, hence a

Sed'asrj"'° *^. "^^ ^^ ^'-^^y ^

2NH3 + 3O = 2N + 3H2O.

somr'.^i 5 ' "l '""'^^"^^ ^"^ (^b^^i^^d by heating
some solution of ammonia ') issuing ^

from a jet be surrounded by oxygen
gas and then ignited. The little ap-
paratus, fig. 72, enables this experi-
ment to be easily performed. ^ is a
short brass tube into which oxygen
gas can be admitted through the side
tube ^ ; « is a glass tube delivering
ammonia; this passes through the
cork . which fits the brass tube a. Ammonia is
allowed to flow through n, and then oxygen gTs de
nved from a bag or gas-holder, is turned on camiously,

this' fppamtur if ' ^•'''"'■' P""^P ^' "'^^g^^'^^^ ^^-ided in
tms apparatus, it is inexpensive. Before usinjj any form

,°'„??!!^i"\^«^^^P--"^« o-he kind described.1t Z,d T

!*'

Fig. 72.

1j<

■>1

200

Ej^periinental Chemistry.

while a flame is applied to the jet. When the propor-
tions of the two gases are properly adjusted a tolerably
steady flame can be obtained.'

If in the last two experiments, but more especially
in Experiment 120, we dry the ammonia by passing
the gas through a tube filled with fragments oi quick-
lime (CaO), the appearance of water as a product of
combustion is proof that hydrogen is a constituent of
ammonia, while the mode of generating the latter
from nitre adopted in Experiment 114 leaves little
doubt that nitrogen is another constituent of the body ;
but the following experiment affords us complete evi-
dence of the composition of ammonia.

Experiment 122.— Fill the eudiometer (fig. 73)
one-fourth -h say 20 ccs. of dry ammonia gas over
mercury. Measure the volume and pass a series of
sparks from an induction coil between the wires within
the tube.2 The confined gas is thus intensely heated
' In these experiments the rapid oxidation of ammonia in-
volves complete decomposition; but when slowly oxidised,
especially in aqueous solution, it first affords nitrous acid, thus—

NH3 + 30= HNO, + H,0.
The nftrous acid then unites with another atom of oxygen, and
produces nitric acid, thus —

HNO2 + O = HNO3.
The organic matter of sewage readily affords ammonia on
decomposition, and the latter then undergoes slow oxidation as
just stated ; hence in sewage -contaminated water nitrites and
nitrates are usually to be found.

2 In this case a Leyden jar must be placed in circuit in order
that the maximum heating effect may be obtained. For this pur-
pose it is merely necessary that one of the coil wires should be
in metallic connection with the knob, and the other with the
external coatinL-^ of the ian

Analysis of Ammonia. 201

and decomposed, and if the sparks are passed for a
sufficienttime the volume of gas increases to 40 c.cs., or
IS doubled. Having obtained the maximum expansion
note the volume, and introduce 20 ccs. of pure oxygen
and explode in the usual way. After correcting for al-
teration of level, the residual gas wiU measure only 15
CCS.; therefore 60 - 15 = 45 ccs. of gas have dis-
appeared, two-thirds of which, or 30 ccs., must be
hydrogen and the rest oxy-

Fig. 73.

f^~~-^~

gen (see Experiment 24).

As 20 ccs. of oxygen were

introduced, and 15 ccs.

have thus disappeared in

union with hydrogen, the

residual gas in the tube

must contain 5 ccs. of

oxygen. This residue

measures, as we have

seen, 15 ccs. ; hence

15 — 5 = 10 ccs. of ni-
trogen left. J To sum up, then, our experiment proves,
firstly, that ammonia gas contains only nitrogen and
hydrogen ; secondly, that it is completely decomposed
into its constituents at a high temperature ; thirdly,
that the resulting mixture of gases occupies twice the
volume of the original ammonia ; fourthly, that this
gaseous mixture contains one volume of nitrogen and
three of hydrogen— consequently the molecule of am-

' By passing up a few drops of caustic potash, followed by
a strong solution of pyrogallic acid (see Experiment 83), the

that it can be easily identified.

Fig. 74.

202 Experimental Chemistry.

nionia gas contains one atom of nitrogen and three
atoms of hydrogen, and must be represented by the
formula NHg,^ and its molecular weight by 17

(14 + 3). This result is confirmed
by the specific gravity of the gas,
which, as we have already seen
(page 49), is 8-5, and 8*5 x 2 =17.
I vol of ammonia gas (112 ccs. at
0° C and 760 m.ms.) weighs 8*5
cgrmr

Experiment 123.— Pour a few
drops of strong commercial hydro-
^ chloric or 'muriatic acid' into a
wide-mouthed bottle ; cover with
a glass plate and turn the bottle
about so as to distribute the acid
over the sides. Fill another bottle
with ammonia gas, bring its mouth down on the
glass plate that covers the first, as shown in fig. 74,
and then remove the plate from between them so as
to leave them mouth to mouth. White fumes are
instantly formed in abundance, and they deposit a
white saline body on the glass after a time which is

' We can recognise the nitrogen acting as a one-link, or
monad atom, in nitrous oxide, N'-0"-N', or N.,0 ; as a threes
Imk, or triad, in ammonia, N'^H',, and as a five-link, or pentad
m ammonium hydrate. N'H',(OH)', the monad group hydroxy]'
OH',^ satisfying the fifth link. In the case of sal-ammoniac,'
N'H'^Cr, we also have evidence of the five-link or pentad
character of the nitrogen atom. In all these cases the links or
bonds appear or disappear in pairs.

Ammonium Amalgam, 203

identical with sal-ammoniac or ammonium chloride
for

^_NH3_^+ HCl = NH'4C1

Ammonia. Hydrochloric Ammonium • '
acid. cliloride.

Thus at the commencement of our experiments we
decomposed or analysed sal-ammoniac, and now we
have reformed it or effected its synthesis, and we have
written the formula of the body in such a way as to
indicate that it is the chloride of the compound radicle
ammonium NH'4, already referred to under Experi-
ment 118, rather than NH3HCI, the formula directly
justified by its mode of formation. Now the former
view assigns to the group NH'^ a pseudo-metallic
character, and it may be fairly asked whether am-
monium has been isolated, and, if so, whether it pre-
sents any of the metallic characters. As a matter
of fact, ammonium, NH'4, is not known in the free
state, but a curious body can be prepared which is
supposed to be a solution of ammonium in mercury.
This body is easily obtained ir the following way.

Experiment 124.— Introduce about one cubic
centimeter of mercury into a wide test-tube ; gently
warm the metal over a lamp an'', directing the mouth
of the tube away from the person, drop in a fragment
of clean metallic scditwt about half the size of a pea.
If the mercury be warm enough, the sodium will at
once dissolve in it with a little explosion— if not, heat
gently. Then introduce another piece of sodium
of the same size, and after its solution a third. A
Slavery white amalgam of sodium is thus prepared

204 Ex'perimental Chemistry.

which retains the metaliic lustre' Now pour out
the warm and still liciuid amalgam (for if allowed to
become cold it will become pasty or solidify) into
about 250 CCS. of a cold saturated solution of sal-
ammoniac (see Experiment 73). The amalgam
quickly mcreases to at least 15 times its original bulk,
and ultimately becomes a large pasty mass, light
enough to float on the surface of the liquid. This
mass can be removed and washed with water; it
presents a brilliant metallic appearance, but it is very
unstable and soon decomposes, evolving ammonia and
hydrogen gases, and after some time nothing remains
but the original mercury. This body appears to be a
true amalgam of mercury and the metal-like am-
monium, the latter taking tlie place of the sodium •
thus— '

JlgxNa^ -f NH.Cl = Hg^^NH^ + NaCl

Sodium Ammonium

amalgam. ' amalgam.

The amalgam then breaks up in the following way-^

Hg^NH^ ^ Hg^+ NH3-f H.

There is therefore some experimental evidence as
to the existence of the compound metal ammonium,
and the close analogies traceable between its saline
and other compounds and those of potassium and
sodium confirm this view; but it would lead us too
far out of our course to examine this question here ;

' Alloys of metals with mercury are termed amalirams ; in
some cases these are mere mixtures of metals, in others feeble
chemical union takes place, but the product in all cases retains
the •metallic appearance. •

Expenmcnts with Iodide of Nitrogen. 2c ^

hence we- shall reserve this part of our study until we
have to deal with the compounds of the alkali metais
in Part III.

Experiment 125. - Powder half a gram or so of
iodine and add it with frequent stirring to 20 ccs.
of ammonium hydrate solution ; allow it to stand for
half an hour until a black powder has completely
subsided, then pour away the clei\r liquid and dis-
tribute the black residue on pieces of bibulous paper.
Put these in some safe airy place to dry. When the
black substance is dry, a touch suffices to make it
explode, when violet vapours of iodine are evolved.
If small quantities are operated upon and reason-
able care exercised, the experiment is not attended
with danger.

