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NATURAL ROCK ASPHALTS
AND BITUMENS
NATURAL ROCK ASPHALTS
AND BITUMENS
THEIR GEOLOGY, HISTORY, PROPERTIES
AND INDUSTRIAL APPLICATION
BY
ARTHUR DANBY
CHEMIST AND PUBLIC CONSULTANT ON rock ASPHALT AND BITUMEN
NEW YORK
D. WAN NO STRAND CO.
TWENTY-FIVE PARK PLACE
1913.

PREFACE
THE entire absence of a modern English work upon the
materials that will be considered in the following pages
is almost inexplicable. Beyond occasional articles in the
technical journals and the necessarily biased pamphlets
of the producer, manufacturer or seller, no English
literature having reference to these most valuable pro-
ducts is to be found until we go back for a space of nearly
twenty years, a period during which much advance has
been made in the production and the use of these articles,
fresh deposits have been uncovered and worked, many
fallacies have been exposed and extensive chemical
research has been made in them. This being so, it is
hoped that the appearance of this volume may be regarded
as opportune, particularly so since the past year (1912),
although not actually celebrated as such, was the bi-
centenary of the re-discovery of the use of rock asphalt
for constructional and waterproofing work.
As one who is daily in touch with the various materials
about to be mentioned, the writer is aware how much the
want of such a work is felt by those who, whilst they are
desirous of obtaining a deeper and clearer insight into
the production, properties, and uses of these articles,
find that such knowledge is inaccessible, owing to the lack
of any recent English work dealing with them. The idea
of the writer, therefore, is to fill this want in the following
pages, and, bearing in mind the difficulties that he him-
self has had to overcome, as well as the problems that
have been placed before him in his position as advisory
expert on these materials, it has been his endeavour to
keep all matters as clear and as lucid as possible. With
this ever in mind, unnecessary technicalities have been
rigidly avoided, tests have been kept as simple as possible,
vi PREFACE .
and if the matter which is dealt with in the introductory
remarks is kept in mind, there should be no indecision
at any time as to the particular material that may be
referred to in any particular place, a difficulty not entirely
overcome by some of the previous writers upon this sub-
ject, though it must be understood that the terms
“ asphalt” and “bitumen’’ are used here in their
restricted commercial sense, and not as adopted in
geology.
It has been his endeavour also to adopt a strictly
impartial position in his remarks, recommending no
particular mine above another, no particular bitumen in
preference to another, unless practical experience has
clearly proved such a superiority. In any case, each
type can usually show some advantage over the others,
so that it rests finally with the prospective user to decide
upon what particularly desirable property he is requiring
in the material to be employed in the work at the time
under his control, and then to specify or to purchase
accordingly. The rock asphalt, for instance, that makes
the best wearing roadway is not, as will be seen in the
following pages, the most suitable for roofing purposes,
nor is a short fibred bitumen always the best to use in
the manufacture of bituminous materials that are to be
subject to any appreciable tension. In all cases it is a
matter of a particular property for a particular purpose,
and it is here that the services of an experienced inde-
pendent consultant in asphalt and bitumen are of
inestimable advantage.
It is the hope of the writer that the reader, having
arrived at the end of this work, will be able to acknowledge
that he has gained information of profit and advantage
to him in his work or profession. No trouble has been
spared by the writer to obtain suitable information and
material for this work with which to complement his own
personal knowledge, and the various foreign works which
bear thereon have been carefully studied for that purpose.
The matter having reference to the ancient uses and
writings regarding these materials, too, has been fur-
nished to him by a scholar specialising in ancient
PREFACE vii
lore, to whom the writer is also greatly indebted for much
of the general information which has also been embodied
in the chapter bearing thereon. A further visit was paid
by the writer to the Continent during the past year, in
order that the matter and descriptions given in the
chapter bearing on the Continental asphalt mines should
be as accurate as possible.
It will be noticed that at times the subject-matter in
the following pages is at variance with that of other
writers, particularly American ones, on certain more or
less technical points, but it should ever be borne in mind
that each country has its own peculiar conditions, par-
ticularly as regards climate, with the result that what is
a success in the one may turn out to be an absolute
failure in another. An article in a recent issue of an
American technical journal bears independent witness of
this, as does also M. Barabant’s reference to certain
London roads inspected by him that had been made up
with a rock asphalt which had given anything but satis-
factory results when used in his own city, Paris. It is
owing to this fact that the writer has preferred to refer
principally to the European writers on this subject as his
authorities, instead of American ones, except, of course,
where their intimate knowledge of local material enables
the latter to speak from first-hand acquaintanceship.
The writer takes this opportunity of acknowledging
his intense appreciation of the unstinted permission
afforded him by Professor Clifford Richardson, of New
York, to make reference to the contents of his well-known
work, “The Modern Asphalt Pavement” in those parts of
this present volume devoted to American bitumens.
Nor can he conclude without expressing his deep sense
of gratitude to Mr. H. W. Brant, of Newcastle-on-
Tyne, by whom the matter dealing with the practical
application of rock asphalt mastic has been almost
entirely written. As the outcome of many years of close
attention to the practical side of this industry, his remarks
can hardly be otherwise than of the greatest value to the
practical user of this material.
In his position as an entirely independent consulting
viii PREFACE
expert upon these materials, the writer will be pleased
at all times to hear of any problems regarding their use
which may be difficult of being surmounted by ordinary
methods and to advise thereon. Should any of the
matter found in the following pages appear to lay itself
open to criticism—for, as has been mentioned above, it is
at variance in certain portions with the statements of
other writers—he will be glad to explain the reasons for
his decisions in greater detail if the debatable ones are
pointed out to him. -
ARTHUR DANBY.
VICTORIA STREET,
BELFAST.
1913.
CHAP,
I.
III.
IV.
IXIII ©
XIV.
XV.
CONTENTS
INTRODUCTORY : NOMEN CLATURE AND DEFINITIONS
GEOILOGY OF BITUMEN AND ROCK ASPHALT e
APPEARANCE AND PEIYSICAL STRUCTURE . tº
HISTORY AND ANCIENT USE . e te ©
MODERN EXPLOITATION OF ROCK ASPEIALT . tº
SOURCES OF ROCK ASPEIALT AND BITUMEN º
SOURCES OF ROCK ASPHALT AND BITUMEN (contá.)
AMERICAN DEPOSITS OF BITUMEN . tº e
AMERICAN DEPOSITS OF BITUMEN (contal.) . tº
IEXTRACTION AND PREPARATION OF ROCK ASPHALT
TESTS AND ANALYSES tº gº cº tº ©
PHYSICAL PROPERTIES OF ROCK ASPHALT . c
THE CARRYING OUT OF ROCK ASPHALT WORK ge
TELE CARRYING OUT OF ROCK ASPEIALT MASTIC
WORK tº ( ) ſº & º g º
MACADAM ROADS g © © ge º sº
OTHER USES OF BITUMEN e e º Q
N.R.A. b
PAGE
1
11
2I
34
47
63
76
92
106
120
134
158
170
180
202
218
NATURAL ROCK ASPHALTS
AND BITUMENS
INTRODUCTORY
BEFORE commencing upon the subject proper, it is
desirable, in fact it is most necessary, that a definite
understanding shall be arrived at, as to the special
material that will be spoken of when any particular
word is employed.
To the average man in the street, the term “asphalt ’’
has but a very vague yet withal an extremely elastic
meaning. Under that heading he would place almost
any jet black or dark brown amorphous substance which,
although hard and brittle at the ordinary temperature,
becomes soft and plastic when heated, until it finally
fuses and melts into a liquid, the viscosity of which is
imore or less dependent upon the degree of heat that is
employed. In this condition it is capable of ignition
when it burns with a very smoky luminous flame, at the
Same time giving off a definite smell. To him, too, the
terms “pitch,” “ asphalt,” and “bitumen º’ are merely
Synonyms—and here, as we shall see later, he is to a
certain extent correct—and they are therefore used at
will and with delicious freedom to describe any substance
that may have the foregoing characteristics. Even the
daily papers are not above reproach in this particular
matter, for it is no uncommon thing to see mention made
in them of “roads made of asphalt and other coal tar
products,” whilst the definition of the word “bitumen. ”
as found in a recently published dictionary is “a pitchy,
ir flammable substance,” a definition palpably incorrect,
N.R.A. JB
2 NATURAL ROCK ASPHALTS
since it fails to embrace the whole genus (including the
liquid types), and at the same time it is extremely mis-
leading, since it omits to mention that the inflammability
is only existent under certain conditions such as when
the flash point of the material has been reached, a point
which is usually only attained after the material is in a
fused state.
In another dictionary—“The Conciselºnglish Dictionary,
Literary, Scientific and Technical,” Dr. Annandale, 1910
—“ asphalt ’’ is defined as “the most common variety
of bitumen, a black or brown substance which melts readily
and has a strong, pitchy odor,” whilst “bitumen. ” itself
is stated to be the name of “a mineral substance of a
resinous nature and highly inflammable, appearing in a
variety of forms . . . asphalt being solid.” Here again
the definitions are not sufficiently wide. “Asphalt ’’ is
recognised as being merely the solid variety of bitumen,
but against this it must be remembered that all solid
bitumens do not melt readily, nor do they ever resemble
pitch in smell. The strength of the odour given off by
bitumen varies with the different types, some being
almost odourless, but in any case the smell of bitumen,
considered by some people as being healthy and pleasing,
but by others as being offensive, is essentially peculiar
to itself, so much so that, as will be seen later, it is some-
times possible to detect an artificial or an adulterated
asphalt merely by heating a sample of it and noticing
the smell that is given off. Again, mention is made in .
this same work of the verb “to bituminise—to convert
(as wood) into a bituminous body.” In his previous
experience, the present writer has never met with this
word used in such a way, for to use it in the manner
mentioned would be to confuse pitch with bitumen;
since the latter is never made by the conversion of wood.
The articles on “asphalt ’’ and “bitumen º’ which are
to be found in the latest (eleventh) edition of the
“Encyclopædia Britannica,” too, are very unsatisfac-
tory. Referring to the former, we are told that this
name was given by the Greeks—some of whose classical
writers also employed the term “pissasphaltum ” (pissa—-
INTRODUCTORY 3
pitch)—to the solid or semi-solid kinds of bitumen, but
practically the entire article is written around a very
incomplete description of the bitumen “lake ’’ found in
the Island of Trinidad. As to “bitumen,” the writer of
this particular article informs us that this word was used
by the Romans to describe the various descriptions of the
natural hydrocarbons, and that “in its widest sense, it
embraces the whole range of these substances, including
natural gas, the more or less liquid descriptions of
petroleum and the solid forms of asphalt, albertite,
gilsonite, or uintahite, elaterite, Ozokerite and hatchet-
tite. To distinguish bitumen intermediate in consistency
between asphalt and the more liquid kinds of crude
petroleum, the term maltha is frequently employed.
The bitumens of chief commercial importance may be
grouped under the three headings of natural gas, petro-
leum, and asphalt.” More definite and detailed exposi-
tions of each of these materials might be reasonably
expected from such an authoritative work as this is
supposed to be, instead of the meagre information actually
given and the vague “it is said " method adopted.
Yet we must not be too critical with those unversed in
the commercial difference between the three materials
which we are considering, when we find in that estimable
annual “Specification ” the following definition :-
“Mastic asphalt is a composition material made of Trini-
dad bitumen or coal tar pitch and quartz sand, crushed stone
or coke breeze with or without the addition of natural rock
asphalt. It is claimed that the best results are secured when
some of the natural rock asphalt is used in the mixture and
Trinidad bitumen added.”
How many architects or Surveyors, specifying rock
asphalt mastic for use in a structure and finding such a
composition as the foregoing being used, would pass the
work as being up to the specification ? The italics are
the writer’s.
The confusion, therefore, seems to be getting general,
and it is becoming intensified by the haphazard use of
the names when entirely different materials are referred
to by each of them. Then, too, in a technical memorandum
B 2
4. NATURAL ROCK ASPHALTS
of the weights per cube foot of different materials
“ asphalt ’’ is given as 100 lbs., whilst that for “bitumen ‘’
is only 87 lbs., thus clearly showing that two distinct
articles are meant by these terms. This being so, it must
be made quite clear what is meant by each word. In the
trade circles themselves, as the foregoing extract shows,
this looseness of expression is fast becoming habitual,
thus rendering it more difficult each day that passes to
define an exact line of demarcation. In his book pub-
lished twenty years ago, Delano refers to the material
extracted from the Trinidad “lake ’’ as even then receiving
all the three terms, whilst to-day we hear of it as “pitch,”
the material obtained in Asia Minor as Syrian “asphalt,”
and that from Cuba as Mexican “bitumen,” although they
are all avowedly and for practical purposes the same
material, though in varying degrees of purity and of
geological formation. In fact, for the materials which
contain the Trinidad product, it is always claimed as a
strong point by the manufacturers that they contain no
“pitch.” Delano even went so far as to affirm that the
adjectival form of “bituminous ” had at the time he wrote
replaced the Saxon form of “pitchy,” though in making .
this statement he must have been considerably exagge-
rating. The question, however, comes as to how such
expressions shall be reconciled and how each class shall
be separated and defined.
Different writers have different ideas upon this point.
Some divide them in accordance with their physical
properties, others according to their chemical properties,
and yet others follow the different geological formation
of each.
Thus, according to M. Thenard, the term “bitumen. ”
applies only to liquids or solids which fuse at low tempera-
tures, give off a strong smell and burn very readily in their
liquid state, whether this state is natural or the result of
the application of heat, and which leave but little car-
bonaceous residue, which last, however, is always very
easily and readily reduced to an ash.
These conditions, though, do not exclude pitch, resin, and
other similar manufactured or vegetable products, so that it
INTRODUCTORY 5
is necessary to add to this definition that the bodies must
have a natural and mineral origin. Again, the difficultly
fusible “wetherilite ” of Canada, the infusible “walaite ”
found in Moravia, and the “wollongonite ” of New South
Wales could not be included in the above, although other
writers have admitted them to be bitumens.
By M. Gruner they are described under the term of
the “petrol series '' as distinct from the “carbon series.”
He defines them as solid, liquid, or gaseous hydro-
carbons which are rich in hydrogen, and he includes in
them marsh gas, petroleum, Ozokerite, maltha, and the
bituminous rocks, with jet as a kind of link between the
two series.
According to M. Descloizeaux, bitumens are liquid and
solid bodies with a badly defined composition, formed
usually of a mixture of various hydrocarbons in different
proportions. He divides them into naphtha or liquid
bitumen, maltha or viscous bitumen, asphalt or solid
bitumen.
M. Jagnaux affirms that petroleum is composed of
88 per cent. of carbon and 12 per cent. of hydrogen, and
that if into this composition be introduced oxygen as
replacing the hydrogen, a series of bitumens are formed
which are more and more viscous as the percentage of
oxygen is increased. This, however, does not take into
consideration the presence of sulphur and the absence of
Oxygen in various solid types.
In a chemical encyclopaedia published some time ago
under the direction of M. Fremy, “bitumen º’ is mentioned
as a rock, at times solid but sometimes viscous. To the
first is given the name of “ asphalt,” and to the latter that
of “pissasphalt,” which, however, is stated to be very
often merely a mixture of asphalt and petroleum.
Other writers are not satisfied with a division that is
merely dependent upon physical characteristics, but they
have studied the action of different solvents upon bitu-
mens. Thus M. Léon Malo considers solubility in ether,
turpentine, and carbon bisulphide as being essential for a
true bitumen, though this requirement has since been
found to be subject to certain reservations. Holde, too,
6 NATURAL ROCK ASPHALTS
understands by this name natural products which are
found either in a pure state or mixed with limestone,
sandstone, and the like, and which in a pure condition are
black and glossy, at the ordinary temperature are either
pasty and viscous or else hard and brittle, have a melting
point of not less than 35°C., and are easily soluble in
carbon bisulphide, oil of turpentine, and chloroform, but
only partially so in ether, petrol, and benzol, whilst they
are almost quite insoluble in alcohol.
The present writer has always steered clear of such
troubled waters by a rigid use of each term for such pro-
ducts as fulfil certain conditions, and for these only. As
this line will be held to in the following pages, it is given
here in full, especially so as, the limiting conditions being
extremely finite and never overlapping, it can with advan-
tage be adopted to replace the existing and present
prevailing looseness and confusion of terms. There will
be, we know, many who will deplore the somewhat
arbitrary manner in using words to define materials to
which the terms may not have been originally applied,
but to these we would merely reply that in this essentially
commercial age antiquity must give precedence to utility.
Because “ asphaltos '' is the Greek synonym of the Latin
“pia, tumens,” and because—to our present knowledge—
naturally impregnated stone was then unknown, are we
to continue to give the material referred to in this work
as “bitumen’’ both these names, whilst the impregnated
stone lacks a distinctive one of its own 2. As the word
“bitumen’’ is to be found with but little change in at
least four modern European languages as descriptive of
the pure material, thus—
English .. tº e tº e tº º bitumen
French . . © e tº º tº gº bitume
Italian . . tº e tº º tº tº bitume
Spanish . . , & © © tº tº º betwm.
it is proposed to continue to limit its use to that material
only, the more so as this use of the word is apparently
the custom on the Continent also.
The suggested manner of dividing for industrial pur-
INTRODUCTORY 7
poses the materials over the names at our disposal is as
follows:—
BITUMENS :—All such substances which are found in
nature and require no further treatment other than the
extraction of the mineral and vegetable impurities that
they may have mixed among them ; which are completely
soluble in carbon bisulphide, but only partially so in
ether, and almost completely insoluble in alcohol. Under
this heading are ranged the bitumens obtained from
Trinidad, Venezuela, Cuba, Mexico, etc., Barbadoan
“manjak,” glance pitch, grahamite, gilsonite, elaterite,
wurtzilite, Syrian asphalt, maltha, goudron minéral,
bergteer, the asphalt oils, and the viscous or solid bitumen
that is found impregnating rock asphalt. -
Also such substances which are derived from the dis-
tillation of any of the above or of the asphaltic petroleums.
PITCHES :—All such substances which are derived from
the destructive or fractional distillation of all other
natural organic bodies or from the distillation of vegetable
oils. This definition then includes the pitches obtained
from coal tar, wood tar, lignite (brown coal), stearin, wool
fat, cottonseed oil or the like, and the residues that are
left upon the distillation of animal or vegetable fats,
resins or balsams of any description.
ASPHALTs —All such substances that are impregnated
—as distinct from being merely mixed—with either
bitumen, pitch, or a mixture of the two. The impreg-
nation condition is necessary so as to clearly distinguish
such bodies from impure bitumen, by which, as has just
bedn mentioned, mixtures are designated. The minerals
usually forming the base of asphalts are limestone or
sandstone, though, in the artificial types, other pulverised
materials are often used. It would, indeed, be preferable
if only the naturally impregnated rock were alluded to
under this name, but certain terms such as “ British
asphalt.” which refer to essentially artificially formed
products, have now such a definite technical meaning,
that to exclude them from this heading would be at
least undesirable, as causing that very looseness of
expression and description that it is so necessary to avoid,
8 NATURAL ROCK ASPHALTS
even if such exclusion were not actually impossible. The
foregoing is, of course, contrary to Delano's statement,
wherein he defines asphalt as being “a natural product,
a bituminous limestone in which carbonate of lime and
pure mineral bitumen are most intimately combined by a
natural agency,” a description which in any case is too
narrow and limiting.
Where possible, however, it is preferable to define the
material that is made artificially from grit or crushed
stone, whether bonded together with pitch or bitumen,
as a “macadam,” qualifying this term with the adjectives
“tar ” or “bituminous ” as ‘the case may be. Even the
so-called “British asphalt ’’ should be regarded merely
as a “tar macadam ” in which the mineral portion has
been reduced to a granular state instead of being used in
the much coarser grades customarily employed.
But even these headings can be, and are, divided irſto
other sub-sections for the sake of clearness and in order
to define the physical state of the body in question.
Thus “bitumens ‘’ receive their sub-titles of “bitumbns
proper ‘’ for the solid types, and “ malthas' for the
viscous or semi-fluid types. “Pitches "... receive their
ordinary sub-headings of “pitches proper’ for the sqlid
types, and “tars ” for the liquid ones. “Asphalts,”
however, being necessarily solid by reason of their mineral
aggregate, are subdivided only as to whether they are of
natural or of artificial origin, the words “natural ” and
“artificial * being used to distinguish between the two.
This method of division will be found to differ radically
from that given by Professor Clifford Pichardson in his
work, “The Modern Asphalt Pavement,” as the present
writer cannot agree with certain of the conclusions º
are drawn by him in that book. The term “asphalt ’’
as used by him is unnecessarily general, and the term
“pyro-bitumen’’ is confusing to the lay mind. Doubtless
this difference of opinion arises from the fact that } the
“ asphalt roads " referred to in that book are princi §ally
those formed of material which would come under the
head of “bituminous macadam ” in the foregoing sum-
mary, owing to the fact that naturally impregnated Woºk.

INTRODUCTORY 9
as we know it here in Europe is but rarely to be met with
in the American geological formations, and even then the
type of the rock is often different, being usually crystalline
instead of sedimentary. The naturally impregnated
rock that is found there is very often a sandstone in which
the grains are merely held together with the bitumen
which only forms a film around each individual grain
without actually impregnating them as is the case with
Limestone. When the impregnated limestone rock is
used in that continent, it is usually imported from one
or other of the better-known mining companies in Europe,
who have their representatives and hold stocks over
there for that purpose. How different is the present
division from the American one is clearly seen when it
is pointed out that the latter includes as a “bitumen. ”
the paraffin oils which, as the practical man in this
cCºuntry is aware, give anything out satisfactory results
if substituted for proper bitumen in asphalt work. Again,
following the purely geological idea, “ asphalt ’’ is included
as a sub-division of “bitumen’’ and merely refers to the
natural bitumen as found in Trinidad, Venezuela, Cuba,
etc., whilst, although “bitumens '' and “pyro-bitumens'
are differentiated, it is nevertheless admitted that “there
is no sharp dividing line between them, as the one is
metamorphosed by time and exposure to varied environ-
ment into the other,” and that the “grahamites,” which
are acknowledged to be bitumens, rapidly shade into
pyro-bitumens. It had better here be mentioned that
the definition given of pyro-bitumens is “those substances
which upon destructive distillation give rise to products
which are similar to natural bitunnens.” As showing also
the difference between British and American nomencla-
ture, it may be pointed out that whereas in England—
and in Europe generally—the term “sheet asphalt ’’ is
givén to those roofing and dampcoursing felts which
consist of a woollen fibre saturated with a so-called coal
tar * asphalt,” it refers in America to rock asphalt mastic
and also to a bitumen-Sand composition when laid as a
pavement. &
The following definitions adopted by the American
IO NATURAL ROCK ASPHALTS
Society for Testing Materials are given here for purposes
of comparison.
“Bitwmens are mixtures of native or pyrogenous hydro-
carbons and their non-metallic derivatives, which may be
gases, liquids or solids, and which are soluble in carbon
bisulphide.
“Bituminous : containing bitumen or constituting a source
of bitumen.”
The summaries which are given by the different
European writers are also open to similar objections as
the American ones, but the subject opens up too vast, a
question to be adequately treated in a few lines, so that
the reader who would go more fully into it is therefore
referred to the works of the American and Continental
authors direct. |
All bituminous bodies, however, have the same quality
of consisting of a combination of carbon and hydrogen,
though in varying proportions. The liquid types are
usually free or almost free from oxygen, sulphur, arid
nitrogen, whilst the semi-fluid and solid varieties contain
more or less appreciable quantities of these latter. The
Smell of all of them is essentially “bituminous,” .
the colour varies from yellow to brown in the liquid formhs,
and from dark brown to black in the semi-liquid and solid
ones. They possess a sharp line of demarcation from
other organic matters to be found in nature which consist
of the same elements (coal, lignite, etc.) by their conduct
with various solvents. . The rather loose expression of
“artificial asphalt ’’ given to the distillation products of
these other organic matters has given rise to the ºpiº ls
though an erroneous one, that the natural types have been
formed in a similar way by a distillation process occa-
sioned by the intense heat of the earth. In the following
chapter it will be shown that this idea has but little
grounds upon which to be sustained.
CHAPTER I
GEOILOGY OF BITUMEN AND ROCK ASPHALT
TriB story of the geological formation of bitumen is
still receiving the attention of some of our greatest
geologists. The intricacy of such research is, however,
enormously increased by reason of the many and varied
types of this material that are to be found, which
range from a very thin liquid—Persian naphtha-to an
extremely brittle and hard solid–gilsonite, glance pitch,
etc.—and of its wide distribution in almost every part of
the globe and throughout the entire range of geological
strata from the Laurentian rocks to the most recent
members of the quaternary period.
The question has been hotly discussed as to whether
bitumen is not more or less intimately related to petroleum
and the mineral oils, if it is not actually an offshoot from
thèm. Professor Clifford Richardson, the well-known
Armerican expert upon bituminous matters, and to whose
writings on the subject reference has already been made,
lºgy affirms his belief that such is the case; and
this stand has also been taken by many other experts in
America, Germany, and France, i.e., those countries most
intërested in the production and use of the material.
Even Delano, who, in common with Malo, his invariable
authority, claims that bitumen is “only similar to itself,”
has to acknowledge this relationship.
In support of this hypothesis (for, like many other self-
evident truths, it does not lay itself open to a direct proof,
hence the controversy arising around it), it is pointed out
that it is often to be found in Europe, Asia, and America in
localities productive also of these oils, and that these oils,
upon distillation, leave a residue which closely approxi-
mates to, even when it is not actually identical with, natural

12 NATURAL ROCK ASPHALTS
bitumen ; hence the inclusion of their residues in this
present work under the heading of bitumen.
In the “Encyclopaedia Britannica” it is stated that
“although the gaseous and liquid forms of bitumen may
be regarded as having been formed in the strata in which
they are found, or as having been received into such strata
shortly after formation, the semi-solid and solid varieties
may be considered to have been produced by the oxidation
and evaporation of liquid petroleum escaping from the
underlying or better preserved strata into other strata or
into fissures where the atmospheric action and loss of the
more volatile constituents can take place. It should,
however, be stated that there is some difference of opinion
as to the precise manner of production of some of the solid
forms of bitumen.” This statement, however, fails, to
explain the formation of such types of solid bitumen in
which no oxygen is to be found, or of those deposits which
are totally isolated from any other deposit of a more
liquid bitumen from which it could have escaped in the
way suggested. º \
Another theory of its formation is based upon volcanic
action. As proving the possibility of such a surmise, it
is shown that most types of solid bitumen contain an
appreciable percentage of sulphur, a mineral usually
discharged during volcanic activity; that the asphalt
mines in Sicily and in Italy are not very distant #.
Mounts Etna and Vesuvius respectively; that the world-
renowned bitumen lake in the island of Trinidad is now
generally accepted as being contained in the crater of
an extinct mud volcano ; that at one of the oldest sources
of supply of bitumen still in existence, the Dead Sea in
Palestine, quantities of this material usually rise to the
surface of the water after the surrounding district has
been subject to volcanic disturbances. This last evidence
is, however, unsatisfactory, since it must be º
that semi-fluid bitumen oozes out of the nearby hot springs
which drain into the sea, so that the probability is that
the masses solidify below the surface of the water and
adhere to the sides, from which they are only released by
the earth tremors. The suggestion has been advanced by
GEOLOGY OF BITUMEN AND ROCK ASPHALT 18
some writers, including Diderot in his Encyclopaedia, that
the fire which rained down from heaven upon Sodom and
Gomorrah (Genesis xix. 24) consisted of burning bitumen
which was thrown out by some adjacent volcano, but
although the district is known to be more or less subject
to earthquake shocks, trace cannot be found of any
mention of any actual volcanic eruptions having taken
place there, so that this supposition has very slight grounds
upon which to be sustained. However, bitumen is to be
found throughout the world and in many places where
no sign of volcanic activity at the time of its formation
can be recognised, so that the volcanic theory cannot
hold good in every case. f
In a departmental report on “The Production, Tech-
nology and Uses of Petroleum and its Products,” issued
by the United States Government, Professor Peckham,
after supporting the theory of the relationship that exists
between petroleum and bitumen, concludes that “all
bitumens have, in their present condition, originally been
derived from animal or vegetable remains, but that the
manner of their derivation has not been uniform.” It
may be of interest to note here that, by suitable treatment
of animal and vegetable remains in vacuo, chemists have
actually been able to prepare substances which approxi-
mate, both physically and chemically, very closely to
bitumien.
Thºre is nothing really definite to oppose to any of
these theories, though at the same time it is difficult to
make a choice between them, or rather, to be more correct,
to find a single one of them that will satisfy all the con-
º necessary in order to be applicable to all deposits
of every type of bitumen. In order to be convinced of this
it is only necessary to consider a few of the more important
deposits of that material. |
At Pechelbronn, the strata of bituminous sand are found
in contact with strata of lignite. The two are often found
on the same level, and the lignite presents itself in greater
quantity when the sand ceases to be rich in bitumen.
This º suggest that the vegetablé matter, the accumu-
lation of which caused the formation of the lignite, also
14 NATURAL ROCK ASPHALTS
gave rise to the bitumen. It was the exploitation of the
lignite deposits here, as a matter of fact, that occasioned
the discovery in 1778 of the deposit of bituminous rock,
though this latter was not, however, worked until 1828.
A similar relationship between lignite and bitumen is to
be found in the Hoering deposit in the Tyrol, whilst the
stratum of bituminous rock near Alais also contains veins
of this mineral.
According to P. G. Wall, bitumen is to be found in the
island of Trinidad in certain schists which originally
contained vegetable debris. This latter, it is suggested,
was submitted to a special decomposition which resulted
in the formation of bitumen instead of lignite. This
theory has the advantage over that of the formation of
bitumen by the distillation of organic matter by the inter-
nal heat of the earth, in that it allows of the existence in
the bitumen of substances which, like “ asphaltene,” could
not have resulted from such a distillation. The fact, too,
that bituminous solutions are not fluorescent, like those of
oil residues or those of the pitches obtained by the dis-
tillation of pyroschists at high temperatures, seems to
bear out this fact. } i
This author also affirms that this special decomposition
is due simply to chemical action induced by the tempera-
ture customary with the climate of the Antilles. An
inspection of the lignite found in the above-mentioned
European deposits results in the recognising in them of
traces of sub-tropical flora, so that the climate favourable
to these changes in Trinidad might equally well have
exercised the same influence in the case of the deposits
in Alsace and the Tyrol. This hypothesis, º does
not allow of an appreciable content of sulphur in the bitu-
men, and it also overlooks the saccharoidal structure of
the impregnated limestones at Lobsann and Hoering.
A more complete explanation of this phenomenon
would be to include in it the intervention of hot sulphur
springs acting either by themselves or in conjunctiºn with
the normal climatic decomposition caused by the high
temperature and the chemical reactions resulting ſº it.
The distribution of these springs follows the lines of dis-
GEOLOGY OF BITUMEN AND ROCK ASPHALT 15
location of the globe, and this suggestion would imply a
similar division of bituminous deposits. Following this
idea, it might be taken that the bitumen is released
from its place of origin, deep down in the bowels of the
earth, and then rises to the surface either in conjunction
with the hot springs that have a like origin, or by pene-
trating through the easily impregnated sedimentary
strata lying above it. If, however, the water is cooled
on its way to the surface, the temperature of the bitumen
rising with it would likewise be lowered, with the result
that the latter would solidify and coat the sides of these
“faults '' which form the great internal canals of this
circulation. This idea is well supported by the degree of
fusibility and the low density of many of the bitumens,
whilst an actual example is perhaps to be found in the
Trinidad “lake ’ deposit.
The idea, too, has been advanced that the formation
of the sandy bitumen that is found in this Trinidad
“lake ’’ took place in the same manner as the volcanic
mud of the numerous mud volcanoes in that district.
At Turbaco, these volcanoes form a score or so of hillocks
about ten feet high, having craters some two feet in
diameter and which are filled with a muddy mass. The
water in them is almost cold and no trace of the action
of heat is to be seen. The gases they give off, however,
âre highly inflammable and are accompanied with
bituminous compounds. It is therefore only necessary
to imagine a fairly high temperature below, and that the
water which these conduits convey to the particular
völcano, the crater of which forms the basin of the “lake,”
is able to obtain the bitumen that it carries from the vege-
table masses through which it passes, mixing it with the
lmud which the other volcanoes eject at a lower tempera-
ture without bitumen, and the intimate mixture of the
two materials as found in the “lake ’’ would appear to
be explained. l
) There are mud volcanoes still in existence in the
Caucasus, whilst in Auvergne the “peperites " or basaltic
túfas, which are often rich in bitumen, probably owe their
fºrmation to a similar procedure by means of which they
!
16 NATURAL ROCK ASPHALTS
were placed upon the limestone shortly after the deposit
of the latter, even if not actually at the same time.
The association of sulphur, pyrites, gypsum and various
salts, bromides, etc., with bitumen is a necessary conse-
quence of the theory of the intervention of hot sulphur
waters, a theory which was first mooted by M. Daubrée,
who, during his researches on metamorphism, was able
to transform wood, by subjecting it to the combined
influence of pressure and superheated steam, into lignite,
oil, and anthracite successively, whilst from the last he
also separated certain hydrocarbons which possessed the
characteristic smell of the Pechelbronn bitumen.
But the question now comes as to the origin of the
bitumens which are found in the primary formation and
in the “gneiss’ of Wermland in Sweden. In this epoch,
geologists have not yet been able to find any other traces
of organic life, so that it is partly on this account that the
theory of the igneous formation of bitumen is based, a
theory which becomes more probable when the bitumen
to be found in granite, the “ophites,” “syenites,” etc.,
is taken into consideration.
However, there is one great objection to this theory,
for the study of bitumen tends to show that usually this
material is not a pyrogenous product and that some of the
elements which it contains, such as the “ asphaltenes,”
do not appear to be susceptible of taking a gaseous state,
as would be necessary had it existed in the molten centre
of the earth. This difficulty is usually got over by the
further supposition that the material in being ejected
from the centre of the earth is subjected to a trans-
formation, in the same way that vegetable matter S
changed into lignite and oil. Be it as it may, however,
there are many geologists who are content to fix the
origin of bitumen as being the result of these volcanić
phenomena. :
If none of the many theories that have been propounded,
including those that are given above, appears to satisfy the
origin of all the different types of bitumen, however, thie
reader will doubtless come to the reasonable conclusion
that it is but a further proof of the infinite variety. pſ
GEOLOGY OF BITUMEN AND ROCK ASPHALT 17
methods which distinguish the working of nature, which,
with absolutely different reactions, at times gives almost
identical results. This idea, too, will appear the more
forcible if, instead of considering only those exceptional
cases in which bitumen, by the accumulation of large
quantities, has formed, either of itself or by impregnating
other rocks, deposits of considerable importance, we agree
with M. Delesse that all sedimentary strata or igneous
rocks contain, in very appreciable quantities, organic
matter to which bitumen may be allied. Their presence
in the igneous rocks was shown by Mr. G. Knox as far
back as 1823, and his researches go to prove that they
are in a greater proportion in the later rocks than in the
earlier ones. As a result of all this, one is compelled to
look upon bitumen no longer as an exceptional product
and a mineralogical curiosity, but as a substance, the
ubiquity of which can only be explained by the infinity
of the procedures that have been employed by nature in
its formation.
The geological formation of the rock asphalt is, however,
more certain. In every case where this material is to be
found, the impregnated rock is either a limestone or a
Sandstone, not, of course, necessarily pure, and in the
former case the fossilised oolites are often clearly percep-
tible. The impregnated layer forms a distinct stratum
Sandwiched between unimpregnated layers of either the
Sanhe rock or of marl, but with extreme rarity in “pockets,”
whilst very often several layers of the impregnated rock
are Superimposed, each being separated from the next by
an unimpregnated layer of the rock. The Lobsann mine
is a very good example of this, for here are to be found no
fewer than five of these veins of bituminous rock, the one
above the other. As is the case with coal, the thickness
of the strata of rock asphalt varies considerably, ranging
from a few inches to many feet, and when mined, the rock
is obtained like coal, by driving galleries and shafts into
the side of the slope. In some instances, as with certain
of the German and Italian deposits, the rock is found almost
exposied, and then the method adopted for the work is
simply, that of quarrying. A strange thing that is notice-
N.R.A. C
18 NATURAL ROCK ASPHALTS
able with this quarried rock is that the weathered surface
has the appearance of practically pure limestone, and it is
only when the face of the rock has been broken down
that the well-known chocolate coloration is to be seen.
From the “smoky" appearance of the unimpregnated
superimposed rock in certain mines, and the fact that in
certain bituminous rocks “pockets * of pure bitumen
are to be found filling up the cavities in the vein, some
authors believe that at some distant period the bitumen
must have penetrated the absorbent mass whilst it was
in a gaseous or thinly liquid condition, impregnating it
more or less richly according to the ease with which it
made its way through the rock, and then, possibly still
under the influence of that enormous pressure which
first compelled it to seek such an exit, cooled. This
would explain why, in the same mine, rock asphalt is
found which show: a percentage content of bitumen
ranging as wide as from over 30 per cent. down to prac-
tically nil.
The question of determining the age of the bituminous
impregnation is rather difficult of solution, since the porous
rock is capable of being impregnated a long time after its
creation, but there are certain fairly frequent circum-
stances met with in rock asphalt which throw a little
light on the subject. For instance, the fact cannot be
overlooked that the greater part of the bituminous rocks
segregate when they are submitted to the influence of
heat, and the easiest explanation of this fact is to admit
that their impregnation occurred whilst the rocks were
still in a mobile state, or at least in a powdered condition.
Although quartz, felspathic, and other similar sands are
to be met with at all geological stages, it is much more
rare for limestone and alumina to be thus found. Thus
it must be concluded that the impregnation of rocks of
this nature must either have accompanied or followed
shortly after their deposit and preceded their cohesion.
An idea of this mode of impregnation may be found
given in the formation of the Caucasian “kir,” the supply
of which is constantly being replenished with the fresh
arrival of petroleum to the surface of the earth, the
f
/
GEOLOGY OF BITUMEN AND ROCK ASPHALT 19
volatile portions of which evaporate out there, leaving
the more solid portions to consolidate and form bitu-
minous rock of the sand through which they percolate.
In this example the impregnation takes place with an
upward movement, but certain authors declare that the
effusion of the bitumen has often taken place above the
stratum of the rock that it has afterwards impregnated,
the saturation in this case taking place with a downward
motion. It is in this manner that the Trinidad “lake ’’
bitumen impregnates the land upon which it overflows
at a fracture in the side of its basin, though its content
of sand is an obstacle to a thorough saturation of the soil.
It has often been affirmed that the impregnation by
the bitumen could not have taken place at the same time
as the sedimentation of the rocks, and in support of this
the fact is pointed out that the bitumen, being insoluble
in water, and being also lighter than it, would have re-
mained upon the surface of the liquid mass when the
pulverulent deposits were being formed. Mr. Hitchcock
is, perhaps, the only writer who definitely declares an
opinion to the contrary, which is finspired by the handling
by him of various limestones in Syria, which contain as
much as 25 per cent of bitume, a proportion which he
considers is much in excess of what would have been
łretained by the rock had the impregnation of the rock
been occasioned by saturation only.
The cause of the segregation | of these bituminous
Fº under the influence of heat is therefore explained
Öy other writers in a different way. They propose to
#dmit that the deposits were impregnated in their solid
State and then reduced to powder, finally being recon-
stituted by the agglutination of this powder under the
cementing action of the bitumen. It is evident, however,
hat, in common with all other rºcks that have been
freduced to powder by the action of nature, the crushing
f these primitive rocks could not; have been carried
ibut without the formation of déposits intermediate
between the original rock and the final powder, and made
up of fragments increasing in size, as the former is
#pproached. In order, too, that the powdered bituminous
C 2
20 NATURAL ROCK ASPHALTS
rock could not be mixed with , any foreign rock, it is
further necessary to imagine the entire process of crushing
and reformation as having taken place in a region which
contains no other rock than it. The complication of
these various geological requirements is of itself sufficient
to demonstrate the impossibility of this hypothesis.
The deposits of rock asphalt which are worked at
Acquafredda, and one or two other places in Italy, are
totally different from the other European rocks that are
impregnated with bitumen, in that they do not segregate
when heated. These, therefore, must have received their
bitumen whilst in their massive condition. -
There are, however, certain deposits that have been
formed from the remnants of other primitive deposits,
in which small fragments, like balls or beans, are to be
found which are impregnated with bitumen and enclosed
in an unimpregnated rock, which, if placed in the presence
of free bitumen, is susceptible itself of being impregnated.
The existence in the same region of two bituminous
deposits belonging to different geological stages does not
necessarily prove that the two impregnations took place
simultaneously. The exudation of the bitumen, if it
were formed on the spºt in both instances, could have
occurred at two very distinct dates. The vein at
Bentheim gives a striking example of the renewal of arh
eruption of bitumen after an effusion of pyrites and à
deposit of crystalline limestone had taken place upon th?
first one. En passant, too, it may be advisable to remar
that the bitumens to be found in the same district are
not necessarily identical.
CHAPTER II
APPEARANCE AND PHYSICAL STRUCTURE
| THE inspection of a sample of a rock asphalt—that is,
ſpf course, of the natural rock, not the mastic form—
$hould always be made with the assistance of the micro-
scope, and at a cut or fracture freshly made for the purpose.
n his brochure upon his experiences with this material,
hich, as has been already mentioned, although published
'some twenty years ago, is appſarently still the only
|English work obtainable upon the subject, W. H. Delano,
well-known expert in this material, states that “the
frock should be of a chocolate color, fine in grain, evenly
impregnated with bitumen, free from sulphur, pyrites,
lay, sand or other extraneous matter.” In general,
that is to say, as regards colour and formation, this still
olds good, but the rigid exclusion of the other minerals
hat are mentioned is quite unnecessary and, in fact,
undesirable, since the material that is obtained from
jcertain of the well-known mines, as will be seen later,
| invariably does contain a small quantity of these alleged
undesirables; yet practical experience covering several
decades has proved that it gives quite as good results
and shows equal lasting power as those few which do
fulfil the foregoing requirements. It is undesirable,
too, since our European sources of supply are not too
\plentiful, and such an elimination would entail their
Murther limitation, from which it naturally follows that
'competition in supply being thus made less keen, and the
'emand for the material being capable of being met only
by the fortunate owners of those few mines in which the
roºk fulfils these very stringent coraditions, the price of
1 “Twenty Years' Practical Experience of Natural Asphalt,” 9.