The black substance is called iodide of nitrogen,
and is really a mixtute of ammonia derivatives. Dr.
Gladstone's formula for the chief substance is NHIj,
or ammonia in which two-thirds of the hydrogen has
been replaced by iodine. Analogous bodies are pro-
duced by the action of chlorine (chloride of nitj-ogen)
and of bromine (bromide of nitrogen) ; but these are
amongst the most dangerous explosives known, and
have caused so many serious accidents that any de-
scription of their preparation is undesirable.

Many other derivatives of ammonia are known in
which various groups of elements replace one dlhiore
atoms of hydrogen in NH3 ; these will be met with
later on in our course, but wt may here give the
formulae of three of these important bodies—

Ethylamine. Diethylamine. Triethylamine.

NHalC^Hs)', NH(C2H,)'2 N(C2H,)'3.

!ipi

iir:

206

Experimental Chemistry,

■ ^

CHAPTER XV.

EXPERIMENTS WITH HYDROCHLORIC ACID AND

CHLORINE.

Hydrochloric Acid (Afuruitic add) = HCl i Vol of
gas weighs i^i^'ic) c.grs. Molecular weight ^ 2>(,-c
Experiment 12a-Mix some sal-ammoniac-am.
monmm chloride, as we shall term it for the future-
with strong sulphuric acid in a test-tube. Even with-
out heat a quantity oj-gas is evolved which has a very
pungent smell and fumes in the air ; it does not burn
or support combustion of a match, but it reddens blue •
litmus-paper, and produces whitg clouds if a rod
moistened u'ith ammonium hydrate be brought near
the mouth of the tube. ' ^

^ The gas evolved is therefore an acidg2.^ capable of
uniting wuh the alkaline ammonia, and' this 'body is
termed hydrochloric acid, and its symbol is HCl Thus
in Experiment 1x7, we liberated ammonia gas from
NH.Cl, and m Experiment 123 re-formed the latter
by effecting the combination of ammonia -with
hydrochloric acid. We have now broken up the
compomjd agam, but in such a way as to make it
yield itTacid constituent ; thus—
2NH,C1 -f £,S0, = (NH,)^4 + 2HCI

Sulphuric Ammonium Hydrochloric

acid. sulphate. acid

In this case, each group, NH„ takes the place in

Ammonium
chloride.

Hydrochio.ic Acid Gas. 207

the sulphuric acid of ont. atom of H, and the latter
unites with the CI of the ammonium salt and forms the
acid. Ihe specific gravity of hydrochloric acid gas,
detcrmmed as in Experiment 27, is 18-19 (H = i) •
and I vol weighs 1819 c grms. Its molecular weight
is therefore 36-5 (if CI = 35-5).

Experiment 127.-Make a similar experiment
with common salt or sodium chloride, and note that
the same acid gas is evolved. In this case
2NaCl + H,80, = Na^SO^ + 2HCI

<^*^lo'''^e. sulphate.

Lower the test tube from which HCl g2i% freely issues
into a small dry gas jar standing mouth upwards, and
loosely cover with a glass plate. After a minute or
two slip aside the glass plate, rapicly remove the test-
tube, and pour in a few cubic centimeters of water ;
cover the mouth with the hand and shake up. Note
that a vacuum is produced, as evidenced by suction
of the hand, indicating that the gas has been absorbed
by the water ; now test the latter with blue litmus-
paper and note that it has acquired an acid reaction.
Therefore hydrochloric acid gas is soluble in water and
produces an acid liquid. As a matter of fact, the gas
is very soluble in cold water, as we shall find presently,
for I c.c. of water at 15° dissolves 450 ccs. of the
gas at the same temperature. It is a strong solu-
tion of the gas in water that constitutes the liquid
hydrochloric acid ('muriatic acid' or 'spirit of salt')
of commerce.

Experiment 128.— A glass flask, / fig. 75, is
provided with a cork through which passes" the^gas

208

Experimental Chemistry.

delivery tube bent twice at a right angle and passed
to the bottom of the wash-bottle w, which contains a
very little water, which a tube leads from 70 into a bottle
b containing cold distilled water. Place about co
grams of common salt or sodium chloride in /and \o
c cs. of water in /;, and connect the apparatus as shown
Measure 50 ccs. of oil of vitriol and add it gradually

Fig. 75.

and with stirring to an equal volume of water contained
ma porcelain dish ; when cool, pour into the flask,
and then, if necessary, apply a gentle heat to/. HCl
IS freely evolved as a colourless gas and passes through
the water in w, where the first portions are absorbed,
and then into ^he water in b. When all air has been
txpelled from the solution, the bubbles that pass into
the water disappear before they reach the snrfarP fhe

Hydrochloric Acid Solution. 209

gas is so easily soluble in water ; but when the latter
IS saturated they pass through without apparent
diminution of bulk, and thus the end of the process
can be recognised. The bottle b must be kept cool
throughout, resting in the beaker of cold water. »

When the gas is being freely evolved it is well to
remove the delivery tube from b, dry it, and pass it
to the bottom of a gas jar placed mouth upwards and
partially covered ^^ith a glass plate. When the jar is
judged to be full of the gas, remove the tube, close
the mouth and bring it under water. The latter
quickly rushes up and almost fills the jar, or quite fills
It if all air has been expelled.
. ^ The solution ultimately obtained in the bottle b
is a nearly colourless and strongly acid liquid, emit-
ting white fumes which have a pungent smell. Its
specific gravity is about i-i6 (water =i-o), and it
contains about ^2 per cent, by weight of actual HCl.
When heated this acid loses gas until the percentage
of HCl is reduced to 20-24, and a solution of this
strength boils at a constant temperature of 110° C if
the pressure does not vary from the normal (760 m m)
The common ' muriatic acid ' of the shops always
has a yellow colour, owing to the presence of iron -
other impurities commonly present are free chlorine'
arsenic and sulphur compounds. Appropriate tests
for these impurities will be found under their respec-
tive heads.

' The process given above is that directed by the British
Pharmacopoeia for the preparation of the pure acid. The crude
commercial acid is chiefly obtained as a by.product in the
manufacture of 'salt-cake,' or crude sodiuL su//>Ta)e!'' sL
irart III. p. 283.

■II

210

Experimental Chemistry.

Experiment 129.-Mix a few drops of the colour-
less acid prepared as above with ten or twelve parts
of water, and add to the diluted acid a few drops of
silver nitrate solution. Note that a white precipitate
IS produced that becomes curdy on shaking. Let the
precipitate subside, pour off most of the liquid and
then divide the precipitate between two test-tubes.

a. To one portion add some moderately strong
nitric acid and boil Note that the precipitate does
not dissolve.

b. To the other part add NH.OH solution ; the
precipitate soon dissolves completely, and can be
repreclpitated wheh the ammonia is neutralised by
nitric acid.

The precipitate possessing these characters is
silver chloride, which is formed when silver nitrate is
added to free HCl, :r to any soluble chloride such as
ammonium or sodium chlorides—

HCl + AgNOg = AgCl + HNO3

Hydrochloric
acid.

Silver
nitrate.

Silver
chloride.

Nitric
acid.

Experiment 130.— Add a few drops of solution of
lead nitrate (Pb(N03),) to some diluted hydrochloric
acid ; a white precipitate is obtained if the liquids are
not very weak, and the body dissolves to a consider-
able extent in boiling water and separates out in white
crystals on cooling the solution. This body is lead
chloride, thus formed—

^^^^li3 + 2HCI = PbCl, 4- 2HNO3

Lead
nitrate.

Lead

^1,1, ...:.4_

Experiments with Hydrochloric Acid. 2 1 1

For another useful test of hydrochloric acid or a
chlonde, see Experiment 137 ; and for the distinction
of the acd from free chlorine, see E neriment 147

acid wrh""?* ^^^r"!;'"'^ ^°"'^ ^''""S hydrochloric
acid with water, and add caustic soda until the acid

IS neutrahsed, as m Experiment 42. The solution

cTrairoffh" " '"°"'!' °^'°""^" ^^''' '^"d affords
crjstals of the compound on evaporation -

HCl + NaOH == NaCl + H^O. ■

Other metallic hydrates afford corresponding chlo-
ndes when used to neutralise the acid

Experiment 132.-Add some black oxide of copper
to a lutle of the acid in a test-tube ; the oxide dis-
solves easily and forms a green-coloured solution which
contams copper chloride—

Cu"0 + 2HCI = Cu"Cl3 + 2H,0.

Other basic oxides are acted upon in a similar way
by hydrochloric acid, and produce metallic chlorides
and water; b.-t certain peroxides, such as MnO„ give
chlorine in addition (see Experiment 137) ''

Experiment 133,-Plunge a strip of zinc into
some of the diluted acid in a test-tube. Brisk efc
vescnce takes pbce, and the gas evolved burns when
a flame is applied to the mouth of the tube. The eas
is hydrogen resulting from the reaction-

+ 2H'a' = ZnXT^ ^ 2H

Zinc
chloride.

Zn''

If iron be used instead of zmc, hydrogen is also

I !
I I

I F

212

Experimental Chemistry.

evolved, but ferrous chloride ^ferrum^;,^^) is ob-
tamed in solution—

Fe" + 2HCi ^ Fe"Cl2 + 2H

Ferrous

chloride.

In each case thg. solid salt can be obtained by
evaporation, of the solution ; for details, however see
the respective metals in Part III. '

Experiment 134.-Take two' test-tubes, pour into
one 3 CCS. of strong nitric acid, and into the other
4 C.CS. of strong hydrochloric acid. Put into each
acid some pieces oi gold-leaf '^nA apply heat. Neither
acid IS able to dissolve the gold, or ' royal metal ': but
on mixing the contents of the^est-tubes the panicles
of gold disappear almost immediately; hence the
mixture of acids is called aqua regia, because it alone
dissolves gold or platinum, which latter is also classed
ad a noble metal.

When the two strong acids react, particularly on
heatmg or long standing, the following products are
obtained —

aHQ 4- RNO3 = 2CI + NOCl + 2H,0

Chlorine.

Nitrosyl-
chloride.

The solution of the gold (or platinum) is due to
the action of the chlorine on the metal -^

Au'"-f 3Cr = Au"'CI'3.

'^\sftdilutednitro-hydrochloricacid{^. P.) is prepared
by mixmg the strong acids in the above proportion
(3 •' 4), standing for twentv-fouf honr« tn nArrp.v v,«.-i..

Fro. 76.

Analysis of Hydrochloric Acid. 2 1 3

complete change, and then diluting with .5 parts of

assmJf r° r"'^""^"' ''^P""'"" ^e have hitherto

L "rnont ? ""^^ *""' "^^ ^as evolved when
sa -ammoniac or when common salt is heated with

^ulphuncactd. We must now examine this bodjmore

use thiTITf """"^ '" '^°'"'"°" «"• "'« ^hall now
aadJas ln^ 1 T°\^ '"^'"""^ f^°'" hydrochloric
ac d gas. Kill the U tube, fig. 76, with hydrochloric
acid by passing a rapid current of tlK gas throuX t
for some time ; then close the .stopcock . ^

and immediately pour sufficient mercury
into the open limb to close the bend /
and partially fill the tube as shown. Now
adjust the level of mercury by opening
the stopcock for an instant, as the gas
must be under a little pressure, then mark
he position of the mercury in the closed
limb and fill up o completely with mer-
cury containing some sodium amalgam,

rrf "J '" E-"''^"'"^"' '^4. Next g asp . firmly
m he hand pressing the thumb on the opening Tnd

tailrth ^ '' "'"'^^ "'^°"g'' 'he mercury con-
tain ng the sodium, at last transferring all the c"s

not t'hat r J""'- ''T ^^-"^^^ *' 'humb ^^
the mercu ; thTr'^""'''. '" "' ='<^J"« '^e level o<:

«">b occupies only /..// ti." ;;L.^rof' thT h^r

214

Experimental Chemistry.

chloric acd. Fill up o with plain mercury brinir ,
flame near to the jet, and cau iously openT-the 1
Sidual gas ru*es out and burns for anfnstant T t

Experiment ISe.-Bend a tube in U form as in

^5f SI"? •E.ri ri-r£»

Fig. ^^,

Now plunge the carbon poles ^ into the arM Jn fi, tt
tube OS «h^«r« r- • , ^ ^^^^ ^" the U

tube as shown. Gas is evolved at each pole-colour

£^hfb:-r^-r^2-5

and neither burns nor rekindle J^tcT ^aS
2r^^l f however, a piece of moistened blue litmu!
paper be Ia.d over the mouth of the tube it is soon

mll^Z tT T' *" "''''• ''''"•'== P'^'i"'™ would be
^.acked by the chlornK evolved during elcc.oly.. of ,he

Experiments with Chlorine.

215

allusion to its greenish-yellow colour ; its symbol is CI
and atomic weight 35.5. The voU mes o7the two
gases evolved during electrolv.ic; . " ""

eoual whpn fi.^ V \ ^'^^"oosis are approximately
equal uhen the hquid becomes saturated with chlo-
rine. The specific gra^ ity of chlorine gas, determined
as m Experiment 27, is ^r.,8 m - r\ .u "-'"'^^'"^^
r=ii2 r pc: \ „,„• t ^o "^ ^ ')' therefore i w/

^-112 CCS.) weighs 35-38 cgrs.

wethfis , l"-\°"^ ''*°"'' °f '^"'^^g"'' -hose
c%ni IS I cgr. Now, since 36-? - i = ,c-c «r

almost exactly the weight of x t./ of chlorine we
conclude that the molecule of hydrochloric add Is
consists only of hy< ogen and chlorine, and of bf^h
chemical y combined without condensation. AkhoS
this proof IS complete, it is well to coni^rm 1he co„

ThlorTne i» o '° °'^'''''" ''''^8^^ ^"'-'"i'ies o

that demenr "7 ''"'\'"^ ''"^^ "'^ -characters of
that element. (For synthesis see page 219.)

Chlorine a.=35-S. i ^^/«'«^/« 35-36 ..^.
Molecular weieht =. 7io_n io „k ■ , , "

rhlnri^ o„-j u ''°- " 's obvious that hydro-
chloric acid ought to afford an abundant supply of
chlorine rf we can remove its hydrogen and avoid

mon salt. ■"' """"-^ ''"'"' ^^'^*""» in com-

2l6

1 b

i i

Experimental Chemistry,

presenting at the same time a body that can combine
with all the chlorine. Experiment 132 proves to us
that a vionoxide like copper oxide will not suit our
purpose, since the metal can unite with all the chlorine
displaced by the oxygen, but if we use a peroxide of
a metal whose atom requires but two of chlorine to
satisfy it, the excess of chlorine should be obtained in
the free state. We shall, therefore, make the follow-
ing experiment vvith a body of the kind referred to
that we have already used, viz., manganese per-
oxide.

Experiment 137.— Heat a little manganese per-
oxide (MnOa) in a test-tube with strong hydrochloric
acid ; note that a greenish-yellow gas of suffocating
odour is evolved which rapidly bleaches moist litmus-
paper laid over the mouth of the tube. The gas is
chlorine, resulting from the following change—

Mn^vQ^a + 4H'Cr= Mn^d'a + 2QV + 2H,0.»

The manganese chloride (MnCla) remains in solu-
tion.

Experiment 138. — Mix a little manganese dioxide
with common salt and sulphuric acid in a test-tube
and note that chlorine is evolved. In this case HCl
is first formed by the action of sulphuric acid on
common salt, as in Experiment 127 ; the hydrochloric
acid then acts as above on the manganese dioxide.

Experiment 139.— Fit a Florence flask with a
delivery tube bent twice at right angles, as shown

• According to Dumas, MnCI, is first formed and then de-
composed by heat into free chlorine and manganese dichloride.

Experimoits with Chlorine. 217

in fig. 78. Introduce into the flask about 20 grams
of MnO.2 in lumps, and 100 c.cs. <^i crude but strong
hydrochloric acid solution, and apply a gentle heat.
Chlorine gas is so much
heavier than air' that it Fir.. 78.

can be easily (ollected
by displacement of air as
shown, the colour c^i the
gas enabling the experi-
mentalist to observe the
rate of filling. As each
jar fills,, remove it and at
once cover with a glass
plate slightly greased so
as to enclose the gas se-
curely. Fill several jars
in tliis manner, and make
the following additional
experiments, which, as
well as the generation of the gas, should be conducted
near to a good draught, as the inhalation of chlorine
is attended with danger, owing to the irritant action
of the gas on the delicate tissues of the lungs.

^ Experiment 140.— Plunge a burning wax taper into
a jar of the gas (see fig. 79). Note that while com-
bustion continues iis character alters, for the flame
is dull reddish, and much black smoke arises from
it, acid fumes bein^ freely produced. The latter

' As already stated (p. 215), it is 35 -5 heavier than hydrogen,
and, since air is 14-47 times heavier than hydrogen, it follows
that chlorine is almost 2\ times heavier than the same volume
of air.

2l8

Experimental Chemistry.

consist chiefly of HCl gas ; and the study of the
change leads to the conclusion that the combustion
in chlorme is due to the rapid chemical union of the
latter with the hydrogen of the wax (a compound of

hydrogen, carbon, and a little oxy-
gen), but the carbon does not unite
directly with chlorine, and therefore
most of it separates, and in the finely-
divided state of black smoke or soot.
The attraction of hydrogen for chlo-
rine must therefore be very great ;
but the following experiment illus-
trates this important point still more
clearly.

Experiment 141.— Moisten a strip
of blotting-paper with a few drops
of turpentine (C.oH.e), previously
warmed, and, holding the paper by
tongs, plunge it into a jar of chlo-
rine. Spontaneous combustion soon takes place and
torrents of black smoke and acid vapour are evolved
as before.