22 NATURAL ROCK ASPHALTS
the material would most certainly be raised and the cost
of rock asphalt work would necessarily go up in
consequence.
Then, too, in his composition of bitumen Delano is
incorrect, as analyses made in later years have clearly
shown. Professors Kayser and Richardson have both,
though independently, clearly demonstrated the exis:
tence of sulphur in bitumen, which element is not men;
tioned by Delano at all, and in this respect, as in many
others, he appears to closely follow the assertions of
M. Léon Malo, and thus weakens his argument against;
the inclusion of this material in rock asphalt, since i
must certainly be present there if the rock is to be impreg-
nated with bitumen at all. In fact, it is further state
by the above mentioned authorities that the older th
formation and the more solid the bitumen, the more
sulphur it contains, which knowledge, it may be added,
has been fully appreciated and extensively utilised in
the manufacture of the artificial asphalts and other
products. In all probability the idea that Delano had
in mind in making this reservation was the exclusion of
sulphur in a free condition in the rock; but even if this
is the case, such an exclusion is clearly wrong, for, as
shown by the analysis given on a later page, the ;
asphalt as found at Lobsann (the second oldest worked
deposit) contains it; yet it has been, and is still, most
extensively used on the Continent, especially for govern-\
ment and municipal work, and, according to the state-
ments made by the proprietors of this mine, it has actually
been substituted by some municipal bodies in preference
to the product as cºbtained in Val de Travers, which
contains no free sulphur. !
As regards sand, itſ need scarcely be pointed out that a
large amount, the majority in fact, of the Americanſ
material is essentially bitumen-impregnated sand, whilst
even in Europe º material is found and successfully

used, though to a very limited extent. Besides this, how-
ever, when the impregnated limestone is being used, it
is customary to add fine grit—which, of course,
includes sand—of Warious descriptions and sizes to the
APPEARANCE AND PHYSICAL STRUCTURE 28
mastic prior to use, in order to give to it the capacity of
better resisting the traffic that is to pass over its surface.
Then, too, Delano allows the use of Trinidad epure for
the fluxing of the asphalt mastic, which bitumen is itself
practically one half sandy matter. If, therefore, it is
permitted to add artificially, sand or bitumen containing
sand, what ground is there for condemning the material
when that mineral is found naturally mixed with it 2
The inspection for physical properties that is recom-
mended is for colour, fracture, fineness of grain, and
uniformity of texture and of impregnation.
The colour should be a deep chocolate, not black, as this
usually shows a poorness of impregnation, i.e., the grains
of the rock are merely coated and not truly impregnated
with the bitumen; nor should it be too light or grey
(unless when obtained from an open quarry where, as
has already been pointed out, the process of weathering
tends to lighten the colour without, however, affecting
the quality of the material in any way), as this shows a
low percentage of bitumen.
The fracture should be earthy, that is, not having a
sharp cleavage, but showing up|rough and irregular as
though it were a handful of earth thrown together. This
shows a looseness of grain that is very essential for the
tº formation of the powder for either compressed
ašphalt work, asphalt mastic, . the manufacture of
compressed asphalt powder tiles. So loose should the
grain be that it should fall to powder when heated on
an iron plate. *
The grain itself should be very fine and minute, of
regular size and shape when examined under the micro-
scdppe. In general, it may be taken that the finer the
grain is, the more close will be the work done with it.
As against this, however, it must be remembered that the
finer the grain is, the softer is the material, which is
therefore more easily worn and marked by traffic.
Time impregnation of the sample (should appear even,
that is, the coloration should be jºi. the same deep
...; a light streak shows º bad piece of rock
diffilcult of impregnation, and so liable to give rise to cracks

24 NATURAL ROCK ASPHALTS
and other weaknesses, whilst, on the other hand, streaks
of a deeper coloration show a softer rock that will wear
away more rapidly than the rest. These weaknesses are
often eliminated by intimately blending the powder
together immediately after the rock has been crushed.
The chemical tests for the quality and the constituents
of the rock are given later in the chapter devoted to them,
but it may be mentioned here that even if traces of foreign
minerals other than limestone are found, provided, of
course, that they are not present in any appreciable
amount, they have no real prejudicial effect upon the
material, since for gritted asphalt work, asphalt cement,
etc., it is essential for foreign matter to be added to the
original rock asphalt. The only exception to this is
perhaps the material used for compressed asphalt work or
in the manufacture of the tiles made from the compressed
asphalt powder, as here it is essential that the powder to
be used shall be absolutely free from such impurities
which, if present, by preventing the adjacent grains
from cohering, would be productive of cracks and similar
weaknesses in the work when finished.
The quality of the rock as obtained from the different
mines varies very considerably, thus enabling the architect
or engineer to specify any particular material that may
prove most suitable for his particular requirements at
the time being. The finest and closest grained rock 'is
perhaps that which is obtained from the Val de Traviºrs
mine in Neuchâtel, Switzerland, although the Lobsann
product runs it very closely. Following these comes the
rock obtained from the mines at Limmer and Worwolfile,
then that mined at Selyssel, the series being completed as
regards deposits still exploited for practical purposes or
which are imported intº the United Kingdom, by the
coarser grained Sicilian, Italian and Spanish rocks. A
fine, close grained rock does not necessarily mean a perfect
material for all classes of work, however. As mentioned
above, it has been º by experience (and this can be
easily proved by cutting comparative samples with a kršife),
that the finer the grgin is, the softer is the rock. Where
therefore, there is much traffic, this class of material is
APPEARANCE AND PHYSICAL STRUCTURE 25
not the most suitable. Again, the coarse rock is of advan-
tage as offering more resistance to friction (traffic, that is
to say), but not being so closely bound together, as in the
case of the finer varieties, it is of little use on roofs, bridges,
iron structures or any place where there is much vibration
or alternate expansion and contraction. Under such
conditions, unless very highly loaded with bitumen, it
would most certainly crack and disintegrate. As,
further, bitumen costs more than double the price of
rock asphalt, the undesirability of such an excessive
addition of bitumen from the economic point of view
alone is at once apparent. -
A method which is ever increasingly being adopted by
well-known professional gentlemen, and one which prac-
tical experience proves can be thoroughly recommended,
is to definitely and invariably specify the medium grained
German rock asphalt for all purposes. When laid pure,
it will withstand excessive vibration in as excellent a
manner as the fine grained and much more expensive
Val de Travers material. The Clifton Suspension Bridge,
which was covered some years ago, with the Limmer rock
asphalt, clearly proves this. Then, too, when required
for use where friction is considerable, it is capable of
permitting a higher proportion (the writer has seen as
mudh as 45 per cent.) of grit to be added and mixed with
it and with more satisfactory results than with the coarse
grained, equal priced Italian varieties.
Whilst making mention of the specifying of rock asphalt
it may as well be advisable to remark here upon the
apparent freedom permitted to builders and contractors
in the choice of both the asphalt material and of the
asphalting firms to spread the material. This cannot be
tojo strongly deprecated. It is only natural that the
º is desirous of increasing his personal profit as
uch as possible (particularly if he lmas only secured the
$ontract as the result of the keen cutting of prices)
(especially upon such items for which, should they prove
faulty, he cannot be held responsible. and who can con-
tº: him when the specification giviès him such a wide
§cope as does the “ or equal ‘’ clause tºº, to be found
26 NATURAL ROCK ASPHALTS
in conjunction with items for this work? The rule should
be made—and rigidly kept—that the exact mine from
which the material is to come shall be definitely stated
without any “ or equal * condition, and, if possible, the
names of a limited number of asphalt contractors of repute,
with the quality of whose work the architect or engineer
is personally acquainted, and quotations from whom he
would be prepared to consider for the work. -
If only this were done, the trouble that is now found
upon occasion with unsatisfactory asphalt work would
at once be done away with, as all defects of this nature
can be divided into those arising from bad material and
those from bad workmanship. As it is, the builder is
allowed usually to accept the lowest tender that is received,
irrespective of the quality of either material or workman-
ship, and as an inevitable result the work is ofttimes
scamped and rock asphalt as a material brought into
disrepute. -
It should be clearly understood that there is a price
limit below which no firm of asphalt contractors can
possibly go and yet put in the proper material and work-
manship. If, however, the German material is specified,
as has been most strongly recommended, the architect
has some means of arriving at his decision, for the output
of all the mines in that district is so controlled that the
asphalt mastic must be sold at the same price in the
United Kingdom to, every purchaser, whether for 10,
100 or 1,000 tons, without any rebate or discount of any
kind. This at oncé leaves the difference in the quota-
tions that may be submitted for work in which it is to be
used to be accounted for in the labour item only, so that
if the difference is such that it shows that the lowest
tenderer has not properly covered himself for this, it
pretty well proves, an intention to reimburse himself
in either material or workmanship, either of º
can only be scamped to the detriment of the work
generally. f \
Yet it is well knpwn that large numbers of contracts for
rock asphalt Nº. given and carried out at rates much
below those at which the work could be possibly done anid
APPEARANCE AND PHYSICAL STRUCTURE 27
still show a working profit to the contracting firm if it
be done properly. Still, the firms who execute this cheap
work continue to exist and even to prosper, so that they
must be making a profit somewhere, and it should now be
fairly apparent to the reader where and how. The
objectionable feature of the case is that the firms who
quote for high-class work are wrongly condemned as
seeking to make too great a profit for themselves on the
contract. It must be borne in mind that an architect
cannot always be upon the building, nor can the clerk of
works spend the whole of his time in watching the progress
of one particular trade at work under his control, whilst
the material itself can be greatly reduced in quality almost
under their very eyes without their knowledge, so that
preventive steps can only be taken at the outset if they
are to be perfectly satisfactory, by a clear and definite
specification of the material to be used and a limitation
of the work to firms of high standing and repute.
A case is known to the writer where an architect was
accustomed to invariably issue an open specification and
to accept the lowest tender, which on every occasion
without exception, was sent in by: the same firm. As,
however, this particular architect had a great deal of
asphalting work continually passing through his hands,
a second firm determined to make a bold bid for the next
contract and, by dint of cutting their tender down to below
cost; they secured it. The outcome was that the second
firm, did the work properly—though at a loss—and then
left it to the architect to make a comparison of the two
iº, of workmanship. Needless to say, the first firm
did no further work for this architect, ) whilst the second
onel was able to recover their temporary loss, in profit on
the other work from this architect which this incident
broºght their way. The first firm had been making
splendid profit, even at their cut figuires, by cheapening
the rimaterial and by cutting down the labour costs.
As with other things, however, sq.metimes the very
caution that is now recommended cáuses the adoption
of the other extreme, and in glancing over the various
form; of tender for the supply of asphalt and bitumen as


28 NATURAL ROCK ASPHALTS
issued by different corporations, it is almost impossible
to repress a certain amount of surprise at the specification
of these materials which is embodied in them.
Thus, in the form of tender issued by the Borough
of Camberwell, it is demanded that the material shall
be “natural mineral rock mastic asphalt of the best
Limmer quality. The mastic asphalt blocks should con-
tain from 12 to 15 per cent. of pure natural refined
bitumen, and not more than 20 per cent. of fine Bridport
grit.” Now let us inspect this specification in detail.
At the outset, the name itself is misleading, as the material
cannot be truly termed “natural Limmer asphalt mastic ’’
—for that, the writer takes it, is the article implied—
since it is permitted to have added to it no less than
35 per cent. of foreign matter, i.e., refined bitumen and
Bridport grit. Then, too, the material is an “asphalt
mastic,” that is to say, a mastic (or cement) made from
asphalt, and not a “mastic asphalt,” whilst, as will be
seen later, “Limrmer * is not a quality but a type, of
which the quality, varies according to the particular
galleries and factories from which it is obtained and in
which it is prepared, Again, the 12 to 15 per cent. of
bitumen, being “refined,” must necessarily be added
during the “cooking ” operation, and so does not include
that which impregrates the rock naturally, since this is
not refined. As this latter is, on an average, some 7 per
cent., the total bitumen content required to truly fulfil
this specificationſ would be approximately 22 per dent.,
an amount which, as those who are intimate with this
particular type bf rock asphalt know well, it cannot
carry. The most objectionable feature of all, however, is
the demand for the inclusion of “20 per cent. of Bridport
grit.” To blend) this with the mastic requires that the
latter must be re melted and recooked here in Fº
when it follows that the brand of the mining company
manufacturing the original mastic, and which is the only
real safeguard of the architect or engineer, is lost. | The
work, too, is both inadvisable and useless; inadvisable
since the further ºboking tends to the loss of the necessary
lighter elements |of the bitumen, and useless since, once

APPEARANCE AND PHYSICAL STRUCTURE 29
the material so prepared is again melted in the asphalt
cauldrons upon the site of the work at which it is to be
used, it requires the same amount of care and attention
as if the grit were only then mixed with it; for, with the
softening of the mastic, the heavier grit at once begins
to $ettle to the bottom of the cauldron, unless the material
is kept constantly stirred. Further, this requirement
eliminates from tendering all those asphalting firms who
do not chance to have a “cooking plant ’’ installed in
their works, and as this piece of machinery is both expen-
sive and entirely unnecessary for ordinary work—so
much so that the writer would be inclined to view with a
certain amount of suspicion any Small asphalt contracting
firm; who did chance to possess such an installation—
marily smaller but reputable firms are thus effectually
debarred from entering into competition with their more
fortiunate fellow contractors.
The specification included in the tender form issued by
the Metropolitan Borough of Bermondsey is slightly
different. This reads, “The asphalt mastic used shall
be a bona fide rock asphalt, and shall be mixed with a
not larger proportion than 20 per cent. of clean washed
Bridport grit; only sufficient bitumen as necessary shall
be ºd, and shall be made from best Scotch shale oil
* refined Trinidad pitch.” ſ'
The ambiguity of the phrase “a bona fide rock asphalt”
is almost too apparent to require to be more than pointed
out. The objectionable remade rock; asphalt mastic
comes well under this heading, although it is one of the
º of the original product that should be most
rigidly excluded. The unnecessary and disadvantageous
inclusion of grit has already been referred to above,
thbugh the specification goes a step in the right direction
i. it does not insist upon a fixed percentage of added
bitumen. A part that could be reviseſ with advantage,
however, is the constitution of the bitumen. By refined
Trinidad “pitch ‘’—and the misuse of the term “pitch"
is to be deprecated—is implied, one would imagine, the
Trinićlad epure, and for this material shale oil or grease
is most certainly not the best flux. Truhe, its use has been
30 NATURAL ROCK ASPHALTS.
extensively adopted in the past, when the use of rock
asphalt, bitumen and bituminous products was more or
less in its infancy, and when the existence, in practicable
quantities, of suitable liquid bitumens for the fluxing of
the solid types was unknown, but with the placing upon
the market of the various malthas and bituminous oils,
the necessity for an artificial product, as is shale oil, is
dispensed witn. \
The rock asphalt mastic and bitumen that are to be sup-
plied to the corporation of Dublin have, according to the
official tender form, to fulfil the following specifications:–
“The asphalt shall be composed of at least 95 per cent of
pure rock asphalt and shall have all volatile oils evaporated,
and be perfectly free from all foreign substances, and shall be
delivered in cakeſ' as it comes from the mines without any
adulteration or recasting. §
“The bitumen to be composed of Trinidad asphalt refined
with not more than 20 per cent. of shale grease ; it shall be
perfectly free from clay and vegetable matter.
“The materials to be supplied shall be fully equal in every
particular to the specimens or samples exhibited, and when no
specimens or samples shall be exhibited, they shall be of the

j best brand and quality of their various and respedºtive
kinds.” {
It is gratifying to see that here, at least, the value of
the brand of the nining company upon the original
blocks of mastic is appreciated, and that the entirely
unnecessary mixing in of a “filler’” is not required.
An impossible demand, however, is made when it is
insisted that the mastic shall contain “at least 95 per
cent. of puré natural rock asphalt ’’ after the sº
elements have been evaporated, for, as already remarked,
the average cortent of bitumen in the Limmer rock
(which the writer is given to understand is the type used
by this corporation) as drawn from the galleries, intº
the lighter oils entering into its composition, is on an
average only 7 per cent. The lowest bitumen conſtent
to allow of the Limmer rock asphalt mastic being properly
and satisfactorily worked, without any fear of charring
occurring in the 'cauldron, is 14 per cent. Making no
allowance, therefore, for the portion of the bitumen


APPEARANCE AND PHYSICAL STRUCTURE 31
naturally present that will be evaporated out, a further
7 per cent. of added bitumen is thus necessary, yet the
specification only permits of a maximum addition of
5 per cent. It is further omitted to mention to what
temperature the bituminous rock is to be heated in order
to extract the volatile oils, a matter which is of great
importance, since these volatile oils are made up of a
mixture of oils which distil out at different temperatures
until only the brittle “ asphaltene '’ bf the original
bitumen is left, a state that cannot be desired. The
composition of the bitumen admits of the same criticism
that has been given above, though, as will be seen by the
chapter on American bitumens, if the Trinidad epure is
referred to, it is an utter impossibility to obtain it abso-
Kutely free from vegetable matter and, if by the term is
meant the very finely divided sand that it contains, clay.
Objection can be reasonably taken, too, to the mere
visual inspection of the samples against which the pros-
pective tenderer is to quote. Without physical and
chemical tests, their qualities cannot be ascertained with
any degree of exactitude. Since the material as supplied
in bulk is to be tested by the city analyst, it is only
Feasonable that the contractors shºuld in a like manner
be in a position to test the material which is exhibited as
a type sample. The analysis of the city analyst, whose
certificate is to be final, whilst no doubt of great value as
showing the comparative chemical properties of the sample
and the bulk, can also be demurred to. As will be seen
by the chapter upon analysis, a chemical test, or even a
series of chemical tests, is totally insufficient to conclu-
sively prove the fact of a rock asphalt mastic being pure
or not. Artificial types can be, and are now prepared so
well that by none but an expert in the material—and
even he at times can be led astray, as the writer once
found when a friend of his prepared 'a sample which,
wº submitted to a German expert, was passed as being
natural Limmer rock asphalt mastic although none of
its ingredients had in reality seen the Continent—can
their true character and formation be detected ; the
sº components are the same in both cases, and so
32 NATURAL ROCK ASPHALTs
both the natural and the artificial materials react and
respond equally to chemical tests and reagents.
The above three specimens have merely been taken at
random out of many, but they clearly show how necessary
it is that the present ambiguous and incorrect specifica-
tions shall be carefully revised and so worded that only
the natural rock asphalt mastic and natural bitumen
let down with a suitable natural bituminous flux, can
possibly be used. To do this a long involved paragraph
is not necessary, but one covering the essentials somewhat
after the following:—
“The asphalt mastic to be natural Limmer (or Seyssel,
Lobsann, Val de Travers, Ragusa etc., as preferred), mined
and prepared by the . . . . . Company, and shall be delivered
on the site of the work where it is to be used, in the originai
blocks as shipped from the factory by that company, each
block having clearly impressed upon its face the brand of the
mining company mentioned.
“The bitumen to be Trinidad (or Selenitza, Bermudez etc.,
as the case may be) epure, cut down with Trinidad liquid
bitumen (or Californian or other flux determined upon) so that
when heated to a constant temperature of 165° C. (or the
maximum degree of heat to which the material will be subjected
when used) for seven hours it shall lose not more than 4 per cent.
of its volume, whilst a o. 2 needle should in five seconds sink
3–9 mms. (according to the degree of softness required in the
bitumen) into it when under a pressure of 100 grammes and at a
temperature of 25° C.” " :
Any further addition to the specification for the rock
asphalt mastic, as for example, the degree of heat necessary
to fuse the material and the percentage content of bitumen,
is rendered unnebessary, as the fact of the material being
used as shipped from the mines, also implies that it is
made to the definite and fixed standard that is adopted
by that particular mining company for the material; it
manufactures. |
In this way each firm which tenders for the supply is
placed upon an equal footing with its competitors, so that,
each having the same opportunities of securing the various
materials requisite, none can complain of preferential
treatment as is i. case at present. The engineer will

* See Penétration Test in chapter on Analysis.
APPEARANCE AND PHYSICAL STRUCTURE 33
also be able to know exactly what material to expect,
and knowing this he will also know how the finished work
will—or rather should—act, so that should any fault
arise, it can only be occasioned by faulty workmanship,
and it is to prevent this that the names of reputable firms
whose work can be accepted should be inserted. Only
too often the workmen at present shelter their own short-
comings by blaming the material that they have been
uSlng.
It may be of interest to some readers to make mention
here that the maximum period that is allowed by the
Local Government Board for the repayment of loans
issued by them for the paving of footpaths with rock
asphalt mastic is ten years.
The following figures, which give the imports of rock
asphalt into the United Kingdom, clearly show how much
greater is the use of the German article than that obtained
from any other rock asphalt producing country in Europe.

-º 1910. 191].
Tons. #9. Tons. * :9.
Germany o 24,960 58,092 24,330 53,784
France . © 11,985 25,301 13,716 32,272
Italy º e 10,308 18,604 12,200 19,943
|
N.R.A. D
CHAPTER III
HISTORY AND ANCIENT USE
To those who are at present dwelling under the belief
that the present day uses of rock asphalt and bitumen are
but modern innovations of no earlier date than the past
century—and the writer has come across not a few—it
will be of much interest to know that the employment
of these materials and the knowledge of their properties
may be referred to with safety as being nearly “as old
as the hills,” for mention can be found made of them
even in writings which themselves take us back into the
mists of antiquity.
The names of “acphalt” and “bitumen” at once carry us
back to the civilised nations of former times. “Asphalt ’’
is derived from the Greek word for mineral pitch,
“&g pa)\tos,” by which this nation described this, to them,
“immovable * body which was unaffected by the acids
and alkalies then known. The Latin word “bitumem. ” is
but a corruption of the phrase “pia tumens,” signifying
“bubbling or fervent pitch,” by reason of the bitumen
springs from which it exuded and from which it was
obtained by them. The derivation of the expression
“pia, tumens '' itself is very uncertain, as it is not really
allowed to be Latin at all, but is said to come from the
Hebrew, a surmise which would appear probable when
it is borne in mind that one of the principal sources of
supply at that time was the Dead Sea in Judea. Delano’s
statement, therefore, that “bitumen is in fact the Latin
equivalent for pitch '' is only very partially correct.
As rock asphalt must be accepted as a branch of
bitumen in that it is a bitumen-impregnated rock, the
ancient history of the one merges into that of the other,
so that although bituminous stone or cement is referred
HISTORY AND ANCIENT USE 35
to as being in use by the most ancient of builders of whom
we can find any record, we cannot at this present age
state definitely whether this stone was a natural product
or one made artificially, except by unsatisfactory deduc-
tion, for, as will be seen later, about the Dead Sea, one of
the oldest sources of supply, is to be found bitumen both
in its pure state and impregnating limestone rocks.
One of the first instances in which we find this material
mentioned in general literature is in that most ancient
of writings in daily use, the Bible, where it is stated that
in the construction of his ark, Noah gave it a protective
coat of “pitch '' within and without (Genesis, vi. 14),
the material in this case being in all probability the
mineral pitch, i.e., bitumen. Following this we have an
account of the kings of Sodom and Gomorrah after the
fight against Chedorlaomer, the Ring of Elam (Genesis,
xiv. 10), fleeing and falling in the Vale of Siddim, our
modern Dead Sea, which was then full of “slimepits ‘’
or “bitumen º’ as the Vulgate more correctly translates
the Hebrew word “hemar.”
Other writers on this subject have been content to date
the earliest use of bitumen for constructional work to the
building of the Tower of Babel, but definite historical
records have been found which assign its use for this
purpose to a far earlier time even than this. Perhaps the
first period in which it can be found playing a part in
building is that during which Babylonia, i.e., the country
at the mouth of the Tigris—Euphrates delta—was inhabi-
ted by its, so far as we can judge, first occupants, the
Sumerians. These ancient but highly civilised people
have left us their inscriptions upon stones, some of which
have been definitely fixed as dating so far back as
the middle of the fifth millennium, whilst others by their
script belong to still earlier times. One of the rulers of
this race—or “patesis '' as they were called—Gudea, we
are told, had made for him some fancy pottery in which,
in order to represent the eyes of animals, pieces of lapis-
lazuli were used and held in position by means of bitu-
men. This pottery is still in existence, and is to be seen
in the British Museum, though in the Louvre in Paris is
D 2
36 NATURAL ROCK ASPHALTS
exhibited a statue of Manishtusu, a still earlier “patesi,”
in which the eyes are formed of pieces of white limestone
also fixed into position in a like manner. From their
stone inscriptions, we find that these people were con-
stantly making expeditions for building material, and
frequent mention is made of the bitumen which they
obtained from a place called by them Magda, which town,
since one king who lived at Lagash, a place almost on
the sea coast, says that he brought this substance many
miles by river, is thought to be the modern Hit.
This nation was followed by the early Babylonians
(2,500–1,900 B.C.), a Semitic race who had gradually
mingled with and finally ousted their predecessors, and
in the Biblical account of the building by them of the
legendary Tower of Babel, we again find a reference
made to the use of this material for building purposes.
Even at this early date it was extensively used for those
very purposes, and owing to the same reasons that it is
being employed at the present day, thus affording another
splendid example of history repeating itself. It has been
asserted with the utmost confidence that the roofs of the
houses of that period were flat in formation and used in
identically the same way as are the housetops of the
Near East to-day. In order to make them watertight,
it is stated that the clay or whatever substance was used
to form the roof, had blended with it a quantity of
bitumen. The inundations of the river Euphrates also
necessitated the use of a permanent water-resisting
dampcourse in every building, and as the city of Babylon,
which was built in the form of a square, was some twelve
miles in extent, the amount of bituminous dampcourse
that was used in that city alone must have been very
considerable. That this is really the case has been clearly
proved by the modern excavations carried out in the
valley of the Euphrates, as a result of which the investi-
gators were able to definitely state also that the dwellers
in Mesopotamia were further accustomed to use bitumen
as mortar for building purposes. Thus the immense
wall which, in conjunction with a deep moat connected
with the Euphrates, defended the city of Babylon, was
HISTORY AND ANCIENT USE 37
built in this way, for we learn from Herodotus that the
bricks of which it was composed were formed of the clay
dug out of the moat or brought in from the surrounding
country, air-dried and burnt, after which they were laid
in hot bitumen, whilst, as an additional binder, rows of
reeds and palm leaves were inserted every thirtieth
COUTSé.
The famous towers of Babylon (the one still in existence
being now known to the inhabitants of that district as
Birs Nimrod) were protected for no less than twelve
storeys with a coating formed of a kind of concrete con-
sisting of crushed brick cemented together with bitumen,
So as to effectually retard the encroachments of both
damp creeping up from the earth and of the waters of the
Euphrates when that river was in flood. There is no
doubt but that the sole reason why the one still in exis-
tence, as well as other very ancient buildings which are
yet extant, has stood for such a great length of time is
that the builders invariably used bitumen as an admix-
ture, even if not actually by itself, in its construc-
tion.
The discovery of a method of forming tunnels below
river beds is generally considered as being an English
discovery dating only from the past century, but upon
plunging into the history of the very earliest times we
find Éhat, according to the German writer Miesbach
(1855), mention is made of a tunnel which is stated to
have been constructed under the river Euphrates and
built in with burnt brick, afterwards coated with bitumen,
more than four thousand years ago by the mythical
Queen; Semiramis. This personage is said to have been
the builder of Babylon, and the successor to Ninus, but
as this latter is now affirmed to be merely a modified
form of Ninua, as Nineveh was originally spelled, the
whole legend in reality resolves itself into a fanciful
allegory of the succession to power of Babylon after
Nineveh.
The bitumen used in all the above mentioned buildings
W8,S º all probability obtained from the springs of Is.
Herodotus (I. 79) refers to them thus: “ The bitumen
38 NATURAL ROCK ASPHALTS
used in the work [the formation of the moat] was brought
to Babylon from the Is, a small stream which flows into
the Euphrates at a point where the city of the same name
stands, eight days journey from Babylon; clumps of
bitumen are found in great abundance in this river.”
At the present time there is a small town about 150 miles
away from Babylon (now known as Hilla) which is called
by the Arabs Hit, around which bitumen is still to be
found in considerable quantities. Midway between
Babylon and Hit there are the remains of an artificial
canal joining the Tigris with the Euphrates, having
Baghdad at the one end and Faluja at the other. This
canal is called Nahr Isa (Nahr being the Arabic word for a
small river), but as there is no bitumen to be found in this
canal,” the Is of Herodotus must be the modern Hit and
not the Nahr Isa, as some writers, confusing the two name
places, have wrongly affirmed. The difficulty lies in the
fact that the Greek language cannot reproduce the initial
guttural sound of the Arabic Hit, whilst the replacement
of “s ” by “t ’’ is quite a regular phonological change in
Semitic languages.
The alluvial plains of Babylonia, however, may also
have been drawn upon, for here are to be found both the
clay for the bricks and the bitumen, which bubbles out
of the ground in a semi-liquid condition, for the cement.
The bitumen here is still collected by the nomadic Arabs
and made use of for waterproofing their tents, and at Hit
it is also employed by the natives for caulking their boats.
Though perhaps outside the scope of the present work,
it may be interesting to know that the various Biblical
accounts that have been referred to in the foregoing pages,
i.e. the construction of the Ark by Noah, the erection of the
towers of Babylon, as well as the formation of Moses’
basket, which we are told was daubed with “slime,” are
all adaptations from the much earlier inscriptions of the
Babylonians. Thus the first is practically a literal
repetition of what is now known as the “Eleventh 'Tablet
of the Gilgamesh Epic,” which dates at least 4,000 B.C.
* My informant rather unkindly remarks, “not even as a waterproof
lining for the banks.”
HISTORY AND ANCIENT USE 39
In the original story, the Babylonian counterpart of Noah,
Utnapishtim by name, relates that:
“I provided a pole (i.e., to paint with) and all that was
necessary. Six sar (a liquid measure) of bitumen I smeared
on . º outside. Three sar of bitumen I smeared on the
inside.”
Apparently the outside received two coats of bitumen
and the inside only one. The word that is used here for
bitumen is interesting (ku-up-ri—Hebrew, kopher), since
it is precisely the same one as is used in the Biblical
account of the construction of Noah’s Ark, and it is only
found in the Bible in this one connection, so that since it
is not Hebrew at all, it forms one of the possible proofs
advanced by such theological students as refuse to
acknowledge the divine inspiration of that book.
The Biblical account of the building of the so-called
Tower of Babel (Genesis xi. 3) too, where we are informed
that “‘slime had they for morter,” cannot be said to
aim at being historical. The writer clearly shows that
his sole intention is to give an explanation of the “con-
fusion * of the human languages. He had heard of the
temple towers of Babylon and had heard the name of
the town of Babylon (Bab-ili)—which was always
rendered in Hebrew as “Babel ”—and he wondered at
the use of such a name. In Hebrew, “babel ” means
“confusion,” and he finally decided that the word was
used in this instance because God “confused '' (babal)
their language owing to their endeavour to raise their
towers too high. Nobody has discovered the actual
Tower of Babel for the simple reason that there must
have been scores of them dotted all over Babylonia.
Every temple here, it must be remembered, had its huge
tapering tower called a “zikkurat.”
The hiding of Moses amongst the rushes on the banks
of the Nile (Exodus ii. 3) finds its original in the Baby-
lonian tradition of the infancy of Sargon I., who, like
Romulus and Remus of the Romans, was supposed to
have been of semi-divine origin. For safety’s sake he
was hidden by his mother by the waterside. Of this
40 NATURAL ROCK ASPHALTS
episode he relates upon the ancient historical tablets
that :
“She [his frightened mother] placed me in a basket of reeds,
With bitumen [kwpril my lid she fastened.”
The “pitch " mentioned in the Biblical narrative is
probably a maltha or some other fluid form of bitumen,
for in Isaiah xxxiv. 9, where the same Hebrew word
“ zepeth '' is used, the context certainly implies a liquid
as replacing the water of the rivers. *
The inclusion of bitumen in all these hoary legends
shows clearly how old is the knowledge of the use of bitu-
men for building and waterproofing purposes.
The next important nation of builders of whom we have
any note are, of course, the ancient Egyptians, numbers of
whose buildings are still extant despite the thousands of
years that have passed since their erection. In their build-
ings we see it playing an important part in the mausoleums
of the Pharaohs—the Pyramids—in the Sphinx and in
the still existent temples, whilst it was also used by this
people as a coating to the internal and external surfaces
of the walls of the ground floors of their dwellings, as a
lining to their tanks and cisterns, to their granaries,
silos, etc., in fact in every building where the seepage of
the Nile water was to be resisted. With this in mind, it
is interesting to know that the same material is now being
used in modern Egypt for exactly the same purposes, in
the form of bituminous sheeting.
But its use with this nation did not stay here. In
combination with cedar oil and other ingredients—the
particular mixture apparently varying with the wealth
and social position of the dead person or animal—it was
employed by them in the embalming of their dead, the
method of procedure being to take away all those organs
of the body in which putrefaction could arise and then to
fill up the cavities thus formed with a mixture able to
resist the decomposition of the organic tissue left behind
when hermetically sealed (by external bandages) from the
influence of the air. The name “mumiya ‘’ (an Arabic
term supposed to be ultimately derived from the ancient
HISTORY AND ANCIENT USE 41
Persian “mum ”—wax) was given to the essential
constituent of this mixture—believed now to have been
either bitumen or an extract of that material—and the
body so preserved became in the process of time to be
referred to by the name of the preservative that was
employed—a “mummy.” How old is the knowledge of
the preservative property of bitumen as applied to organic
matter will be recognised from the fact that mummies
are known which are nearly 5,000 years old, one of the
oldest being perhaps that of King Mereure at present in
the museum at Boulac, and who belonged to the Fourth
Dynasty, ruling the country about 2,800 B.C.
It was apparently the custom of the ancients to build
their defensive walls in bitumen, for, according to Diodorus
Siculus, the walls of Nineveh were built in the same way
as mentioned above for those of Babylon, as was also the
Median Wall, as described by Xenophon in his “Anabasis,”
whilst Nebuchadnezzar states of his city that he “built
it with burnt brick and bitumen.”
One of the oldest sources of supply was, as has been
already mentioned, the Dead Sea, so that it follows that
the Jews were intimately acquainted with the substance,
whilst to this day the bitumen obtained in Syria generally
is often known as “Jewish pitch.” Not only did this
supply suffice for their own requirements, but they also
sold it in the markets of Tyre and shipped it even so far
as Egypt for embalming purposes. In Josephus’ “An-
tiquities '' (I. 43), Herodotus (I. 179) and Tacitus (Hist.
Jud. V. 6) are to be found interesting accounts of the
methods that were employed in their day to obtain the
bitumen from the Dead Sea—the Bahr Lwt of the Arabians,
the Lacus Asphaltites (from which name some writers
incorrectly declare that the term “asphalt ’’ is derived) of
the classics, the Jam Hamelach or Jam Hacabarah of the
Hebrews—of which Strabo informs us that in his time it
was filled with bitumen, whilst Diodorus the historian
states that at the period at which he wrote, large masses
comparable to small islands floated on the surface of the
water, this of course being due to the high degree of salinity
of the latter. We are informed by the writers mentioned
42 NATURAL ROCK ASPHALTS
that the collectors were wont to go with their boats to these
floating masses and to pick up as much of the bitumen
as they were able to carry. At first some trouble was
experienced in drawing it into the boats owing to its semi-
fluid condition. To harden it, therefore, vinegar was
poured over a portion of the mass which thereupon con-
gealed and could then be handled and pulled into the boat,
the remainder of the soft material following by reason of
its viscosity. A further difficulty had then to be contended
with, for when sufficient bitumen had been stowed away
into the bottom of the boat, it was discovered that the
material could not be cut asunder with a knife having a
blade of brass or steel, as these metals merely stuck into it
without making any severance. Blood, therefore, was
smeared over the point at which the bitumen was to be
separated, when the latter could be broken with the utmost
€3,SC.
Other ancient writers besides those already mentioned,
who refer to this material in their works are Homer
(900 B.C.), Aristotle (355 B.C.) and Pliny (100 A.D.), of
whom the last especially deals with the subject in a
particularly exhaustive manner. He writes (Hist. Nat.
II. 106): “Nihil in Asphaltite Iudaeae lacu, qui bitumen
gignit, mergi potest,” and that he was also quite conver-
sant with maltha we see from the same work (II. 108),
where he relates that “in Commagene urbe Samosata
stagnum est, emittens limum (maltham vocant) flagran-
tem.” In his thirty-fifth book he also mentions how
multitudinous and varied were the uses of bitumen in
the times of the ancients. Thus we learn that it was
used by the poorer Romans to coat their household goods
to protect them from decay. Herodotus informs us that
the “bitumen liquidum,” apparently petroleum, was
imported from Babylon and Zakynthos, the most southerly
of the Ionian islands, and used instead of oil in their lamps
as an illuminant. As an unfailing remedy for many ills
it was held in the highest esteem, and it was regarded as a
certain preventative against boils, ringworm, gout, epilepsy,
blindness, toothache and colic. Even on the toilet
tables of the Roman ladies it was always to be met with,
HISTORY AND ANCIENT USE 43
and it was used by them to colour and to beautify their
eyebrows, whilst by the nervous and the hysterical it
was also used in a similar way and for a similar purpose as
the eau de cologne in the smelling bottles of the ladies
of the present day.
It is further stated that bitumen was the principal
ingredient in “Greek fire,” the exact composition of
which, however, being a state secret, is not now known.
This material is said to have had the peculiar property
of being capable of burning strongly even when under
Water.
From the Roman period onward, no attempt appears
to have been made to discover the lost secret of the use
of bitumen for constructional purposes,” although one
would have thought that such knowledge would have
been of inestimable value to the Romans in the building
of their roads, bridges, viaducts, etc., especially so since
the Italian deposits were so ready at their hand. Of the
material itself it can be reasonably stated that, from the
time of the ancient Sumerians down to the present age, it
has not been lost sight of, but after its disappearance as a
building material, perhaps the only practical use to which
it has been put to any great extent was the caulking of
boats. •
In the writings of later times it is still to be met with.
Valerius refers to it under the name of “ bitumen solidum
coagulatum”; Libarius, in 1601, looks upon it as belonging
to that classification of compounds which included mineral
oil, amber, sperm, etc. He was apparently acquainted
with the deposits in Brunswick and Alsace, whilst he
asserts that naphtha is merely the more volatile portion
of mineral oil. In general, however, his writings on this
subject are merely reviews of the mention made by Pliny,
Discorides, Hippocrates, etc., as to the use of bitumen,
though he also says that for the previous fifteen centuries,
1 Since the foregoing was written, the writer has chanced upon a
passage in Moxon’s “Mech. Exerc.,” p. 243, written in 1677, where
mention is made of a “mortar used at Rome, called Maltha from a kind
of bitumen dug there.” The knowledge of the constructional value
of bitumen must therefore have been lost after this period.
44 NATURAL ROCK ASPHALTS
mineral oil—petroleum, that is—had been used for illu-
minating purposes by the civilised European nations and
that this was also the fuel used in the famous “igne
Vesta,” whilst, according to him, too, Hannibal used it in
his military campaigns, possibly as an adaptation of the
older “Greek fire.” Kopp makes some interesting allu-
sions as to its use in the Middle Ages, when it was employed
to protect the vines and fruit trees from insects and blight,
but more especially by the alchemists of that age. Many
years of labour and numberless fortunes have been spent
by these persons on this material in the fruitless attempt
to extract from it the “materia prima,” the substance
from which the much sought after “ philosophers’ stone *
was to be prepared.
But many references to this material under the alternate
names of “ asphalt” and “bitumen’’ are to be found in
the literature of our own country from the very earliest
times. Thus in an early alliterative work of about 1325
we find mention made of
“The spumande asphaltown that spyserez sellen.”
At least two other allusions in the writings of the
fourteenth century are Maundeville (IX. 100) who states
that
“It castethe out of the water a thing that men clepen
aspali,”
and Trevisa who, referring to this material, says that
“Asphaltis glewe of Judea is erthe of blacke colour and is
heuy and stynkynge.”
In Copgrave’s “Chronicles” (ca. 1460) we find mention
is made of
“A vessel of wykyris filled the joints with tow erde cleped
bitwmen,”
whilst it is interesting to note that even as early as the
sixteenth century, the word “bitumen º’ is to be found in-
correctly used to refer to an artificial product—wood tar—
for in Turner’s “Herbal ’’ (ca. 1551) it is affirmed that
“The Frenchmen seth out of it (i.e., the birch tree) a certain
iuce or suc otherwise called bitwmen.”
HISTORY AND ANCIENT USE 45
In that century, too, the knowledge of the application
of the waterproofing properties of bitumen to building
work must have existed, although we can find practically
no mention of it in works on building subjects, for in
Whitehorne’s “Ord. Souldiours ” he instructs his readers
when forming certain military structures
“For every portion of such thinges (to take) five of aspalto.”
But even in our classics it is also to be met with. Thus
in Shakespeare we find the material (although with his
usual poetic licence he uses the word as a verb and so
has caused certain editors to incorrectly read it as
“bottomed ”) mentioned in “Pericles " III. I. 72 and
ibid. III. II. 56. -
“We have a chest beneath the hatches, caulked and bitwmed
ready.
y
How close ’tis caulked and bitwmed.”
Milton, too, uses the two words “bitumen. ” and
“ asphalt,” and in his “Paradise Lost " I. 729 (c.f I. 411)
we read of
“Blazing cressets fed with naphtha and asphaltus,”
and in the same work, XII. 41, we also find mention made
Of
“The plain whereon a black bituminous gurge
Boils out from underground,-the mouth of Hell.”
How vague an idea people then had of the exact type
and formation of this material may be gathered from
Blount’s Glossary (1656), in which it is described as
follows:
“Bitume : a kind of clay or slime naturally clammy, like
pitch, growing in some countries of Asia.”
This reference, however, is of value as showing that
even at that time bitumen and pitch were regarded as
two distinct substances although having certain physical
properties in common.
Again, the use of bitumen as a toilet preparation did
not end by any means with the Roman period. As late
as 1752 we find that it is alluded to for this purpose in a
publication on “Taste ’’ (I. 1) written by Foote, a well-
known “beau’’ of that time. In this he refers to
“The salutary application of the asphaltwm pot.”
46 NATURAL ROCK ASPHALTS
-
Even the modern use of the compressed asphalt powder
for the pavements of Paris can be found mentioned, and
by no less an English poet than Robert Browning, who
refers to them in his “ Apparent Failure,” stanza 4:
“Who last night tenanted on earth
Some arch, where twelve such slept abreast,
Unless the plain asphalt seemed best.”
Of the old uses of bitumen, that as a medicine seems to
have died hard. Even in the sixteenth and seventeenth
centuries a certain kind of bitumen was, under the name
of “mumia,” recommended as an excellent dressing for
flesh wounds and fractures, and was apparently very
extensively used to this end; whilst it is worthy of note
that it is not long ago that there was a patent in exis-
tence for the manufacture of a plastic dressing composed
of bitumen which was recommended for use instead of
the ordinary plaster of Paris type. Gradually, however,
even the medicinal use of bitumen has disappeared
with the advance of medical knowledge, and now, per-
haps, the only use to which this material is put by that
profession is in the formation of tinctures.
Thus this material, which was so highly appreciated
and so extensively used by the ancient civilised nations,
came to be entirely lost and, but for a very fortuitous
discovery, might have been unknown even to this day.
From this accidental find dates the modern application
of rock asphalt, which has now grown to be an important
trade in itself, the possibilities of which are ever increasing
as requirements which can only be filled by the peculiar
properties of this material in one or other of its various
forms, arise.
CHAPTER IV
MODERN EXPLOITATION OF ROCK ASPHALT
THE position of expert in some particular department
in the administration of Berne, in Switzerland, was, about
the year 1712, filled by a Greek doctor named Eyrinis.
In his official capacity he visited in the year just mentioned
the Val de Travers, the most important canton in the
Swiss Jura, and situated at the lake of Neuchâtel. Whilst
there, he either heard of, or came in contact personally
with, a German workman called Jost, who had discovered
that a rock was to be obtained from the cliffs which sur-
round the lake which was capable of being burnt to a
certain; extent and which, by reason of its exceeding
softness, could be easily worked to any desired shape with
the most simple of tools. As fuel, however, the stone was
found to be practically of no value, owing to the very
large proportion of ash which was left behind in the grate,
and Jost had tried in vain to find a suitable use to which
the peculiar material which he had discovered might be
put with advantage.
From his former studies of the ancient Greeks and
Romans, Eyrinis in all probability must have learned of
the use made by the great builders of old of asphalt,
whilst no doubt his own knowledge of natural science also
came to his assistance in making his discovery. Be it
as it may, the discovery made by Jost interested him
very greatly, so much so, in fact, that he himself pro-
spected the district and found that the most important
stratum of the rock was to be met with in the vicinity
of Iłois de Croix. From this place he obtained a number of
specimens which he subjected to several careful analyses,
as the result of which he discovered that the material
contained in the rock was no other than that substance
48 NATURAL ROCK ASPHALTS
which had been known for a long time previously as
bitumen. Being of an essentially practical turn of mind,
he determined to find out if this strange stone could not
be employed with advantage industrially, and in this he
was more successful than the original discoverer Jost,
since finally, by following the precedent of the ancients,
he proved it to be of the greatest value for waterproofing
structures. His method was practically identical with
that adopted at the present day in the carrying out of
“mastic ’’ work. He first crushed the rock to a fine
powder, of which he then made a cement or “mastic *
by adding to it a suitable quantity of pitch. With the
fusible mass thus obtained, he coated erections of both
brick and wood, and found that by so doing they were
then completely protected from the attacks of damp,
wet or decay of any description, and so were rendered
much more durable.
His petition to the King of Prussia—at that time the
Protector of Neuchâtel—praying that a concession might
be granted him of all the asphalt strata which might be
discovered in that principality, was favorably replied
to, and the concession thus obtained may reasonably be
looked upon as the birth certificate of the modern employ-
ment of rock asphalt for building purposes.
In his work entitled “Dissertation sur l'asphalte ou
ancien ciment naturel, découvert depuis quelques années
au Val de Travers dans le comté de Neufchâtel par le
Sieur E. d’Eyrinis, professeur grec et docteur en médicine,
avec la manière de l'employer tant sur la pierre, que sur
le bois,” which appeared in 1721 and which was again
published in 1784, he refers to the material and its use
as follows:–
“As he has discovered by the help of God, in the munici-
pality of Neuchâtel, a mountain which contains a true asphalt,
which is from every point of view as good as the asphalt of
Babylonia or of the Vale of Siddim, the which are so well known
to scholars, and further, as a great quantity has already been
extracted, he finds it advisable to acquaint the public pro-
visionally of it by the mediary of these few lines, until such time
as his work bearing the title ‘Asphaltasphaltae sive inverti-
bilis veritas ac securitas' is published. (This work, how&ver,
MODERN EXPLOITATION OF ROCK ASPHALT 49
appears to have never been put on the market or else (which,
however, is very improbable) all trace of it has been lost.
Having in mind the hasty departure of Eyrinis from this dis-
trict later, it may be possible that the Volume referred to was
never published. A.D.)
“As this asphalt consists of a mineral, earthy and non-
conductive material, which is softer and more sticky than pitch,
is less porous and is more solid than the latter, as is shown by its
Specific weight, it resists all attacks from the air, cold and water
So well that it cannot be saturated by the latter, and is there-
fore more useful than any other substance known for cementing
or coating every kind of constructional work, since it protects
the Woodwork against rot, against insects, and, above all,
against the destructive action of time, and this to such a
degree that, when continuously exposed to water, air, and all
kinds of weather, instead of being destroyed thereby, the
building is, so to speak, rendered indestructible by the coating.
From this it is easy to conclude that this is a natural cement
and one which is serviceable for bonding together wood, stone,
and other materials with which bridges, wells, ships, and all
; structures which must resist Water or damp, are to be
uilt.
“The method of using the cement is very simple. The stone
is taken just as it comes from the mine and heated a little so
that it can be ground to a coarse powder. A little pitch is
added to it so that it will fuse the more readily and also cause
the entire mass to become thinner, and then the whole is heated
Over a moderate coal fire.
“The wood or stone upon which the cement is to be spread
must have been previously well dried and also heated a little.
When using the cement upon stone, the present custom has
been to add one part of pitch to ten parts of the asphalt. For
use with wood rather more pitch must be added. When, how-
ever, marine work is being put in hand, it will be necessary to
supervise the workmen with the greatest care in order that
their work shall be as may be best Suited for the particular
purpose, though it will suffice for the present to add that the
asphalt in question becomes softer and more liquid the more it
is heated. In carrying out the fusing of the asphalt, however,
it is always necessary to add a little pitch. This fusing should
be carried out in a copper cauldron containing the exact
quantity of asphalt that may be required for the work then
being put in hand.
“The pitch must be melted first, then the asphalt added
little by little, the mixture being continuously stirred through-
out with a stick or shovel, until both materials have become
intimately mixed together. Resin makes it harder and causes
it to withstand the heat of the Sun better. Dutch pitch,
obtained from the roots of trees, makes it tougher. The
N.R.A. IE
50 NATURAL ROCK ASPHALTS
mixture must consist of one part of pitch (i.e., common pitch)
and eight or nine parts of asphalt according as to whether it is
desired to make it more or less liquid—depending upon the
nature of the work to be done—and before it is quite cool, this
cement can be levelled or brought to a smooth surface by means
of a hot iron, such as is used by builders for cement work.
Above everything else, the workman must take care that the
stone or other material to be coated shall be thoroughly
cleaned before the cement is laid upon it, and then if any weak-
ness is found afterwards in the work, it cannot be occasioned by
the material used but only by the kind of use and the method
adopted in the spreading of it.”
It will be seen from this that during the two centuries
that have passed since the above was first written
practically the only variation made from the instruc-
tions furnished by the discoverer is that of making two
operations out of the one. Instead of using the mastic
immediately it is prepared, or rather, instead of preparing,
it on the site of the work at which it is to be used, it is
now customary to make and “cook '' the mastic at the
mines and then to send it away in blocks which are
afterwards broken up and remelted as required. Certain
ideas embodied in Eyrinis’ remarks, however, time has
proved to be wrong. The use of “common pitch,”
instead of pure bitumen as the flux, caused his work to
disintegrate with age, as did also the use of the other
admixtures he mentions.
The results which he obtained by the use of this material
received official confirmation. In a certificate issued in
1716 at Neuchâtel it was attested that a large number of
cisterns and basins made of both wood and stone were
lined in a most excellent and durable manner with his
asphalt mastic and were thoroughly waterproofed thereby.
A balcony and a warehouse roof were also coated in a like
manner, to the entire satisfaction of their owners.
From this we see that Eyrinis had rightly judged the
principal methods of using asphalt, for which even at the
present time it is almost exclusively used, that is, as an
insulation against cold and damp, as a water retainer, and
as a paving. As, however, with many other benefactors
of mankind, it was not permitted to him to enjoy the fruit
of his discovery himself. By this time, too, he must have
MODERN EXPLOITATION OF ROCK ASPHALT 51
interested several high placed and influential people in
this material, for we find that M. de la Sablonnière, the
appraiser to the Confederation, after having first endeav-
oured to come to some arrangement with the original
discoverer, himself succeeded in obtaining property in
France in which he carried out various types of asphalt
work of which hemust be acknowledged to be the originator,
a title to which he did not himself omit to lay claim.
For some reason, which is not now known with an degree
of certainty, but which is believed by many to be directly
traceable to the failure of his work as the result of his use
of common pitch in the making up of his mastic, as referred
to above, we find that Eyrinis had to leave Switzerland,
and about the year 1735 we next hear of him in the Rhone
Valley, in Alsace, where he lived in the mill at Merkweiler,
between Sulz unterm Wald and Pechelbronn, and where
he discovered and opened out the important rock asphalt
mine at Lobsann, which has been continuously worked
ever since its inauguration by him, right up to the present
time. After his departure from Val de Travers that mine
ran to ruin, the work being in the end limited to the
distillation of the rock in order to extract the bitumen
contained in it, the medicinal value of which had also
oeen made known to the public there by Eyrinis. How-
ever, at the beginning of the past century, both the
discoverer and his discovery had entirely sunk into oblivion
there.
An undertaking which in 1797 attempted the working of
the then discovered veins at Seyssel under a concession
granted by a government decree dated the 9th Fructidor
V. had a no better result, and for a long time even here
the principal use of the rock was merely to extract the
bitumen with which it was impregnated. It was dis-
covered here, however, that an excellent mastic could be
prepared by the addition of five to ten per cent. of the
bitumen so obtained to the powder formed by crushing
the broken bituminous rock, but as the great mistake was
made of promiscuously recommending the use of such an
asphalt mastic, even for such purposes for which it could
not possibly be employed with success, it could not result
E 2
52 NATURAL ROCK ASPHALTS
otherwise than to throw discredit upon the possibilities
of the material, so that it rapidly fell into disusé again,
and the undertaking came to nothing, as in Switzerland.
If Dr. Eyrinis must be regarded as the re-introducer
of rock asphalt for building purposes to modern civilisa-
tion, no less a share of the honour must be given to Count
Sassenay, who first caused the mines to be worked with
success and in a practical manner. The unsatisfactory
methods adopted at Val de Travers and at Seyssel played
no small part in the closing down of these mines, and it
was only the appearance of this gentleman upon the scene
at this juncture that caused more suitable and less crude
means of extracting the rock and manufacturing the mastic
to be employed, for prior to his arrival, the entire process
was not carried out on a really business basis at all, but
rather on more or less experimental and elementary lines.
In the year 1802, just ninety years after the first
discovery of rock asphalt by Eyrinis, Count Sassenay
secured the concession and territory of the Seyssel mine
and at once introduced more rational methods of working,
which he had, as the result of carefully investigating the
properties of the bituminous rock, found to be more suit-
able and to be greatly preferred to the ones previously
adopted. To this end, and so that the peculiar minera,
could be studied with particular care, he had a special
laboratory erected at the mine in which he also trained
his workmen in the practical carrying out of rock asphalt
work of all classes. In this way he was successful in
quickly bringing the material back into the esteem which
it formerly enjoyed. Its use was rapidly adopted in
France, where the open Squares, market places, bridges and
roads were coated with a layer of this mastic, whilst case-
mates and other military constructions were protected
from damp in the same way. To such an extent did its
use spread in that country that even at the present time
France can perhaps show more rock asphalt work than can
any other country.
To Count Sassenay, too, belongs the credit of correcting
the mistake made by Eyrinis of using pitch in the prepara-
tion of the mastic and also of discovering that, where the
MODERN EXPLOITATION OF ROCK ASPHALT 53
mastic is to be subjected to much traffic, the material can
be made more durable by the addition of a certain per-
centage of dry pea gravel to it.
The success of the Seyssel working naturally gave an
impetus to that at Lobsann, which, on the death of
Eyrinis, who, in common with so many other inventors,
died without any effects, passed into the hands of de la
Sablonnière, whom we have already mentioned as having
worked with him at Val de Travers. As near here, at
Pechelbronn, there was in existence a well of mineral oil
of which Eyrinis must have been aware, since he identified
the oil from it as being the same material as that which
saturated the rock asphalt found in his mine, it is possible
that he, too, may have modified his method of preparing
his mastic by substituting it for the common pitch which
he had previously used with such disastrous results in
Switzerland. If this be so, then he can claim priority to
Count Sassenay for this discovery, but as there is no real
proof to be found that he actually did so, the credit must
needs be given to the latter.
Respecting this mineral oil well, we find that, according
to Engler, there is a report by Wimpheling as early as
1498 which bears upon it, wherein it is stated that it was
then known as the “Pechelbronnens,” i.e., “pitch
spring,” owing to a jet black, thick mineral oil that
issued from it and which even in the sixteenth century
was, according to Daubrée, collected by the peasants in
the neighbourhood for use as an illuminant in their lamps
and as a lubricant for their cart wheels.
In the year 1768 we find this mine (Lobsann) in the
possession of the le Bel family, who also acquired an
adjacent deposit discovered about the same time at Sulz
unterm Wald by a M. Rosentritt, who was the owner of
some salt pits there. From this family it passed into the
hands of a firm styled Dournay Frères, who made use
of the success of the Seyssel product in pushing their
own, following which, at the time when the Seyssel material
was the one principally used, the mine was owned and
worked by another French company, with a working capital
of close upon £50,000. After the Franco-Prussian War of
54 NATURAL ROCK ASPHALTS
1870–1871, Alsace passed into the possession of Germany
and the ownership of the .mines was then handed to
Count von Oppensdorp, and finally it devolved upon the
“Lobsann Asphaltgesellschaft m.b.H.,” by whom it is
at present being worked.
The mine at Val de Travers had meanwhile sunk com-
pletely into oblivion, and it remained for the indefati-
gable Count Sassenay to resuscitate the rock asphalt
production there until it reached its greatest height.
He obtained the concession for the extraction of the rock
here also, and after having formed an important company
in Paris to carry on the work, he was also successful in
securing the remission of all duty upon the importation
of the products of this mine into France. The result of
this was that at that period all the deposits of rock
asphalt then being worked were in the hands of French
proprietors or capitalists, but although this created a
brisk competition between the various mining companies,
as the result of which the prices of rock asphalt mastic
were being constantly reduced, the heavy freight and
transport charges involved effectually prevented the
use of this material in other than the most important
towns. For some considerable time, therefore, we find
that the employment of rock asphalt mastic for roadways
was limited to Paris, Lyons, and a few other towns
situated near the mines. This material was introduced
from France into London for foot pavements in the year
I836.
It was much later in the past century before the
German mines were first exploited. The occurrence of
bitumen here had been known for some centuries pre-
viously, the allusion to the mineral oil well at the Tagern-
see being traceable back as far as 1430, whilst the
Hannoverian deposits were referred to by Agricola in
1546. The village of Limmer in Hannover was known
even in 1730 as a spot where bitumen-impregnated
limestone was to be found, the discovery being made,
according to some writers, by Eyrinis himself during
his travels after his departure from Switzerland and
before he settled down at Lobsann. It was in 1843,
MODERN EXPLOITATION OF ROCK ASPHALT 55
however, before the vein here was worked with any success,
first by Hennig, but to-day there are several important
firms, both English and German, who are busily engaged
in the extraction of the bituminous rock from this and the
near-by Worwohler deposits. As is the case with the
Val de Travers, Lobsann and Seyssel materials, to which
this rock shows a great similarity, both as regards chemical
composition and formation, the crude rock is principally
ground up and fused together with the addition of a
certain amount of bitumen in order to form a mastic,
though a large amount is also sold as the crude powder
or as the prepared powder for compressed work.
The Italian industry is of still more modern growth,
although here, too, the extensive deposits of rock asphalt
had been known for some considerable time prior to their
actual working. The first mine from which it was
extracted industrially on the mainland is apparently
that in Abruzzi, where in the year 1868 a company was
floated with the title of “Asphaltene * to work the vein
which is found at Letto Manopello, in the province of
Chieti. This firm, however, merely extracted the light
oils that were contained in the bitumen which impreg-
nated the rock. The very costly plant which was installed
for this purpose did not extract more than 13 per cent.
of bitumen even from the best class of rock, and of this
bitumen there was never obtained more than 20 per cent.
of oil lighter than 0-875. Even this oil when obtained
was so very impure that it could not be used either for
illuminating purposes or as a lubricant, whilst the fumes
and vapors that were given off during the extraction of
the bitumen and the distillation of the oil proved so
objectionable and tainted the air to such a degree, that
the inhabitants of the village of Grottamare near by were
successful in obtaining an order for the closing down of
the works.
At Rocca Morice, the asphalt vein was worked at a
later date by an English company under the name of
“The Anglo-Italian Mineral Oils and Bitumen Company,”
but there again the same mistake was made as at Letto
Manopello of working the mines merely for the oils to be
56 NATURAL ROCK ASPHALTS
extracted from the bitumen in the impregnated rock.
An extensive extracting and distilling plant was erected
near San Valentino in which steam was used as the heating
medium. The crude rock was drawn from the mine some
five miles away by means of a light railway specially
laid for the purpose, and though the bitumen which was
extracted from the rock was small in quantity, averaging
only some 5 per cent., yet the amount of oil which was
distilled over was much greater, being about 65 per cent.
Of this oil the lighter half could be used as an illuminant
and the remainder as a lubricating oil. The illuminating
oil, however, proved to be of an extremely low grade and
the lubricating oil contained so much bituminous resin in
it that, even after both had undergone a very extensive
purification, they were only able to obtain a very slight
demand, and that only in Italy. The company therefore
finally stopped operations in 1882, though now the vein
is again extensively worked by another company, but
for its legitimate purpose, that of the extraction of the
rock asphalt from which to form rock asphalt powder
and rock asphalt mastic in the same manner that is adop-
ted in the other European rock asphalt mines.
In Filettino and Colle San Magno, in the province of
Caserta, rock asphalt deposits are also worked, but the
vein being high up the mountain side, the crude rock is
carried down into the valley where the factory is situated
by women and made there into rock asphalt powder
and mastic, in which latter, according to Köhler, as
often as not, cheap coal tar pitch is substituted for
the natural bitumen. This material is used principally
in Rome and Naples, to which cities it is despatched
by rail, for roofing and terrace work. The high freight
involved in its transit, however, prevents this particular
type from obtaining more than local employment. This
last remark equally applies to the material that is obtained
from the fairly extensive deposits in the Lariano district
of the province of Salerno which have been mined by a
Naples firm since 1878.
The best known Italian rock is without doubt that
which is obtained in the island of Sicily. It has been
MODERN EXPLOITATION OF ROCK ASPHALT 57
worked here at Ragusa by two firms constantly ever
since 1884, at first the crude rock itself being exported;
but now, as in all the other mines mentioned, the pre-
paration of the rock asphalt powder and mastic is also
carried on fairly extensively. The material, whether
crude or prepared, is sent to Mazarelli for shipment, at
which port ships belonging to certain of the Mediter-
ranean lines call regularly for cargo. In Sicily, too, the
softness of the rock is taken advantage of in the manu-
facture of fancy articles both for use and ornament.
Prior to 1840, however, it was only used locally as a
building stone, for which purpose it was found to be
particularly suited by reason of it being naturally water-
proof, permitting of easy ornamentation and carving,
and although chocolate in colour when first erected, it
soon bleaches with constant exposure into a pleasing
cream tint. It was first exported for compressed rock
asphalt work about 1856, and then by foreign firms, but
now the quantity exported annually in its various forms
reaches six figures. The stone itself closely approximates
Seyssel rock asphalt in its properties, is perfectly free
from pyrites, contains but little clay and is insoluble in
hydrochloric acid.
Up to the middle of the past century, although rock
asphalt in its mastic form was very extensively employed
in laying pavements and footpaths and as a dampcourse
or a water retainer, as the purpose demanded, yet owing
to the bad results obtained on experimental stretches,
it was rarely, if at all, used for road work which was sub-
ject to heavy traffic. An accidental discovery made
almost simultaneously, though independently, in the Swiss
and the French mines about this time altered this state
of affairs. At the mines at Val de Travers, Seyssel and
Lobsann, it was noticed that the surface of the floors of
the rooms, yards, and roads in which the bituminous
rock was handled or over which it was drawn, in the
process of time attained such a firm, resilient and water-
tight condition that better could not be wished for on
the most perfect road. Professor Dietrich claims the
discovery for the Lobsann mine, but Meyn Aates, when
58 NATURAL ROCK ASPHALTS
writing of a visit which he paid to the Val de Travers
mine in 1856 remarks that “the road between the mine
and the factory had a peculiar appearance and possessed
a thoroughly close, firm and elastic surface, along which
the horses were able to draw their loads with ease, yet
without perceptibly wearing away the road.” He regarded
this road with the greatest esteem, but does not appear to
have recognised the cause of the peculiar surface that had
drawn his attention, or the very extensive use that could
be made of the idea by adopting this system, so success-
fully demonstrated by nature, to the roads of large
towns. M. Léon Malo has it that this discovery was made
by M. Merian at Val de Travers in 1849, some seven
years earlier, but if this is the case, it seems very strange
that the above mentioned writer is apparently not aware
of the fact. There is no doubt, however, that in 1858,
three sides of the Palais Royal in Paris were laid in this
way and with Val de Travers material. This was laid
on a bed of concrete some 6 ins. thick, and was
compressed to a thickness of approximately 2 ins.
Some years before the discovery of this practical
application of the property of rock asphalt powder for
road making, a French engineer, M. de Coulaine, had
already made various experiments upon his roads with
the material as the result of his observations upon it.
He had a short stretch near Saumur, between Rouen
and Bordeaux, laid, by making up the road in exactly
the same way as for an Ordinary macadam surface,
except that, instead of finishing it with the customary
road metal, he used rock asphalt which had been, previous
to use, broken up into Small pieces and heated. This
surface coat, he found, rapidly became firm, as the rock,
being plastic when in a warm state, was pressed into the
interstices between the granite chippings which formed
the first layer, and gave a quite dissimilar resultant
finish to the road than was the case when ordinary
broken stone was rolled in, since it became quite even and
elastic. Other tests which he made upon the arches of
bridges gave equally satisfactory results, since a surface
was thus formed which was absolutely impervious to
MODERN EXPLOITATION OF ROCK ASPHALT 59
rain, a property which had not been previously obtained
even when the surface had been most carefully coated
with hydraulic cement. In addition to this, the new
paving had the advantage of having no smell, of being
perfectly clean, and, as it proved, of having very great
durability since the variations of the weather conditions
did not affect it in any way. Later, however, a trouble
arose which caused this new method of road making
which had given so much promise, to be abandoned for
the time being. It was discovered that in the summer
the heat of the day permitted the granite chippings to
have a certain amount of play, since the bituminous
covering and binder, which the heat caused to become
plastic and soft, was unable to withstand their movement.
The result of this was that cracks began to appear in the
surface layer through which the rain filtered in the wet
weather and which in the dry season became filled up with
all kinds of dirt and detritus, which thus prevented the
re-amalgamation of the bituminous rock with the advent
of later heat. The necessary opening was thus given for
the commencement of deterioration and the ultimate
breaking up of the road. No attempt seems to have
been made by this engineer to overcome this difficulty,
and his idea of thus utilising the crude rock asphalt for
road making fell through. -
The idea was again experimented with later by
M. Merian, of Bâle, who, as engineer to the asphalt mine at
Val de Travers, had noticed, as we have already mentioned,
that the road between the mine and the mastic factory
was altering appreciably for the better, despite the fact
that nothing was being done to it. Instead of becoming
very dusty in dry weather, or extremely muddy in wet
weather, or breaking up into holes and ruts with continu-
ous use, the surface had become a dense solid mass which
retained its even surface in all weathers. Upon investi-
gating this interesting change he found that whilst the
springless carts were passing over the road, part of their
load was scattered over its surface. This rock was
naturally crushed by the other carts which followed, and
the iron tyres of their wheels, acting in a similar manner
60 NATURAL ROCK ASPHALTs
to the rollers and the rammers used for the present day
compressed rock asphalt work, bonded the powder thus
formed into a close, durable, dustless and waterproof
skin. -
Acting upon this idea, he had the road between
Travers and Pontarlier laid in a similar manner, by first
reducing the rock to a powder by suitably heating it and
then, after spreading this evenly over the surface, having
it well rolled. Notwithstanding the fact that the founda-
tions upon which this work was carried out were not
prepared in any way, and were therefore not too suitable,
an excellent road was formed which gave no sign of the
weakness developed by the road previously put down
by de Coulaine. When this road was examined by
M. Léon Malo some twelve years later he declared that,
despite its very irregular maintenance, it was even then
still in an excellent condition.
To M. Merian, therefore, must be given the credit of
creating the modern compressed rock asphalt powder
roads—for, although his methods, as can only be expected,
have been brought more up-to-date, they have not,
however, been appreciably altered fundamentally—even
though the crude idea first presented itself to de Coulaine.
In England the first roadway to be laid in this manner
was Threadneedle Street, London, where, near Finch
Lane, a stretch of the compressed Val de Travers rock
asphalt powder was put down in May, 1869, which was
followed in October of the next year with further similar
work in Cheapside and the Poultry.
With the extensive adoption of this method upon a
large scale in the more important cities on the Continent,
other suitable rock asphalt powder was looked for by those
interested in its use, with the result that the rock asphalt
previously mined in other districts exclusively for the
manufacture of the rock asphalt mastic, or for the oil to
be extracted from the bitumen that it contained, was
now also employed for the preparation of the powder with
equally satisfactory results. It may with truth be said
that the rise of the Italian rock asphalt industry can be
traced directly to this discovery, as the coarseness of its
MODERN EXPLOITATION OF ROCK ASPHALT 61
grain and the uniformity of its impregnation single it
out as being of special advantage for this purpose. The
coarseness of its grain, which, as already mentioned, makes
it unsuitable for work subject to much vibration, enables
it to successfully withstand such traffic that would rapidly
wear away the softer varieties, whilst the uniformity of
its impregnation renders unnecessary either the addition
of further bitumen, or the intermixture with a more or
less richly impregnated bituminous rock as is requisite
with the other types of rock asphalt.
In America the use of rock asphalt, both as mastic and
in its powdered form, has greatly advanced, particularly
with the discovery of further beds of the impregnated
rock in that continent, though it has now a very formid-
able competitor there in the bituminous concrete or
macadam. The rock is now mined there to a large degree
in many of the states, including Utah, Texas, Kentucky,
California, etc., though in a great number of instances the
rock thus found impregnated with bitumen is a sandstone
and not a limestone, as is usual in Europe. Practical
experience in that country goes to prove, however, that
the substitution of the one for the other—it should be
borne in mind that the customary asphalt work in that
continent is compressed—is in no way prejudicial to the
life or wearing capacity of the road surface that is formed
with it, whilst the methods adopted in both cases are
practically the same, the sandstone of course, not lending
itself to reduction to so fine a powder as the limestone.
As there are but few deposits in Europe which furnish
bitumen in a state of purity, it was endeavoured for a
long time, before the wholesale importation of the Ameri-
can types, to extract this material from the various rocks
which are most richly impregnated with it and which will
surrender their bitumen content the most readily.
The method carried on at Pechelbronn was also applied
to the “molasses '' at Seyssel, to the “falums ” at Bas-
tennes and the “arkoses '' of Auvergne, and is based upon
the fact that though water is less dense than the impreg-
nated rock, it is denser than the bitumen which impreg-
nates the latter, so that this bitumen, when made to
62 NATURAL ROCK ASPHALTS
liquefy by the boiling water, rises to the surface. With
the exception of the Pechelbronn type, however, the
bitumens referred to are denser than water when at
the ordinary temperature, and though this density
diminishes more readily than that of water as the tempera-
ture is raised, and finally becomes less than it at 100° C.,
yet the difference is not sufficiently great to give the
bitumen the power to rise to the surface quickly. Again,
the bitumen, whose fusing point is not always below
100° C., does not sufficiently release itself from the
impregnated rock, which seems to be able to retain it
by a kind of capillary attraction. In the case of the
Bastennes bitumen, the salts contained in the bituminous
sands dissolve in the water and so both increase its
density and raise its boiling point, thus assisting the
extraction of the bitumen.
Although this method is practicable, it has the incon-
venience of (a) heating the entire mass of the rock together
with a certain quantity of water, and (b) the evaporation
of the water which remains mixed with the bitumen that
has been freed from the rock. This bitumen, too, always
retains a certain proportion of the rock, no matter how
often it is refined—the refined Selenitza, for instance, shows
a mineral content of 10 per cent.—in which feature it is
similar to the Trinidad bitumen.
The method of extraction as carried on in the Abruzzi
and the Tyrol always allows the bitumen to reach its
melting point, but the heating of the rock with an open
fire always gives rise to the risk of decomposing portions
of the bitumen by overheating. The bitumen thus
obtained has invariably to be again refined in order to
reduce the percentage of the rock that it still retains after
the preliminary heating. -
A further method has been suggested which it is stated
has been carried out successfully with other industries,
that of dissolving out the bitumen in carbon bisulphide
and then evaporating off the latter, when the bitumen in
its pure state will be left. In the present state of the
market, however, the cost of such a method of treating the
rock would be too expensive for practical purposes.
CHAPTER V
SOURCES OF ROCK ASPHALT AND BITUMEN
So as to afford an opportunity for comparison between
the sources of supply of bituminous compounds and of
bitumen in ancient and modern times, we give here a list
of such places in which these substances are now found.
It is interesting to note how widely dispersed throughout
the entire globe these spots are.
The requirements of the ancient civilised nations were,
so far as we can at present discover, supplied from but
three sources :—
The Dead Sea and the small bituminous springs on
its shores.
The fountains of Is (the modern Hit).
The alluvial plains of Babylonia.
Our modern necessities are filled with difficulty, if we
are to judge by the prices ruling at the present day for
this material, even though it is now obtainable from, or
found in, all the following countries :—
Argentina France S. Africa
Austria Germany Spain
Barbadoes Honduras Switzerland
Burma Hungary Syria
Canada Italy Trinidad
China Japan Turkey
Colombia Mexico United States
Cuba. Persia. Venezuela
Egypt Peru
Equador Russia
A large number of these deposits consist of more or less
bitumen itself as distinct from the rock impregnated with
it, though in varying qualities and consistencies, and in
64 NATURAL ROCK ASPHALTS
certain parts it is not in sufficient quantity as to Inake
its extraction profitable for other than local use. With
the soft or viscous bitumens, as will be readily gathered
from their fluid consistency, it is very unusual to find them
pure, but rather they are detected saturating some bed
of a mineral which from its softness has permitted of such
impregnation.
Pure bitumen, as distinct from that which is mingled
with foreign matter, is found in nature in the cavities
of the various rocks which are difficult of impregnation,
such as the “ophites' of the Landes, the “peperites’’ of
Auvergne, the “syenites * of Cuba, etc. In this condition
they sometimes form veins of more or less importance.
These veins, without being immediately connected with
the sedimentary deposits of bitumen, are usually to be
found in the same districts, though at the same time it
must also be acknowledged that they do exist in localities
in which no bituminous beds are known. Thus in the
Pays Bas to the south of the two ranges of hills around
Bentheim a vein of solid bitumen averaging from 20 to
30 ins. thick is found in the middle of an argillaceous
schist. Of this bitumen we are informed that its specific
weight is 1:07, that it is unaffected by caustic potash or
alcohol, although ether dissolves out a small and turpentine
a large amount, whilst carbon bisulphide only extracts
rather less than a quarter of it. When heated this
material distils, but without fusing any further than to a
wax-like mass. This semi-infusibility, and its partial
insolubility in carbon bisulphide, place it on the extremes
of bitumen, but its complete insolubility in either alcohol
or caustic potash prevents it from being included as a
“retina asphalt,” whilst its fairly appreciable solubility in
turpentine excludes it from the “pyroschists.”
The deposits of bitumen occasioned by sedimentary
formation are to be found in all geological epochs. The
same district, and sometimes even the same mining
concession, often possesses beds of bitumen belonging to
the formation of different earths. In the following pages
only those are referred to and described in detail which
are in use daily in commerce.
SOURCES OF ROCK ASPHALT AND BITUMEN 65
Bitumen occurs in a solid state and in its purest con-
dition in the Old World, in the Dead Sea. This is, as is well
known, a large inland lake in the south-east of Palestine,
lying some 1,300 ft. below the level of the Mediterranean
Sea. It lies deep down between precipitous and bare
cliffs and has been aptly described as a huge grave.
It is about forty-seven miles long, its average width is
about six miles, whilst its surface is some 22,000 acres in
extent. The lake receives a considerable amount of
water from the river Jordan and other streams and
springs, but despite such additions its level is gradually
lowering, as the entire amount of water thus received
is evaporated from it by the tropical heat that prevails
there. The whole district is absolutely barren, without
the least vestige of vegetation, and gives one the impres-
sion of being completely burnt up. All nature seems to be
dead, from which arises the name of the “Dead Sea,”
though the lake itself, according to recent visitors in the
district, “ lies at the gazers’ feet, blue and smiling like the
Bay of Naples.”
Its origin has given cause for dispute. According to
van de Bilde, it is to be attributed to volcanic activity
which opened out a huge subterranean cavity, causing
at the same time the occurrence of the bitumen, sulphur
and pumice stone deposits which have been found in
that district, the opening thus created in the earth forming
the bed of the lake. The Biblical description of the
destruction of Sodom and Gomorrah, which would imply
a volcanic eruption, is held out in confirmation of this
view. The district was carefully inspected in 1866, how-
ever, by Fraas who, on the other hand, states that no
trace of volcanic formation could be discovered. On
the contrary, he affirms that he found that the earth
in the neighbourhood of the lake was composed of
pure chalk through which the water forming the
lake had worn its way. Instead, therefore, of the
Biblical narrative just mentioned confirming the vol-
canic theory, it is now alleged that the latter is based
upon it.
The water of the lake is clear but extremely saline; its
N.R.A. F
66 NATURAL ROCK ASPHALTS
specific gravity is approximately 1:21, but this figure
varies according to the season of the year and also to the
part of the lake from which the sample is taken. In
the year 1778 Lavoisier determined it at 12403, in 1807
Marcet placed it at 1.211, whilst some years ago Mitchell
gave the figure as 1203. Ordinary sea water, it may be
added, has a specific gravity of 1.027. Bitumen flows
into the lake from several hot springs adjacent to it,
together with water, and solidifies there in lumps which,
owing to their lighter specific gravity (1-104), float to the
surface, from which they are collected by being scooped
up in suitable vessels. The quantity thus obtained is very
variable, becoming much greater after local earthquake
shocks, whilst, as we have already seen, in the ancient
times, according to the Bible, to Strabo and Diodorus, it
must have been very considerable. After the earthquake
there of 1834, a mass rose to the surface at the Southern
extremity of the lake from which the Arabs carried off
some twenty tons, whilst in 1837, after one of the greatest
shocks to which that district has been subject in modern
times, a mass was seen floating upon the surface of the
lake from which fifteen tons were taken and sold in the
bazaar in Jerusalem at £40 per ton.
Of these periodic appearances of “islands' of bitumen
on the lake in the olden times we have a fairly detailed
account left us by Strabo, who describes them as follows:
“The lake is full of bitumen which at irregular intervals is
thrown up from the depths of the lake. The bubbles burst on
the surface of the water, which latter thus appears to be boil-
ing. The mass of bitumen protrudes out of the water and has
the appearance of a hill. At the same time it gives off Smoky
vapors which rust copper and silver and which tarnish the
lustre of all polished metals generally, even gold, although these
vapors are invisible. The natives can tell when the bitumen is
about to come to the surface, as then their metalutensils begin
to rust. Noticing this, they at once make their preparations
for collecting the bitumen by means of rafts made up of a
collection of rushes.”
This writer mentions, too, that it is the weight of the
water of the Dead Sea which causes the bitumen to rise
to the surface.
SOURCES OF ROCK ASPHALT AND BITUMEN 67
According to M. Terreil, this water contains an organic
material which furnishes the characteristic odour of the
bitumen that is found here, and which is particularly in
evidence in the neighbourhood of Ras-Mersed at a point
where the foetid emanations referred to by Strabo as
accompanying the appearance of the bitumen can still
be noticed.
Without attempting to explain the occurrence of the
bitumen in the Dead Sea, it may be accepted that hot
springs existing at the bottom of the lake cause the bitu-
men there to separate from the rock that it originally
impregnated, in a similar way to the methods adopted on a
smaller scale in many of the factories engaged in extracting
bitumen from the rocks or sands impregnated with it by
boiling them with water.
The bitumen obtained at the Dead Sea possesses a
characteristic odour, is black in colour and forms a black
powder when crushed. It begins to fuse at 135° C.; it
is partially soluble in alcohol and ether, more so in
benzine, and completely and quickly so in chloroform,
carbon bisulphide, oil of turpentine, and the petroleum
distillates. It is insoluble in the alkalies, whether con-
centrated or dilute, hot or cold. With concentrated
sulphuric acid it evolves, upon heating, sulphurous acid,
and forms a dirty brown solution. It is not attacked by
nitric acid even when it is heated.
Regarding the deposits in the district of Palestine, the
following extract from a consular report issued by the
Foreign Office is of interest; and it might here be remarked
that the concession for the working of the Hasbeya
deposit, at present exploited by the civil list of the Sultan,
was offered for tender by the Turkish government as
recently as the beginning of the past year.
“The principal occurrence is in Syria. The bitumen is found
principally at Hasbeya, South-east of Mount Hermon, where
during the last eighty years it has been obtained with more or
less interruption. Originally the estate and the mines were
owned by the well-known Moslem family of Shehab, who
worked it only when they were in need of money and stopped
again when the temporary financial embarrassments were
cleared off. Under the Egyptian administration the mine was
F 2
68 NATURAL ROCK ASPHALTS
f
confiscated and so remained idle for a long time. About 1856
some merchants belonging to Damascus received from the
Turkish government permission to extract from the mine as
much of the bitumen as they wanted. This concession was
temporarily renewed conditional to the payment of an annual
allowance, until finally the authorities determined to lease the
mine properly and so put it up for tender. In consideration of
a payment of 65.5 per cent. of the annual output, Ibrahim Abssi
became the lessee. This lease was held about six years, until
the death of Abssi, and since then it has not been renewed, as no
lessee is to be found up to the present who will accept such
terms.”
The deposit at Hasbeya was worked at a place called
Bir el Hummar, but, the demand being very limited, its
yearly output was only a few hundred tons. Here a
score or so of pits, rather more than a yard in diameter,
have been dug into the ground, which open up a very
rich deposit having the appearance of a “fault,” the
numerous openings in which have been filled up with
bitumen. M. Lartet, when he inspected these workings
after they had been abandoned, found near their mouths,
amongst heaps of waste debris, some flint strongly
impregnated with bitumen and coloured a beautiful
black with it. In the rock, too, he found numerous traces
of petrified remains of fish. Dr. Anderson, who visited
this mine during the time that it was being worked,
analysed the bituminous rock to be found there and found
it to be largely (77°36 per cent.) of limestone impreg-
nated with, on an average, 10 per cent. of bitumen. The
bitumen as obtained at Hasbeya is only slightly soluble
in alcohol, more so in ether, and almost entirely so in
oil of turpentine. It softens in hot water and fuses at
121°C. It burns with a yellow flame, leaving a grey
cinder, which even a blowpipe does not reduce to an ash.
Near the source of the Jordan, amongst white chalky
marls, is also to be found a marl which possesses a bluish
tinge, so faint, however, that it could be easily passed
by without being noticed. On breaking off a fragment
from the surface of the rock though, a brown fracture is
perceived, which loses its colour with a long exposure to
the sun. The Khaliwet deposit between Rascheya and
SOURCES OF ROCK ASPHALT AND BITUMEN 69
Hasbeya is of this type, whilst similar deposits are also
to be found to the north-east in the vicinity of Damascus.
Near the hot saline springs of Hamman, near Tiberiad,
Father Hebard found a deposit of bituminous limestone,
whilst these waters themselves, according to Dr. Anderson,
contain bromine associated with an organic compound.
At Nebi Mousa, near the north-west extremity of the
Dead Sea, is again to be found limestone which is rich in
fossilised remains of marine life, which shows a beautiful
black fracture and gives off a strong aromatic Smell,
though it only shows its presence by large bluish spots
to be seen in the white cliffs, which spots correspond to
the more highly impregnated parts. By reason of its
great combustibility, it is used by the Arabs in that
neighbourhood as fuel, besides in its customary employment
as a paving for courtyards. It is known to these people
as “the stone of Moses,” and is now also made use of by
the Christians in Bethlehem for the manufacture of pious
articles. According to the analysis made by Dr. Anderson,
it contains 69 to 82 per cent. of limestone and 14 to 25
per cent. of bitumen, the remainder consisting principally
of earthy matter. It is the richness of the impregnation
of this stone that occasioned the suggestion of the idea
that it might have been formed by an emulsion of a
liquid bitumen, or a bitumen in a liquid state, with a
strong solution of lime in water, and this, it may be
mentioned in passing, is held by some authorities to be
the true theory of the formation of the bitumen-impreg-
nated limestone, the fact of the material falling to powder
when the binding agent is softened under the influence
of heat being held forward as one of the sustaining
proofs. Against this, however, is the uncontrovertable
fact that the impregnated stone mined at Acquafredda
in the Abruzzi does not segregate with heat.
According to the Arabs, bitumen is to be found in the
red sand cliffs on the east shore of the Dead Sea opposite
Ain Jidy on the slopes of Belkan, but European travellers
have not been able to verify this statement. M. Lartet
has, however, in his researches near Kerak, discovered
bitumen on the shore between Ouadi el Draa and Ouadi
70 NATURAL ROCK ASPHALTS
Kerak. The limestone and the beds of flint here appear
to have been penetrated by a bituminous material
which has coloured them a deep black. He believes, too,
that in the vicinity of the west coast near Masada, he
has discovered the rocks mentioned by Strabo as dis-
tilling pitch. The bed at Ouadi Sebbi which is enclosed
in the middle of a dolomite limestone, in fact, shows
numerous pieces of bitumen which have penetrated the
rock in a fluid condition and gradually solidified there in
the numerous cavities in it, filling them with a hard,
black and brilliant bitumen in such a way as to lead one
to imagine that there is a true bitumen “fault ’’ there.
About a day’s march from Ouadi Sebbi, near the salt
deposit of Djebel Usdom, are to be found lying on the
shore “conglomerates '' formed of pebbles and flint
gravel cemented together with bitumen and deposited
there by the waters of the Ouadi Mahaouat on their
way down to the lake. On making one’s way up the
Ouadi, the quantity of these remains is seen to increase,
and at 300 metres from the shore an important deposit
of bitumen is reached which has been explored by different
travellers. Here the bitumen exudes out of cracks in
the limestone, falling at times in the exact form of stalac-
tites, and at certain points it cements together the sand
and gravel which compose the old alluvial soil deposited
on these limestones, and thus gives birth to the bitu-
minous conglomerates that have been seen washed down
the stream by the Ouadi Mahaouat.
On the west shore of the Dead Sea, and on the banks of
the Lisan, the Arabs gather pieces of a hard and brittle
bitumen which they offer to travellers. It is stated that
ligneous fibres have been recognised in samples thus
obtained, thus showing that this particular bitumen had
a vegetable origin. It is affirmed, too, that there are
springs of a semi-fluid bitumen opposite the town of
Nasarieh in the province of Busreh. They are not,
however, exploited, the use of the material there being
apparently limited to that of a cement for building
purposes locally and as a substitute for sealing wax.
In general the Syrian bitumen is so pure and so free
SOURCES OF ROCK ASPHALT AND BITUMEN 71
from extraneous matter, that it can be used for the finest
classes of work, such as for the best types of black varnish
and for photography. +
Of the lesser known European deposits, passing mention
may be made of those found in Albania, worked princi-
pally by the Société Anonyme des Mines de Selenitza.
This material is very similar to that obtained from the
bitumen “lake ’’ in Trinidad in many respects, and
though it has not the tenacity of and is more brittle than
the latter, it has a higher melting point, and is much
more pure, as the analysis given later shows. This
bitumen is now largely employed in both well-known
German, French, and Austrian rock asphalt factories as
well as by many of the large firms of rock asphalt con-
tractors. In a large amount of the rock asphalt work
carried out upon the world-famed Parisian boulevards,
this bitumen is stated to have been exclusively used.
On the coast of Albania, near Durazzo, is to be found
the Apollinia of the ancient Greeks, the high hill upon
which the priestess of the renowned Delphic oracle was
wont to sit and inhale the fumes of the gases which were—
and still are—emitted from it, until she became stupefied,
a condition supposed to be necessary for the pronouncing
of those inspired prophecies which have rendered that
shrine so famous.
In Spain the “Compañia General de Asfaltos y Port-
land,” whose territory lies near Pobla de Lillet, at the
extreme north of Catalonia at the foot of the Pyrenees,
are working important mineral deposits which bear
bitumen in conjunction with lignite and petroleum.
Bitumen is also found in Russia, particularly in con-
junction with the petroleum oil fields, a matter which is
looked upon as tending to confirm the hypothesis of the
close relationship supposed to exist between the two
materials. It has been stated that the peculiar “wurt-
2ilite ” is obtainable in the Ural district, but up to the
present the writer has not been able to ascertain whether
it is present in such quantities as to enable it to be placed
upon the market. Later advices, however, would show
that it is found in Semirietschensk in Asiatic Russia
72 NATURAL ROCK ASPHALTS
some twenty kilometres from the Balchasch Sea and
twenty kilometres from the river Ili which flows into it.
This material is like bitumen, of a brown colour, has a
specific gravity of 0.9 to 1:25, is easily cut and is elastic
like rubber.
In the Caucasus the ground is saturated with a bitu-
men that has been formed by the evaporation of naphtha.
It is known locally as “kir” and is found in large tracts
near Goriatchevodsk. True bitumen deposits, however,
are to be found situated near Mikailovsk and the mineral
waters of Sleptzow. “Kir” is soluble in ether leaving
behind it an earthy matter, and is heavier than water.
A very impure variety of this material, known as “katran,”
is also to be met with which finds a very extensive use
locally as fuel.
On the banks of the Volga there is to be found a small
region of deposits belonging to the carboniferous forma-
tion amongst Permian, Jurassic and Cretacean rocks,
which, however, belong to the geological stage earlier
than that of the carboniferous limestone. They stop to
the north at a bend of the river Volga known as the
“Tumulus of the Tzar.” These deposits are found still
further east in the banks of the Sisranka, the Krunza,
and the Oussa. When a forage pit was dug near Batraki,
no oil was met with either above or below this forma-
tion.
To the south-east, carboniferous limestone is found in
a succession of layers of ordinary limestone and of this
rock impregnated with bitumen, which last material
is also met with in a pure state in globular form. These
globules are of but secondary importance, although the
bituminous limestone is worked and employed in the
manufacture of rock asphalt mastic. Particularly rich
beds are found near the town of Sisran, along the banks
of the Sisranka and its tributaries, along the Oussa and
along the Volga between Kostyachi and Petcherskoie.
In these last instances the carboniferous limestone shows
a number of outcrops in the precipitous banks of the river,
thus rendering their working more easy. Near the village
of Petcherskoie the limestone beds dip below the level
SOURCES OF ROCK ASPHALT AND BITUMEN 78
of the Volga, and are replaced with beds of Permian
formation which, however, are very poor in bitumen.
To the north of the Samarskaia-Louka, in a wooded
district known as Bahilova-Askoulska, is found a deposit
of maltha. This deposit occupies an area some 400
metres long by 100 metres wide, and at the centre it is
some 10 metres deep. It is in a layer of sand belonging
probably to an alluvial soil and which contains 20 per
cent. of a semi-fluid bitumen. It is only covered over
with a thin layer of vegetable soil, and is surrounded by
unimpregnated sand. It lies about three kilometres
away from the river Volga.
The rocks containing bitumen in this district have
been worked since 1874. They are extracted from open
workings by quarrymen and used for the manufacture
of rock asphalt mastic in three factories, of which the most
important is perhaps that at Sisran, where the rock is
especially rich in bitumen, as the following analysis made
at the Technological Institute at St. Petersburg shows.
Bitumen . . tº e tº Q tº º 30°50
Limestone tº º tº º tº º 66°23
Magnesium Carbonate .. tº gº 3-27
In Europe generally the occurrence of bitumen is
fairly extensive, but it is usually found impregnating
some mineral or rock, and not in really true deposits of
a more or less impure type.
In Austria Hungary it is to be found scattered amongst
lignites and clay in the bituminous sand of Tataros,
which contains approximately 15 per cent. of bitumen.
It forms here a black, soft and sticky rock which gives
off a penetrating odour, and commences to fuse even when
held in the hand for a short time. In the Tyrol, about the
Inn, veins of impregnated rock are found which are called
by the inhabitants of that district “stinkstein ‘’ or “gallen-
stein ‘’ according to the comparative richness or poorness
in bitumen.
A little above Innsbruck the river Inn forms the
natural boundary between the eruptive rocks and the
Jurassic limestone which forms the left bank. The
74 NATURAL ROCK ASPHALTS
asphalt beds of the Seefeld district (some 5,000 to 6,000 ft.
above the level of the sea) belong to this last formation.
Their thickness varies from 6 ins. to 4 ft., and they are
sandwiched between dolomite. There are, however, some
beds of “gallenstein '' which are rich in iron and copper
silicates and show, especially low down the deposit, Small
veins of anthracite. “Stinkstein ‘’ has the following
composition :-
Bitumen . . © & tº e © . . 26°41
Calcium and Magnesium Carbonates .. 38'22
Clay © tº tº wº © ſº tº to e Q 6-67
Sand tº tº tº ºt tº º º º . . 19°03
Iron Oxide tº º º to º tº @ 5°95
The analysis of the bitumen reveals the presence in it
of nitrogen as well as sulphur. This bitumen has been
extracted from both “stinkstein ’’ and “gallenstein '' on
a commercial scale in both vertical and horizontal retorts,
the first allowing the escape of the more volatile parts,
That obtained from “gallenstein '' is the lighter of the
two, the densities being 0-946 to 0-977 and 0.954 to 1-080
respectively, according as to whether horizontal or
vertical retorts are employed. This bitumen is used in
the manufacture of rock asphalt mastic.
Following the course of the Inn, a siliceous limestone
is found a little above Kufstein, at Hoering, on the right
bank of the river, which is also called “stinkstein “” and
which is similar to the bituminous limestone which is
obtained at Lobsann. At Gratenbergl, near Hoering,
the Jurassic limestone encloses a large amount of viscous
bitumen accompanied by numerous veins of crystalline
limestone. In Dalmatia a deposit of bituminous lime-
stone has been known in the island of Brazza, opposite
Spalatro, since 1839. This, however, only shows an
average bitumen content of 7 to 8 per cent. It is found
in conjunction with a dolomite of the Jurassic earth,
having the chemical composition of 3CaCO3.2MgCO3.
The bitumen is obtained from it by a kind of liquation
as a black pitch-like mass with a lustrous fracture, fusing
at 90° C., and is completely soluble in oil of turpentine.
SOURCES OF ROCK ASPHALT AND BITUMEN 75
At Morroviuzza, near Sebenico, a similar bitumen is
found filling up the cavities in a Jurassic limestone. In
1843 a bed of rock asphalt consisting of dolomite impreg-
nated with bitumen and identical with that at Brazza
was discovered at Porto Mandolo, near Trau, also in
Jurassic limestone.
CHAPTER VI
sourcES OF RocK ASPHALT AND BITUMEN (continued)
IN Germany, of course, are the well-known deposits of
Limmer, Vorwohle and Alsace (Lobsann), near which
latter are also found springs of the more fluid maltha,
of which mention has already been made of that at
Pechelbronn.
The deposits of Limmer and Worwohle, as well as those of
Ahlem and Velber, are in the neighbourhood of Hannover.
The two former belong to the white Jurassic formation,
whilst the latter are found in earths of the Cretacean
epoch, and are of but little value owing to their low per-
centage of bitumen.
The Limmer mines are in the plains of Acker, in a
slightly undulating earth. The asphalt beds are not very
thick and extend only very slightly beyond their outcrop.
The upper portion, which is 3% metres thick, consists
of a very pure rock rich in fossil shells, and lies upon
a deposit of clay of a similar thickness. Below this
clay is found the principal layer of rock asphalt, which is
Some 6 to 7 metres thick and much richer in bitumen.
Near the outcrops these beds are very dislocated and form
thin layers which show a very variable bitumen content.
They slope at an angle of 30 to 40 degrees from north
to south, and are worked in the open by cutting a trench
some 5 or 6 metres deep, though in those parts which
are more distant from the outcrop the work is carried
on by means of shafts and galleries in the ordinary way.
According to certain authors, this rock asphalt increases
in richness as the work advances, and variations have
been noticed of from 8 to 20 per cent.
SOURCES OF ROCK ASPHALT AND BITUMEN 77
The following is an analysis made at the mines of a
typical Sample :-
Bitumen gº º & º tº e ... 14°30
Limestone . . tº e tº º . . 67°00
Clay, etc. e e tº º tº e . . I'7°52
LOSS . . tº tº tº e tº dº tº tº I*I 8
The Worwohle mines are in a more mountainous district.
The deposit here forms a succession of beds having a total
thickness of 20 metres but with varying impregnation.
They slope at an angle of 20 degrees towards the Hils
mountains, and their bitumen content varies between
6 and 10 per cent. The following analysis was made by
one of the mining companies here :—
Bitumen tº º tº tº º º tº e 8°50
Limestone . . º º tº º . . 80°59
Clay, etc. . . & ſº tº º . . 4'03
Insoluble in acid . . tº gº . . 4°77
LOSS . . tº ſº e - tº e Q & 2°II
Not far from the Hils mountains it is stated that
between Creiensen and Holzminden, and near Wintjenberg,
in Brunswick, important deposits of rock asphalt have
been discovered in the white Jurassic formations below
the limestone. There have also been noticed masses of
gypsum impregnated with bitumen in the intermediary
Jurassic formations and chalk. Further deposits in
Germany of lesser note are in Westphalia, at Darfield,
Buldern, Hangenau (Coesfeld) and Oppelhülfen (Münster),
whilst in Alsace are found liquid, viscous and solid
bitumens under very varied geological conditions. They
are occasionally met with in the transition soil of the
Upper Rhine in the metallic veins,
In Low Alsace, at Rothbach, Westerweiler, Rauschend-
berg and Molsheim, the “faults * which form the limits
of the “shell’’ limestone show bitumen in both liquid
and solid states.
In the Sulz unterm Wald district, the bitumen is found
for a length of ten to twelve kilometres, impregnating
the sedimentary layers at Sulz unterm Wald, Pechelbronn,
78 NATURAL ROCK ASPHALTS
Hatten, Schwabweiler, Oberkützhausen, Kinderloch and
near Prentschdorft as a liquid, and in a more solid form
at Lampertsloch, Lobsann, Walkmühle, Bulenbach,
Drachenbronn and Lochmühle. According to M. Daubrée,
these last deposits, although in strata-like masses, also
appear to be connected with the dislocations of that dis-
trict. They are crossed by numerous “faults '' which
run parallel with the terminal “fault ’’ of the Vosges
sandstones, which, whilst they were formed at the Tertiary
epoch by outflows of iron ores, etc., were again opened
at a contemporaneous epoch by the outflow of basalt at
Gundershoffen, eight kilometres away from Lobsann.
The deposits of salt, whose existence in the Tertiary earths
has been proved by M. Daubrée, and which now feed the
numerous saline and bromine springs there, have in all
probability been formed in a similar manner. It may
be mentioned that it was the working of one of these,
salt deposits that led to the discovery in 1771 of a
bituminous deposit here, whilst it is said that the first
petroleum wells that were worked in the United States,
were discovered under the same circumstances.
The bituminous sand at Pechelbronn forms veins
amongst the unimpregnated Sand, and has a thickness of
0-8 to 2:0 metres, though at times it reaches to as much
as 4 metres, and a width which varies from 30 to 60
metres. The general direction of these veins is almost
parallel with the general direction of the stratum of which
they form part, and of the limiting “fault ’’ of the Vosges
sandstone. A large amount of iron pyrites is found in
them, whilst they also contain thin beds of lignite. At
Schwabweiler and Pechelbronn gases are evolved, which
in 1845 occasioned the death of five miners, whilst later,
in 1849, the emission was so great in the St. Joseph
workings that it caused the entire stoppage of the opera-
tions there for some time.
The bituminous limestone at Lobsann is in three
layers, of which the thickness varies from 1 to 2% metres,
divided from each other by a soft friable limestone
which itself possesses a bituminous smell. In it are found
pyrites, calcium sulphate and masses of grey and red
SOURCES OF ROCK ASPHALT AND BITUMEN 79
sandstone. The following is the composition of the bitu-
minous limestone :—
Bitumen tº º tº º tº Q . . 11'90
Limestone . . tº º e e . . 69°00
Sand and Clay © o tº e . . 4°30
Sulphur e - © Q e e . . 5°00
Iron oxide . . © e tº ſº tº tº 4'45
Water, etc. . . © º tº º ... 3°40
| The Pechelbronn bitumen is black and viscous, with a
density varying between 0.90 and 0.97. It is extracted
for use in mixing with the bituminous limestone at
Lobsann, for the fluxing of Trinidad and other hard and
brittle bitumens, and also in order to obtain illuminating
and lubricating oils from it. Where it is brought to the
surface by natural springs or as the result of boring
operations, it is merely collected from the surface of
the water upon which it floats, and when found in the
bituminous Sands, it is extracted by means of boiling the
mineral with water, as has already been mentioned.
When the stills used in the distillation of the bituminous
limestone are taken to pieces, there is often to be observed
‘ining the interior of the pipe through which the oil is
discharged, a very solid and hard deposit, steel grey or
black in colour, having a sharp metallic ring. This
incrustation consists of almost pure arsenic, mixed only
with traces of carbon, and often reaches 3-in. in
thickness. The arsenic thus deposited forms a millionth
part of the weight of the distilled rock, though some
limestones give much less. According to M. Daubrée,
all the arsenic contained in the limestone is not condensed
in this way, but an appreciable quantity passes over with
the oils that are extracted. It has not been determined
absolutely in what state the arsenic is associated with the
rodk, though by dissolving out the bitu
stone successively, 2 per cent. of a
which gives the reactions of arsenious
In Switzerland the Val de Tº
pre-eminent, although in 1900 a.
discovered near Credo, on the