^ Experiment 142.-Take. a strong and well-filled '
^ jar of chlorine, and another of the same size full of
hydrogen gas. Bring them mouth to mouth, and
keeping them close together, invert several times so
as to mix thoroughly, then separate and cover with
glass plates. The mixture has a yellowish colour.
Remove the cover from one of the jars and apply a
flame ; an explosion results, and acid fumes of HQ
are produced. Bring the second jar, which should
be very securely closed bv a wPiL^r^oo.^ .

Synthesis of Hydroc/Uonc A cid. 2 \ 9

glass plate, into diffused daylight, but not into direct
sunlight.' Note that the yellow colour slowly dis-
appears, and when the contents have become quite'
colourless, carry the jar to (he mercury trough, bring
the mputh under the mercury, then remove the plate
and note that the gas has not changed in volume, as
gas does not escape, neither does mercui-v enter to
any extent. Now pass up a few drops of water by
means of a curved pipette, and note that the mercury
now rises in the tube and will completely fill it if the
original gases were pure and mixed in equal volumes
We have thus effected the synthesis of hydrochloric
acid referred to under Experiment 136, and equal
volumes have united without change of bulk, and the
fact of their union is proved by the solution of the
product in a small quantity of water, by which a mere
mixture of hydrogen and chlorine would be very
slightly affected. Synthesis therefore completely con-
firms the conclusion drawn from the analytical data.
In these cases

H + CI = HCl.

Experiment 143.-Plunge a small piece of dry
phosphorus into a jar of CI, using the long spoon

_ 'If the tube were exposed to direct sunlight, almost
instant combination of CI and H would have taken pice with
exr^osion. Small and thin glass bulbs are sold ready fdled
with the mixture of gases, and when exposed to direct sunlight
(or to the light emitted by burning magnesium, which is also
rich in chemically active violet and ultra-violet rays) the bulb is
sha teied to fragments, owing to the sudden expansion of the
contents ].y the heat evolved on the combination < of rh. ._

' 1

^^i.

220

Experiiuental Cheviistry.

for the purpose. The phosphorur. soon takes fire
, in the gas, and produces a mixture of chlorides of
phosphorus, PCI3 and PCI.,.

Cl^ can also be made to unite with sulphur, though
heat IS necessary, but it does not directly combine
with either oxygen or carbon, though compounds
with these elements can be obtained by indirect
means. ^

Experiment 144. -Powder some metallic antimony
very finely, and shake the powder into a jar of CI
As the particles of metal fall throu-h the gas they
burn, evolving much light and producing a most
irritating vapour of antimony trichloride—

Sb'" + 3CI' =

Sb'"Cr,

Chlorine acts upon arsenic with equal energy and
when aided by heat, on all the true metils also,'
forming therewith chlorides, in which it acts as a
smgle-link or monad element.

Experiment 145.~-Write across the printed matter
on a piece of newspaper a word or two in black writing
ink, and plunge the paper into \ jar of CI. After a
short time the writing ink, whose colour is due to
gallo-tannate of iron, will be bleached, while the
printing ink is unaffected, as the colouring matter
of the latter is finely-divided solid carbon, which
IS not attacked by chlorine. Chlorine is therefore
not an universal bleaching agent.

Experiment 146. -Remove a jar of dry gas to the
pneumatic trough, and, having allowed some water
to enter, close the mouth with the hand and shake
up the gas and water ; the hand is drawn in. nrr.vJn.

Chlorine Water. - 23,

that absorption has taken place, and on renmving the
hand under water the hitter ri.es in tl,e jar-there-
fore CI IS moderately sohihle in water, i cc of
water at 15- diss6lves 2-368 ccs. of CI fras. 'surh
a saturated solution of CI in water forms the Z,-pu,r
CA/on of the British Phannacopa-ia, and is easily
obtained by passing chlorine gas evolved from hydro-
chloric acid and manganese peroxide through a little
water in a wash-bottle (as in ng. 75), and then through
distilled water, until gas ceases to be absorbed. A
hquid IS thus obtained which rapidly bleaches indigo
solution, writing ink, &c., and possesses the character-
istic odour of the gas. If this solution be cooled by
surrounding the bottle that contains it with melting
ice, fine white crystals slowly separate which, when
drained froni the liquid in which they are formed
and analysed, are found to consist of Cl'sH O
Very slight rise of temperature suffices to decoinpose
this body into chlorine gas and water. Faraday first
succeeded m obtaining liquid chlorine by sealing up
some of these crystals in a strong glass tube anS
melting the solid, when two layers of liquid were
obtained, the lower and heavier consisting of liquefied
chlorine, the lighter of a solution of chlorine in water
Experiment I47.-Take two to ^ tubes half full
of distilled water, add to on . few drops of the
solution of rhiorine, and to t.. other a similar quantity
of diluted hydrochloric acid. Kow add to each a little
silver nitrate solution and note that a similar white
precipitate is produced in each case. Repeat the ex
periment with fresh solutions, but add potassium

locliae instead nf <.iKro». „.v^^*.„ ^„j . ,

_. ...,,^^ xiitiatw aim note limt no

222

Expei'iniental Chemistry,

change follows its addition to the hydrochloric acid,
while a strong brownish yellow colour is developed in
the free chlorine solution, and a black precipitate if
the solutions are strong. This change is
due to the separation of iodine (see Ex-
periment 159), and serves at once to dis-
tinguish free chlorine from pure hydro-
chloric acid.

"Experiment 148.— Take a tube of the
form shown in fig. 80 and quite fill it with
solution of chlorine ; ' now expose it to
strong sunlight and observe that bubbles
of gas are evolved and collect in the top
of the tube, while the liquid gradually
loses its yellow colour. Note that the
liquid acquires a strong acid reaction. Since we have
only chlorine and water present, and a colourless gas
is separated, there is a strong presumption in favour
of the gas being oxygen liberated from the water by
the superior attraction of chlorine for hydrogen, and
in accordance with the equation —

2CI + H2O = 2HCI + O.

We have already found the acid ; we now test the
gas by filling up the little side tube with water, if it be
not already quite fulL then closing the mouth with a
finger and so inclining the tube as to oblige the gas
collected to pass into the small limb. Then have a
match ready with a glowing tip, remove the finger and

• In this experiment the chlorine solution could not be con-
fined in a tube over mercury, as the latter is quickly attacked
by free chlorine.

Bleaching Experiments.

223

test the gas, when the wood will be rekindled and the
presence of oxygen ascertained.

In the absence of light the same change can be
effected by passing a mixture of chlorine and steam
through a red-hot porcelain tube.'

The ease with which chlorine decomposes water
and sets free the oxygen leads us to e'nquire whether
water plays any part in the bleaching action of free
chlorine.

Experiment 149.-Take two perfectly dry stop-
pered bottles, warm them and fill each with chlorine
by displacement of air, but dry the gas before it
reaches the bottles by making it slowly bubble through
some strong oil of vitriol. Now place in each bottle
a strip of red flannel (madder-dyed) previously dried
thoroughly by heat, insert the stopper and expose the
flannel to the action of the chlorine for half an hour
If proper care was taken to exclude moisture, no
material bleaching effect will be observed. Now in-
troduce a few drops of water into one of the bottles
and the colour of the flannel will slowly fade while
the dyed stuff in the dry chlorine will retain its colour.
In this case, then, the bleaching effect of chlorine is
indirect, and due to the powerful action of the nascent
oxygen (see page 190, and note) derived from water •
and similar experiments have shown that in most cases
the presence of water is necessary, though we shall
meet later on with some exceptions to this rule.

» We infer from these H. >ts that chlorine does not tend to
unite with oxygen directly, and it is not known to do so ; never-
theless many oxygen compounds of the element are ohfnmaKU
oy mairect means (see lixperiments 151 ^/ seq.)

224

Experimental Oiemtstry.

Chlorine is used in enormous quantities as a
bleaching agent, but neither the free gas nor its
solution in water are now employed for the pur|)ose,
as It is more convenient in practice to liberate the
body from ' bleaching liriVe ' and analogous compounds
in contact with the materials to be bleached (see
Experiments 151 and 152).

Experiment 150.— Introduce a few drops of am-
monium sulphide— 2i yellow liciuid of very offensive
smell— into a bottle and gradually add chlorine
water to it with agitation. Note that the unpleasant
odour disappears, and the smell of chlorine is not
detected unless too much of the latter has been
added. In this case, then, the free chlorine acts as a
deodorant, and it is commonly used for removing un-
pleasant smells, for which purpose a small cjuantity is
generally sufficient. It is, moreover, believed to act
as a disinfectant, either by direct corrosion of disease-
particles or by its indirect oxidising action, though it
is improbable that it usually produces much effect
unless employed in large quantities. The most con-
venient source of chlorine for these purposes is
♦bleaching powder,' which affords the gas when a little
acid of any kind—vinegar, for example — is added to
it (see Experiment 152).