80 NATURAL ROCK ASPHALTS
and the Val de Travers deposits, which consists of beds
of sand impregnated with a readily flowing maltha. Of
the first named, the beds at St. Aubin, Vallorbes, Char-
venay and Orbe are too poor in bitumen to be worked
with any degree of success, though that obtained at
Epoissats has been used for the manufacture of the rock
asphalt mastic. -
The bituminous limestones which are to be found between
the villages of Travers and Couvet are of varying but very
appreciable thickness. They belong to the superior
Urgonian (Cretacean epoch) and rest upon a pebbly lime-
stone which is broken and faintly impregnated. They
are covered with “crappe,” which is itself nothing more
than an asphaltic bed, but being less impregnated with
bitumen it is much harder. Towards the hamlet of Presta
the bed crops out parallel with the Reuse for a length of
800 metres. To the south-west, towards Couvet, the
bitumen content diminishes and the bed disappears below
the level of the valley. To the north-east it slopes sharply
towards Travers.
Above this formation is a black asphaltic sandstone,
separated from the bed of Urgonian asphalt by the entire
thickness of the beds of the inferior Aptien.
The rock extracted from the Urgonian bed looks very
much like soot and gives off a bituminous odour. Its
content of bitumen varies between 10 and 20 per cent.
An average sample shows the following composition :-
Bitumen tº e • & © e . . 10'10
Limestone and Magnesium Carbonate 88.25
Clay and Iron oxide . . tº e . . 0°25
Water . . e G © e © e . . 0'50
This rock asphalt is slightly attacked by dilute hydro-
chloric acid. Alcohol extracts but very little of the
bitumen, thoug \ether dissolves out almost all, leaving
Shind a resi of limestone which shows scarcely any
isne is about a kilometre away from
by an English company, both for
Which is sent away in its crude