Experiment 161.— Instead of dissolving CI gas
in water, pass it into cold solution of potassium hy-
drate (KOH)'— the Liquor Potasses (B. P.) answers

' If NH^OH be substituted for KOH in the above experi-
ment, a very different change occurs, for a quantity of nitrogen
gas is obtained instead of a bleaching solution, thus -

4NH.OU + aCl - N + iNHf-i J. aU n

Experifnents with Hypochlorites. 225

well; when partially saturated with the gas, stop
the current. The solution so obtained is colourless,
and smells somewhat like ' bleaching lime.' A few
drops of any acid added to a portion causes the
evolution of chlorine, which is easily recognised by
its colour and odour.

The action of CI on KOH in the cold results in
the production of a mixture of potassium chloride
and hypochlorite in solution, thus —

2CI + 2 KOH =r KCl + KOCl + H,0

Potassium
chloride.

Potassium
hypochlorite.

If into this liquid a piece of madder-dyed wool be
stirred, the red colour is not destroyed, as the
alkaline hypochlorite does not bleach, but, on the
addition of a few drops of dilute hydrochloric or
other acid, the colour is discharged. In this case the
bleaching agent is chiefly chlorine, resulting from the
following reaction —

KOCl + 2HCI = KCI + 2CI + HA

Potassium hyp : jrite is therefore a convenient
^ source of chlorine for bleaching, deodorising, and
disinfecting purposes, but in all these cases acidulation
is necessary in order to obtain the bleaching or de-
odorising effect.

The solution of chlorinated soda (B.P.) is obtained
by passing CI gas through solution of sodium car-

This is, in fact, a good method for the preparation of nitrogen
gas, but the ammonia must always be present in excess, else
there is risk of forminc the damreroua chloridp n( nJir.uro,, ^e»-
under Experiment 125).

226

Experimental Chemistry,

bonate, when sodium hypochlorite and chloride are
formed, and carbon dioxide gas is evolved —

Na^COa + 2CI = NaCl + NaOCl + CO2.
Experiment 152. — If we line the interior of
a wide-mouthed bottle with moist slaked lime
(Ca"(OH) ,) and pass a slow current of CI gas mto
the vessel, the gas is absorbed and combmes with the
lime, forming the ' bleaching lune' or chlorinated lime ,
of the B.P., commonly called 'chloride of lime' » :—

Bleaching lime.

4CH-3Ca"(OH)'2 = cH^T^c^ciwr+liEo

Calcium

Calcium
chloride.

Calcium

hydrate. chloride. chlorhydrate.

On the large scale the slaked lime is spread in thin
layers on shelves in large chambers to which Cf gas is
admitted ; the latter is absorbed (just as in the bottle),
and ' bleachmg lime ' obtained as a dull white powder
with a feeble odour like chlorine and only partially
soluble in water, calcium hydrate separating and im-
purities in the lime used remaining undissolved. The
aqueous solution contains the two calcium salts above
named. Bleaching powder or its solution affords HOCl
and CI gas on treatment with any acid (as in the case of
KOCl), and is therefore a most convenient source of
those bodies for bleaching or deodorising purposes.

The three bleaching salts above referred to are
derived fron^i the acid named hypochlorous acid,
H'0"C1', which is best obtained by the action of
' Its empirical formula is Ca^Cl.O.H,, which requires ^9 per
cent^of chlorine. ^ The best samples rarely contain more than
l^'% percent., and aiwap contain mere or ics.s caiciuai chlorate.

Potassiu7tt Chlorate,

22J

its anhydride upon water. The anhydride is prepared
by passing dry chlorine gas over dry mercuric oxide,'
placed in a tube which is cooled. An orange yellow
gas results from the action of the CI on the oxide,
and this is the anhydride Cl.^0, which can be easily
liquefied by reducing the temperature to — io'» C.

4CI + 2HgO = Cl^O^^ + Hg^Cl^O

Hypochlof-ous
anhydride.

Mercury
oxychloride.

Tlie gas is very explosive, the heat of the hand
being often sufficient to decompose it into 2CI and
O ; it is therefore not a safe body for the junior
student to prepare, i c.c. of water dissolves 20 ccs.
of cthe gas, and forms solution of hypochlorous ax:id—

CljO + H2O = 2HOCL

The solution is a powerful bleaching agent

Experiment 153.— Instead of dissolving CI gas
in cold potassium hydrate, pass it into the boiling
solution until gas ceases to be absorbed, and allow
the liquid to cool. If the potash solution were
originally strong, colourless crystalline plates will
separate out even before the liquid is quite cold ; but
if these crystals do not separate on cooling, evaix)rate
the solution down to half its bulk and then cool ,
collect the crystals deposited on standing and throw
them on a suitable filter ; pour a small quantity of
cold water over them to wash away impurity, repeat
the washing if necessary, and then dry. This body,

» Prepared by precipitation. See Tart III:

228

Experimental Chemistry.

when pure, has a cool saline taste and is sparingly
soluble in cold water, though easily dissolved with the
aid of heat ; its name is potassium chlorate and its
formula KCIO3 or K'-O"— O"— O"— CI', the body
from which we have already prepared oxygen gas (see
Experiment 57). In its preparation »—

601 + 6K0H = KCIO3 + 5KCI + 3H,0

Potnssium
chlorate.

Potassium
chloride.

The KCl is a very soluble salt, and therefore
remains in solution, while the slightly soluble chlorate
crystallises out. When the latter is heated in a test-
tube it melts and gives off oxygen, which can be easily
recognised by its property of rekindling a match with
a glowing tip. Here —

KCIO3 = KCl + 3O.

The white residue in the tube consists of potassium
chlorid(, which is easily distinguished from the
chlorate by its solution affording a white precipitate of
silver chloride (AgCl) when tested with silver nitrate.
Potassium chlorate does not give a precipitate with

' Instead of pure caustic potash, as above, the B. P. directs
CI g,ns to be passed through a mixture of solution of potassium
carbonate (K.CO,) and slaked lime {Ca(OH),). In this case-

I3C1 + K,CO, + 6Ca(OH), = 2KCIO, + CaCO, + sCaCL

+ 6H,0.

The mixture is afterwards boiled, then filtered from excess of
slaked lime and the chalk (CaCO,) produced in the process,
concentrated by evaporation, and the chlorate crystallised out
from the solutioiL

Tests for a Chlorate. 229

sil /er nitrate, because silver chlorate is a very soluble
salt. • '

Experiment 154.— The ease with which the
chlorate parts with its oxygen renders it a very power-
ful oxidising agent ; hence, if a few grains are mixed
with a little powdered charcoal and heated on a knife
blade, explosive combustion ensues.

Experiment 165.— Pour five or six drops of strong
sulphuric acid into a test-tube and add a very small
crystal of the chlorate, and gently warm ; the mixture
becomes yellow, and a yellow gas is evolved which
explodes very easily ; hence a loud crackling noise
occurs on heating. The gas is a mixture of oxides of
chlorine, which decompose into their constituents
with explosive violence on gentle heating. This
effect is very characteristic of a chlorate, but in apply-
ing the test direct the mouth of the tube away from
the person.

Experiment 156.— Powder separately a gram or
so of potassium chlorate and of dry loaf sugar ; mix
the powders on paper with a glass rod, place the

> F-ee chloric acid (HCIO3) is obtained by adding to a
saturated solution of potassium chlorate a strong solution of
hydrofluosilicic acid (HjSiF,, see page 267) ; the potassium
unites with the latter, forming the sparingly soluble salt KjSiFg,
which is precipitated, while monobasic chloric acid remains in
solution —

2KCIO, + H,SiF, = 2HCIO, + IC.SiF«.
No anhydride of this acid is yet known. We are ac-
quainted with another body, chlorous acid (HCIO,), which
is intermediate between hypochlorous and chloric acids,
but, like the latter, it is not as yet of any practical importance.
The anhydride CljjO, is known.

230

Experimental Chemistry,

mixture on a metal plate and touch the powder with
a rod dipped in oil of vitriol; violent combustion en-
sues, the sugar (a compound of carbon, hydrogen, and
oxygen) burning in the available oxygen of the
chlorate.

Experimei t 157. — Dissolve some of the chlorate
in water, add a few drops of indigo solution, and then
some strong sulphuric acid. Note that the blue
colour is destroyed ; as might be anticipated, this
bleaching action is due to oxidation.

Experiment 168. — Again heat some potassium
chlorate in a tube of hard glass. The salt fuses as
before, and oxygen is given off ; but, if the heat be
steady throughout and not very strong, the contents
of the tube become solid, and the evolution of gas
ceases. On raising the temperature still higher, gas
is again evolved, and in larger quantity than before.

The check just observed occurs when only one-
third of the total oxygen has been driven off as gas,
and the residue is found to consist of two salts,
potassium chloride and potassium perchlorate— a
body which is very slightly soluble in cold water, and
which is therefore left behind to a great extent when
the cooled mass is digested with cold water. The
following equation represents the change —

2KClOa = KCl + KCIO4 + 2O

Poiassium
chloride.

Potassium
perchlorate.

The perchlorate is much less easily decomposed
than the chlorate, but ultimately yields up all its
oxygen like the chlorate. Hence, in ureuariiiff oxy.