SOURCES OF ROCK ASPHALT AND BITUMEN 81
condition, and for the manufacture of the rock asphalt
powder and mastic. Operations are carried on some 15
metres below the level of the Reuse, the water of which
oozes in and has to be kept down by powerful pumps
which have been installed for that purpose.
In France the mines at Ain and Haut-Savoie (Seyssel)
are also well known, though for practical purposes,
compressed work especially, it is usually necessary to mix
the products of these mines, owing to their low percentage
of bitumen, with the richer products of other mines,
according to some experts; for although the type of the
limestone is such that it does not require the same per-
centage of bitumen as do the softer rocks when used for
any purpose, yet the percentage naturally present is not
sufficient in itself.
The first working of rock asphalt here dates back from
the end of the eighteenth century. Very precise details
on the subject are given in a letter from M. Secretan, the
then lessee of the mines, addressed to the Minister of Mines,
which is to be found in the Journal des Mines (Vol. 14),
from which the following extract is taken :—
“DU PARC, LE 22 PRAIRIAL II.
“We continue to meet with kidneys of pyrites in our
galleries, from the cracks of which, as soon as an opening is
made, there sometimes exudes a very pure bitumen.
“We have noticed that the rock asphalt surrounding these
kidneys is several metres thick, being usually much greater
than elsewhere, and contains more bitumen.
“Despite our constant study of the mine, we have not yet
been able to obtain any definite knowledge regarding its forma-
tion. The bed we are now working is sometimes three to four
metres thick, when it will end abruptly. Sometimes it reduces
to ten centimetres thick and at other places it ends by splitting
into two beds, each being from ten to twenty-five centimetres
thick, separated by a layer of blue clay between which and the
lower bed of asphalt is often to be found a narrow bed of very
hard pyrites some three to four centimetres thick.”
M. Léon Malo, in his work, “L’Asphalt,” p. 31, mentions
the existence of certain portions of the Seyssel deposit
in which the impregnation is incomplete, that is to say,
where portions only of the bed of limestone are bituminous,
The deposits at du Parc, Surjoux and Pyrimont are
N.R.A. G.
'82 NATURAL ROCK ASPHALTS
now exhausted and the work is being carried on in the
Volant deposit by means of shafts and galleries, the
bottom beds being some 35 metres below the level of the
Rhone.
The rock obtained from these deposits shows a fine
homogeneous grain without the interposition of particles
of white limestone. The appearance of a fracture,
whether made parallel or vertical to the direction of the
bed, is the same, but sometimes the rock is dotted with
spots which are not so deeply coloured, that is to say,
which are less impregnated with bitumen. In other
places it encloses numbers of shells 1 to 3 mms. in
diameter, which are filled up with crystalline limestone
and impregnated with bitumen like the rest. Often
large rhomboidal crystals with planes of cleavage
of 1 to 2 mmS. are found which are similarly im-
pregnated. -
Under the microscope this rock has the appearance of a
powder cemented together, each grain of which is
enveloped in a thin film of bitumen by means of which
it is stuck to the neighbouring grains. Another still finer
powder, made up of small crystals of limestone and coloured
brown by the bitumen, fills up the voids between the larger
grains. In short, this limestone has a semi-crystalline
structure and therefore is not capable of receiving more
than a low impregnation of bitumen. This is verified by
the following analysis made by the École des Ponts et
Chaussées:–
(a) (b)
Bitumen .. © tº º tº tº º 2-25 8°00
Limestone tº e tº gº . . 97°00 89° 55
Clay and Iron oxide .. . . 0°15 O'I 5
Magnesium Carbonate . . . . 0°20 O'LO
Loss on heating to 90° .. . . 0°20 I'90
According to M. Berthier, this bitumen is readily and
entirely dissolved by both ether and turpentine. If the
rock is crushed and then treated with hot hydrochloric
acid, it cakes together and then forms into brownish black
clots which rise to the surface and adhere to the sides of
SOURCES OF ROCK ASPHALT AND BITUMEN 88
the vessel. It is, however, necessary to heat it constantly
for a long time, in order that the acid shall dissolve all the
limestone.
Besides the impregnated limestone, sandy rocks of the
“ molasse ’’ formation are also found in this district. They
consist of grains of milky quartz, from the size of a millet
seed to larger than a lentil, stuck together with a soft
intensely black bitumen. Similarly rounded grains of
white compact limestone can also be recognised amongst
the quartz. -
Alcohol but slightly attacks this rock asphalt, merely
receiving a faint yellow colouration, whilst the residue does
not apparently change except, perhaps, by becoming
rather less fusible. Ether dissolves the bituminous matter
almost completely, whilst oil of turpentine acts most
energetically and dissolves it entirely. When treated with
boiling water, as at Pechelbronn, only 3 per cent. of
bitumen can be extracted.
At the commencement of the Tertiary era, Limagne
formed a vast fresh-water lake, but to-day it is covered .
with important deposits of granite, “arkoses * and sandy
clays, limestones, “peperites” and basalt. Bitumen
impregnates the “arkoses * at Chamalières, near Royat,
and the limestones at Pont du Château, Lempdes, etc.
It has been found as veins in the granite, and it is also to
be met with amongst the “peperites '' (basalt cinders
cemented together with a limestone slime). To this last
category belongs the deposit at Puy de la Poix, described
in 1759 by Guellard in the journals of the Académie des
Sciences, from which the following is taken :-
“Le Puy de la Poix is divided in two levels, the higher of
which is twelve to fifteen feet thick and the other a little less,
though it furnishes more bitumen than does the first and also
in it is found a quantity of a liquid bitumen in two or three
spots. This hill faces towards the north and is formed of a
more or less soft stone of a bluish colour dotted with black
pockets of bitumen. The rock around these pockets is white
or yellowish. Some of the rock is black without any pockets;
other parts are only partially speckled and partly black; there
are pieces of a reddish brown colour with round pockets of a deep
iron grey ; some pieces are incrusted with a hard and lustrous
G 2
84 NATURAL ROCK ASPHALTS
bitumen, others are coated instead with a yellowish material
which is spathic and almost crystalline. Many are dotted with
pyritous spots showing the yellow colour that is peculiar to
pyrites. At the side of the hill is a small mound about three
feet in height and with a diameter of fifteen feet. It appears
that this is formed solely of bitumen which apparently has
Solidified on the ground as it has emerged from below. The
Spring must be in the middle of the elevation, for no other sign
of it is to be found although the ground around and below it
has been dug up.”
As a mauter of fact, bitumen still exudes from the rock
in Gonjunction with water. It seems to be expelled by
certain gases which form bubbles in the bitumen and which
can be ignited if a lighted match is put to them.
Le Puy de Crouelle shows similar phenomena. At
Malintrat, the oozing out of the bitumen has given rise to
the formation of underground workings which consist
principally of a method of draining this material from the
rock impregnated with it, the bitumen obtained being
employed commercially in the same way as the Syrian
bitumen.
Ebelmen has examined specimens of a bitumen found
in this district which is solid at ordinary temperatures,
but softens in the hand and fuses completely at a fairly
low temperature. The following is an extract from the
report he made upon this material as the result of his
investigations :—
“The fracture is conchoidal and of a beautiful black colour.
It can be reduced to a coarse powder, but it is not possible to
pulverise it completely, as the powder which is formed coheres
spontaneously. The colour of the pulverulent mass is a dark
brown. At 12°C. its density is 1:068; it is only partly soluble
in ether but almost completely so in turpentine. When thrown
upon a bright fire it burns with a crackling noise, at the same
time throwing out sparks in all directions. If it is heated care-
fully in a tube to 110 to 120° C., it swells up greatly, giving off
a considerable amount of water which retains (probably owing
to the light oils which evaporate with it), though to a faint
degree, the odour which is peculiar to this bitumen. The
faculty of decrepitating with the action of strong heat, possessed
by this bitumen, is attributed to the giving off by it of this
water. When submitted to a temperature of 160° C. for two
hours, 1:885 grammes gave off 0-382 grammes of water, i.e.,
20:26 per cent. This water appears to be intimately mixed
SOURCES OF ROCK ASPHALT AND BITUMEN 85
with the bitumen, from which it only separates out when the
material is at a low temperature and coarsely ground.”
The proportion of water mentioned by Ebelmen is,
without doubt, greatly exaggerated, as the bitumen con-
tains a certain quantity of oils which are volatile at less
than 160° C. -
The rocks impregnated with this bitumen differ amongst
themselves, both by their special characteristics, like the
“arkoses * of Chamalières, the quartz sand of Lussat,
the limestones of Pont du Château, and also by their
mode of impregnation. Amongst these deposits, some
distance away from their outcrop, there exist beds where
the diffusion of the bitumen is quite complete, so that the
rock when fractured shows an even chocolate colour.
Their thickness, though at times Small, rapidly increases
and often reaches 6 metres. They are worked by the
Société des Mines du Centre, who are the concessionaires
of Pont du Chateau, Cortal (Champ des Pois), Colombier
des Roys (Dallet), Lempdes (Puy de la Bouriere), Lussat,
Malintrat and Chamalières. The analyses of samples of
the rock taken from (a) Champ des Pois, (b) Colombier des
Roys, (c) Chamalières and made by the École des Ponts
et Chaussées, are as follows:—
& Ҽ g (a) (b) (c)
Loss on boiling . . © (º . . 0°20 0°25 0°10
Bitumen tº º © tº . . I9°75 22°40 8:20
Insoluble in acid tº º ge tº I-30 2-17 77.50
Clay and Iron oxide .. . . 0-52 O'93 0-92
Limestone and Magnesia . . 34'32 31°89 O'54
Sulphur . . tº tº tº º 0-04 0-08 0-17
Carbonic acid, water, combus-
tible matter and loss . . 43°87 42°28 12°57
Samples (a) and (b) are very rich in bitumen, but the
evenly impregnated beds that have been studied by
M. Bartet, engineer of the Ponts et Chaussées, only show
a content of 11:59 to 12:56 per cent. of bitumen. It is
the rock that is obtained from these last beds which is
used in the making up of the roads with this type of
86 NATURAL ROCK ASPHALTS
rock asphalt, though M. Bartet also recommends the
employment of the richer rock for the work.
The following are the terms in which he expresses
himself with regard to this question :-
“The richness in bitumen is not corrective, for we have
noticed that there are limestone beds in the galleries which are
almost unimpregnated and yet which only differ from the
bituminous rock of which use is made in the proportion of
bitumen found in them. If they were mixed with the richer
parts, a powder could be formed, the average bitumen content
of which would be less than that of the latter, but whose
chemical composition would otherwise be similar in every way.
Whilst on this subject, we would remark that we entirely agree
with those engineers who, in the manufacture of rock asphalt
powder, reject all idea of mixing limestones, and who consider
that the blending together of rocks obtained from different
districts is never sufficiently intimate as to give the resultant
layer of rock asphalt a sufficiently homogeneous character.
But if this opinion is perfectly true, it does not follow that the
result of the mixture of portions obtained from the same mine
or quarry cannot be accepted.”
To the south-east of the town of Dax is found, in
la Chalosse, amongst Tertiary earths, an important outcrop
of “ophites '' ranging from east to west. Around these
“ophites * are the bituminous deposits of Brassenpouey,
Gaujac, Bastennes and Caupenne. The first named
bitumen is so fluid that it is usually looked upon as a
petroleum. A hill of partly earthy “ophite ” rises
amongst reddish and gypseous marls, and upon it is
built the Château de Gaujac. From this rock are seen
to proceed from three orifices, some 5 to 10 cms.
in diameter, streams of water on the surface of which
floats a pure bitumen. Five kilometres away to the
north-west is the bituminous deposit of Bastennes.
The bitumen here is mixed with a large proportion of
micaceous quartz sand, which at times is of such a hard
nature as to defy being worked. This deposit, which is
not now worked, has a thickness of 2 metres, and
enclosed in its lower part are found broken shells, bivalves,
and the teeth of fish. It rests upon an “ophite ” earth
surrounded by beds of compact cretaceous limestone and
of marls of different colours. It is covered with an
SOURCES OF ROCK ASPHALT AND BITUMEN 87
arenaceous deposit of a micaceous quartz sand more or
less thick and which, in certain places, principally towards
the bottom, is mixed with clay. This arenaceous deposit,
which seems to have been formed by the destruction of
the sandstone rocks of the cretaceous earth upon which
it rests, has a thickness of 5 metres above the bitumin-
ous layer. It can readily be imagined that the bitumen
proceeded from the “ophite ” rock in a pure condition,
as at Gaujac, and in doing so mixed with an oolitic
“molasse,” but during the time that these deposits were
worked, no orifices were met with by which the bitumen
could have found an exit from the “ophite ” rock in the
way suggested.
According to M. Berthier, the rock is compact, of a
dull brownish black colour and homogeneous appearance,
although in reality it is very gritty. Although solid, it
cannot be pulverised. When digested with boiling water
it gradually releases the bitumen it contains, which rises
to the surface of the water by reason of the latter dis-
solving the iron and aluminium sulphates out of the rock
and by this means increasing its density. The density
of this bitumen at 12°C. is 1*181, and when heated to
180° C. for an hour it only loses 0.002 per cent. of its
weight. When strongly heated in a closed vessel, the
bitumen fuses into a compact mass, decomposes without
swelling up, and gives off thick oils, leaving behind it a
slightly lustrous residue. When subjected to an open
flame it fuses, burns for a long time with a long flame
accompanied with a large amount of smoke, and leaves
behind a white or slightly purple sand which is composed
of small grains of white quartz sand mixed with a little
clay. Ether and oil of turpentine extract almost the
whole of the bitumen from this rock, but cold alcohol has
no effect upon it, and even when it is heated to boiling
point it only dissolves out a small quantity.
In Italy the Tertiary earths of the Appenines are very
rich in bituminous deposits. Near Rome and Naples
there are quite a number of them which are of fairly
greatimportance, such as those at Chieti, Pepoli, Lanciano,
Venotro, Ponte Corvo, etc. They are usually to be found
88 NATURAL ROCK ASPHALTS
cropping out in those places where the water of some
stream has washed away the soil. The bitumen found
in them is sometimes liquid and at times solid. A
sample obtained by Ebelmen from the neighbourhood
of Naples was found to be a very brittle solid with a
lustrous conchoidal fracture. Ether has but little effect
upon it, though oil of turpentine dissolves it to a very
great extent. Its density at 13°C. is 1:175; it begins
to soften at 100° C., and is completely fused at about
140°C., without any emission of steam being noticeable.
The deposits on the eastern slope are worked to a much
greater extent than on the western one, in particular on
the spur of the Maiella, where, by the side of the petro-
leum deposits of Tocco, an asphaltic zone stretches for
sixty square kilometres along the Valle Romana (Mano-
pello) to the valley of San Spirito (Caramanico) including
Serramonesca.
Two types of rock are to be distinguished, the one
formed of fragments cemented together with bitumen,
to be found between sulphur and limestone formations,
and the other composed of these last mentioned limestones
impregnated more or less richly and having a depth
which, at the rivulet of Acquafredda, exceeds 50
metres.
In Sicily, important rock asphalt beds have been worked
for a very long time in the province of Syracuse, some
kilometres to the South of Ragusa in the direction of the
port of Mazarelli, itself some twenty kilometres or so
further away. They appear upon a plateau known locally
as Rinazzo or “Contrada a pece.”
The rock asphalt which is obtained here possesses all
the shades between a light yellow to a deep chocolate,
in which numerous glittering specks are noticeable which
are identical with similar grains found in the surrounding
unimpregnated rock. This latter is a limestone composed
almost entirely of the debris of shells, amongst which
have been found several “ clypeaster altus ” and a large
“siliquaria.” This rock, which belongs to the Tertiary
epoch, is usually classed in the Miocene. The asphalt
deposit at Rinazza is not more than twenty kilometres
SOURCES OF ROCK ASPHALT AND BITUMEN 89
away from the outcrop of basalts and basaltic tufas at
Militello, Franco Conte, Bucheri, etc., and although
split up by numerous “faults,” it is not connected with
an intruding vein of bitumen at any point.
The inspection of the cliffs that have been broken down
with picks near Leperino reveals the succession of beds
of which this plateau is composed. The rock asphalt
occupies two distinct levels, the lower one being
5 metres thick. The upper layer is separated from
this by about 25 metres of limestone, and it has the
advantage over the lower one of not being entirely covered
in. It slopes slightly to the north, and has a thickness
which varies from 5 to 20 metres, from which,
however, 2 or 3 metres should be deducted for the
intruding limestone bands. Beside these important
formations, large masses of rock asphalt which are not
connected with the main ones in any way are found in
the middle of the same limestone near Ragusa. The
amount of the Sicilian rock asphalt that was exported
in 1911 was approximately 120,000 tons, the greater
portion of which was shipped to Germany, Great Britain,
and the United States.
The following analysis of this rock was made by the
laboratory of the École des Ponts et Chaussées:–
Water, etc., volatile at 100° C. . . 4.95
Bitumen © tº tº ge & ſº . . II“20
Limestone . . © º tº º . . 83°79
Sand . . tº C tº dº tº º . . 0°06
The rock asphalt here has also been worked in order to
obtain large blocks, which are afterwards cut up and used
as paving stones, chimney pieces, door and window frames,
stair treads and balcony bases. Being susceptible of
being sawn, bored or carved with mouldings and sculp-
tures, a very important opening was assured for this rock
in the neighbouring towns. The dark colour that this
material shows when freshly quarried disappears after a
fairly brief exposure to the influence of the atmosphere,
giving place to a bluish grey, a property common to all
rock asphalt when so exposed. At a certain depth, how-
90 NATURAL ROCK ASPHALTS
ever, the rock asphalt is so loaded with bitumen that the
latter exudes of itself from the pores of the stone. It is
then too soft for building purposes and clogs the teeth of
the saw when any attempt is made to cut it. If used as a
paving stone, it “sweats,” i.e., the bitumen works to the
surface, and so it has to be heated prior to use, in order
that this excess of bitumen shall be extracted, the fuel
used for this purpose being the richer rock. The chief
aim now, however, in working this rock is to use it in the
manufacture of rock asphalt powder for compressed work,
for which it is particularly suitable, and of rock asphalt
mastic. The great value of this rock for the manufacture
of the rock asphalt powder lies in the fact that the majority
of the rock is ready for use with no further treatment than
the necessary grinding. The usual bitumen content is
from 9 to 11 per cent. and appears to depend upon the
consistency of the bitumen.
In Spain an immense deposit of bituminous rock is
found at Maestu, some fifteen kilometres from Vittoria.
This rock is a sandstone, slightly argillaceous and impreg-
nated with 8 to 9 per cent. of bitumen. The analysis
made by the laboratory of the École des Ponts et Chaussées
of a sample of this material is as follows:—
Water, etc., volatile at 100° C. . . 0-40
Bitumen © e © e © tº . . 8°80
Sand . . tº gº © tº tº ſº . . 68°75
Clay and Iron oxide.. tº º . . 4°35
Chalk and Magnesium carbonate ... 17:25
In Africa bitumen has been discovered in the province
of Oran, in Algeria, whilst a deposit of solid bitumen has
also been found in the desert in Egypt between the Nile
and the Red Sea which only fuses between 225° and
240° C. Its ash contains about 12 per cent. of mineral
matters, principally the oxides of iron, calcium and mag-
nesium. Mention, too, has been made of late of a deposit
of bitumen which is stated to have been discovered to the
north of Rhodesia, in South Africa, but at present fuller
details and particulars are not forthcoming, though a
company is at present being floated to exploit certain
SOURCES OF ROCK ASPHALT AND BITUMEN 91
petroleum oil-bearing properties in the Transvaal, in
conjunction with which it is hoped to discover deposits
of bitumen.
In the north of India, and in Persia, extensive beds of
minerals impregnated with a very fluid maltha are to be
found, as well as springs of the pure material itself. They
are not worked to any great extent, however, the rock
asphalt that is used in the first mentioned country at
present being imported from Europe. It is also claimed
that bitumen is to be found in China, but details of the
type and of the exact locality in which the deposits are
supposed to lie are not given.
From the foregoing it will be recognised that the Old
World is fairly well supplied with this particular material
in some form or other, so that there need be little fear that
the ever extending use of it will result in a shortage of
supplies, at all events for some centuries yet.
CHAPTER VII
AMERICAN DEPOSITS OF BITUMEN
THE most important deposits of bitumen are those
found in America, and of these the oldest and best known
is that situated in the island of Trinidad in the West
Indies.
This bitumen is much less pure than that obtained from
certain European sources, such as that taken naturally
from the Dead Sea or extracted from the different bitu-
minous beds or rocks, but the almost inexhaustible
quantity of it has rendered its use world wide. Sir Walter
Raleigh touched here during his many voyages in these
waters and “tarred ” the hulls of his ships with this
material, whilst we find that two shiploads of the crude
material were forwarded to England about the year
1830 by Admiral Cochrane, from which year its extensive
commercial use dates. Even in 1799 Kirwan, in his
“Geological Essays,” informs his readers that “a whole
lake of asphalt is said to exist in the island of Trinidad.”
The island in question lies at the mouth of the river
Orinoco. The “lake ’’ itself occupies a bowl-shaped
depression in a truncated cone, situated some thirty-six
miles south of Port of Spain. It is now considered that
the hollow thus filled is the old crater of some extinct
mud volcano, of which we unfortunately have reason to
know that there are some still in existence in that district
which have not by any means ceased to be active. In
fact, the nearest volcano of this description in the
vicinity of the “lake ’’ is only forty miles away at Point
du Cac. The position of the “lake ’’ in the highest point
of the island, known as Vessigny Hill, some 140 ft. above
the sea level, tends to confirm this view.
It had better be explained here that, contrary to the
AMERICAN DEPOSITS OF BITUMEN 93
idea which seems to be prevalent in the minds of many
people, this “lake ’’ is not an expanse of water. The writer
has found innumerable instances where persons, being
acquainted with the Dead Sea as a supply of bitumen,
have come to the conclusion that all the other so-called
bitumen “lakes '' are of a like description, that is to say,
a large tract of water upon the surface of which masses of
bitumen are to be found floating about ready for collection.
Quite contrary to this belief, all the American “lakes '' of
bitumen are merely deposits of a more or less solid bitumen
which have certain well defined borders comparable to the
shores of an ordinary lake of water.
The west end of this particular “lake’’ of bitumen lies
about half a mile from the nearest point on the sea coast,
and, as just mentioned, the deposit possesses well defined
limits or shores. In area it is approximately 99.3 acres
(Encyclopædia Britannica, 11th edition), though it is
gradually shrinking by reason of the enormous demand
that is being made upon its contents. The rate of this
shrinkage may be judged by the fact that eighteen years
ago the area of the “lake” was 127 acres. At one side the
rim of the crater has broken down, so that practically the
whole of the ground between this fissure and the sea is
covered with bitumen, which thus gives it the appearance
of a large stretch of black rock. This is the so-called
“land ” bitumen, of which mention will be made later.
The surface of the bitumen “lake ’’ is split up into
numerous small islands of bitumen, varying from 60
to 150 ft. in diameter, which are separated from each other
by channels of water several feet wide and of varying
depth, formed by the accumulation of rain water, in which
are to be found small fresh-water fish and frogs, though
the water during the dry season becomes slightly alkaline
and contains considerable quantities of metallic sulphides.
The water is drawn off through outlets cut in the rim,
but owing to the continuous motion of the bitumen, which
the Encyclopædia Britannica affirms is the cause of the
interior of these islands rising and flowing centrifugally
towards the edges, the position, size and shape of these
channels are ever changing.
94 NATURAL ROCK ASPHALTS
Though under ordinary conditions heavier than water,
the bitumen here is enabled to float upon the surface
owing to the large volume of gases contained in it, which
have been estimated as being one third of its entire bulk.
The “lake * itself has the appearance of a flat field of
bitumen, and is some 6 to 9 ins. higher in the centre than
at the sides. It has been likened to “a vast asphalt
pavement with many holes filled with inky water in which
swim ugly fish and black beetles.” R. T. Hill states that
“anything more black or repulsive can hardly be
imagined.” It is roughly circular in shape, as would be
expected of the crater of a volcano, and is about half a mile
in diameter. Near the sides it is covered with a thin
layer of earth which supports a luxuriant growth of
tropical vegetation, and some of the islands in the “lake’’
itself are also covered with undergrowth of a similar
description. The rim of the crater now rises above the
surface of the “lake ’’ for 3 to 8 ft., though prior to 1886
it was not noticeable.
The surface of the bitumen, with the exception of the
centre of the “lake,” where it is always soft and in a state
of constant ebullition, is sufficiently firm in the cooler
parts of the day to permit of being walked upon, and it
will even support the weight of mules and laden trucks.
It is necessary, however, to be constantly moving, other-
wise the bitumen begins to give with the weight upon it
which, if at rest, would gradually sink into the “lake.”
During the heat of the day, the material is exposed to the
direct rays of the tropical sun and commences to melt,
when the surface becomes a thick semi-liquid mass.
Owing to the large amount of water that is intimately
mixed with it, the bitumen, even in this condition, is not
sticky, so that although the “islands' of this substance,
which are in perpetual though slow motion, often come in
contact with each other, they never appear to combine
together.
As the centre of the “lake” is approached, the tempera-
ture of the material becomes appreciably higher, so that
from giving the firm footing which is obtained near the
shore the mass becomes softer and softer until it finally
AMERICAN DEPOSITS OF BITUMEN 95
alters into a viscous liquid, in which state it has a constant
bubbling motion without, however, any jets of steam or
other gaseous emissions being perceptible, although gas
is always being evolved, sometimes in such quantities that
it can be readily ignited with a lighted match. The strong
pungent odour of sulphuretted hydrogen is ever present
there, whilst it is stated that carbon dioxide, too, is evolved
(Encyclopædia Britannica, 11th edition). This same
authority asserts that this bitumen continues to evolve
these gases for some time after the material has been
removed from the “lake.” It is the outward flow of this
liquid portion, which gradually solidifies as it moves
further away from the spring owing to the heat of the sun
overhead evaporating from it the more volatile portions,
that causes the centre of the “lake ’’ to be raised slightly
higher than the ordinary level of the bitumen.
The depth of the “lake ’’ has never been properly
ascertained, owing to the constant motion and liquid
consistency of the bitumen at the centre, though at 100 ft.
from the shore the bottom has been found to be about
90 ft. below the surface level of the bitumen. In
the centre boring operations have been taken down to
135 ft. below the surface, but even at that depth the
samples brought up showed no difference from the material
to be obtained on the surface. There is reason to believe,
however, that the depth at the centre of the “lake ’’ is
not more than 150 ft.
On the surface of the “lake ’’ is a certain amount of
decayed vegetable matter upon which grow the dense
undergrowth and trees already mentioned, some of which
latter reach a height of from 30 to 40 ft. As these decay,
the dead fragments become mingled with the bitumen of
the “lake ’’ and so render the purification of this latter
imperative, even before it is shipped. These vegetable
islands, like those composed of bitumen, are ever in motion,
some having moved a distance of 25 ft. within the year.
These movements are controlled by the currents and
eddies of the surface water, which are occasioned in their
turn by the evolution of gases below and the constant
flow of fresh supplies of bitumen from the centre.
96 NATURAL ROCK ASPHALTS
*
When the light circular railway upon which the trucks
used to convey the broken up material to the side of the
“lake’’ are run was being constructed upon its surface—
in the carrying out of which the rails had to be supported
upon the surface of the bitumen by means of palm leaves—
this motion of the bitumen created an ever-recurring source
of difficulty, for stakes which had originally been driven
into the material in a true line with each other would
on the day following be found to be in the worst possible
alignment, some of them moving as much as a foot per day.
As has already been mentioned, the steady extraction
of the bitumen from the “lake ’’ is causing a corresponding
shrinkage of the surface area and a lowering of the surface
level. Still, as the latter is only approximately 6 ins.
per year, despite the fact that the annual output reaches
to more than 100,000 tons, it will be recognised that there
is little fear of any shortage of this valuable commodity
occurring within the next century or so. The “lake ’’
is leased by the government of the island until 1930 to
an American company and yields a revenue of roughly
£30,000 per year, the minimum royalty payable by the
company to the government for the concession being
£10,000 annually. During the past year (1912) the
export of this material from Trinidad to Europe reached
138,773 tons, of which 31,118 tons only had been
purified prior to shipment.
The approximate quantity of bitumen in the “lake ’’
has been calculated in the following way. If it is taken
that 80 cubic feet of bitumen weighs on an average
1 ton, then the sinking of the surface by 1 ft. represents
the extraction of 1,450 tons per acre, or, for the entire
surface area of the deposit, 203,000 tons. For certain
reasons that cannot be gone into here, the greatest depth
in the centre of the crater may be taken as being 150 ft.,
so that, taking this to be the depth of the deposit, and
considering the deposit as being a spherical segment in
shape, then the “lake ’’ should contain about 150 million
tons of bitumen. The “land ” deposits, referred to later,
cover an area of about 70 acres, with an average depth
of 30 ft., and so contain approximately a further two
AMERICAN DEPOSITS OF BITUMEN 97
million tons. The Encyclopædia Britannica, by another
method of calculation, gives the total bitumen content
of the “lake ’’ as being only 3,618,000 tons, which figure
it then immediately goes on to acknowledge cannot be
correct, since, although in the thirty-five years prior to
1908 no less than 1,885,000 tons had been removed, or,
in other words, more than half the alleged contents of
the deposit, there is but little shrinkage in the bulk still
untouched. It can only be presumed that the compiler
of those figures was unaware even of the approximate
depth of the deposit, especially so as he mentions the
average depth as being 20 ft., a figure apparently taken
from a very old report by Cumenge, and he even goes on
to suggest that the Bermudez “lake ’’ in Venezuela may
have a greater depth than that of Trinidad, which, if it
were the case, would mean that the former, being some
nine times as large in area as the latter, would contain a
supply that would survive ten centuries of constant
extraction of the quantities that are now being taken
from the latter.
The method adopted in order to obtain the bitumen
from the “lake ’’ is very simple. During the cooler
hours of the day, usually before dawn, the rainy season
naturally affording a longer period than the hotter
months, the surface is fairly brittle, and whilst in this
condition it can with ease be dug up and broken by
means of picks or mattocks. The holes thus formed,
which are usually a foot or so deep, are gradually closed
up again by fresh material rising up from below and
filling the cavity. The pieces thus broken up are loaded
into trucks running on the light railway referred to above,
which transfers them to the shores of the “lake.”
Formerly they were conveyed to La Brea, the port of
shipment, in carts and stored there pending the arrival
of the small sailing ships in which the material was to be
forwarded to its various destinations. If the ships were
at the time lying at anchor off the shore—for at that time
there was no convenience for the mooring of vessels at the
port—the material had to be put into barges, from which
it was transferred into the hold of the ocean-going vessel
N.R.A., EI
98 NATURAL ROCK ASPHALTS
half a mile away. As business increased and some larger
quantities of bitumen were being handled, it became
necessary to have some more rapid and economical
method of handling the material, so that now use is made
of the higher altitude of the “lake ’’ above the sea coast,
and a system of overhead runways erected in 1894 conveys
the pieces as obtained from the “lake ’’ to the factories
and warehouses on the coast, where the material is either
stored in its crude state or else “purified ‘’ and then run
into the very light barrels in which it is shipped. For this
last operation of shipping, the handling of the material is
also greatly facilitated by a similar system of runways,
which extend from the warehouses along the specially
constructed jetty down to the wharf at which the ships
to be loaded can now be moored. The runways consist
of a double line of steel rope supported at intervals by
steel lattice work; down the one line comes the laden
iron cradle from the “lake,” the additional weight of
which is sufficient to return a similar but empty cradle
up to the “lake ’’ again by the further rope.
The nominally purified bitumen obtained from the
“lake ’’ is known as “Trinidad epure,” but this, to say
the least, is a most unsatisfactory and misleading term,
since it would imply a thorough purification of the material,
which, however, is far from being the case. Instead, it
might reasonably be concluded that the main idea in
carrying out the “purification ” of the crude Trinidad
bitumen is merely to effect a saving in freight and storage
by the extraction of a portion of the worthless and
undesirable admixtures. A natural consequence of this
is that where this bitumen is to be used in the manu-
facture of certain materials such as, for instance, bitumen
sheetings, bituminous felts and the like, it is absolutely
essential that it shall be submitted to a further refining
process in order to extract the vegetable and the mineral
matter that it still contains, otherwise the tanks in
which the process of manufacture is carried on would be
rapidly choked up with this dirt, from which it is not an
easy matter to clean the container. The writer well
remembers having his attention drawn by a certain
AMERICAN DEPOSITS OF BITUMEN 99
manufacturer of bituminous products, to the extreme
rapidity with which his tanks became filled with dirt
and his rollers clogged up ; as the reason for this was
beyond him he was anxious to know of some means by
which to obviate it. His astonishment can be imagined
when it was demonstrated to him that his so-called
“purified " Trinidad bitumen contained a very high
percentage of extraneous matter which, by falling down
to the bottom when the bitumen was fused, filled his
tanks.
In general it may be taken that the crude material
consists of one-third of bitumen, one-third of impurities
(decayed wood, vegetable matter, sand, earth, etc.), and
one-third of water. The “purifying ” process as carried
on in the island serves merely to extract the water and
a small portion of the foreign matter, so that the “epure *
Trinidad is really composed roughly of one-half of bitu-
men and one-half of impurities. The purifying is effected
by a very crude type of liquation which may be described
briefly as follows:—
The impure bitumen as it is obtained from the “lake ’’
is thrown into large cauldrons in which it is heated
continuously for twelve hours. By the end of this time
the greater part of the water that was originally contained
in it has been driven off, ebullition ceases and the molten
mass then becomes at rest. With the absence of motion
in the liquid, theoretically, the heavy impurities should
settle out and sink to the bottom, whilst those of a less
specific gravity than the bitumen should rise to the top.
The vegetable matter, branches and the like, which float
on the surface of the molten bitumen at this juncture,
are ladled off, and then the bitumen itself, still in its
liquid state, is drawn away from the heavy residue at
the bottom of the cauldron and filled into barrels in
which it is allowed to cool.
This theoretical purification is, however, very incom-
plete and most unsatisfactory, since it fails to fulfil the
very purpose for which it is used. All the vegetable
matter does not come to the surface, nor does all the earthy
matter sink to the bottom. As a reference to the analysis
H 2
Q
; :
2 gº e *
>
• *r. ; :- * is
I00 NATURAL ROCK ASPHALTS
of the Trinidad epure which is given later clearly shows,
a large quantity of these matters is still retained by the
bitumen; but what is more unfortunate than all is the
fact that with the steam also evaporates out a quantity
of those volatile oils until then mixed in with the solid
mass and which have to be replaced later when the
Trinidad bitumen is being used for any purpose, by the
addition of liquid or semi-fluid fluxes. As “steam
distillation * is often used in organic chemistry and
different technical industries, in order to distil over other
liquids which have a much higher boiling point than
water when under normal conditions, it will be understood
that in the present case a large amount of those bitu-
minous oils which under ordinary circumstances are
only volatile at a much higher temperature than 100° C.
are lost. It may appear rather strange at first sight
that a liquid boiling at a high temperature can be distilled
at a much lower one merely by passing steam through
it, but this phenomenon is explained by that law of
physics which states that “the boiling point of mixed
liquids which do not dissolve in one another is determined
by their combined vapour pressures. If this is equal to
atmospheric pressure, both liquids will distil.” As
illustrating this, reference may be made to the manu-
facture of aniline, where the finished product is distilled
over in this manner although under Ordinary conditions
its boiling point is 182°C.
Another cause for regret in the “purification ” of the
crude bitumen is the fact that the Trinidad epure is
usually found to be richer in free carbon, otherwise
coke, than is the untreated material. This is held to be
due to the operation being carried out in open vessels,
which thus permit of the surface oxidation of the hot
material, whilst further, owing to the fact that bitumen .
is a very bad conductor of heat, it is thus extremely
difficult to heat a large solid mass of it evenly throughout,
except with specially prepared plant. It follows, there-
fore, that in this “purification,” where the material is
subjected to a continuous heat for twelve hours, those
portions which are nearest the sides and bottom of the
&
p • ‘: .* e º
AMERICAN DEPOSITS OF BITUMEN 101
cauldron must be sadly overheated, or, in plain words,
charred, even before the centre of the mass has become
melted.
It cannot be wondered at that so many firms, particu-
larly American, prefer, as the figures already given of
the output for 1911 clearly prove, to purchase the
mineral in its crude state and to purify it for themselves.
Although the refining as done by the private buyer is
based upon the same idea as is that used on the Island of
Trinidad, the method of carrying it out is slightly modified.
Some of these refiners, it is true, still prefer to heat the
material over an open fire and so chance the possibility
of the molten bitumen catching fire, but the majority now
carry on the work by means of superheated steam. This
is done sometimes in a closed horizontal cylindrical boiler
10 to 15 ft. in diameter and 20 to 25 ft. in length, sometimes
in an open bath-like vessel approximately 10 ft. wide,
some 22 ft. long and 18 ft. deep. Both are built after
the Cornwall type of boiler, that is to say, with two flues
about 2 ft. in diameter running across the top half and
which carry off the smoke and gases from the fire box
below. By this means the heat is more evenly dis-
tributed throughout the entire mass, so that the possi-
bility of any local overheating and the consequent
charring is greatly diminished.
A simple yet apparently efficacious method of refining
the Trinidad “brut’ bitumen has been suggested as
follows:–
The crude mass should be heated with hot air to a
constant temperature, which must not, however, exceed
120° C. at any time, until all the water that is contained
in it has been driven off. When this has been done,
the temperature should be increased up to, but never more
than, 150° C., in order to make the mass thoroughly
liquid. After the bitumen has thus been freed from water
and given a sufficiently thin consistency, it should be at
Once drawn off and passed over a sloping wire sieve of a
very fine mesh. The pure bitumen will then pass through
the meshes and can be conveyed by means of a suitable
channel direct into the casks in which it is to be filled for
102 NATURAL ROCK ASPHALTS
export or store. The foreign matter, whether vegetable
or mineral, will be trapped on the surface of the sieve,
and can be occasionally raked to the sides in order to
keep the meshes open. Although the bitumen thus
obtained should, theoretically, be perfectly free from
impurities, yet such is the intimate nature of the mixture
of the mineral matter and the bitumen, whilst at the same
time the former is in such a fine state of division, that it
is a physical impossibility to obtain a perfectly pure
Trinidad bitumen unless it is separated from its impurities
by means of solvents. This intimate mixture of the
mineral impurities, and their extremely finely divided
condition, which it will be recollected is found also in
the bitumen extracted from the European bituminous
rocks, is considered by Professor Richardson as being of
great advantage when the material is being made use of
in the preparation of bituminous macadam for road
making.
As has been already stated, bitumen is also obtained
in the island of Trinidad from the land itself as well as
from the “lake,” for the entire ground of which the
island is composed seems to be more or less impregnated
with this substance. The “land ” bitumen, as it is still
usually called for the sake of convenience, and in order to
keep it distinct from the “lake * variety, is usually,
however, less pure than this latter by reason of the addi-
tional earthy impurities that have become mingled with
it, though in Some cases it is stated that it is found in an
even purer condition, especially if it is extracted from the
lower part of the deposit. Queries have occasionally
arisen as to whether the two types of Trinidad bitumen
are identical, but the well-known United States expert,
Professor Peckham, who visited the island in person and
inspected, investigated, and analysed both the materials
and their respective sources, as the result of disputes in
that country respecting the superiority of the one over
the other, very aptly uses the expression “a distinction
without a difference ’’ as applying to the two terms used.
This decision was upheld in the English courts of law
Some three years ago, when a case was brought up for
AMERICAN DEPOSITS OF BITUMEN I03
consideration in which the plaintiffs, as the British agents
for the concessionaires of the material extracted from the
“lake ’ deposit, endeavoured, though unsuccessfully, to
obtain an injunction to restrain the defendants, who are
extensive users of the “land ’’ bitumen in their various
bituminous products, from describing these last materials
as being manufactured from “Trinidad asphalt.”
According to Professor Peckham, the land deposits
have been formed by the leakage of the bitumen from the
“lake’’ through the fissure at its side, and this leakage,
which has been going on for an indefinite period, has not
even yet ceased, despite the enormous amount of material
that is annually extracted from the “lake ’’ at its surface.
The leak is located in the broken side of the crater in the
La Brea property, and the outflow from it, even so far
back as 1832, was described by a visitor to the island
as being then immense. The grounds through which the
bitumen deposits are distributed are known as the
“pitch lands' and lie to the north of the “lake,” the
best known being the narrow stretch which presents the
appearance of a glacier and runs towards the promontory
of Pointe la Brea in a north-easterly direction. The
length of this deposit is about a mile, and its average
breadth rather more than 150 yards. This river-like mass
has been dug through in various places, where the depth
of the bitumen averaged from 15 to 18 ft., though at one
spot excavations were made 50 ft. below the surface
before the bottom was exposed. Whilst engaged in
making these borings, it was also found that the deposits
rest upon a layer of clay from 3 to 15 ft. thick, which was
also more or less impregnated with bitumen, whilst at
a depth of 80 ft. signs of peat were discovered.
The entire district between Pointe d'Or Lagune, in the
east, to Pointe Rouge, in the west, contains deposits of
bitumen of larger or smaller extent, which, however, are
distinct from the “lake ’’ material by reason of the higher
content of earthy matter which they usually possess.
Similar layers are to be found in the Brighton district,
whilst in the neighbourhood of Pointe Rouge there has been
opened up a small spring of bituminous oil, and although
104 NATURAL ROCK ASPHALTS
the output of this is too small to be of much commercial
value, its occurrence is of interest, since, when it is exposed
to the air and the Sun, the oil thickens and gradually
forms a material very similar to the “lake ’’ bitumen.
This is taken to prove that all the Trinidad bitumens have
their origin in One common source, a fluid maltha, their
condition being merely dependent upon the amount of
exposure they have undergone.
Although the “land ” bitumen is practically identical
with the “lake ’’ type, it is, however, obtainable in three
well defined formations, “cheese,” “slate ’’ and “stone *
or “iron,” according to the depth from which it is taken
out of the deposit. Of these the one which is most
largely used is the “stone * variety. The first is softer
than the “lake’’ bitumen which it closely resembles,
except for being slightly darker in colour. It forms the
lowest part of the deposit, the evaporation of the oils
contained in it having been prevented by the protection
from the sun afforded it by the harder material which
lies above it. The second type is practically the same,
but it has the peculiar property, owing, it is said, to the
air enclosed in it, of having a laminar, slaty structure,
hence its name. “Stone ‘’ bitumen is formed from the
first named, but having been subjected to the intense heat
of the sun, owing to it forming the surface of the deposit,
it has become extremely hard and brittle, so that it only
fuses at a high temperature, hence its alternative title
of “iron ’’ bitumen. “Manjak’’ as it is often, though
inaccurately, called, is capable of taking a very high polish
when purified—a new fracture shows a beautifully clear
jet black gloss—and for this reason it is very widely used
in the manufacture of black varnishes and japans where
this is a desideratum. Its high melting point is made use
of when it is exported, for instead of the wooden barrels
required for the Trinidad epure, it is merely packed in
bags containing approximately 2 cwt. each, thus affording
a slight saving in both the cost of the package and in the
freight. In the year 1910–11 the production of this
material, which is apparently in the hands of two firms,
represented a value of £3,979.
AMERICAN DEPOSITS OF BITUMEN I05
An analysis of this material made by Professor Richard-
son, shows an average content of 94.2 per cent of bitumen
soluble in carbon bisulphide, and 5.8 per cent. of inorganic
or mineral matter. It intumesces rather than fuses.
The composition of the purified and of the crude Trinidad
bitumens according to Cumenge is as follows:—

Sample taken from cº, Ritumen. Ash.
Crude | Trinidad “lake ’’ (ordinary) .. 3:00 50-00 47-00
, (centre) . . 5:00 62:00 33-00
3 y “ land ’’ º º 18:00 28.00 54°00
Epure | Trinidad “lake ’’ (ordinary) .. 5:00 58:00 37-00
93. 25 (centre) .. 8-36 55-36 36°34
33 “ land” º º 11-05 51'46 37-47
It should be noted that all the water had been extracted
from the samples prior to the above analysis being put in
hand. -
A deposit of maltha in the island is now being worked
by the concessionaires of the “lake,” the residue from
the distillation of which, being highly asphaltic, they have
recently placed upon the British market for fluxing and
road-making purposes under the name of liquid Trinidad
asphalt. It is stated by them that the results obtained
by the use of this material in the United States are highly
satisfactory.
CHAPTER VIII
AMERICAN DEPOSITS OF BITUMEN (continued).
THE claim once made that the Trinidad “lake ’’ was
the only one of its kind in existence has been disproved
by the discovery of a similar huge deposit of bitumen in
Venezuela, in the state of Bermudez. In fact, in this
country two distinct deposits of this material have been
found and are now being worked for export, one of which
is a “lake ’’ of a much larger area than its older and better
known rival in Trinidad, although it cannot boast of a
similar depth. It is stated that this Bermudez deposit
covers an area of about 1,000 acres, but in many places
the depth is only some 2 ft. or so. The material that is
obtained from it, too, varies greatly in consistency accord-
ing to the particular spot from which it is taken, and ranges
from the viscous maltha to the solid bitumen, which latter,
however, is much more pure, even in its crude state, than
that obtained in Trinidad. Like the bitumen from the
latter the material taken from the Bermudez deposit, or
“lake ’’ as it is now known, although softer, is broken up
with a pick or spade and then subjected to a refining
process before being shipped abroad, this refining process
being practically identical with the one carried on in
Trinidad. An average analysis of the crude bitumen as
obtained from this Bermudez deposit has been given as
follows:–
Bitumen tº º * * tº e ... 66 per cent.
Water. . tº e tº ſº tº e ... 81 ,
Mineral matter e ſº tº º . . 1 ,
Organic, non-bituminous matter .. 2 ,
The following comparison of refined Trinidad and
Bermudez bitumens is taken from the ‘Encyclopædia
Britannica (11th edition).
AMERICAN DEPOSITS OF BITUMEN 107
tº-sº Trinidad. Bermudez.
Specific gravity * @ tº º tº º e tº 1:373 1.071
Bitumen soluble in carbon bisulphide .. 61-507 92°22
Mineral matter (ash) tº º © tº * , ſº 34°51 1°50
Non-bituminous organic matter . . e e 3'983 1°28
Loss on heating to 212°F. . . tº e e e 0.65 1.37
3 y 95 55 ,, 400°F. for 10 hours .. 7-98 17-80
,, of total bitumen after last . . tº dº 12°811 18°308
Evolves sulphuretted hydrogen at e ºf 410°F. none at 437°F.
Softening point © tº tº º tº º tº tº 160°F. 113°F.
Melting point tº º e e º º tº ºn 192°F. 150°F.
It must, however, be acknowledged that Bermudez
bitumen varies very much in composition, the water
content ranging usually between 10 and 40 per cent.—
crude Trinidad bitumen from the “lake ’’ has a constant
water content of 28 per cent.—whilst the non-bituminous
organic matter varies from 1 to 6 per cent. A large
proportion of this bitumen consists of the “petrolene ''
of which more will be said later; for the present it will
suffice merely to state here that the “petrolenes '' con-
situte the volatile portion of a bitumen, so that the
greater the content of this, the more readily will the bitu-
men dry out and become brittle with exposure to tempera-
tures at which this portion evaporates. For this reason
it has been stated by Professor Richardson that this
material is not suitable for asphalt paving purposes,
though practical experience does not appear to bear out
this statement. The “lake ’’ is being worked by the same
American company that owns the concession of the
Trinidad “lake,” and the material that has been extracted
from it has only been recently placed upon the market
here in England although it has been in use in the United
States for some time.
This deposit lies near the river Guanaco, west of the
town of Guariquen, some twenty miles away from the
Parian Gulf as the crow flies. Professor Richardson has
described it as follows:–
“The so-called “lake ' is situated between the edge of the
swamp and the foot hills in what might be termed a Savanna.
108 NATURAL ROCK ASPHALTs
It is an irregular shaped surface with a width of about a mile
and a half from north to south and about a mile east to West.
Its area is a little more than 900 acres, and it is covered with
vegetation, high rank grass and shrubs, one to eight feet high,
with groves of large moriche palms called morichales. One sees
no dark expanse of pitch on approaching it as at the Trinidad
pitch lake, and except at certain points, where the soft pitch is
welling up, nothing of the kind can be found. The level of
the surface of the deposit does not vary more than two feet
and is largely the same as that of the surrounding swamps.
In the rainy season it is mostly flooded, and at all times very
wet, so that any excavation will fill up with water. These
conditions make it very difficult to get about upon it or to
excavate the pitch easily.
“It is readily seen that this deposit is a very different one
from that in the pitch lake of Trinidad. It seems to be, in fact,
merely an overflow of soft pitch from several springs over this
large expanse of Savanna and one which has not the depth or
uniformity of that at Trinidad. -
“Being on a level with the mangrove swamps and with the
foot hills on its other side, any large amount of asphalt could
hardly be held in position here, as in the old crater in Trinidad,
but would burst out into the swamp and be lost and, as far as
borings have been made, they seem to indicate but a small
iºn anywhere as compared with that of the Trinidad
ake.
“At different points there is at most a depth of seven feet
of material, while the deepest part of the soft maltha is only
nine feet and the average of pitch below the soil and coke only
four feet. At points there is not more than two feet of pitch,
and in the morichale, or palm groves, it is often five feet below
the surface. At several points scattered over the surface are
areas of soft pitch, or pitch that is just exuding from Springs.
The largest area is about seven acres in extent and of irregular
shape. This has little or no vegetation upon it, and, from the
constant evolution of fresh pitch, is raised several feet above
the level of the rest of the deposit. This soft asphalt has
become hardened at the edges, but when exposed to the sum is
too soft to walk upon. The material is of a nature of a maltha
and it is evidently the source of all the asphalt, in the lake,
from these exudations the pitch having spread in every
direction, so that no great depth of pitch is found even at
this point.
“A careful examination of the surroundings shows that in
one respect there is a resemblance between the point of evol-
ution of the soft pitch at the Bermudez and at the Trinidad
lakes. Gas is given off in considerable quantities at both
places, and in both cases consists partly at least, of hydrogen
sulphide. At the Bermudez lake I was unable to determine
AMERICAN DEPOSITS OF BITUMEN 109
whether it was accompanied by carbonic dioxide, but the odor
of hydrogen sulphide was strong.
“The consistency of the soft pitch at the centre of the
Bermudez lake is much thinner than that of the Trinidad
lake. It will run like a heavy tar and does not evolve gas
in the same rapid way or harden so quickly after collection.
It therefore does not retain the gas which is generated in it,
nor does the deposit as a whole do so to the same extent as
the Trinidad pitch. Where, however, the surface of the soft
pitch has toughened by exposure to the Sun and air, and where
gas is given off beneath it, it is often raised in dome-like
protuberances, the beehives which were spoken of by early
visitors to the Trinidad lake. These have a thin wall of pitch
and are filled with gas which readily burns, and have been seen
two feet or more in height and eighteen inches in diameter.
They are, of course, found only near the soft spots.
“There is no evidence of the simultaneous boiling up of
water with the fresh soft pitch that has been determined at
the Trinidad lake, but that there is none at all is not certain,
as at the time I visited the locality heavy rains were falling
which prevented the detection of a small amount. It seems,
however, improbable, as the soft pitch contains little or no
water and the traces found in the samples collected are pro-
bably derived from rain.
“The edges of the areas of the soft asphalt are covered here
and there with masses of glance pitch and with black and
brittle cinders or coke, and which seem to have been produced
from the maltha by fire. This is evidently the case, since the
rank growth of the grass, which is very dry in the dry season,
is particularly adapted for a rapid and intense combustion.
Such fires have been even recently started intentionally and
accidentally, and to them are due the condition of the present
surface of the deposit and the character of much of the
pitch. -
“The general surface of the lake is very irregular and hard.
There are many very narrow and irregular channels or depress-
ions, from a few inches to four feet deep, filled with water, and,
not being easily distinguished, one often falls into them. At
the foot of the growth of grass and shrubs are ridges of pitch
mingled with soil and decayed vegetation, which have been
plainly coked and hardened by fires of the nature which have
been mentioned. When this hardened material which forms
only a crust is removed, asphalt of a kind suitable for paving
is found. The crust is from one and a half to two feet in
depth and very firm, while the asphalt underneath would not
begin to sustain the weight which that of the Trinidad pitch
lake does easily. There are breaks in the crust here and
there through which soft pitch exudes as has been de-
scribed.”
IIO NATURAL ROCK ASPHALTS
The second deposit of bitumen in Venezuela is on the
coast of the Gulf of Maracaibo, about fifty miles west of
the town of Maracaibo. The deposits here cover an area
of some 97 acres and are worked by the United
States and Venezuela Company, the principal deposit
being that of Inciarte. Here the crude material is
collected, and after being roughly purified it is sent down
the river Limon to Toas, from which port it is then shipped
to the United States. As far back as 1902 we find that
the output from this deposit for the half-year reached a
total of close on 3,500 tons.
The analysis of the bitumen obtained from this par-
ticular deposit has been given thus:—
Crude. Refined.
Bitumen . . tº º . . 94° 13 99-07
Woody fibre gº º . . 4'85 0-25
Ash . . . . . . 1-02 O'68
Besides these a liquid bitumen is found in the territory
bordering the mouths of the Orinoco, being thus very
handy for shipment, which material contains about 40
per cent. of oil. This is obtained from the stratum which
is found saturated with it, from 13 to 27 yards below the
surface of the ground. Borings have shown this stratum
to possess a thickness of nearly 50 ft. This deposit was
first worked by a German company in 1891.
Another bitumen “lake,” but one of more moderate
dimensions, is to be found in Peru, near Coxitambo,
and has been worked since 1860. Other deposits there
are located in the Condorocana mountain—which was
known as early as 1763—at Sacmarea, Pastos de Mito
and Clumpi. The material from these sources is not,
however, shipped to Europe in any great quantity.
After the Bermudez material perhaps the most dan-
gerous rival of the Trinidad bitumen is that which is
obtained from the island of Cuba. Here numerous
deposits of this material are to be found, some of which
have been mistaken frequently for coal, a mineral which
does not exist on this island, but it is principally in the
neighbourhood of Havana, where they present a thickness
AMERICAN DEPOSITS OF BITUMEN 111
of 18 ft., that they have been worked to any great extent.
The other more important deposits are near the harbour
of Cardenas (70 ft. thick), at Canas Tomasita (105 ft.
thick), whilst a particularly pure variety is found at
Vuelta. The purity of this Cuban material is remarkable;
on an average it shows a bitumen content of 73 to 93 per
cent. An analysis of the crude material gives the fol-
lowing figures:—
Bitumen tº º - e. e G e e 73°05
Water © º tº º tº e tº º 1°25
Mineral Matter © e tº tº e - 25'69
Dumas, in describing this bitumen, to which he refers
under the title of “Mexican bitumen’’ or “chapapote,”
says that its density is but little different from that of
water, its Smell, although strong, is not disagreeable,
whilst it is absolutely unaltered by acids or alkalies.
Alcohol has but little effect upon it, though ether and oil
of turpentine dissolve out part of it. It has a very high
softening point, and, as might be expected, the percentage
of the “ asphaltenes '' is much greater than that found
in the Trinidad or Bermudez types.
The material itself is obtained here in a slightly different
way from that which rules in the island of Trinidad.
Instead of being extracted from the surface of the ground,
as with the material taken from the latter, shafts and
galleries are driven into the deposit as if it were an
ordinary mine. Here, too, are found considerable quan-
tities of maltha, thus enabling the raw material, after
having been subjected to a refining process, to be fluxed
to a suitable consistency upon the spot, a very necessary
procedure, owing to the lack of the “petrolenes,” or
“ malthemes,” as Professor Richardson prefers to term
them. The principal places where these liquid or semi-
fluid bitumens are found and worked in this island are
perhaps Sabanilla, east of Cardenas, and Minas, some
twenty miles from the town of Camaquey.
This local fluxing of the Cuban bitumen gives it a
distinct advantage over the Trinidad type, as in the
fluxing of the latter, such as when required for rock
II2 NATURAL ROCK ASPHALTS
asphalt work, etc., foreign asphalt oils are usually used,
the exact kind varying with different firms. Very often
Scotch “shale grease ’’ is employed for this purpose in
the United Kingdom—a similar product obtained at
Autun being used in France for a like purpose—though
American malthas and Continental “bergteers,” or
“goudrons minérals,” are also not infrequently preferred.
The controversy as to what forms the most suitable flux
has led to the employment of many varied types of oils
and greases with more or less successful results, whilst
petroleum residues, by reason of their comparative
cheapness, are often substituted for the more expensive
though naturally produced maltha. This undesirable
feature in Trinidad bitumen is eliminated from the
material shipped from Cuba, by the fluxing process being
carried out before despatch, with the result that, further
mixing being thus rendered unnecessary, the reputation
of the bitumen cannot be prejudiced or made to suffer
thereby, unless, of course, a deleterious adulterant is
wilfully added.
The bitumen to be obtained in this island has been
worked spasmodically for some decades, but the political
restlessness of the people and the incorrect ideas of its
possibilities have prevented its proper development
until recent years. One of the largest deposits here, the
writer has been given to understand by one of the prin-
cipals of the firm in question, has recently been taken
over by a well-known firm manufacturing bituminous
materials in the United Kingdom, so that no doubt a
great impetus will be given to the adoption of the Cuban
material in this country on that account.
A monster block from one of the deposits here, the
Angelo Elmira mine, situated some five miles away
from Bejucal, at that time in the possession of the West
Indies Company, was on exhibition at the World’s Fair
at Chicago in 1893, and turned the scale at over a
thousand pounds.
The presence of bitumen here has been known for
centuries, in fact from the time of the conquest of the
island by Spain, for in Oviedo’s “History of the Antilles,”
AMERICAN DEPOSITS OF BITUMEN 113
published in the early part of the sixteenth century,
express mention is made of a spring of “pitch ‘’ near the
coast in Puerto Principe and of the occurrence of “pitch ‘’
upon the shores of Habana Bay, the first being appar-
ently maltha and the second solid bitumen. At that
time, however, the use of both these types was limited
to the caulking of the ships sailing in these latitudes,
and no doubt the presence of these materials so ready
to hand in nature was one of the principal reasons why
this island was so often made use of by men-of-war of
various nationalities, as well as by the “buccaneers ” so
beloved of our younger days, for that operation, so very
necessary in that district, of “careening ” or cleaning
and repairing the hulls of their vessels.
In the nineteenth century we find numerous references
to these materials, all more or less voluminous in character,
in the memoirs of the various travellers and navigators
who visited this island, from Humboldt, who called here
in 1803, onwards.
One of the most important deposits of bitumen is
found near Mariel Bay, the proprietors of which declare
there are apparently some millions of tons, containing
in the crude state about 60 per cent. of pure bitumen and
only 3 to 4 per cent. of water. Thousands of tons of
this material have already been extracted and shipped
away both to the United States and to Europe in both
crude and refined conditions, packing in bags being
sufficient in both cases owing to the very high melting
point even of the second—126°C.—though it is cus-
tomary in the case of the latter to ship it in barrels.
Near Cardenas there are extensive wells of maltha.
These are sunk some 80 ft. into the rock, and the amount of
the material that is extracted from them is constantly
replenished by further quantities of fresh material oozing
in through the sides. In the bottom of the Bay of
Cardenas itself are to be found deposits of a very pure
bitumen, so pure in fact that by the very simple method
of dissolving it in turpentine, a very serviceable black
varnish is obtained, This material has been collected
for the past forty years by mooring a lighter over the
N.R.A. I
114 NATURAL ROCK ASPHALTS
place of operation, which is approximately 100 ft. below
the surface of the sea, and then loosening pieces of
bitumen by the very crude expedient of dropping a pointed
iron bar into it from the vessel. When a sufficient amount
has been thus broken off, a native diver is sent down,
who fills it into a common scoop net in which it is brought
to the surface. This bitumen is much like cannel coal in
appearance, but it has a much more brilliant lustre. From
the Constancia deposit near Diana Key, fifteen miles from
the town of Cardenas, which has an area of about
200 yards, it is stated that some 30,000 tons have already
been taken without appreciably reducing the deposit
which, like that at Trinidad, is levelled up with new
material. Near Villa Clara there is an unusually large
deposit of this material, the thickness of the bed being
12 ft. It resembles lignite in appearance, and for more than
fifty years it has supplied the material for the manufacture
of the illuminating gas for that city.
The Encyclopaedia Britannica (11th edition) gives the
following comparative composition of refined Trinidad
and Cuban bitumens :—