Oxides and Acids of Chlorine, 2^ i

gen gas from potassium chlorate, the decomposition
takes place in two stages, though we commonly express
the change by means of a single equation.

When potassium perchlorate is heated with strong
sulphuric acid, an acid distillate is obtained which
Roscoe found to contain perchloric acid, HCIO,—
one of the most powerful oxidising agents known, as
mere contact with it suffices to kindle paper oi woodJ
No anhydride corresponding to perchloric acid has
been obtained.

Neither the acid nor its potassium salts are as
yet of any practical importance, but much interest
attaches to the former as the highest term of the
following series of chlorine acids-

Hydrochloric acid
Hypochlorous acid
Chlorous acid ,
Chloric acid ,

Perchloric acid .

Acids.

HCl

HCIO

HClOa

HCIO3

HCIO4

Anhydrides.

C1,0

Cl.Oa

C1A(?)
CI2O; (?)

All these acids contain but one atom of hydrogen
within the molecule replaceable by a metal, and are
therefore monobasic. They may be regarded as
successive oxides of hydrochloric acid (HCl), and
their formulae will be most easily remembered when
they are thus viewed. Moreover, the series of bodies
may be cited as remarkable illustrations of the Zavt
of Multiple Proportions,

" The perchlorate does not bleach indigo in presence of
SUipisunc aciu, and « ihus caaiiy diaUuguishcu from the chlorate.

232

Experimental Chemistiy.

CHAPTER XVL

EXPERIMENTS WITH IODINE.

Experiment 159.— Dissolve in water, in a test-
tube, a few crystals of the salt potassium iodide
(KI), and add a few drops of chlorine water to the
liquid. Note that a brown-red colour is immediately
produced, and black, heavy particles separate from
the liquid if the solutions are strong and sufficient
chlorine is added. When the particles have subsided,
pour off the coloured liquid, and drain it away as
completely as possible from the deposit. Now, with-
out drying, apply a gentle heat to the black substance ;
a violet-coloured vapour is produced, which condenses
on the cool upper part of the tube in black, shining
metallic-looking scales, the water present volatilising
and condensing at the same time. This metal-like
substance (or ' metalloid '), characterised by its easy
volatility and beautifully coloured vapour, is an ele-
ment, and is called

Iodine — F =127.

The compound with potassium used in this experiment
is easily decomposed by chlorine, as we have seen ;
the latter seizes the metal and forms potassium
chloride, while iodine is displaced, thus —

K I^ -h Cr = K Ci' + V.

Preparation of Iodine.

^l^

Experiment 160.— Potassium iodide and chloride
are obviously analogous bodies ; hence the method
already used for the separation of chlorine from its
metallic compounds (Experiment 137) might serve
for the separation of iodine from the metallic iodide.
Mix the latter, or its solution, with some manganese
peroxide (MnOj) in a test-tube, add a few drops of
strong sulphuric acid, and apply heat Violet vapours
of iodine are given off, and condense on the sides of
the tube as before ; the by-products manganese and
potassium sulphates are left —

2KI + MnOa + 2H,S04 = 2I + MnS04 +
K2SO4 -h 2H2O.

The reaction is therefore precisely analogous to that
in which chlorine is evolved by the action of MnOj
and H2SO4 on common salt.

Iodine is widely distributed throughout nature, but
in small quantities, and always in combination, though
chiefly with potassium, sodium, or magnesium, and
sometimes, though rarely, with silver. It is present
in many mineral waters, and in sea water ; ^ from
the latter the iodides are extracted by various sea-
weeds, and these, when collected, partially dried, and
burned, afford an ash which is termed 'kelp,' and
from this ash much of the iodine of commerce is
extracted. The process of extraction consists in di-
gesting the kelp with water, which dissolves out a
considerable number of soluble salts, including the
iodides (and bromides, see page 250) ; the solution

' It is also present in small quantity in 'Chih nitre '—sodium
nitrate — in cod-liver oil, sponge, &c.

234 Experimental CJumistry,

is filtered, evaporated, and the kss soluble salts
crystallised out and tlius separated from the very
soluble iodides. I'ho remaining licjuor is treated with
strong suli)huric acid, and some sul[)hur is then sepa-
rated and removed 'I1ie acid li()uid is next poured
into large stills or retorts, manganese dioxide added
and heat applied Iodine is separated from the
iodide as in the above experiment, and distils over ;
Fig. 8i *' ^* condensed in a number of

tubular receivers, from which it
is removed, and, when sufficiently
dry, is sent into commerce in a
somewhat crude condition. Free
iodine and some of its compounds
are largely employed in medicine,
but it is desirable that the crud€
element should be purified before
it is so used.

Experiment 161.— Place a few
grams of crude iodine in a cru-
cible, which is to be covered as
shown (fig. 8i) with a flask con-
taining cold water. A gentle heat
IS applied to the crucible, and after a few minutes
the flask IS removed ; then the small (juantity of iodine
deposited upon it, with a few whitish needle-shaped
crystals of ' iodide of cyanogen,' which usually accom-
pany It, must be scraped off; the flask is replaced
and gentle heat again applied. After some time large
crystalline plates of pure iodine will be found attached
to the bottom of the flask ; these are to be removed
and preserved Tf fh*» i/v^in^ ^^^r.A ;« ^.u- £__. •

Experiments with Iodine,

235

were pure, no residue should be IcP. in the crucible
at the end of the operation. This process is one of
sublimatwn—m which a solid is deposited from a state
of vapour.

The specific gravity of pure solid iodine is 4ot;
(water=i).

The element gives off vapour at ordinary tern-
peratures, and it becomes a li(juid when heated to
ri4° C. ; it boils at 200° C, and afTords its mag-
nificently coloured vapour in abundance, as wc have
already seen. The specific gravity of the va|)our is
125-9, but the atomic weight is slightly higher, or 127.
Experiment 162.— Add to some water in a test
tube a few fragments of solid iodine ; shake, and
allow to stand for some time. The water gradually
acquires a brownish yellow tint, but the proportion
ultimately dissolved is very smal', a$ nreful experi-
ments have shown that iodine r„H njres learly 6,000
time^ its weight of water at rnti's^ ter; perature for
solution.

Experiment 163.— Add some litmus to a pi»rtion
of the dissolved iodine ; little or no bleaching is
observed, unlike the rapid decoloration that takes
place with chlorine.

Experiment 164.— Rub a few pieces of common
starch with water in a mortar, and pour the mixture
into a capsule. Heat nearly to boiling, with constant
stirring, and when the mixture thickens and becomes
gelatinous remove the source of heat. Stir the ' made
starch' up with warm water until a thin 'mucilage'

"•" ^-' """ j-scricivc iiiis lor use. /Aod a few

drops of the mucilage to half a test-tube full of

236 Experimental Chemistry.

aqueous solution of iodine, and shake ; a beautiful
bl«e l,.,u.d ,s obtained, owing to the formation of an
Ill-defined compound of starch and iodine. This is
an excellent and most characteristic test for the free
element. Heat the contents of the test tube nearly
to boilmg, note that the colour disapfears, but, or,
cooling .t reappears. Therefore the starch test should
always be applied in cold liquids.

JExp3riment 165,-Add a drop or two of starch
mucilage to a solution of potassium iodide.' No
change whatever is observed ; therefore iodine in

NoTn*;! r?i '•'°" ^"^^ "" eive the reaction
Now add to the mixture a drop of chlorine water, or
of strong brownish-coloured nitric acid ; iodine is
instantly set free and the blue compound formed.

Experiment 168.-Again, put some pieces of
lodme into a test-tube with .some water ; we already
know that very little dissolves, even on long standing ;
but now throw m a few crystals of potassium iodide
and observe that on agitating the liquid it becomes of
a deep reddish-brown colour, and the solid iodine
disappears as the potassium iodide dissolves. The

10 .de solution han in plain water. In this case so-
ution IS probably due to the formation of a potassium
tri-iodide of the formula KI I2.

of the T'"^" '' !f'''" °^ "^'^ ^"^' '" "^^ preparation

spirit of wine is the solvent, the solubility of iodine
» A very dilute solution.

Experiments with Iodine,

237

Fig. 8».

in alcohol also being increased by the presence of
potassium iodide.

Experiment 167.— Add a few drops of chloroform
to a simple aqueous solution of iodine, and shake.
The chloroform subsides on standing, and has a fine
purplish colour, as it carries with it the iodine, which is
very soluble in it, and is thus easily removed from the
water. lodme is also soluble with ease
in ether and in carbon disulpiiide.

Iodine does not burn in, neither
does it directly combine with, free
oxygen ; but it readily unites with
many metals and non-metals.

Experiment 168.— Rub a frag-
ment of iodine with some mercury
in a mortar ; a reddish powder is first
produced, which becomes green if a
little more mercury be added and
the trituration be continued for a
sufficient time. * The resulting com-
pound is 'green iodide of mercury'
— Hg"2l'2 — thus formed by direct
union of the elements.