Trinidad. Soft Cuban. Hard Cuban.
Water tº º e G 0.17 0-13 0-11
Wolatile bitumen.. 57.81. 64'03 8:34
Sulphum .. tº º 10:00 8°35 8-92
Ash (earthy matter) 28°30 19'51 16'60
Fixed Carbon 9-72 7-98 66-03
Melting point 1859 F. 1159 F. 1609 F.
The West Indies appear to be singularly fortunate as
regards the presence of bitumen, which ranks next to
iron as the principal mineral product, and owing to the
entire absence of coal deposits in that region, it is used
locally, as in Barbados, for fuel and also, as mentioned
above, in Cuba, for the manufacture of gas. It is affirmed
by the mine owners that from a ton of the bitumen is
obtained 3,000 feet of gas, 60 gallons of oil and half
a ton of coke, which latter finds an industrial use as fuel,
AMERICAN DEPOSITS OF BITUMEN 115
whilst the oil is used to advantage as a flux for the more
solid bitumen.
That obtained from the island of Barbados is found
in the chalky soil of the Scotland district, so called from a
fancied resemblance it bears to the scenery of that country,
and in a length of cliff called Burnt Hill in the Consett
district. This latter has been successfully exploited, and
a large tonnage has already been extracted. Owing to its
very high degree of purity, this particular type of bitumen
was greatly in demand for high-class varnishes and
similar products, but its production has now fallen from
842 tons in 1909 to 174 tons in 1911. Although the
bitumen contained in the land deposits in the island
of Trinidad is sometimes given the same name, the true
“manjak º' is the Barbadoan bitumen.
The following comparative analyses of these two sub-
stances are interesting :-
Barbadoan Trinidad
“manjak.” “glance pitch.'
Specific gravity. . © . tº º tº º 1-123 1 : 139
Melting point .. tº º tº gº tº 420° F. 360° F.
Soluble in CS2 .. & © tº º • * 97°), 88°lo
Ash e tº & © tº gº & e * Q 2:32°le 7:44°ſo
Loss on heating tº º © tº e e 2.61°), 9:4°lo
According to W. Merivale, who first developed these
deposits, there is an enormous reservoir of maltha beneath
the island which is still trying to force its way to the
surface. -
In the island of San Domingo there are extensive
deposits both of solid bitumen and of maltha. Only
recently the writer received a prospectus of a company
then about to be floated in order to exploit some of
these, which naturally gave a glowing account of their
possibilities, but up to the present nothing further has
been heard by him of the enterprise. The rather unsettled
state of the government of theislandis, of course, prejudicial
to a large export trade in this material being developed.
f I 2
116 NATURAI, ROCK ASPHALTS
The principal deposit here is near Azua de la Compostela,
about fifty-five miles to the west of San Domingo city,
where it is said that the adjacent country abounds in it.
A large export trade is done with the United Kingdom
in Mexican bitumen. This material, however, is not a
true natural bitumen like the ones mentioned above, but
is the residue left from the distillation of maltha, numerous
occurrences of which are to be found in that country,
particularly along the coast of the Gulf of Mexico and in
the states of Tampulipas and Vera Cruz. It is credibly
affirmed by the firms who are now using this material
that it gives equally as good results as those obtained by
the use of a natural bitumen, but this seems to be a matter
of opinion. Professor Richardson, however, does not
appear to have a very high opinion of the material, which,
he believes, owing to the large quantities of volatile
matters which it loses upon heating, will not prove of
any great importance in the paving industry, although
no doubt a certain proportion could be incorporated with
other and more satisfactory bitumens if it were a matter
of economy to do so. This material is very short in fibre
and cannot be drawn out into a thread of any length.
In the continent of North America itself bitumen is to
be met with very extensively and in very varied forms,
from asphaltic oils, semi-fluid malthas, the peculiar
rubber-like “wurtzilite ” or “elaterite,” the brittle,
difficultly fusible “grahamite ” and “glance pitch,” to
the impregnated limestone and Sandstone. The territory,
too, ranges from Texas and California in the south to
Alberta province in Canada in the north. To the Euro-
pean consumer, however, but few of these are of direct
interest, the majority finding a sufficient home demand
for their output, whilst the high freights required for
others, particularly those in the western states, effectively
prevent their successfully competing with the other
bitumens at present on the European market. How the
opening of the Panama canal will modify this state of
affairs remains to be seen. A
In California both the solid and the liquid types of
bitumen are found, as well as a thin flowing asphaltic oil
AMERICAN DEPOSITS OF BITUMEN 117
which finds a very extensive use for road spraying. The
different kinds are marketed in Europe and find a ready
demand particularly for paving purposes.
Other well-known deposits of bitumen here are those
in Colorado and Utah, where the solid material is that
known as “gilsonite ” or “wintahite,” the latter name
being derived from Uintah county, Utah, where it is
found. This material is black in colour with a most
brilliant lustre and breaks with a coarse conchoidal
fracture. Where a vein is exposed to atmospheric action,
it becomes a dead black, but this change is merely super-
ficial, for when this surface is removed, the material found
behind it shows its customary brilliance. When pulver-
ised, it forms a very fine chocolate brown dust, and if fluxed
with suitable Californian malthas, it forms a peculiar
rubber-like mass which, however, is rather short in fibre.
It is a very pure type of bitumen, the best qualities con-
taining as much as 99.5 per cent. as extracted from the
earth. It has a slightly lower density than other bitumens
and has a much higher softening point. It possesses but
a low percentage of “petrolene,” with the result that, as
might be expected, it is a brittle material.
The type known as “wurtzilite,”and found principally
in Utah, is of a very unique character, though it is not
to be met with in sufficient quantities to enable it to be
used to any appreciable extent in commerce. It is a
tough, lustrous material, difficult to fuse and to dissolve.
Although somewhat short in fibre, it is very rubber-like
in character when cut in thin strips, so that it is difficult
to fracture. It does not fuse even at high temperatures,
but it is fluxed with heavy malthas by gradually “crack-
ing ” it at high temperatures. Its scarcity, however,
precludes its extensive use so that the fluxed gilsonite, as
mentioned above, is usually employed in its place.
“Grahamite ” is another solid form of bitumen found
in various parts of North America, but it is distinguished
from the various other bitumens in that it is infusible.
When it is heated, it swells up with the evolution of gases
and can be softened sufficiently to enable it to be drawn
out into threads. It has another distinguishing feature
II8 NATURAL ROCK ASPHALTS
in that it has but a comparatively low sulphur content,
and it can be distinguished from gilsonite from the fact
that, whilst the latter is brown when in a pulverulent con-
dition, grahamite is quite black when crushed.
The liquid or semi-fluid malthas in America are found
principally in Texas, California, and Indian territory,
where they permeate and saturate strata of sandstone
from which they are usually extracted by heating the
rock. Towards the end of 1911 endeavours were made
to tap the soft bitumen whose existence under the Salt
Lake, Utah, near its northern shores, has been known for
some time, but the writer has not yet heard of it being
actually placed on the market.
The material found in Canada is, as its local name of
“Albert coal * would imply, a very hard and lustrous
bitumen. When placed in a flame it fuses, burns almost
without smoke and falls into burning liquid drops. It
dissolves in naphtha if slightly heated, more readily in
carbon bisulphide, and forms a brilliant black varnish,
as it is usually quite free from mineral matter. It is
however, stated that this deposit is being exhausted and
that it is now only used for Canadian requirements.
The American natural rock asphalt can be divided into
that consisting of impregnated limestone and that of
impregnated sandstone. Perhaps the most important of
the former are the deposits which are found in Oklahoma
and in Uvalde county, Texas. These, contrary to the
best European types, show numerous cavities which are
filled with pure bitumen, whilst in other places in the
same rock portions are found which are totally unim-
pregnated, thus giving the face of the deposit a very
mottled appearance. The average percentage of bitumen
found in these rocks is stated to be 14 to 15, and
owing to this high percentage it is usual to crush and heat
it without the addition of any further bitumen when
preparing it for compressed work. Another deposit of
bituminous limestone is also met with in Indian Territory,
but this is of very imperfect impregnation, and the average
percentage of bitumen is only five to six.
The naturally impregnated sandstone is, however, of
AMERICAN DEPOSITS OF BITUMEN 119
much more frequent occurrence, being found in Kentucky,
Utah, Missouri, Indian Territory, Texas and California.
With the sandstone, the bitumen acts merely as a binder,
and does not truly impregnate the mineral as in the case
of the limestone. The most important fields are those
in Kentucky, which show an average impregnation of
6 per cent. The material has been used for paving
purposes in a similar way to the compressed rock asphalt
powder, but although the pavements thus prepared give
a fair amount of success, they cannot compare in that
country with the artificial mixtures that are used for
similar purposes. A deposit of this material has been
found about ten miles east of the celebrated Mammoth
cave, in which the impregnated sandstone is a very fine
siliceous rock, which has a bitumen content of from 5 to
25 per cent. The sand is very hard and each grain is
coated with a film of bitumen of from 7 to 15 per cent.
CHAPTER IX
EXTRACTION AND PREPARATION OF ROCK ASPEIALT
THE rock asphalt as it is despatched from the factories
which are run in conjunction with the different mines
is prepared in no fewer than five distinct types, according
to the work to which it is to be put. The best known are,
of course, the “mastic ’’ and the “powder ’’ forms, but
besides these, large quantities are also sent away as the
crude rock just as it is drawn from the mine, as the “crude
powder,” i.e., the crude rock merely crushed without the
addition of any bitumen, or a richer rock to give it the
percentage of bitumen necessary for compressed work,
and as compressed tiles made from the prepared powder.
During the commencement of the past year (1912),
the writer inspected in person the asphalt mines, quarries
and factories at Eschershausen, Brunswick, and under
the guidance of the works manager of the Union Worwohler
Asphaltgesellschaft had the pleasure of having all the
details in connection with the extraction and preparation
of the material as carried on there, from the blasting of
the live rock to the despatch of the finished material in
one or other of the foregoing forms, fully explained to him.
The village of Eschershausen itself is but a small place
and contains quite a number of picturesque old half-
timbered, slate-roofed houses, although a large number of
the more recently erected dwellings are hung with cement
tiles. It nestles at the foot of the Hils mountains, in which
latter are found the veins of limestone impregnated with
bitumen. The mountains are pierced with galleries at
different points, and by means of these the various
asphalt mining companies in this district obtain access to
the veins as these appear in their particular property.
Passing through the village, it is noticed that the road
PREPARATION OF ROCK ASPHALT 121
from the station is paved with rock asphalt tiles which
have been made from the prepared powder as produced
from the material obtained from the rock asphalt quarry
here. Despite the fact that these tiles were laid down
some eight years ago, they proved upon inspection by
the writer to be still in perfect condition and, as the
manager of the firm which owns the particular quarry
from which the powder used in their manufacture was
obtained, pointed out, not one of them is cracked and the
surface is practically as flat as when first the pavement
was laid down, despite the fact that all the traffic to and
from the station passes over it. The particular morning
chanced to have been wet, yet no “basins '' retaining
water were to be seen on the pavement, thus clearly
showing the durability of this class of paving which,
besides, presents an extremely pleasing and neat
appearance.
On leaving the village behind the road leads to the
factories of the various asphalt producing firms, in which
the raw rock is worked, and then a moderate rise in eleva-
tion brings one to the mouths of the galleries themselves.
The entry to any one of these is identical, consisting merely
of a small cutting into the base of the hill, and a short
walk of a hundred yards or so on a medium downward
gradient inside the gallery brings the visitor to the face of
the rock then being worked, each layer of the impregnated
material—in this particular instance there are two—being
got at from a different gallery in the mine. The bitumin-
ous rock in the mine proved—to the writer, that is—rather
difficult to distinguish from the dark coloured unimpreg-
nated stratum of clay immediately between the layers,
especially with the dim light of the oil lamps provided,
but the sound obtained by tapping the rock with a
hammer soon showed the difference between the two.
The workmen, however, have no difficulty in distinguishing
between the two classes of rock, but could point out on
the face of the live rock exactly where the one stratum
ended and the other began.
The rock is first drilled with a hand drill and a charge
of ordinary black powder is then inserted into the cavity
I22 NATURAL ROCK ASPHALTS
So formed. It is found that ordinary black powder is
much more satisfactory to use for this particular purpose
than is dynamite, owing to the latter having a tendency
to split the rock too much. The fuse is lighted, the
workmen retire to a suitable distance for the explosion,
after which they again go forward to break down the
masses of rock that have been thus loosened, by means of
heavy hammers. These masses are further broken up
if necessary, to allow of their being loaded into the iron
tip trucks which, running on a light railway which
connects the mine with the factory, transfer the rock
from the underground vein to where it is stored in the
factory in readiness for use in the different processes or
for despatch as crude rock.
Before returning to the factory itself, the quarry here
which is also worked for the extraction of rock asphalt,
was next visited. As distinct from the mines, which, as
before mentioned, are at the base of the mountains, this
quarry is away up on the summit, necessitating a very
stiff climb. It has been referred to on previous occasions
how bituminous rock generally when exposed to the
atmosphere loses its dark colour, and this is a matter
which immediately strikes one upon arriving before the
face of the quarried rock. On the way up the hill, too,
trucks have been passed which contain a greenish-white
broken mineral, and the stone itself where exposed in the
quarry shows a similar colour, so much so that the casual
observer would not dream that such a rock had any
bitumen impregnating it at all. Yet immediately the
face of the rock is broken down, also by blasting with
common black powder, the dark colouration of the rock
asphalt is at once apparent. The powder obtained from
this rock is not very rich in bitumen, the guaranteed
content as given by the quarry owners being 4 per cent.,
but the fact that the rock has already been weathered
seems to make it especially advantageous for rock
asphalt work which will be subject to exposure to extreme
atmospheric conditions. This was the rock asphalt
from which the paving tiles remarked in the street
leading from the station were made, The depth
PREPARATION OF ROCK ASPHALT 123
of this stratum of bituminous rock is stated to be
over 16 ft.
Returning to the factory, the broken pieces of rock
asphalt, which have been seen sent from the mine and
the quarry in trucks, are broken up smaller, approximately
to the size of an apple, and are then fed into a special type
of disintegrator. The use of an Ordinary disintegrator
is unsatisfactory with rock asphalt, since the bitumen
contained in the latter material causes the pieces of rock
to become greasy in a very short space of time, and so to
clog up the working of the machine. The type adopted
for this work therefore consists of a number of concentric
drums, one working within the other, the sides of which
are composed of a number of sharp edged steel rods.
When the disintegrator is revolved, the centrifugal force
that is occasioned causes the pieces of rock to be thrown
against these rods with a moderate violence until they
are broken sufficiently small as to be able to pass between
the rods. Here the pieces find themselves in a second
chamber similarly provided with rods, so that the rock is
broken up still smaller, and this operation continues until
a powder is formed which is sufficiently fine as to pass
through a sieve of a very fine mesh, which is placed round
the disintegrator for the purpose of retaining any coarse
powder that may be thrown out with the finer grade.
The rock asphalt powder thus formed is the base upon
which all other types of rock asphalt materials are made.
A number of rock asphalt contractors nowadays prefer
to purchase the asphalt powder in this form, the so-called
“crude powder,” and then to “cook " their own mastic
in their own works with their own materials. When this
is done by firms of repute, such a method of procedure is
highly commendable, since it assures them of being in a
position of being able to personally guarantee the con-
stituents and the manufacture of the material. At the
same time, however, it opens a door also to less scrupulous
firms, who are thereby enabled to adulterate and to
cheapen the mastic to their own liking, either by the
addition of an insufficient quantity of bitumen, by using
a low grade bitumen if not actually a coal tar or similar
124 NATURAL ROCK ASPHALTS
artificial product, by adding powdered limestone or a
similar mineral adulterant, or by insufficiently cooking
the material. It is not incumbent upon them to stamp
their blocks with the name of the mine from which the
rock asphalt they use originally came, and even if they
do so, they have a large number of stamps from which
to choose. With the rock asphalt mastic as imported
direct from the factories which work in conjunction with
the mines, the specifier is in a safer position, since the
Customs authorities, in carrying out the Trade Marks
Act, insist that upon each block of this material that
enters this country shall be branded the place of origin.
It is this brand that constitutes in part his safeguard
if he insists that all blocks of rock asphalt mastic that may
be used upon work under his control shall bear the brand
of the particular mining company whose material he has
decided upon for that contract. This, however, is im-
possible as long as the “ or equal ‘’ clause continues to
be inserted in his specifications.
From the powder obtained from the crude rock by
means of the disintegrator as just described is prepared
the special rock asphalt powder as used for compressed
work. In only few instances does the asphalt rock as
taken out of a mine contain naturally sufficient bitumen
to form a suitable powder for this class of work, so that
the quantity of bitumen impregnating the rock has to
have assimilated with it additional bitumen, in order
that the total amount shall be such that experience has
proved to be most suitable for that particular type of
rock asphalt. This proportion varies with different rocks
and seems to depend upon the class of rock and the method
of impregnation. When, however, the mine produces an
extremely rich rock as well as a poorer variety, it is usual
to blend the two together in such proportions as to arrive
at a like result. It has been recommended in some
quarters that to obtain a material showing a suitable
percentage of bitumen, rocks from different mines should
be blended, but the advantage obtained by this means is
questionable, as the more richly impregnated rock is
invariably softer than the less impregnated one, so that
PREPARATION OF ROCK ASPHALT 125
a pavement formed from such a mixture has not the
capacity of wearing evenly that is shown even by a
similar mixture, but formed of rock of different impreg-
nations and obtained from the same mine. This prepared
powder, when produced by mines in which no such
extremely rich layer can be found, has necessarily to be
prepared by enriching the rock with added bitumen.
This is done by thoroughly “cooking ” a quantity of the
crude powder with the requisite amount of bitumen until
the latter is thoroughly merged into the whole. When
this stage is reached, the material is again passed through
the disintegrator and finally packed in bags containing
approximately 2 cwt. each in which they are sent away
to the various consumers.
From this prepared rock asphalt powder are formed the
compressed asphalt tiles. A special press has been built
for their manufacture by the firm of C. Lucke, Eilenburg,
who specialise in presses for particular trades, which press
exerts a surface pressure on each tile of 120 tons. The
powder is first slightly heated before being used, in order
to drive off any minute quantity of water that it might
still retain, and also to bring it to that temperature which
is found to be most suitable for the work of compression,
and it is then filled into moulds of the size of the tile
required (usually 25 cms. by 25 cms.). These moulds are
then placed in the press, the powder they contain is
subjected to the intense compression that this machine
is able to exert, when firm, sound and extremely durable
tiles are formed. The thickness of these varies from 1 to
2 ins. according to the particular purpose for which they
are required, a side walk, for instance, not requiring such
a thick tile as would a much used roadway. They are
packed in strong wooden crates, bound with wire,
which contain approximately 8 cwt. each, and in which
they are despatched both by rail and water.
The rock asphalt mastic, however, is prepared from the
crude powder itself, and the work is carried out in a
special plant which is known technically as a “cooker.”
Its use has been alluded to in the manufacture of the
prepared powder. It consists of a cylindrically shaped
126 NATURAL ROCK ASPHALTS
boiler in which are fitted strong rotating arms. The
special boilers used for this purpose are usually of such a
size as to contain 3 to 5 tons of the finished mastic,
and are built by several of the Continental engineering
firms who make a speciality of rock asphalt tools and
machinery. They are customarily ranged in couples,
and are heated from a fire box below, the waste gases
from which, after passing round them in the covering
jacket, find their exit in a flue fitted at the top of the
boiler. The agitators are fixed upon an axle running
through the boiler, and this axle in turn is connected with a
driving shaft. So that there may be no possibility of the
material coating the sides of the “cooker * during the
operation, these agitators are made so that in their
revolutions their radius is only slightly less than that of
the inside of the boiler, with the result that no material
is left untouched.
The finished mastic usually contains in all 14 to 16
per cent. of bitumen, so that the content of the crude
powder being known, the amount of extra bitumen
required to bring about this desired percentage is easily
calculated. In the process of preparation of the mastic,
the major portion of the bitumen which will be required
for the operation is first placed in the “cooker,” which is
then heated. This bitumen, like that used in the pre-
paration of the prepared asphalt powder for compressed
work, is usually the refined Trinidad material fluxed
down to a suitable consistency, though now that other
bitumens have proved their worth for this purpose,
which do not require such fluxing, there is no doubt that
as time goes on their use will be preferred. The
fact of these other bitumens being much more pure than
even the refined Trinidad bitumen means that a less
quantity is required in order to bring about the requisite
bitumen content. Thus in the Lobsann and the Russian
mastic factories, a local bitumen is employed; in certain
Austrian and French factories the Albanian type is used,
whilst some German firms have for some time past been
adopting Cuban and Mexican bitumens.
The bitumen is first melted in the boiler to a thick
PREPARATION OF ROCK ASPHALT 127
liquid, for if it is allowed to fuse too thinly there is a
liability of the material either charring or else catching
fire, and then the crude powdered rock is added by degrees.
This is effected by means of Small flap doors which are made
in the side of the cylinder, through which the powder is
shot in quantities of approximately 2 cwts. (i.e., a bag)
at a time. It is usual to regulate the time of this filling
so that the powder is thrown into the boiler immediately
the slowly rotating arm of the agitator has passed the
door, in order that there may be no fear of the bag being
caught by it and so dragged into the mixture. Two
doors are usually made in each “cooker,” on the same
side of the upper half of the cylinder and next to each
other, so as to secure a more even distribution of the
powder. The two arms of the agitator are so arranged
that they are at right angles with each other, so that
when one has just passed its respective door the other is
approaching the second door. By this means the two
doors can be fed alternately, and the mixture receives
fresh agitation with every 90 degrees made by the
rotary axle.
This gradual addition of the powder enables the entire
mixture to be evenly and intimately blended with the
bitumen, but further than this, it materially assists in
the convection of the heat applied to the “cooker *
throughout the mass, for, were it all inserted together,
the bad conductivity of heat possessed by the powder would
cause that portion nearest the shell of the “cooker * to be
burnt before that in the interior would be barely warmed.
When the powder thus gradually added appears to have
thoroughly absorbed the amount of bitumen originally
placed in the boiler, the remainder of the arranged
quantity of bitumen is then thrown in, and the further
amount of rock asphalt powder added until the exact
quantities of the two materials as required for the opera-
tion have been put into the boiler. The entire mixture
is now constantly agitated at a temperature of about
200° C. for a period of five hours, when the fused mass
is drawn off through a suitable treacle valve into an iron
tip truck, from which it is transferred into the moulds
128 NATURAL ROCK ASPHALTS
the shape of which the mastic blocks are to take, and in
which it is allowed to cool. The material that first
makes its appearance is a small quantity of unmixed
powder which, having become lodged in the outlet, has
not been reached by the agitators. This is received into
a separate bucket and thrown to the back of the “cooker,”
so that by the time it passes through the outlet a second
time it has become intimately mixed with the bulk.
The moulds that are used for the formation of the
rock asphalt mastic blocks are made up of metal parts
which permit of a ready setting up, and are usually
circular, six-sided, semi-rectangular, and square in shape,
though others even than these are at times to be met with.
A number of these moulds are assembled together so as to
render the filling of the one after the other an easy matter.
They are usually set upon a concrete floor which has been
previously dusted over with a quantity of the crude
powder in order to prevent the mastic from adhering to
the concrete when cooling. So that the moulds shall not
stick to the sides of the block when cold it is customary
to give them, prior to their being used, a coat of whiting
to which—when the grey sides thus caused to the block
are objected to, which colour, of course, disappears if
the block has been weathered—is added a quantity of
lampblack, or else it is substituted by a soap solution.
This last method, however, although leaving the sides of
the desired natural colour, is not always successful for
the principal purpose of eliminating the sticking of the
material to the mould.
On the face of these blocks is impressed the name and
sometimes the trade mark of the particular mining com-
pany by which the mastic has been made, and as this
is the only real guarantee that the architect and engineer
can have that the material that is being used for his work
is of the type that has been specified, it should invariably be
demanded that every block of the material employed
shall have impressed upon it this distinguishing mark.
The blocks thus formed are stacked in the open ready
for immediate shipment in bulk, without any packing of
any description, and each block nominally weighs between
PREPARATION OF ROCK ASPHALT I29
60 and 65 lbs., though this weight is never true, owing to
the loss of corners and other small pieces which are
accidently broken from the blocks during transit.
It will be remarked that there is no pressure employed
in the making of these blocks, so that, contrary to the
crude rock or even to the samples which may be made up
from the mastic, they invariably show a number of
“blowholes '' when fractured. In inspecting rock asphalt
mastic in its block form, therefore, this fact must be
borne in mind and the presence of such blowholes
ignored.
Although the different types of bitumen added to rock
asphalt in the manufacture of the mastic appear to give
equally satisfactory results to those obtained by the use
of Trinidad epure, a certain amount of caution has to be
employed with the use of some, owing to the extreme
readiness with which their “petrolene' content evaporates
out to leave a brittle and therefore useless solid. There
are, however, less reputable firms who make use of the
cheaper petroleum residues and even coal tar products
in the preparation of their material, and although this
latter is, for this reason, initially low in price, its use
only leads to the early disintegration of the work done
with it. In France, too, the shale oil as obtained from
Autun is extensively employed, though it fails to give
as excellent results as does the properly fluxed bitumen,
A further caution must be given regarding certain
other low priced German rock asphalt mastics which,
being manufactured by firms which do not belong to the
syndicate which has been referred to in an earlier chapter,
are obtainable at much lower rates, sometimes at a figure
as much as 20 per cent. lower than the standard fixed
for the true natural product. These are often manufac-
tured from time-worn rock asphalt which has been lifted
from old asphalt work. This is sometimes mixed with
new material, though very often not, and then blended
with a sufficient quantity of bitumen, petroleum residue,
or even coal tar products, according to the price to be
obtained, the process of manufacture being the same as
the “cooking ” of the true natural rock asphalt mastic.
N.R.As R
I 30 NATURAL ROCK ASPHALTS
This material is much inferior to the true product, and
that it could not be otherwise will be recognised when it
is borne in mind that by exposure to the atmosphere it
has lost a large portion of those malthenes so requisite
for the flexible nature of the work for which the mastic
type of rock asphalt is specially employed, and also that
it has amalgamated with it the detritus and dust inevitable
in streets from which the old material is customarily
obtained. Work done with this material rapidly wears
into holes or cracks, or else forms rough unsightly parts,
as is known to their cost by the innocent victims upon
whom it has been inflicted. Such material, being
formed from substances derived ultimately from the
natural rock, comes under the heading of natural
rock asphalt mastic, but it may truthfully be said
that there is no greater enemy to rock asphalt and
rock asphalt work generally than this inferior and
remade material.
The idea of utilising this old material in the manufacture
of rock asphalt products is not even confined to the mastic
material, but compressed asphalt tiles and the prepared
asphalt powder for compressed work which have been
prepared from it are also to be found on the market, selling,
of course, at a much lower rate than what is required for
the genuine material, and the same warning equally
holds good for them too.
An architect or engineer who has had the opportunity
of comparing side by side the two, the genuine product
and the prepared article, in actual use, not merely in
small hand samples, will have no hesitation in deciding
upon the one which is the most suitable and which gives
the most satisfactory work and results.
There are on the market, in England especially—for
upon the Continent their use appears to have been dis-
carded to a very great extent—blocks which are prepared
from the rock asphalt mastic for use as a paving material.
They do not give such good results as do those which have
been prepared from the compressed powder, but being
initially cheaper, their use is sometimes preferred. These
are usually prepared by mixing together suitable propor-
PREPARATION OF ROCK ASPHALT I31
tions of rock asphalt mastic and bitumen with grit,
crushed stone and other fillers, the final mass in its molten
condition being filled into moulds and subjected to an
intense hydraulic compression, as in the case of those
made from the compressed powder. Even these have
their substitutes, composed of a mixture of bitumen and
mineral matter into which natural rock asphalt does not
enter at all, but these give but very poor lasting results
when used.
Of late, increasing attention has been devoted to the
use of bituminous macadam for road making, and this
material will be found referred to in the chapter on
macadams, in conjunction with tar macadam, a material
to which, except for the use of bitumen as a binder instead
of tar, it very closely approximates.
In compressed work, of course, no further material is
required other than the powder itself, but for the asphalt
mastic work and for the making watertight of the joints
in the pavements made up with the tiles, whether com-
posed of the compressed powder or of the gritted mastic,
a bitumen is required. The exact type of this seems to
vary almost with every user, each apparently having a
personal preference for some special one. Thus some firms
are found who will still uphold the use of the refined
Trinidad bitumen fluxed with shale grease, whilst others,
on the other hand, with less conservativeness, allege
their preference for the more newly marketed types. In
any case, whatever the exact type may be, its qualities
should be such that whilst it will retain its elasticity at
the extreme cold to which the finished work will be subject,
it will not liquefy or soften to too great an extent at the
extreme heat that the work will be submitted to in summer
from the sun.
As with practically every other trade, novelties have
been prepared in the different classes of the rock asphalt
material, and only recently the writer had submitted to
him samples of a coloured mastic, a coloured bituminous
paint, and a hydraulic asphalt powder which only required
the addition of water to cause it to set. The sample of
the second was insufficient to enable satisfactory con-
K 2 ‘.
I32 NATURAL ROCK ASPHALTs
clusions to be drawn, but in the other two cases the
writer has occasion to believe that the method of manu-
facture necessitates the addition of a large amount of
foreign matter to the natural rock asphalt, and as this
does not act solely as a filler as in the case of grit, etc., it
leaves it very much open to question whether its presence
will not act detrimentally to the mixture. This line of
thought is caused by the handling of the two samples
referred to, which in the case of the first is really too soft
to be able to withstand continuous traffic, even if laid in
the interior of a building, where it is intended that it
shall be used as a floor covering to do away with linoleum
and the like. An oil is apparently employed to carry
the colour, and although it seems to be well and evenly
distributed throughout the sample, it seems also to
prevent the bitumen of intercalation from cohering as
firmly together as it should. Then, too, the surface
readily retains dirt, which rapidly discolours the original
tint and leaves an effect which would not be countenanced
for a moment in any public building. The hydraulic
powder, on the other hand, when set, results in the forma-
tion of a very hard brittle solid, which has not the elas-
ticity looked for in asphalt mastic work, and so could not
withstand much vibration or alternate expansion and
contraction of the structure in which it may be used.
If, as is surmised, the hydraulic set is obtained by the
use of a cement, then the limestone and marl which
constitute this latter, being in such a finely divided
condition, is capable of absorbing a large amount of
bitumen, which, if added to the point of saturation, would,
by forming a protective coat around each grain, obstruct
the proper setting of the cement. If, on the other hand,
an insufficient quantity of bitumen were added, the
result would be an unevenly impregnated material, which
is very strongly condemned by various authorities for
asphalt mastic work, and one in which the bond is not
occasioned by the adhesion of the bitumen as in the case
of the ordinary asphalt mastic, but by the coherence of
the grains of mineral matter. This bond, not being
resilient, would naturally crack under tension, and where
PREPARATION OF ROCK ASPHALT 138
the material is used as a dampcourse—for the principal
idea in its adoption is to do away with the present diffi-
culty of applying asphalt mastic to damp walls—would
render it ineffective for the very purpose for which it was
intended.
CHAPTER X
TESTS AND ANALYSES
THE ever dominating idea of cheapness and short-
sighted economy even in rock asphalt work, has resulted,
as can only be expected, in the placing before the unwary
consumers, of adulterated bitumens and, too often,
substitutes for the real article, which, whilst initially
cheaper and apparently just as good, fail to maintain
the claims of durability that have been made for them,
to the dissatisfaction of all parties concerned in their use.
Then, too, the range of materials over which a choice
can now be made covers so many types that it is necessary
to define certain conditions that the particular one required
for a particular purpose shall fill. The following pages
will show what an advance has been made in the demand
for quality in bitumen since a date so recent as 1893,
when Delano merely mentions that “the best way to
test the quality is to draw it out into threads; the longer
they stretch, the better the sample.” How he would
reconcile several modern bitumens with the statement
that “bitumen to be good should be free from dross,
non-evaporative and contain no oils that will evaporate
at 480° F. (250° C.), be perfectly black, not brilliant,
and at 70°F. (21°C.) have the consistency of beeswax,”
the writer is at a loss to imagine, seeing that many, of
which the Trinidad epure may be taken as an example,
contain a large content of “dross,” if under that term
be implied all matter, mineral and organic, that is not
bitumen; that all bitumens lose a certain amount of
their “petrolene '’ content when heated; that some are
brown in colour; that no less an authority than Professor
Richardson states that “all the native bitumens are
lustrous if pure ‘’; and that many, such as gilsonite,
TESTS AND ANALYSES 185
glance pitch, etc., are extremely hard at Ordinary tem-
peratures, whilst some of them are very difficult, in fact,
almost impossible to fuse.
With regard to rock asphalt, it must not be overlooked
that, as previously mentioned, a series of purely chemical
tests is unsatisfactory, since the artificial varieties,
being composed of the same materials, will give identical
reactions. It is imperative, therefore, that this product
shall be submitted to both chemical and physical tests .
should the question be involved whether or no the sample
under consideration is one of natural or of artificial
formation. The tests given in the following pages are
such as can reasonably be performed by persons who are
in the habit of handling both bitumen and bituminous
compounds, but the more delicate ones, which require an
intimate knowledge of analytical chemistry and the use
of delicate and expensive apparatus, such as the ordinary
person or firm would not have an opportunity of using,
are not given, particularly so since for practical purposes
the ones which are to be found here are usually sufficient.
For the more delicate ones the analytical expert in these
materials should be called in.
It is always necessary when handling large quantities
of a naturally produced material that a type sample shall
be periodically taken from the different consignments
and carefully tested. With standard qualities obtained
from firms of high repute this, of course, is usually un-
necessary, though at the same time it is often interesting
to compare even in these cases the figures obtained from
the analysis of the sample from bulk with those of the
nominal analysis. Particularly is this essential, however,
in the case of prepared material, such as residuums,
where it is not always possible to obtain the material
of an unvarying quality owing to the slightly altered
conditions which arise around each individual distillation.
At the outset, the preparation of a uniform sample is
of the utmost importance. If this is not properly and
carefully effected, then the whole analysis is quite worth-
less, and the result may even lead the investigator
altogether astray.
136 NATURAL ROCK ASPHALTS
In the case of finely pulverulent substances, such as the
crude or the prepared rock asphalt powder, this prepara-
tion of a satisfactory sample presents no great difficulty,
but in all cases certain rules of procedure must be followed
in order to obtain a correct average sample. As Professor
Richardson truly remarks, there is a very great difference
between a sample of a material and a specimen. Whilst
the latter is usually selected in order to bring out most
prominently the best characteristics of the particular
material for any special work, the former is chosen as
showing the average composition and character. In
submitting any material to tests, it is the sample and not
the specimen that must be handled.
To obtain a sample that may be regarded as an average
type it is essential that it shall not be drawn from only
one spot in the bulk. Portions should be taken from the
consignment at different places and then these intimately
mixed together. With a powdered material this is a
simple matter, but when the investigation of solids in
lump is being carried on, it is necessary to crush each
sample before mixing. Nor must it be forgotten that
the larger the size of the sample the more typical of the
entire bulk it will be. In blending the different samples,
a good sized quantity of each should be taken, and the
resultant mixture can then be diminished to such a
quantity as may be deemed most suitable for analytical
purposes.
It should be borne in mind also that the finer the
grains into which the material is comminuted, the speedier
the test will be. Powdered materials, of course, require
no further crushing, but solids must be ground up to a
more suitable condition, and this is usually effected by
pulverising them in an iron mortar, though when a very
fine powder is desired, porcelain, agate, or even steel
mortars are sometimes employed. Moderately plastic
substances can often be reduced in this way if the mortar
is set in a bath of cold water, in order to prevent the rise
in temperature which would otherwise be occasioned by
the friction that is developed in the process of crushing.
In this case, however, great care must be taken that none
TESTS AND ANALYSES - 137
of the water is allowed to getinside the mortar, as moisture
is one of the various component parts of the bitumen
or rock asphalt that has to be detected and determined.
When even this is found to be impracticable, the only
alternative is to cut the sample up into Small pieces with
a clean dry knife, taking the greatest care to handle it
as little as possible.
In analysing an impure bitumen, the principal matter
to be taken into consideration is the quantity of that
body that is soluble in a known solvent, and the melting
point of the bitumen thus extracted. The simplest
method of doing this is perhaps as follows:—
A weighed quantity of the material, after having been
powdered, is left for some days in a desiccator. It is
then taken out and carefully re-weighed. After being
replaced, a further suitable time is allowed to elapse,
when the sample is again weighed, and if no difference is
to be found between the last two weights, the loss in
weight, as shown by the difference between the first two
weights, gives the amount of water that had been pre-
viously absorbed or become mixed mechanically (as
distinct from chemically) with the bitumen. Should no
loss in weight be detected, then the bitumen is thoroughly
free from water. The actual procedure of this experiment
will be described a little later.
The powdered bitumen thus dried is now placed in a
tall, narrow-necked flask—usually an Erlenmeyer flask
(cone shaped)—which is provided with a thoroughly air-
tight cork, and then covered with approximately ten times
its weight of pure carbon bisulphide. The flask is now
closely corked up and the contents repeatedly agitated
for some days. The carbon bisulphide is an excellent
solvent for bitumen—such solubility being, in fact, one
of the tests for a bitumen—and readily extracts it from
rocks containing it, or from its impurities if the crude
mineral is so treated. Further than this, it is very
volatile, boiling as it does at 48°C., so that after being
used it can readily be evaporated without needing the
higher temperature requisite for the other solvents of
bitumen at which the latter often undergoes a partial
138 NATURAL ROCK ASPHALTS
chemical change. The narrow-necked flask is used in
the extraction so as to reduce the surface area of the
liquid to a minimum, and so to retard the evapora-
tion of the solvent which goes on even at the ordinary
temperature.
After a few days the solution thus made is filtered
through a previously weighed filter paper, into a shallow
porcelain bowl, which has also been previously weighed.
It is recommended that the filter paper be folded in pleats
instead of in quadrants as is the customary manner, since
by doing the former a larger filtering surface is obtained,
hence a quicker filtering operation and less fear of the
solvent evaporating upon the filter paper and so deposit-
ing the bitumen dissolved in it there instead of passing
it through in solution. The residue remaining on the
filter paper is carefully and thoroughly washed with a
further quantity of carbon bisulphide until no more of
it dissolves, i.e., when the liquid passing through the
filter paper is uncoloured with bitumen, when the paper :
is allowed to dry. In that condition the paper and its
contents are weighed, and the increase in the weight of
the paper gives that of the extraneous matter which was
previously mixed with the sample of bitumen. This may
be organic matter with or without mineral matter, or
even only the latter. If these are also to be analysed
separately, the residue is carefully taken from the filter
paper and weighed. Following this, it is put in a small
porcelain basin and heated on a sand bath over a Bunsen
flame. Any Organic matter that may be present ignites
when the basin becomes red hot, and finally burns com-
pletely away. If there are any mineral bodies present
mixed with these organic substances, they remain un-
changed even when the basin is brought to a constant
white heat and that temperature sustained for a long
time. When it is seen that no more of the contents of
the basin will burn away, it is allowed to cool, and the
residue which remains is then analysed for its properties.
According to this mineral matter, it is possible to deter-
mine the place of origin of the bitumen, but as this
requires an intimate knowledge of the different bitumens
TESTS AND ANALYSES 139
and an acquaintance with the rules and tables of inorganic
analysis, it is not given here, the more so as it is usually
sufficient for the practical man, if he knows whether there
are organic or mineral impurities in the bitumen, without
actually requiring to particularise as to the exact mineral
or organic compounds that may be present.
The filtrate in the basin is, of course, pure bitumen
dissolved in carbon bisulphide. It is put in a water bath
and heated to about 48°C., when the solvent quickly
evaporates out and leaves the bitumen behind as a dark
amorphous mass. As this still contains traces of the
solvent, it is advisable to raise the temperature to 110°C.
for a short space of time before taking the final weight.
Care must be taken, however, that this increased heat is
not sufficient to drive off the more volatile oils of the
bitumen itself. By subtracting the weight of the basin
from the weight thus obtained that of the pure bitumen
in the sample under consideration is obtained, which,
when added to that of the impurities, should be equal to
the weight of the original sample.
As is well known, bitumen contains certain bodies
which are volatile when subjected to heat, and others
which will withstand very high temperatures without
evaporating. The volatile elements have been termed
“ petrolenes * and the non-volatile ones “ asphaltenes,”
though Owing to false ideas that have at times been
created by the use of the former term, Professor Richard-
son prefers to give them the name of “ malthemes.” As
a general rule, a bitumen is harder in proportion as it
contains more asphaltene to petrolene, until finally some
of the very hard types are reached in which but little
trace of the latter is to be found.
The first scientific investigation of bitumen seems to
have been carried out on this line by Boussingault in
1836. He submitted the Pechelbronn bitumen to dis-
tillation and obtained a distillate to which he gave the
name of “petrolene,” whose chemical composition he
determined as Csohiga, and which he pointed out was
isomeric with that of oil of turpentine. To the non-
volatile portion he gave the name of “ asphaltene.” These
I40 NATURAL ROCK ASPHALTS
terms are now, however, often misapplied, with the result
that the term “petrolene * is given to the portion which
is soluble in petroleum spirit, ether or acetone, and
“ asphaltene '' to that portion dissolved by boiling tur-
pentine and cold chloroform. Many engineers fix a limit
to the proportion of the one to the other in a bitumen to
be used in road making and similar work under their
control, and it will therefore be readily understood that
a bitumen should be analysed for this comparative com-
position. Many methods are now in vogue for this pur-
pose, by means of which it is possible suitably to extract
the one fraction from the other.
One of these methods consists in placing a weighed
quantity of the bitumen to be tested into a distilling
apparatus and covering it with water. When the
apparatus is heated, the petrolene distils over with the
steam and condenses as an oily liquid, which, since it floats
upon the water by reason of its lighter specific gravity,
can be readily separated from it. A satisfactory deter-
mination, however, is only possible when the distillation
has been carried on for such a length of time that the
water coming over is absolutely odourless, and this con-
dition is only reached after the bitumen has been con-
stantly heated with the water for several hours.
“Petrolene * is also soluble in boiling alcohol, but in
order to obtain a result which can never be more than
moderately satisfactory, the boiling operation must be
kept up and the inevitable loss of alcohol constantly
replaced for a very long time, so as to extract the last
traces of the petrolene.
For the practical man, though, the following method
of estimating the quantity of petrolene and asphaltene
contained in a sample of bitumen is perhaps the most
suitable and at the same time the simplest to carry out.
A weighed quantity of the bitumen is placed at the bottom
of a porcelain bowl which is provided with a porcelain lid
in the middle of which is a small opening. It is then
placed over a strong Bunsen flame, which is so regulated
that the contents of the crucible are kept at an even tem-
perature of about 250° C. At first the heat must be
TESTS AND ANALYSES 141
applied very gently, otherwise the mass, which at times
Swells up very strongly, will boil over, but after the
greater part of the vapour has been evaporated the bowl,
having reached the required temperature, is kept con-
stantly there for some hours. As soon as it is seen that
it has been heated for a sufficiently long period, that is
to say, when no further quantity of vapour is to be seen
rising from the crucible, the latter is allowed to cool in a
dessicator and then weighed. It is again heated for a
second time, but to 260° C., at which temperature it is
kept for an hour or so, and afterwards again cooled in the
dessicator and its weight taken. If no variation in the
two weights is to be observed, the operation is complete
and the substance left behind in the bowl is pure asphal-
tene, whilst the loss in weight is that of the petrolene.
The determination of the melting point of a bitumen can
be done by a very simple piece of work, to which, however,
at the same time is joined the difficulty that it is very
hard to recognise with any degree of exactitude the true
point at which the mass, which at first is only softened
throughout, changes into a liquid. This difficulty is
further increased by the non-conductivity of the material,
which results in the outer portion of the sample being
completely fused and in a liquid condition even before the
interior can be truthfully accepted as being very soft.
The test is usually done in the following manner. The
bitumen is put in a shallow porcelain basin, which in its
turn is placed in a glass beaker standing upon a tripod,
and the whole is then heated with a small Bunsen flame.
Within the beaker and near the basin, so that it can
register the temperature of the air surrounding the latter,
is hung a thermometer. In order to find at what tempera-
ture approximately the bitumen melts, the apparatus is
first of all heated fairly rapidly, until it is observed that
the sample has melted, when the temperature which
occasions this is noted. A second sample of the bitumen
is then treated in the same way, with the exception that it
is heated to a temperature some 10° C. lower than that
which fused the previous sample. If at this heat the
fresh sample is not melted, the temperature is gradually
142 NATURAL ROCK ASPHALTS
raised until the formation of a glossy surface on the
bitumen shows that the melting point has been attained.
In order that the result to be recorded shall be as accurate
as possible, this operation should be repeated with other
samples for several times and the arithmetic mean of the
various readings taken.
One of the most important causes for the submission
of samples of bitumen to analysis is to ascertain whether
the alleged bitumen is of natural or of artificial origin.
As a rule, however, the artificial bitumen usually found
on the market is composed of, or contains, the products
of coal tar. With these there are always variable quan-
tities of free carbon, from which one would conclude that
certain constituents of the coal tar decompose under the
strong heat which is used during its distillation and
separate out as carbon. This carbon is present in the
finest condition possible throughout the entire mass, and
as it is insoluble in all the solvents known up to the present,
its quantity can be easily found if a weighed quantity of
the suspected bitumen is treated with a suitable solvent.
It is best to use for this purpose the hydrocarbons of the
benzol series, and the powder which remains behind upon
the filter paper upon the filtration of the liquid should
be well washed with the hot hydrocarbon until nothing
further dissolves, when the black mass left behind is
pure carbon.
Another simple method of determining the amount of
free carbon in a bitumen is to heat a weighed quantity
of the material which has been previously reduced to a
fine powder, with three parts of aniline and then to pour
away the thin liquid and the matter which is held in
suspension by it, into a small plate of unglazed porcelain.
The solution of bitumen is at once soaked up by the
porous porcelain, and a black mass of a flaky consistency
only is left on the surface, which can be easily collected
with the blade of a knife and put into another vessel.
This second vessel is then heated until the last traces of
aniline evaporate out, when the weight of the black mass
gives the amount of the free carbon in the sample that
has been tested. *
TESTS AND ANALYSES I43
In such cases where it is merely required to find out
whether a so-called pure natural bitumen consists of, or
contains, an artificial product, the test for free carbon
furnishes a very good stopping place for the determination
of the question. In this case, however, so as to obtain
an exact result, the powder should be treated with carbon
bisulphide, ether and chloroform successively, in order to
extract the carbon in a thoroughly pure form. Since
pure natural bitumen often contains a certain amount
of ash as well, the weight obtained when a sample of it
is being thus tested does not give the true weight of the
free carbon. To find this, the residue after the extraction
of the soluble bodies, must be heated in a clay crucible
with a strong flame for some time, so as to burn up all the
carbon in it, when the residue, which now consists solely of
ash, is again weighed. The loss in weight is that of the
pure carbon that was previously contained in the material.
Another of the very important tests in the analysis of
bitumen is always to solve the question whether the
material has been adulterated or not, and the addition
of coal tar products can be detected in a sample of so-
called natural bitumen, instead of testing for free carbon,
as just mentioned, which takes up a certain amount of
time, by making the following test :-
Eight grammes of the substance to be tested are
reduced to a very fine pulverulent condition and then
shaken up in a closed vessel with 5 gms. of benzine
—free from water—until a very dark coloured solution
has been formed. This is filtered, and in the meantime a
mixture is made up of equal parts of benzine and 85 per
cent. alcohol. Into this mixture a few drops (five or six)
of the dark solution are added and the whole is then
thoroughly shaken. After this is done, the vessel is
allowed to stand, when its contents will separate out into
two layers, the upper one being the benzine and the lower
one the alcohol. If the alcoholic layer is colourless, the
original substance is a natural bitumen only, but if that
layer takes a golden brown colouration, then an artificial
product is present. -
Even when dissolving the substance about to be tested
144 NATURAL ROCK ASPHALTS
in the benzine only, an indication is recognisable by one
accustomed to carrying out this test, as, whilst the natural
product dissolves out with a pure brown colour, coal tar
products give a strong yellowish green fluorescence.
However, it is best for the ordinary practical man to
continue this test through to the end, as the result will
then clearly prove the composition of the sample without
any possibility of doubt.
There is also a very simple method to adopt in order to
tell one artificial bitumen from another, consisting of
merely holding the product in question over an open
flame and then smelling the vapours which are given off.
Besides coal tar residues, there are often employed
others, such as those made from wood tar, turf tar, or
stearin, each of which has its own distinctive odour, which is
easily noticeable when the material is heated, and, when
once known, will be readily recognised again. In cases
where a query may arise it is usually sufficient to heat a
small portion of the pitch, either coal tar pitch, turf tar
pitch, stearin pitch, etc., according to the doubt, and to
compare the odour arising from it with that which is given
off by the material then being tested.
Another definite test for the presence of coal tar pitch
in a suspected material is based upon the fact that, as
already pointed out, it contains a quantity of free carbon
in contrast with the natural bitumen which contains none.
Natural bitumen presents a uniform brownish appearance
when a very little of it is fused upon a hot microscope
slide and examined under a microscope. In the suspected
sample the free carbon may be seen suspended in the
bituminous matter like Small black dots, though to the
naked eye the mass appears to be a true bitumen.
A means of determining the exact character of a material,
providing that it is not a mixture of two or more, can be
found by noticing the effect of concentrated sulphuric
acid upon it. True bitumens give a colourless, or at the
most, a very faintly coloured liquid, whilst coal tar
products show up intensely brown. The method of pro-
cedure is as follows:–
A quantity of the substance is digested in carbon
TESTS AND ANALYSES 145
bisulphide, and the clear solution thus obtained is then
filtered off. This filtrate is now evaporated to dryness
and the heat applied continuously until the material
becomes hard and brittle after being cooled. Of this, a
tenth part of a gramme is taken and shaken up for a few
minutes with 5 c.cs. of fuming Sulphuric acid in a
stoppered flask. The mixture is then allowed to stand
for twenty-four hours after which 10 c.cs. of water are
added drop by drop, the whole being constantly agitated
all the while and kept from becoming too hot when
necessary, by holding the flask under a stream of water
from the tap, and finally filtered. If the conditions of
the tests are kept uniform, i.e., if the same weight of
the sample and the same volumes of carbon bisulphide,
sulphuric acid and water are taken in every instance, an
approximate qualitative comparison of the samples may
be made according to the following colours:
Rock asphalt .. tº º ... faintly coloured
Trinidad, bitumen e G ... slight brown
Petroleum pitch tº e ... no colouration
Shale oil pitch .. gº tº ... hair brown
Coal tar pitch .. tº e ... very dark brown
Bone pitch tº º tº Q ... intense brown
A further test to differentiate between natural bitumen,
petroleum residue, and coal tar pitch, has been thus des-
cribed by Kovacs :-
“A sample of the substance is first extracted with carbon
bisulphide and filtered. The filtrate is then dried in a water
bath and finally heated to 110°C. This dried residue is dis-
solved again in two and a half times its weight of carbon
bisulphide, thus forming a concentrated solution of the alleged
bitumen in carbon bisulphide. A cubic centimetre of this
solution is now put into a flask with 25 C.C.S. of oil of turpentine,
and should the material consist of coal tar pitch, a light brown
solution and precipitate is formed, whilst with pure bitumen.
the solution remains dark in colour and forms no deposit. To
the original solution is now added absolute alcohol in the pro-
portion of one to ten, when a brown precipitate is formed if
coal tar pitch is present ; a black, sticky, pitchlike precipitate
if it is matural bitumen, and a black, flocculent deposit if it is
petroleum pitch. If this precipitate is now filtered and dried
N.R.A. L
146 NATURAL ROCK ASPHALTS
to 90° C. to 95°C., the coal tar pitch obtained is powdery,
dull and of a light brown colour; the natural bitumen is black,
sticky with a fine gloss, and can be drawn out into fine threads
if it is warmed in the fingers; whilst the petroleum pitch is
black, dull, earthy and can be broken between the fingers
with the greatest ease.
“If one cubic centimetre of the original solution is shaken
up with only five cubic centimetres of absolute alcohol, then
coal tar pitch gives a brown deposit, petroleum pitch a black
slimy precipitate and bitumen a black precipitate. The liquid
is a reddish brown with petroleum pitch and light brown with
both ‘coal tar pitch and with pure bitumen, hence the earlier
distinguishing test. On the filter paper, when dried to 90° C.
to 95°C., the precipitated coal tar pitch and the pure bitumen
are shiny, pitchlike and bind together when heated, whilst
petroleum pitch on the other hand is dull, easily broken and
leaves behind it a transparent oily brownish red stain on the
paper.”
Besides the foregoing tests for purity, it is also necessary
to test the bitumen for composition and quality, and for
this purpose the solid and liquid types have to be treated
separately.
With the crude-solids, one of the first tests is that for
moisture. For this Professor Richardson suggests two
alternative methods, one by heating in a steam oven and
the other by drying in a desiccator. Of the two, the
writer much prefers the latter as being the easiest and
simplest to carry out, whilst at the same time the first
has the objection that the second has not, in that a certain
amount of the light oils contained in the bitumen also
evaporate out with the steam. The simplest method to
be adopted then is as follows:—
A portion of the sample is placed in an ordinary mortar,
which is provided with a lid through which the pestle is
able to pass. In this the material is reduced to a coarse
powder of which a weighed quantity is placed upon a large
dry watch glass, the weight of which has been previously
noted, and so spread over it that as large a surface as
possible is secured. In this condition it is placed in a
desiccator and left there for some twenty-four hours. It
is then weighed, and the loss found is the weight of the
moisture which has been extracted during that time.
The sample is now ground to a very fine powder, and again
TESTS AND ANALYSES 147
put into the desiccator, where it is allowed to remain,
until upon weighing at intervals of twelve hours it is
found that it loses no further weight. The total weight
thus lost by the powder is taken as the amount of moisture
originally present in that quantity of the sample which has
been treated, and the percentage content is calculated
from that.
The actual test used for this investigation when carried
out in the laboratory is the fractional distillation test,
when the moisture comes over in the first fraction,
from which it is allowed to settle. As the fractions are
collected in graduated cylinders, the amount of water
thus collected is readily read off and its weight calculated.
In carrying out this test, however, it is usual to dissolve
the bitumen in benzol prior to the actual process of dis-
tillation.
The tests for the specific gravity of a bitumen are carried
out in different ways, according as to whether they are
liquid, semi-fluid, or solid. In the case of the first, the
hydrometer is employed, for the second, an apparatus
known as the picnometer, whilst the amount of water that
a weighed quantity replaces forms the base of the test for
the third.
Another test with which it is desirable to be acquainted
is what is known as the penetration test. For this, how-
ever, a specially built apparatus is necessary which, being
both expensive and delicate in operation, will rarely be
employed by the practical man, its use being relegated
rather to the technical laboratory. In brief, the penetra-
tion figure, as the result of this test is called, is the distance
in one hundredths of a centimetre that a No. 2 needle will
penetrate a sample of the material under consideration in
a space of five seconds when under a superimposed weight
of 100 grims. and at a temperature of 25°C.
When the material is too soft to allow of this test, and
yet is too viscous to permit of the use of the float, it is
usual to make use of an Engler's viscosimeter. This
consists of a metal vessel which contains the material to
be tested, in the bottom of which is a conical outlet, the
internal diameters of which are 2.9 mms, and 2.8 mms. at
L 2
148 NATURAL ROCK ASPHALTS
the top and the bottom respectively. Under this outlet
is placed a graduated cylinder so as to catch any droppings
from it. The sample is now heated by means of an oil or
a water bath, and the outflow of the substance through
the outlet at a certain fixed temperature, is noted. The
outflow of water is taken as the unit, and this, at 25°C., is
11 seconds for 50 c.cs., and 22°8 seconds for 100 c.cs.
The usual figures for light flowing oils, viscous and semi-
liquid malthas are approximately 100 c.cs. at 25°C.,
50 c.cs. at 50° C., and 50 c.cs. at 100° C. and over
respectively.
When any bitumen or a bituminous product is to be
heated before use in any manufacturing process, especially
if it is a liquid in its natural state, it is necessary to deter-
mine the flash and the ignition points. This is sometimes
done very crudely by heating a sample in an open basin,
but the results so obtained are very unsatisfactory and
cannot be depended upon. A proper oil tester should
always be used, and this instrument consists of a metal
receptacle for the sample, which sits in an oil bath and is
heated from below by a Bunsen burner. The receptacle
is fitted with a lid through which passes a thermometer,
which, by dipping in the sample, indicates the temperature
of the latter at the various stages of the test. A small
hole is also made in the lid so as to allow of the insertion
of a tiny gas jet. This jet is made by connecting a small
piece of glass tubing having a small bore to the gas service,
and arranging the pressure of this so that a small gas flame
of about 15 mms. is formed. The oil bath is now heated
gradually, so that the temperature of the sample increases
at a rate of about 5° C. per minute, and the test flame is
inserted in the chamber from time to time without, of
course, coming in contact with the sample itself. Finally
a bluish flame will be seen formed when the test flame is
dipped into the vapour, and when this stage is reached,
the temperature of the sample is taken and the reading
so obtained is known as the flash point.
To determine the ignition point the thermometer is
now raised out of the sample, though still left in the closed
chamber, and the test is continued by further increasing
TESTS AND ANALYSES 149
the temperature. When the oil itself takes fire when the
test flame is inserted, the ignition point of the sample has
been reached, and the degree at which this occurs is also
noted from the thermometer.
As the volatility of the malthenes is an important
point in the use of a bitumen for industrial purposes, it
is customary to submit liquid, semi-fluid, and even low
melting solid bitumens to an evaporation test. For this
purpose a vessel is used which has a perforated lid.
Through this latter pass two thermometers, one dipping
into the sample that is being tested and the other being
suspended in the space above it. The sample is now
heated to a temperature of 165° C., at which it is kept for
a period of five hours, during which the temperatures as
shown on the thermometers should not vary from that
mentioned by 2° at the very outside. The sample is
then allowed to cool and the loss in weight noted, after
which it is usual to again test the resultant product for
specific weight, the float test, penetration test, etc. At
times, though it must be admitted that they are of very
infrequent occurrence, this test is also carried out at
other temperatures as well.
A test of more recent growth is that for the “carbene *
content. The fraction of a bitumen known by this name is
that which is soluble in carbon bisulphide but insoluble
in carbon tetrachloride. This test is of particular value
when it is believed that a bituminous material has suffered
from overheating during the process of manufacture that
it has undergone, since such over-heating increases the per-
centage of the bitumen which would respond to this test.
As distinct from the amount of “free carbon ’’ that a
bitumen contains, it is sometimes required to ascertain
the percentage content also of what is known as “fia.ed
carbon,” i.e., that carbon which is present in the bitumen
but in a state of chemical combination with some other
element or group of elements to form an organic com-
pound. To determine this content, a gramme of the
material to be tested is placed in a crucible, preferably
of platinum, provided with a close-fitting lid. This is
submitted to the full play of a Bunsen burner, the flame
150 NATURAL ROCK ASPHALTS
of which is so arranged as to completely surround the
crucible. This is kept up for a period of seven minutes,
when the crucible is removed, placed in a desiccator and
carefully weighed after cooling. The lid is now removed
and the contents of the crucible burnt to an ash, again
placed in the desiccator and weighed after cooling. The
weight of the ash as thus obtained is then deducted from
the weight of the residue obtained from the first heating
of the sample, and the result is the weight of the so-called
“fiaſed carbon ’’ that is found in the particular sample then
tested.
A bitumen which contains an appreciable quantity of
paraffin is very undesirable for various manufacturing
processes as well as for paving purposes. It is therefore
often necessary to determine the percentage of this
matter in a sample of bitumen, in order to ascertain if the
latter is suitable for some particular purpose. To do
this, 100 grms. of the sample are taken and distilled as
rapidly as possible to a dry coke, whilst the distillate is
collected in a suitable vessel and weighed. From this
distillate 5 grms. are taken and mixed with 25 c.cs.
of ether in a 100 cms. capacity flask, after which 25 cms.
of alcohol are added. After the flask and its contents
have been submitted to a freezing mixture at a tempera-
ture of —18°C. for half an hour, the liquid is then filtered
by means of a filter pump, the upper portion of which is
packed round with a freezing mixture in order to keep
the liquid which is being filtered at the temperature
mentioned. The mass left on the filter paper is the
amount of paraffin contained in the sample treated, and
when weighed the percentage content of it in the material
itself can easily be calculated. It must be confessed,
however, that this test is not always too satisfactory in
actual practice, and it is therefore usually used merely to
obtain an approximate idea of the paraffin content of a
bitumen.
As coal tar and its products are now largely used in a
similar manner and for similar purposes as bitumen, a
few remarks on the principal tests for such products
may not be out of place,
TESTS AND ANALYSEs I51
Coal tar is usually examined only as to its specific
gravity, as this figure at Once demonstrates if, and to
what degree, the crude tar has been distilled. Before
ascertaining this, however, it is absolutely essential that
the tar shall be free from water, and this condition is
arrived at by the simple expedient of allowing it to stand
for at least twenty-four hours in a narrow-necked flask,
which is stood in a water bath by means of which the
tar is kept at a constant temperature of 50° C. The
water which separates out is then removed by decanting
it off the tar and afterwards removing any small quan-
tities which may remain floating on the surface by
absorbing them with blotting paper. The tar is now
allowed to cool to the temperature of the room—that is
to say to about 15° C.—and as the usual instruments for
determining specific gravity cannot be employed with
viscid tar with any degree of accuracy, it is best to make
the test in the following way:-
A cylindrical weighing tube of 50 c.cs. capacity, having
a groove filed through the stopper, is used, and its specific
gravity is determined by (a) first weighing the tube when
empty and (b) when filled with water. After this, it is
emptied and dried, and then filled with about two-thirds
its capacity of the water-freed tar. In this condition it
is placed for an hour in hot water until all the air bubbles
have been expelled from the tar, when it is again allowed
to cool. When it is cold the vessel and its contents are
again weighed. (c) The tube is now filled up with water,
the stopper inserted and the excess of water carefully
removed, after which a further weighing is carried out
during which the tube is stood in a large vessel of water
at a temperature of 15° C. (d) The specific gravity
sought is now calculated from the following formula
according to the results obtained from the foregoing
experiment:—
C - 0,
b -- c – (a + d)
To accurately test the quality of the tar it is necessary
to find the yield of the various constituents contained
152 NATURAL ROCK ASPHALTS
in it, and this is done by distilling a sample of about
250 c.cs. on a small scale at a rate of about 40 to 50 drops
of distillate per minute. This distillate is collected in
fractions divided at the temperatures of 170° C., 270° C.
and 315°C. The mass which then remains behind in
the retort is regarded as the residue. If there is water
in the tar, it passes over with the first fraction, in which
it forms a lower layer, since the light oils, by reason of
their inferior specific gravity, lie upon its surface.
In the residue thus formed is always to be found a
certain amount of solid matter made up of ash and “free
carbon.” As for certain purposes a high proportion of
this is prejudicial to the material prepared from it, it is
customary to find in the specifications, especially for
material for road spraying, etc., a maximum limit beyond
which a material will not be accepted. It is therefore
necessary to determine this content in a tar, and the
method adopted in this case is as follows:—
Ten grammes of the tar is exhausted with 25 c.cs. of
glacial acetic acid and 25 gms. of toluol. It is then
passed through a weighed filter paper and the latter after-
wards well washed with toluol and dried to 120° C. The
increase in the weight of the paper is that of the ash and
free carbon contained in the quantity of the tar taken for
the test, and when multiplied by ten it gives the percen-
tage of these solid bodies that are present in the tar
under consideration.
Coal tar pitch is usually examined only for its softening
and melting points, and this in some factories by the
“mastication ” test only. This latter consists merely of
placing a sample of the pitch between the teeth and noting
the results. Soft pitch is readily pressed out flat;
medium hard pitch will barely receive the impression of
the teeth, whilst hard pitch crumbles between the teeth
and falls to a powder. For more accurate examination,
the apparatus of Kraemer and Sarnow is employed.
Twenty-five grammes of the pitch to be tested are melted
down in an iron pan which is heated over an oil bath
to 150° C., so that the pitch forms an even layer
approximately 1 cm, thick at the bottom of the pan.
TESTS AND ANALYSES 158
A glass tube having an internal bore of 5 to 7 mm.
and open at both ends is now taken, and one end
dipped into the molten pitch. The upper end is closed
with the finger, the tube is removed from the pan and
the pitch is allowed to solidify inside it, after which the
excess of pitch which adheres to the outside of the tube
is carefully removed. There now remains in the tube a
column of solid pitch about 5 mm. in height. Upon
this is poured about 5 gms. of mercury, and then the
tube is tied to a thermometer and both hung in a
beaker of water which acts to them as a water bath and
which in turn is heated by an ordinary water bath. Heat
is applied gradually to the outer bath until it is noticed
that the mercury commences to penetrate into the pitch.
The temperature at which this occurs is recorded as the
softening point of the pitch. In the case of soft pitch,
this temperature should be between 50° C. and 51° C., for
medium hard pitch between 60° C. and 70° C., and for
hard pitch between 80° C. and 89° C.
To ascertain whether a coal tar pitch has been made
from blast furnace tar or the tar produced from gas works,
and for certain purposes this is a matter of paramount
importance, the simplest method is to ascertain its ash
content, the experiment being carried out in a similar
manner to that adopted for bitumen. If the resultant
figure is high, then the material is a blast furnace pitch,
but if it is under 1 per cent., the sample is of a gas works
itch.
p When rock asphalt mastic or any other product of rock
asphalt is being tested, the procedure is to first extract
the bitumen contained in it, which is then submitted to
the various tests given above for natural and artificial
bitumens, and afterwards to analyse the rock itself
separately. The separation of the bitumen and the
mineral matter may be done in the following manner:—
A sample of the mastic is crushed to a fine powder and
then extracted with carbon bisulphide until no more of it
can be dissolved out. The material thus dissolved is then
regarded as bitumen and tested as such after the carbon
bisulphide dissolving it has been driven off. The residue
154 NATURAL ROCK ASPHALTS
is mineral matter, and the proportion of this which is
limestone is ascertained by treating the whole with
hydrochloric acid when the limestone is dissolved out,
leaving behind it small quantities of other materials such
as sand etc., according to the particular type of rock
asphalt that is being tested.
In addition to this, however, the four following quali-
tative tests are recommended to the practical man as being
both simple to execute and quickly carried out, for it must
be borne in mind that whilst it is one thing for a material
to meet a chemical standard, it does not necessarily follow
that by fulfilling these chemical conditions it will also
fulfil the essential physical ones.
(1) Mastic should be able to be cut with a knife. If the
material proves to be too hard or of too stony a nature,
it proves that there is an insufficiency of bitumen or that
the bitumen has not been suitably fluxed, and therefore
liable to speedy segregation.
(2) Cuttings of the mastic must resist tension at the
ordinary temperature of the room—say 20° C. If the
rock is too soft, if it has been fluxed too much, if there is
too great a quantity of bitumen than is necessary, the
material will be too soft to hold together properly, with
the result that any work that may be done with it will
readily receive indentations and rapidly form into ruts
and holes if subjected to much vehicular traffic.
(3) When held above a lighted taper for a minute or so
it should give off the smell of bitumen only. Should the
Smell of tar or pitch, as found in the gas works and such
places where these products are treated for any purpose, be
distinguished, then the sample is either an artificial asphalt
or one that has been adulterated with a coal tar product.
(4) When held for some time over a gas flame it should
soften, but it should never run or begin to ignite. If it
burns, then the mastic contains too much flux—in all
probability a petroleum residue at that—and for practical
purposes the material will prove to be too soft, whilst
further, after being subjected to a constant summer heat,
it will rapidly become brittle—owing to the evaporation
of the volatile portions of the flux—and so quickly decay.
TESTS AND ANALYSES
155
ANALYSES, ETC.
RoCK ASPHALTS.
*=== º Seyssel. Lobsann. Ragusa. S. Mººn. §.
Bitumen 10-15 8-15 | 12-32 8-92 8.83 || 11-40
Limestone . . . . . 88-40 || 91.30 || 71.43 88-21 || 80-00 || 77.52
Aluminium and iron
oxides 0-25 0-15 5-9] 0.91
Sulphur tº e * * 5-18
Magnesium carbon-
ate 0.30 0.10 0-3] 0.96
Sand tº gº © tº *º- tº- 3.15 0-60
Insoluble in acids . . . 0-45 || 0-10
Undetermined 0.45 || 0-20 I-70 || 0-40
*R*===º §: Mons. | Limmer. Wii. Sysran. Cesi.
Bitumen . . . 12.46 || 10-20 | 14-30 8-50 || 30-50 7.15
Limestone .. ... 77.53 | 84-63 || 67.00 80.04 || 66.23 | 73-76
Calcium sulphate .. 2.63 *sº tº-e ſº-ºººº- Eºse 1-72
Aluminium and iron
oxides 2. IT *
Sulphur e e *s * *= 4-03 *=== 3.02
Magnesium carbon-
ate 4-71 *== 17-52 0-55 3.27 *-*-
Sand ſº tº e º 0-50 *- tº-º-º-º: *E===º tº-e 14-24
Insoluble in acid .. *Eºs ºmmº &= -º 4-77 *===s 0-10
Undetermined *s * 1, 18 2-11
AMERICAN ROCK Asphalts.
*E**E=- California. Kentucky. Texas.
Bitumen 15-13 5-76 12.05
Sand . . 83-40 94-22 -
Limestone tº- &= -º-º: 87.94



I56
NATURAL ROCK ASPHALTs
CRUDE BITUMENS.
Californian.
- Mexi- | Trini- | Vene-
-*s i. | Cuban.|*...* | *# M.
Hard. | Soft.
Bitumen 72-69| 24/68 |35/94 || 35/40 45/95 99.10 99.68
Mineral matter 17.19 | 73|26 55/4 || 41/26 40/2 0.36 0-20
Organic , 1-00 || 2/1 8/2 | 10/4 7/1 0-54 || 0-12
Water 9-12 1/5 2 14/30 8/2 - -
SOLUBILITY OF BITUMENS.
Solvent. #: Trinidad. | Maracaibo. Barbadoan. Syrian.
Water . . Insoluble | Insoluble Insoluble | Insoluble | Insoluble
Dilute acids 5 y 95. y5 93. 33
alies 55 5 y 55 55 55
Alcohol . . Partly 5% Slightly Partly 5%
Ether Entirely 57% Partly 55 44%
Chloroform 35 Com- Com- Com- Com-
pletely pletely pletely pletely
Oil of turpentine 52 25 35 5 5 2 3
Melting point ... (liquid) |130/165°C 130°C 110°C 135° C.
CHEMICAL COMPOSITION OF BITUMENs.
-*º C. H. O. N. S. Authority.
Pont du Château. . . 77.52 9.58|| 10-53 2-37 — Ebelmen
Abruzzi . . . 81-83 || 8-28 || 8-83 || 1-06 || – 5 y
Cuba, 82-67 9-14 8-19 — | Wetherill
Coxitambo 88.63 || 9-69 1°68 *-*. 3 3
Pechelbronn 86-60 | 11-40 || 0-40 || 0-30 | 1.40 Rayser
Egypt . . 85-29 8-24 || 6-22 || 0-25 | – | Boussingault
Dead Sea. . . 80-00 || 9-00 || – 0.40 || 10.00 95
Syria e - 80-50 9-06 || – 0.38 || 10-06 Kayser
Trinidad . . 78-80 | 9-30 || – 1-40 || 10.00 35
Barbados . . 87-04 || 9-56 || – *me 2.67 35
Maracaibo 81-65 9-59 || – * - 35



TESTs AND ANALYSEs
157
SoLUBILITY IN PETROLEUM SPIRIT AND SULPHUR ContFNT.