Experiment 169.— Take a large .
and wide test-tube— about 10 ccs.
long by 3 CCS. diameter; introduce a few frag-
ments of iodine, and support the tube in a convenient
holder. Apply heat to the tube so as to convert the
iodine into vapour, and when the latter half fills the

' The addition of a few drops of alcohol hastens the process

Dy uissuiViiig MJin-^ ui Ulc UXItiic utiu mUa iciCutiaiiii^ Cficuiiw&i

action, as in Experiment 6, I'urt I.

eiG. 83.

23 8 Experimental Chemistry,

tube plunge into the vapour a very small piece of

(fi« E7 Tr 'r'^r' ^" ^'^ ^^^-g^ating spoon
(ng. «2). 1 lie phosphorus takes fire in the iodine

vapour and burns for some time ;
if the phosphorus be in excess,'
the colour of the iodine vapour
disappears, owing to complete
combination of the latter with
the phosphorus, an iodide of the
latter body being formed— thus,
P + 3I = PI3. If, when the
tube and its contents have cooled
down, a few drops of cold water
'are allowed to fall upon the dark-
coloured body left in the tube,
a fuming gas that reddens blue
litmus-paper will be given off-
<his gas proves on examination
r. , , . . , to be a compound analogous to
hydrochloric acid, and is termed hydriodic acid--HI-
the only known compound of the two elements. We
shall now repeat the exi)eriment in such a way as to
afford a considerable supply of this gas.

HYDRIODIC Acid = HI. , Vol mig/.s 6376 cgrs.
Molecular weight = 1 28.

Experiment 170.-Fit up a llask as shown, fig.

83. Remove the cork and tubes and introduce into

two grams of red or ^amorphous ' phosphorus-not

th. ordmary waxy variety, as its use in .,uan,ity is

--.- _,. „^,„ ,^ grains oi puwuered

Preparation of Hydriodic A cid. 2 39

iodine A very little heat serves to determine the
union of the two bodies, and a nearly black mass,
consisting chiefly of phosphorus tri-iodide, is formed,
as in the last experiment. Insert the cork and
support the flask as shown ; then close the stopcock
of the funnel and half fill the latter with water.
Now turn the stopcock so as to allow the water to
fall drop by drop on the iodide in the flask. As
each drop of water falls, a colourless and heavy gas
is evolved which can be easily collected by passing
the straight portion of the delivery tube into a dry
jar ; the air is displaced and a jar full of the dense
gas obtained. In this way several jars are to be
filled and then covered with glass plates. The hy-
driodic acid gas thus obtained results from the
following reaction —

Phosphorus
tri-iodide.

+ sHaO = 3HI + H3PO,

Hydriodic Phosphorous
acid. acid.

The phosphorous acid remains behind in the flask.
When sufficient gas has been, obtained, stop the evolu-
tion by turning the stopcock so as to prevent the
entrance of more water until a further supply of gas
is required. Now turn to the jars of gas.

Experiment 171.— Note that it is colourless, but
on removing the plate from a jar it fumes in air ; it
has an irritating smell and acid reaction to litmus -
paper. Pour some chlorine gas from a lube in which
it is generated (by the action of asi acid on a little
bleaching powder) into the bottle of hydriodic aad
maturity the bcauuful vioiet vapour of ire^

240 Experimental Chemistry,

iodine appears, thus proving the presence of that
element in the gas. In this reaction—

CI + HI = HCl + I.

Experiment 172.— Take a large beaker or a turn-
bier and drop a little strong and brown-coloured
nitric acid into it Then pour from a considerable
height hydriodic acid gas from a jar into the tumbler,
and note that free iodine quickly appears in the latter!
We thus prove that the gas is decomposed by the
powerful oxidising agent nitric acid, iodine being
liberated ; and we also prove that hydriodic acid is
a very heavy gas, since it can be easily poured, like
a liquid, through ^air. Its specific gravity is 6376
(H = i), I vol weighing 6376 cgrs. Its molecular
weight is 63 76 x 2 = 12752, and its formula HI.
It is nearly 4-5 times heavier than air.

Experiment 173.— Remove the plate from another
jar and immediately bring its mouth under the surface
of some water. The latter rapidly rises, proving that
HI is very soluble in water.

Experiment 174.— .V, strong solution of HI gas in
water is used in medicine to a small extent, and it is
easily prepared in the following way. Take a clean
jar, introduce some water into it, and allow the
delivery lube of the flask (fig. 83) to approach the
surface of the water, but not to touch the latter. On
allowing water to fall slowly from the funnel on the
remaining phosphorus tri-iodide, more heavy hydriodic
acid gas is evolved, which then falls on the surface of
the water and is at once absorbed. If the delivery

tunc HinTV>H xynAt^r i\\et etirAir>A n.C ^\s.st .js.~*-s- -i-_ ^' . ^

Salts of Hydriodic Acid,

241

would take place so rapidly that the solution would
rush back into the flask. A liquid can be obtained
containing 57 per cent, of hydriodic acid, whose spe-
cific gravity is 1*9, or almost double that of water.
The aqueous solution and the gas are easily decom-
posed when exposed to air and light, iodine being
liberated and water formed—

2HI + O = H2O + 2L

The iodine is not deposited from the aqueous acic'
unless decomposition has proceeded very far, but ib
dissolved by the acid, in which the element is very
freely soluble.

£zperi]r.ent 175. — Pour into a capsule some of
the dilute solution of hydriodic acid prepared in the
last experiment, and just neutralise with solution of
caustic potash ; then evaporate the solution until a
crust begins to form on the surface of the liquid, and
allow to cool. Small cubic crystals separate out which
are identical with the potassium iodide employed in
Experiment 159. The following change takes place
on neutralising the hydriodic acid with the alkali —

HI + KOH = KI + H2O.

This is the easiest mode of preparing potassium iodide
and many other iodides (Le., by saturating the acid
with the hydrate, oxide, or the carbonate of the
metal or other basic radicle), but much of the com-
mercial potassium iodide is prepared by the method
employed in Experiment 1J81.

• We have already seen that potassium iodide and
diluride are analogous bodies, and can aiford the

242

Experimental Chemistry.

non-metallic radicle by similar treatment. Now we
know from Experiments 126, 127 that a chloride affords
hydrochloric acid v/hen treated with oil of vitriol ; we
have therefore to ascer^^<in whether or not an iodide
will afford hydriodic acid by similar treatment.

Experiment 176.— .\dd a few crystals of potassium
iodide to a small quantity of strong sulphuric acid
contained in a test-- ne, and warm. Instead of the
colourless hydriodic .cid gas we should expect to see
evolved, violet vapours of iodine are given off, while
a yellow body that can be idei .Mfied as sulphur
separates in the tube, and a suffocating smell is
perceived (sulphur dioxide), or an odour of rotten
eggs is developed (sulphuietted hydrogen). The
sulphur and its compounds separated ir this rerHtion
are all produci « of deoxidation of sulphuric acid, and
the most prt>b.ab]e cause of this is hyd iodic add,
which, as we uready k?iow, puts easily with itf.
hydrogen, and tht latti- then available forms water
with more or less of the oxvge-. of the sulphuric acid,
and iodine is set free. Here ,, though hydriodic acid
is doubtless Ibrmed according to the equation

KI + H2SO4 « HI + KHSO,,

H is inirnediately de.^tfoyed in the way just indicated ;
but the ietailed exami?\ation of the reaction must be
reserved ui til w, study oil of vitriol.

If this view be correct, we ought to get hydriodic
acid gas alone on heating the iodide with a strong acid
not so readily reduced or deoxidised as sulphuric acid

Experiment 177.— Heat a few crystals of the
potassium iodide as befhr<*. wirh ct/ntt^ j.Lj^..j.l..^^

h^^

Tests for Iodides. 243

acid} and note that hydriodic gas is evolved and little
if any iodine is sei)arated.

Experiment 178— Add a few drops of silver nitrate
to a solution of potassium iodide, and note that a pale
yellow precipitate of silver iodide is formed—
AgNOg + KI = Agl + KNO3.

The precipitate is insoluble in dilute nitric acid, and
IS very slightly soluble in anmionia solution.
^ •Experiment 179.--Add to some disscaed potas-
smrn jodidea few drops of lead nitrate solution. Note
tha: a fine bright yellmv precipitate of lead iodide
IS ai once obtained —

2K'r 4- Pb" (NO3)', ^ Pb"I, + ,KN03.

This precipitate is somewhat soluble in boiling water

and separates out on cooling in fine golden spangles. '

experiment 180.- To another portion of the

iodide solution add mercuric chloride (Hg^Cl^) or

*corro.sive sublimate.' By the addition of the first

drop, a precipitate, varying in tint from salmon colour

to bright scarlet, is obtained, but this dissolves on

shaking the liquid. On continuing the addition of

the mercury solution, a point is reached at which a

scarlet precipitate is obtained which does not dissolve

on agitation ; this is scarlet mercuric iodide—

Hg"Cl, + 2KT = HgIa + 2Ka
This scarlet iodide is easily soluble in excess of
potassium iodide, producing a col'ourless solution, as we
have seen ; the latter contains a soluble and colourless
double iodide of mercury and Dotassinm Ua\

* See Phosphorus.

244

Experimental Chemistry.

A strongly alkaline solution of this double iodide
constitutes Nesslet^s test^ for ammonia (see page 21).

Hydriodic acid and iodides are thus easily dis-
tinguished by the reactions we have learned in the
course of these exper'ments.

Experiment 181. — Warm some caustic potash
solution in a test-tube, and add iodine, in small
portions at a time, until the liquid assumes a per-
manent yellowish colour. The element dissolves and
forms two salts— one potassium iodide^ KI, the other
potassium iodate., KIO3, thus —

61 + 6K0H = sKI + KIOj + 3H,0.

This reaction is precisely similar to that which occurs
when chlorine acts on a hot and strong solution of
caustic potash, as in Experiment 153, but the iodate
cannot be separated from the iodide^ quite as easily
as can the chlorate from the chloride.

Pour the solution into a small porcelain dish and
evaporate to complete dryness. Remove a small
portion of the dry residue, which is a mixture of the

' NessUr's test solution is thus made — Dissolve 5 grams of
potassium iodide in a very small quantity of hot water ; add to
the liquid a saturated solution of mercuric chloride until the red
iodide just ceases to redissolve. Now add 12 grams of caustic
potash, previously dissolved in a little water ; mix and make up
the total volume to 100 cubic centimeters .vith distilled water ;
finally add a few drops more of the mercuric chloride solution,
allow to stand, and draw ofT the clear liquid for use ; but it must
not be filtered through paper. For the action of the test see
under Mercury Salts, Part III. p. 104.

« The separation is best effected by evaporating the solution

to comolete drvness and dicestincr the residue with stromr alco.
. . .. .. — J,

hul, which dissolves the iodide but not the iodate.

Preparation of Potassium Iodide. 245

^vo iodine salts ; dissolve in some water in a test-
tube, add a drop of starch mucilage and then some
dilute acetic acid. Note that a blue colour is quickly
developed after the addition of the acid, proving that
lodme has been set free. In this case the acetic acid
displaces hydriodic acid from the iodide, and iodic
acid from the iodate, and the two acids thus liberated
at once react, producing free iodine and water
thus — *

HI03 + sHI = 6I-}-3 HjO.
Now return to the dry residue of evaporation ;
powder It m the dish and mix with one-fourth its
bulk of powdered charcoal. Heat the mixture until
It is seen to melt, before which it glows for a short
time, owing to the combustion of the charcoal or
carbon m the oxygen of the iodate, carbon dioxide
gas being formed and evolved, while the iodate is
reduced to potassium iodide—

2KIO3 + 3C = 2KI + 3C0^
Then allow the mass to cool, add some hot water
and filter from residual charcoal. The solution now
contains only potassium iodide (which can be crystal-
lised out), for on adding starch and acetic acid no
olue colour is produced.

Most of the potassium iodide of commerce is
prepared by the process just followed, and samples
of the iodide can be tested for iodate by the method
mdicated.

Potassium iodate is sometimes used as a test foi sul-

Dhuroiis ac'd ''«'*» fKnf k^^.a : .r^ s _ •

* " ''^'" "' '■""■- '■^-^j) i" ucciiv, rtuu uluer acids :

the iodate used for this purpose may be separated from

246 Experimental Chemistry.

iodide as stated, or, better still, may be sperially pre-

Tn H ,7 .":^ /""o^ing instructive method directed
m tlie Br tish Pharmacopteia

Experiment 188.- Heat together in a fla.k two or
three grams of powdered iodine «ith an oiual wei-ht
of potassium chlorate and ab„ut .0 ccs. of wa'ier
acdulated with 5 or 6 drops of strong nitric acid.
Lhlonne gas is evolved, and the mixture is diffested
untd ,he colour of the iodine ^n- ■' Hisap,,ears ;
then bo>l for a minute or two , ,( 'Jj „„j'

mto a capsule, and evaporate to dryness at a gentle
heat 1 he residue consists w!,;,lly of potassium iodate,
the chlorine and the nitric acid having almost coml
pletely disappeared.

This amounts to p replacement of chlorine in
potassiu.n chlorate by iodine, thus—

KCIO3 -; i = KIO, + CL

The small anaount f f nitric acid used facilitates this
replacement by libeniting small successive quantities

This decomposition is remarkable, because it
proves that chlorine is displaced by iodine from its
^«<//«</ compound (he chlorute, whereas we already
know that chlorine easily displaces iodine from the
umxidtse^ compound KI. The order of • affinity ' of
chlorine and iodine is theretuie here detemiin^d by
he presence or absence of oxygf : aim this is ound
to be generally true.

Iodine is converted into iodic arid wh-n h„ii»H
m a dask with str. iig nittK acd, and colo ..les^

Constitution of Iodic A ctd, 247

crystals of H IO3 are obtained on evaporation. WTien
these crystals arc heated for some time to 170'' C
they are decomposed into water and iodine pentoxide
(IgOj) or iodic anhydride, thus—

2H1O3 = r^Oft" + h 1.

The anhydride, when further heat, d to the tern-
perature of boiling olive' oil, is resolved into iodine
and oxygea

Although the formula of iodic anhydride is pre-
cisely similar to that of nitric anhydride (Nv.^O",), it
IS not necessary to assume that iodine is a five-link' or
pentad element like nitrogen, or that it is more than
a monad or uni-link body, as the constitution of the
iodic anhydride and acid can be thus explained on the
latter sui)position —

Oxide, r— O"— O"— O'— O"— O''— I'.
Acid, H'—C'—O"— O"-— I'.

The salts of a still higher acid are known, viz.
penodic acid-HI04-the analogue of perchloric

aa. J. «afle * Co'0. ^eto ebucatianal iBRorkfl

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most fmmrtant of the older fomw of English, with the way hi wJi'id wordS
S« °°rdr*1' ?"^^!i**' *l'° elements ^f which modern%:nS^^
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English Grammar

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iTtZtnT'^ '"'.'^ '^ "Ir"* "^S?- 'Iho work contains ample Z^c^aS
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The Shorter English Grammar.

Islntended for learners wfio have but a limited amount of time at their dis-
posal f..t Eng MhHtiHics; but the experience ..f s. lu.oM In which it lias
been tho otily KngliHl. ..ramtnar u«<d. has Hhown that, when well mastered
this work also m suincient for tho I/)ndon Matriculation Kxamiimtioii

THE BEST ELEMENTARY TEXT^BOOK OF THE VEAr!

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Mr. Reld, H. S MoHter hej^rtily rctK)inincrHlH the work a„d onlor..! T '

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Hamblin Smith's Arithmetic.

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Authorized fer use In the Scboole^Ontario
The Epoch Primer of English History.

By Rbv. M. CREiainoM, H. A., Lato Follow and Tutor of MoVton iktlUtm,

Oxford.
Sixth Edition. - >„ • • P rtca. 80 Cents.

Most thorough. ABWRDKKH JoirHKAL.

Thb volunio, token with the eight small volumw containlnir tho m-
oounta of the dMroreiifc epochs, prosontii what may be rcganlcrt m the most
thorough course of cicuicntary KngliHh History ever puhliahod.

What was needed. ~"^' torokto Da.it Gu>ih.

IlisjuststtchamanualM is needed by public school pupibwhoare

going up for a High School course.

We are uainir thiv IlistArv in ruir o^^nu^n* »,*a an.,^^ '

We are using this History in our fJonvent and Sepftrato Hdxook in Liud'.

Very concise. Hamilton Tisibs.

A very concise little book that should he used In the Schools, in its
pages will be found incidents of Knjjilsh HUt.;ry fit)ni A. D. 43 to 1870, In-
teresting alike to young and okl.

A mvorlte. Londom Aovrrtisrk.

The iMjok will prore a favorite' with toachom preparing pupils for ?.he
entrance exauiiuations tc th« High Schools.

Vesy attractive. BRmsn Wmo, Kiwobt«)i».

This little book, of on« hundred and forty pages, presents history in a
very attractive shape.

Wisely orransred. ^"^ Cakada Prsssytrrsah.

The epochs chosen for the division of English History atti well marked
-nol nure artiflt lal niUt-Ktones, arljltmrily erected by the author, b:ir reai
natuml landntarka, consisting of groat and important events or remarkable
chaniret.

Interesting. Yarmoitii Trihcni, Nova Sootia.

With a iMsrfect freedom from all loowsncNs of stylo the Interest is so well
sustaltiod throughout the narrative that those whp comnience to road it
win find it difflcuU to leave oH with its p«nisal inwnnplcte.

Comprehensive. Litrrart World.

Tht; t iHctMal value of this historical outline Is that It gives the r«ad«,r a
eomprahcnsive view of the course of mentorabUi events and e|>iM:hi,

t0.

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ata.

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