Solubility in Petroleum Spirit.
Sulphur content.
*sºmºsºme Ash. Soluble. º .* º, º:
- Percent. | Per cent. | Per cent.
Val de Travers 90-24 9.76 *E*- 100 0.41 4-20
Fine Syrian 0.68 || 48-16 || 51-16 || 48-49 6.13 6-19
Trinidad 37.76 36-24 26-00 || 58-22 3-47 5-58
Stearin pitch e tº 5-50 71.05 || 23.45 75.18 0-04
Stockholm pitch 0.84 || 91.46 7.70 || 92.23 ().01
Resin pitch 0.58 || 86.94 | 12-48 || 87-45 0-26
Coal tar pitch 1-06 | 18.70 || 80-74 | 18-90 || 0-41
SPECIFIC GRAVITY OF BITUMENS.
Mexican 1-04
Gilsonite 1.04
Bermudez 1*05
Wurtzilite 1.05
Maracaibo I-06
Californian 1-06
Manjak 1-08
Albertite *. 1.08
Syrian . . 1. 10
Grahamite 1.16
Cuban * I-30
Trinidad 1-40
CHAPTER XI
PEIYSICAL PROPERTIES OF ROCK ASPHALT
IN considering the use of rock asphalt for road making
purposes, it is necessary to handle the question both as
regards the type of the rock that is impregnated, and the
nature of the bitumen which impregnates it, together
with the proportion of the latter and the state of impregna-
tion.
It must always be borne in mind that the impregnation
of a rock with bitumen results only in a mixture, more or
less intimate according to circumstances, but not in a
combination, so that although at times they may be
masked, the chemical properties of the rock are not
changed. Thus for example, any of the sulphides that
may be mingled with the rock will always be capable of
conversion into sulphates as the result of atmospheric
oxidation. Still, the action of chemical or physical
reagents can be withstood by the bitumen which, to give
a further example, would protect the limestone from the
attack of cold hydrochloric acid. The properties, however,
that are most interesting from our point of view are resist-
ance to crushing, wearing, etc., properties which are
subject to certain conditions that will be gone into in the
following pages.
To begin with, bitumen is found distributed in the rock
that it impregnates, in ways which vary according to the
state of division in which the rock chanced to be at the
moment of impregnation. Thus it is possible to distin-
guish between an impregnation in bulk, in the powdered
form and in the molecular state.
In the last are included those rocks which for some
chemical or physical cause, owe their origin to a precipita-
tion from an aqueous mass. Such are the sandstones,
PHYSICAL PROPERTIES OF ROCK ASPHALT 159
deposits of “geyserite,” limestone “travertins,” tufas,
and perhaps some of the clays, to mention only the most
interesting from our particular standpoint. These are a
few examples of rocks which during their sedimentation
found themselves in the presence of a bitumen itself
in such a condition as to be susceptible of mixing with them
at the moment they were in that molecular state. The
Trinidad “lake ’ deposit probably comes under this
category.
It is rare, however, to find rocks that have been impreg-
nated with bitumen in their massive or even in a frag-
mentary state. An exception to this is, of course, the
material that is obtained from the mines at Acquafredda,
which, as has already been pointed out, does not segregate
as do the other types of natural bituminous rock, upon
being heated. This rock has a cohesiveness of its own,
so that in this case the bitumen does not play the part of a
cement binding together the integral grains, but is merely
a material filling up the voids in the rock. To this type
of impregnation is given the term of “porous penetration.”
The presence of the bitumen, though, greatly increases the
capacity of the rock to resist crushing, since the fact of
the viscous substance being confined in its pores in such
a way that it cannot be extracted by the most powerful
pressure that may be exerted upon the rock, prevents
that alteration of shape which results in a fracture with
the unimpregnated rock. Thus an unimpregnated sample
which breaks under a pressure of 95 kgs. per square centi-
metre is able to withstand a pressure varying from 153 to
189 kgs. per square centimetre when impregnated with
12 per cent. of bitumen.
The majority of the naturally impregnated rocks are
those which have received their bitumen content whilst in
a powdered state. They segregate under the influence of
heat, so that roads made from the rock asphalt mastic
or the compressed rock asphalt powder are merely formed
by coating the surface with a covering produced by the
re-union of a pulverulent material with a bituminous
cement. The characteristic of this impregnation is that
each grain has its own coat of bitumen, the adherence of
160 NATURAL ROCK ASPHALTS
which to those coating the other grains surrounding it
occasions the cohesion of the rock, and as this adherence
varies according to the consistency of the bitumen, the
cohesion of the rock also varies with the temperature. To
distinguish it from the “porous penetration,” this impreg-
nation is known as “bitumen of intercalation.”
In order to ascertain the respective values of different
rocks for road making, Messrs. Durand-Clay and Debray
carried out experiments by means of which to determine
the coefficient of wear of two compressed powders, one
made from a bituminous limestone and the other from
a natural bituminous sandstone, both materials being
obtained from the same district. The method adopted was
to find the thickness which was worn from a rectangular
prism when loaded with an evenly distributed weight of
300 gms. per square centimetre and rotated round a circle
I metre in circumference for 1,000 times. Under these
conditions the ordinary sandstone as used for paving pur-
poses has a wearing coefficient of 58, whilst the bituminous
limestone was found to vary between 42 and 49 as against
the bituminous sandstone whose figures were from 51 to 60.
The same difference was observed when the point of
resistance to crushing stress was considered. Blocks
of equal sizes were made of the two materials, and though
that composed of the bituminous limestone broke under
an average pressure of 328 kgs. per square centimetre,
that made with the bituminous sandstone only resisted
up to a pressure of 217 kgs. per square centimetre.
A further point for consideration is the power that the
rock possesses of retaining the bitumen which impregnates
it. M. Daubrée, in seeking to explain the difference in
the richness in bitumen between the impregnated lime-
stone and sandstone of the Sulz unterm Wald district,
placed pieces of the unimpregnated rock of both types
into a bath of Pechelbronn bitumen, the operation being
assisted by slightly heating the latter. Although viscous
at the ordinary temperature, the bitumen was quickly
absorbed, impregnating the whole mass in both cases
right through to the centre. Whilst the limestone
absorbed 17 to 24 per cent. of its own weight of bitumen,
PHYSICAL PROPERTIES OF ROCK ASPHALT 161
the sand, even with the assistance of additional heat, only
absorbed 8 to 9 per cent. Further than this, however,
the bitumen was so absorbed by the limestone that even
when it was pulverised into a fine powder and immediately
Submitted to boiling water, it could not be brought back
to its original colour again, although at that temperature
this particular bitumen is perfectly fluid. With the sand,
although some of the bitumen is retained, it is, however,
a much less quantity than is the case with the limestone.
Clays and marls have a still greater affinity for bitumen
than even chalk. It need only be pointed out again that
at Pechelbronn the greatest difficulty in the extraction
of the bitumen is caused by the clay which is present
in the impregnated rock, and this clay retains the bitumen
impregnating it most firmly, so much so, in fact, that in
refining, a rich residue is always left which, known as
“calphonium,” consists of clay intimately mixed with
bitumen and from which the latter cannot be extracted
economically by the usual industrial methods. The same
difficulty is met with in the purification of the crude
bitumen extracted from the Trinidad lake, which sub-
stance may also be looked upon as a clay impregnated
with some 50 per cent. of bitumen and mixed with a
certain amount of water.
This property of clay has been made use of from the
most ancient of times, the Babylonians having used it, as
a reference to an earlier chapter will show, in the formation
of bituminous dampcourses for their buildings.
The bitumens, too, show so many differences amongst
themselves that it is also necessary to examine the com-
position of the rock in detail according to the use for
which it is intended. The principal properties for our
purpose are fusibility and tenacity; for they possess
widely differing melting points, and it is, of course,
essential that they shall not fuse at the extreme heat to
which they may be exposed. Fusing proper is really
preceded by a viscous state, and it is with reason affirmed
that it is to this viscosity that the elasticity of work done
with the asphalt mastic or compressed rock asphalt
powder is really due, for when extracted the bitumen
N.R.A. MI
162 NATURAL ROCK ASPHALTS
which naturally impregnates the rock asphalt is usually
soft, if not actually semi-fluid. A bitumen which is
hard and solid at the ordinary temperature would not
admit of this flexibility, whilst one which is liquid or
easily flowing would be too soft to withstand the pressure
exerted by traffic upon it. Both can, of course, be
suitably modified, the one by the use of a suitable flux
and the other by evaporating from it the more volatile
portions. In the first case, however, precautions must
be taken to use a suitable flux, i.e., one that will truly
blend with the original bitumen, will not “bleed" in
hot weather or dry out and leave the bitumen in its first
stage; whilstin the second case the process of heating must
be carefully controlled, otherwise a decomposition of the
bitumen will result, giving rise to entirely new products
with totally different properties from the ones desired.
The tenacity of the bitumen in its viscous state
diminishes as its fusing point is approached and increases
as the temperature is lowered, becoming fairly weak in
the hot weather during which the bad condition of some
rock asphalt roads is particularly noticeable. In order
to compare the tenacity of two bitumens in their viscous
state, it is usually sufficient to note whether they can be
drawn out into threads, and the fineness of the thread
that is obtainable before it breaks. Blown oils and cut
back infusible bitumens usually form no thread at all,
but merely break in two when any tension is exerted
upon them.
The bitumen which impregnates the rock must also be
considered as regards the type of impregnation, and for
this it is essential to distinguish between the proportion
of bitumen of “porous penetration ” and that of inter-
calation. In other words, a proportion of bitumen which
would be considered satisfactory in a pure limestone
which is non-crystalline and non-compact would be too
great for a more compact and crystalline one, since in
the latter case the proportion of bitumen of “inter-
calation ” required would be less, with the result that
the bitumen of porous penetration would be increased
accordingly. Thus the crystalline Seyssel rock requires
PHYSICAL PROPERTIES OF ROCK ASPHALT 163
a less proportion of bitumen in its mastic form than does,
for example, the Limmer type, whilst this latter again
requires less than the still finer Val de Travers material.
This point is one that is very often overlooked, the value
of a rock asphalt in many instances being considered as
being enhanced or otherwise according to the percentage
of the bitumen that it can show. This is to be regretted,
as it has the tendency to cause the mastic now on the
market to be made too soft for first-class work, merely
in order that it can show a large proportion of bitumen.
We have already remarked that the material which is
obtained from the mines at Acquafredda in the Abruzzi,
must have been impregnated in bulk, since it will not
segregate when it is heated. It only contains, therefore,
bitumen of “porous penetration,” and as it is success-
fully used for the making up of compressed rock asphalt
powder roads, it may be reasonably concluded that the
amount of bitumen necessary to penetrate the pores of
the rock is sufficient for this class of work. At the same
time, this does not mean that a certain amount of bitumen
of intercalation would be objectionable; rather it would
appear that a percentage of this latter would be of advan-
tage, for even with our present methods of compressing
the rock asphalt powder after it has been spread upon
the road, it is impossible to eliminate all the voids between
the grains of the material when finally compacted, so
that the presence of the bitumen of intercalation would,
by acting as binder, leave the bitumen of porous pene-
tration free to fill these voids, and so give an additional
watertightness to the layer. On the other hand, tests
made with a rock composed essentially of a felspathic
sand, and bound—not penetrated—with 8 to 9 per cent.
of bitumen, have shown that the simple intercalation
of bitumen around the grains of a rock asphalt that
cannot have been impregnated in bulk does not preclude
its use for compressed work for which it is used to a great
extent in America.
With the asphalt mastic, which is spread without
pressure, the cohesion, and to a minor degree the filling
up of the voids between the grains, must necessarily be
M 2
164: NATURAL ROCK ASPHALTS
effected by the bitumen of intercalation. As already
pointed out, the percentage of bitumen as found in the
different types of rock asphalt mastic differs according
to the type of the rock that is impregnated with it, but
it is now usual to increase this figure above the nominally
desirable one in order to secure a product that will be
moister, and so spread more easily and freely under the
workman’s float. The pressure and the motion given to
the material during the operation of spreading causes
this excess of bitumen to rise to the surface of the layer,
where it forms a kind of black varnish over the asphalt
mastic, though for roads and pavements it is rubbed
with a fine sand or dust before cooling, so as to afford a
foothold upon it for traffic.
The influence of the regularity of impregnation with
bitumen of a rock asphalt, although it has been keenly
disputed, does not seem to have ever been settled. For
a long time it was believed that a regular impregnation
was essential for satisfactory work, but now it is usually
recognised that it is sufficient to examine the state of
impregnation only. Thus M. Bartet, whilst speaking of
a mineral the irregularity of whose impregnation was such
as to give it almost the appearance of concrete, says:–
“We are not afraid of the concrete nature of the mineral,
for as has been actually proved, this mineral considerably
increases its homogeneity when it is reduced to a powder and
slightly heated, the unimpregnated limestone apparently
attaching itself to the bituminous threads so that the white
specks are very soon only perceptible here and there. (It
should be remembered that all bituminous rocks when suffi-
ciently magnified show a large number of white spots.) A
piece of compressed work was made with it in our presence
and then ground down at a grindstone. Its wearing co-
efficient was 6:21, whilst that of a piece of Val de Travers, as
obtained from old streets, when subjected to a like test, showed
a co-efficient of 6'63. As compressed rock asphalt powder
when laid on roads loses in thickness in the course of time
without being appreciably reduced in weight, there is appar-
ently not so much wearing away as an additional compression,
so that the sample of the old material should have resisted this
wearing test even better than that freshly made.”
As the Italian rock asphalt generally has been considered
PHYSICAL PROPERTIES OF ROCK ASPHALT 165
preferable for compressed asphalt powder work, samples
taken from different mines were examined by Herr
Dietrich, of the Berlin Technical School, at the request of
the Italian government. The rocks tested were taken
from (a) Acquafredda (b) St. Angelo and (c) Cesi. In
these he found the following characteristics:—
(a) The rock is very hard, crystalline, and not uniformly
impregnated. It does not fall to a powder under
the influence of heat like the natural bituminous
rocks of other localities, but retains its cohesion.
It contains 9:14 per cent. of a bitumen which is
tenacious and strongly agglutinating. When
this bitumen has been extracted from the rock,
a residue of almost pure calcium carbonate is
left with a few spangles of mica.
(b) This rock has the same hardness and texture as the
above, with the same bitumen impregnating it.
Its bitumen content is 6'69.
(c) This rock is compact, of a dark chestnut or black
in colour, and is very well impregnated with a
bitumen, the content of which reaches 12:26 per
cent., and is of the same nature as the preceding.
This rock is more suitable for use in the manu-
facture of the rock asphalt mastic.
The conclusions arrived at by Herr Dietrich as a result
of these investigations are as follows:—
“The limestone of the rock asphalts mentioned is so crys-
talline and compact that the bitumen cannot properly impreg-
nate it ; further the powder prepared from it, as well as that
made by heating and recompressing it, contains an appreciable
number of white specks, which are usually regarded as being
objectionable in material which is to be used in compressed
rock asphalt powder work. In practice, however, these do
not preclude the use of the above mentioned rocks for the
work in question and should not diminish its durability if
care is taken to reduce the rock to a very fine powder.
“The bitumen contained in the rock asphalt is rather harder
than that to be found in other types of rock asphalt used for
compressed asphalt work, so that this rock should be used for
preference in those towns that are not subject to intense
wintry cold. However, the bitumen can be made softer by a
suitable sprinkling of the heated powder with petroleum that
166 NATURAL ROCK ASPHALTS
has been previously heated for a considerable time at 100° C.,
and then carefully and repeatedly mixing the material.”
Two types of rock were taken from the Acquafredda
mines, one showing a percentage of bitumen of 9:14,
whilst the other only possessed 7-38. Of these, Herr
Dietrich mentions that :
“The proportion of bitumen in the first rock is very favour-
able to the utmost stability and hardness in roads constructed
with it in the ordinary way, but the second rock is not so
suitable, as it would not be possible to prevent damp and
frost from penetrating the surface of the road unless the asphalt .
powder was very firmly compacted and rammed again after
being again well warmed.
“The experiments proved conclusively that it is not neces-
sary to heat the powder for a lengthy period in order to get
rid of that amount of the liquid bitumen which might by
chance be there, but it is more necessary to keep the rock
asphalt powder at 100° C. to 130° C. in order to evaporate
absolutely every trace of moisture, for it is when it is
thoroughly free from water that the powder is best applied
to the road.”
The conclusions of Herr Dietrich express the incon-
veniencies which arise from the use of a powder which
is not homogeneous even after the preliminary heating,
and they clearly show the utility of holding to the con-
dition referred to by M. Bartet, as to the homogeneous
impregnation of the bitumen throughout the asphalt
powder before compression.
The following are the results of further tests made to
investigate the effect of heating the asphalt powder
immediately before use, as regards its effect upon com-
pression. The wearing coefficient of the rock asphalt
powder when used hot was 4'64, but when compressed
in its cold state it was 5'60, even when compressed under
a much heavier weight. Both samples were similarly
affected by a Superimposed pressure of 160 kgs. per square
centimetre, each losing a third of its thickness, although
it must be remembered that the one made up of the
powder in its cold state had previously received a far
greater initial compression than had the other. Of two
PHYSICAL PROPERTIES OF ROCK ASPHALT 167
samples, one made up of the hot and the other of the cold
powder, both were heated to 160° C. and immediately
afterwards placed under a hydraulic press, when the first
began to lose its shape under a pressure of 60 kgs. per
Square centimetre ; under 80 kgs. the edges began to open,
and under 110 kgs. per square centimetre the thickness
was decreased by two fifths. The second sample lost its
shape and fractured under a load of 25 kgs. per square
centimetre, and when this load was increased to 30 kgs.
the lateral faces separated. e
In the case of work carried out in rock asphalt mastic,
the possible variations arising from different degrees of
heat or of pressure during the progress of the work are of
course absent. With it, instead, the life, durability and
general condition of the work are dependent upon the
quality of the material only. In this case, too, a certain
amount of judgment must be exercised with the degree
of heat at which the mastic is fused, but so long as this is
such that it reduces the material to a thickly flowing mass
without allowing it to burn, it does not play that great
part in the binding of the material when spread, as is
the case with the rock asphalt powder. The work done
with the rock asphalt powder has one very important
advantage over that carried out in the rock asphalt
mastic in that, since it contains a less proportion of
bitumen, the heat of the day has a less effect upon it.
It is owing to this fact that the mastic form of rock
asphalt cannot be used with any satisfactory degree of
success as a road covering where the surface is to be sub-
jected to much vehicular traffic, or if the loads to be
drawn over it are very heavy. On the other hand, for
pavement work the mastic is to be preferred to the
powdered form, as here it gives much more satisfactory
results. This apparent incongruity finds an explanation
in the fact that the powdered asphalt surface, having
been placed in position with pressure, requires also a
certain amount of pressure constantly passing over it in
order to enable it to retain that compactness which, by
sustaining the close layer that has been formed upon the
surface of the powder by the initial pressure, is conducive
I68 NATURAL ROCK ASPHALTS
to durability. With the mastic, on the other hand, con-
stant pressure would result in the gradual displacement
of the material immediately beneath the weight, when,
as in the summer months, it is also subjected to a high
degree of heat. Being, however, more coherent than the
powdered form, by reason of its higher percentage of
bitumen, it is thus able to better withstand the friction
occasioned by foot traffic than is the compressed material.
This resistance to foot traffic is assisted too by the fact
that it is usual to add to the mastic when used for this
purpose a percentage of Small grit, the purpose of which
is to harden the surface of the material against the wearing
action of the traffic, a method which could not, for obvious
reasons, be adopted in the case of the compressed asphalt
powder.
With bituminous macadam the dominating idea is
still somewhat similar to that borne in mind in the case
of the rock asphalt mastic, but here the work is essentially
to lay a road-forming material, the pieces of which are to
be held in position by being coated with the bitumen in
such a way that the latter forms a bond between the
adjacent pieces, and not merely a road surface. The
adoption of the bitumen as the binder has as a result
the absorption of a certain amount of the pressure and
vibration caused by the traffic passing over the surface,
which there is no doubt plays a very important part
in the breaking up of Ordinary macadam road surfaces.
The putting down of a richer bituminous layer upon the
bituminous base serves as a further shock-absorbing
cushion, and, in addition, as a dust preventative.
The formation of the bituminous macadam has been
carried out in two distinct ways, one by the penetration
of the macadam road after the latter has been laid, with
a semi-fluid bitumen—the “penetration ” method—and
the other by mixing the mineral aggregate with a solid
bitumen prior to use—the “mixing ” method. Both
methods have their adherents, but the former would
appear less susceptible to that evenness of bituminous
intercalation that is so necessary for this kind of road
surfacing, whilst the latter offers less possibility for the
PHYSICAL PROPERTIES OF Rock ASPHALT 169
element of chance, and so is to be preferred. Where, of
course, the intention is merely to adapt an existing water-
bound macadam road into a bitumen-bound one, the first
method is the only one that can be reasonably used. This
subject will be found treated in more detail in a later
chapter, -
CHAPTER XII
THE CARRYING OUT OF ROCK ASPHALT WORK
As a paving material many advantages can be claimed
for rock asphalt, of which mention may be made of the
following. Such roads show extreme durability, permit of
the greatest ease of traction over their surface, are
easily repaired, are economical to maintain, are free
from vibration, facilitate cleaning, create an absence of
dust and mud, are pleasing in appearance, have numerous
sanitary qualities, are poor radiators of heat, are essen-
tially noise deadening, and provide an ideal surface for
motor traffic. Of its disadvantages the principal ones
are the difficulty of horse traction on gradients of more
than 1 in 60 and the greasy surface created in damp
or foggy weather.
For roadmaking the material is used in three different
forms—as the prepared powder for compression in situ, as
the prepared tiles ready for immediate placing in position,
and as the mastic. In all cases, however, it is absolutely
necessary for the well-being of the finished road that an
irreproachable foundation be provided for the rock
asphalt surface. With regard to this, it must be borne
in mind that it is this foundation which supports the
weight of the traffic passing over the road, the rock
asphalt surface merely fulfilling the purpose of forming
an unchangeable elastic protective coating against the
wear of the foundation by such traffic. If the foundations
are not suitably prepared, so that it settles or becomes
distorted under the weight it is called upon to bear, the
asphalt layer, by following its modified profile, soon
becomes full of hollows and ruts even if it does not actually
crack.
The road should be excavated so as to allow of the
CARRYING OUT OF ROCK ASPHALT WORK 171
laying down of a 6-in. layer of concrete and the thickness
of the rock asphalt layer that may be decided upon.
The street itself should be brought to as plane a surface
as possible, all dips and rises being levelled up, as this item
is of great importance to the durability of the rock asphalt
surface. It is recommended, too, that before the asphalt-
ing work is put in hand, the various water and gas mains,
electric conduits, sewer pipes and the like should be tested,
so that there will be little possibility of a need to open the
surface of the road again from such a cause. The subsoil
being thus suitably prepared, the cement concrete founda-
tion is put down, and for this purpose it is found that
concrete made from natural cement is useless, as it does
not possess the requisite firmness and solidity. Only
the best Portland cement should be used, and the best
results are said to be obtained with a 2: 3: 9 mix. This
is laid and given the camber that the finished road is to
show, after which it is left to set for seven to ten days,
according to the weather conditions. Any hollows in
the concrete should be levelled up with a cement mortar
made up of a 1: 1% mix. No concreting should be done
in frosty weather, and it should not be permitted for the
concrete to be retempered or otherwise treated. Ample
time should be given the concrete to mature, as upon this
depends the wearing capacity of the roadway to a large
extent.
It is essential for the compressed powder work that it
is done on a dry foundation, in as dry weather as possible,
whilst the powder itself must be free from moisture. If
this matter is overlooked or scamped, the moisture forms
cavities in the hot powder which, by preventing the
coherence of the bituminous grains, gradually create
holes and cracks in the surface. Before laying the powder,
too, it is necessary to bring it to such a temperature
that all dampness shall be driven out without, however,
evaporating any of the valuable bitumen. This tempera-
ture, which varies between 90°C. and 150°C., is dependent
upon the particular type of rock that is being used.
Thus the Val de Travers rock asphalt powder is heated
to a temperature of from 180° C. to a maximum of 150°C, ;
172 NATURAL ROCK ASPHALTS
the Seyssel material to a temperature of from 110° C. to
120° C., whilst that obtained from the Sicilian mines only
requires to be heated to 90° C. This heat, besides
evaporating the moisture that may be present in the
material, also leaves the powder in a more suitable and
pliant consistency for compression than when cold.
When compressed, the rock asphalt powder is reduced
some 40 per cent. in bulk, so that when marking out on
the kerb the height to which the layer of the hot powder
is to reach this must be remembered. The heating of the
material is done in both fixed and portable boilers accord-
ing to the position of the work, and usually requires some
three or four hours to properly and evenly heat the
powder all through. From this boiler the hot powder
is transferred into wheelbarrows in which it is taken to
the site upon which it is to be spread, its heat being
conserved during transit by a protective covering of
tarpaulins or asbestos cloths. It is now laid across the
road in stretches and then raked out into an even layer
according to the depth to which it is to be laid. Following
this, the material is rammed down with hot rammers,
weighing approximately a stone, until just about level,
when it is smoothed with hot irons to a level surface,
and on this a fine dust can be swept over before the entire
surface is finally well rolled with a 10-ton roller until the
rock asphalt powder thus compressed is cold.
Roads made in this way are very satisfactory where the
traffic is heavy and so helps to consolidate the material,
but for light traffic the rock asphalt mastic has super-
seded it.
It has been stated that the weather resistance of the
rock asphalt surface is increased by mixing in with the
powder litharge and glycerine. The best results are
obtained when to a hundred parts of the powdered rock
asphalt are added fifteen parts of litharge and ten parts
of glycerine. With this addition it is affirmed that the
asphalt powder gives an extraordinarily firm layer,
probably owing to the formation of lead glyceride.
Instead, too, of heating the powdered rock asphalt, in
which case the concrete surface, as mentioned above,
CARRYING OUT OF ROCK ASPHALT WORK 173
must be quite dry, it is stated that the powder can be
spread in a cold condition if it has been previously moist-
ened with a solution of rubber in petroleum spirit.
A type of rock asphalt paving that has not received
in the United Kindgom the attention and adoption that
its possibilities would merit is the compressed rock asphalt
tile. This class of material, as has already been mentioned,
may be divided under two headings, those prepared from
the crushed rock and those prepared from the mastic form
of the rock asphalt. Allusion, too, has already been made
to the superiority of the compressed form of roadway over
that prepared from the rock asphalt mastic, and a like
difference is to be found in the durability of the respective
kinds of tiles.
An inevitable drawback with the use of the compressed
asphalt powder when laid in situ is the large and expensive
plant that is requisite for the proper carrying out of the
work. When the area to be so covered is appreciable,
the overhead charge per yard entailed by the use of this
plant is not very noticeable, but when only small stretches
are to be laid, or if some Small repairs are necessary, or
should the work have to be executed in provincial
districts in which such plant is not permanently situated,
this standing charge greatly increases the price of the
work. It is therefore to eliminate this expense that the
tile prepared from the rock asphalt powder is now used.
The preparation of these tiles closely follows the line
of procedure that is adopted in the laying of a compressed
rock asphalt powder pavement in that the powder is
first raised to a suitable degree of heat and then subjected
to an intense compression. As a result of this it would
appear that the material thus compressed in the factory
is much more sound than when the material is worked
in large quantities in the open, as, whilst the question of
the prevailing atmospheric and climatic conditions is
entirely absent, the Small area that is subjected to com-
pression at a time—25 cms. Square—entirely does away
with the possibility of slack places, such as are found in
compressed roads where for some reason or other the
roller or rammer has not exerted the same pressure as
I74 NATURAL ROCK ASPHALTS
upon the surrounding material (at times the cause of
disintegration in compressed asphalt work), since the
hydraulic press exerts the same pressure upon each of the
tiles, and this pressure, too, is evenly distributed over
their entire surface. Further than this, a pressure much
in excess of that possible in work on roads can be used,
thus materially increasing the already great durability of
the Ordinary compressed asphalt powder by creating a
much denser and therefore a much more coherent
material.
Economy is also effected in the work of laying itself,
for instead of the large squad of men that is demanded
by the process of laying the powder in situ, only the men
actually employed in the setting of the tiles are needed.
Granted, therefore, that a surface equal, if not actually
superior, to that formed by the spreading of the powder,
can be obtained by the use of the compressed asphalt
powder tiles, it follows that their use is extremely advan-
tageous in narrow, yet heavily travelled alleys or narrow
streets where the requisite rolling of the surface is imprac-
ticable, for short stretches of work, or in districts to which
the carriage of plant and the transference of skilled labour
would render the adoption of the compressed asphalt
powder itself prohibitive. On the Continent it is quite
usual for the road contractors to cover work of this
description with a guarantee for ten years, and the writer
has personally come in contact with roadways so formed
which have undergone the traffic of the past twenty
years without becoming appreciably worn or pitted.
It must, however, be understood that the tiles formed
of the compressed asphalt powder are serviceable only in
such places and under such conditions as those in and
under which the asphalt powder compressed in situ would,
under ordinary circumstances, be permissible. That is
to say, they can be used with advantage for roadways
and carriageways where the bulk of the traffic is vehicular,
i.e., compressive, but not where the traffic is mainly
pedestrian, i.e., frictional. The reason for this has
already been discussed, and is based upon the fact that
whilst the vehicular traffic augments the compression so
CARRYING OUT OF ROCK ASPHALT WORK 175
necessary for the homogeneity of the work done with the
compressed rock asphalt powder, foot traffic tends to
loosen the bond between the individual grains which are
then gradually removed either as dust or by adhering
to the cause of their release.
For the actual work of laying down the tiles manu-
factured from the compressed rock asphalt powder it
is, of course, essential, as with all other methods of rock
asphalt roadmaking, that a firm and level concrete
foundation is first provided upon which to set the tiles.
This should be from 3 to 6 ins. thick, according to the
volume and the weight of the traffic that will be passing
over it, and should also be brought to the particular
camber it is desired that the finished road shall possess,
since the tiles, being perfectly flat, cannot of themselves
create any fall or slope for drainage. According to the
exigencies of the traffic, too, the tiles are prepared in
varying thicknesses, being usually between I in. and 2 ins.
thick.
The method of laying the tiles itself is a simple matter
and one that can be easily done by any labourer of
ordinary intelligence. In order to obtain a seal between
the adjacent tiles when laid, and also to prevent any
possibility of dust or wet working their way through the
joints, it is usual to use a flexible bitumen. This material
is heated in a suitable Small cauldron, and, with a small
quantity of this at his side, the layer begins to put down
the tiles immediately upon the concrete foundation with
butt joints. Before placing them in position the edges
of each that will come in contact with the edges of other
tiles already in position on the road are first dipped in
the molten bitumen, somewhat after the manner adopted
in the putting down of wood paving, and this bitumen, by
adhering to the grains of both adjacent tiles, results in
the final work becoming, for practical purposes, one
homogeneous sheet of compressed asphalt powder.
The work is commenced from the kerb on the one side
to that on the other, but where manholes, tramway rails,
sewer grates, or the like may occur in the road surface,
it is usual first of all to lay around them two or three
176 NATURAL ROCK ASPHALTS
courses of wood blocks so that, should they have to be
lifted or renewed at any time, the work can be done
without any interference with the asphalt tile surface.
In the case of tramway rails, the use of a grooved concrete
kerb has been suggested, in which to fix the rails and so
allow the asphalt tiles to be laid flush up to the kerb.
Occasionally the fitting of the asphalt tiles around these
obstructions necessitates the use of a smaller size than
the standard one of 10 ins. (25 cms.), and for this purpose
a special cutting machine has been built with a guillotine
action by means of which a tile can be cut into pieces
without the powder forming the tile being loosened or
otherwise injured at the point of severance. With but
little experience a workman can lay a very large stretch
of road per day in this manner.
In some cases the manufacturers of these tiles have
recommended that, instead of dipping the edges of the
tile in the molten bitumen in order to obtain a bond, the
tiles should be laid in their original condition, and then,
after the work is completed, a thin wash of pure Portland
cement should be brushed over the surface and into the
crevices. This suggestion has also been made by Delano,
but, as Köhler points out, the intrusion of the cement
into the joints between the tiles prevents that adhesion
which is absolutely necessary if a homogeneous sheet of
rock asphalt is to be the result.
Upon occasion the writer has seen instances where,
after the compressed tiles have been laid in the customary
manner, the surface has then been coated with a thin
(say #-in) layer of ungritted rock asphalt mastic to serve
as a wearing coat. Whether any additional advantage is
to be derived by so doing is a very moot point, though
for pavement work there is no doubt that such a method
would do away with the weakness demonstrated by the
compressed asphalt powder of wearing away under foot
traffic.
The initial cost of these tiles has perhaps a great deal
to do with the present paucity of their use in the United
Kingdom, but their ultimate economy, both as regards
cheapness in laying, durability, ease and cheapness of
CARRYING OUT OF ROCK ASPHALT WORK 177
repair—should any be required by the breaking up of
the road surface for any purpose—should be at once
apparent. The rock that is usually employed in their
manufacture is either Limmer or Sicilian, the other types
being either too soft or too rich in bitumen to allow of
satisfactory use for this purpose. They are made 25 cms.
(approximately 10 ins.) Square and in thicknesses varying
from 1 to 2 ins., according to which the prices range
from 8s. 6d. to 6s. per super yard.
The tiles which are manufactured from the rock
asphalt mastic are better known in the United King-
dom than are the compressed asphalt powder type, if
only from the fact that whereas the latter are almost
exclusively imported from the factories abroad, the former
are actually prepared in England by various firms. As
with the compressed asphalt powder tiles, the process
of manufacture closely follows the procedure of asphalt
mastic laying in situ, in that the mastic is fused with
additional bitumen and heavily gritted. In addition to
this, however, they are also subjected to hydraulic pres-
sure, and whilst this without doubt results in the reduction
of the number of voids in the mass, it is a question whether
this extra operation serves any other useful purpose.
With the compressed powder the mass is held together
by the mutual coherence of the particles, for which com-
pression is essential, but in the case of the mastic, the
bond is obtained by the intercalating bitumen, that is
to say, by adhesion and not by cohesion. It is perhaps
this unnecessary pressure upon the asphalt mastic tiles
that causes them to be much more brittle than is a piece
of an asphalt mastic pavement if cut out from work done
in the ordinary way but without any pressure other than
that exerted by the “rubber * during his work.
In any case, there is not the necessity for the mastic tile
that there is for the one prepared from the compressed
powder. In the spreading of asphalt mastic the plant is
easily moveable and the number of men employed in the
work is small. The material being put down and spread
in a molten condition fills up any uneven or irregular
surfaces in the concrete foundation in a way that the solid
N.R.A. N
178 NATURAL ROCK ASPHALTS
tile cannot possibly do. The ordinary rock asphalt
mastic when laid has a certain amount of elasticity,
but the tile, owing to the very fact of it being compressed,
although much harder, has attained its increased hardness
at the expense of becoming non-elastic and therefore more
brittle. Although the writer will not take the extremist
view voiced in a recent article in one of the Continental
rock asphalt trade journals that, “the presses used in the
manufacture of mastic asphalt tiles are mostly regarded
as scrap iron and the tiles themselves as things of the past;
although there are probably a few still to be found in
odd streets, it is, however, time to send the last of them
to the museum,” he must confess that the results obtained
in cases which have been brought to his notice where they
have been used, have not created a very high opinion of
their durability.
It must, however, be acknowledged that they are much
cheaper than any other type of rock asphalt paving,
and where this initial economy is a desideratum, the fact is
of great importance. Their highly gritted condition and
their compression too cause them to be much harder than
the ordinary mastic pavement, with the result that they
are able to withstand the wear and tear of the traffic
passing over their surface much better. Their inherent
weak spot is, however, at the joints, where, unless the
greatest precautions are taken, dust and moisture intrude,
which, with the advent of frost, render the pavement liable
to rupture.
The method of laying them is identical with that
adopted with the tiles prepared from the compressed
asphalt powder, and here, too, the alternative ideas of
bitumen and a liquid Portland cement grout have been
advanced for the filling in of the joints. In the former
case, however, it is doubtful whether the thin coat of
bitumen can obtain a lasting bond with the cold mastic
upon which it is placed, whilst in the second case the
mutual binding power of the cold rock asphalt and
Portland cement is also open to question.
These asphalt mastic tiles are usually made in a rectan-
gular shape measuring 4% by 9 ins. and vary in thickness
CARRYING OUT OF ROCK ASPHALT WORK 179
between 4 in. and 2 ins. Their price ranges from 2s. to
5s. 6d. per super yard, according to their thickness. n
The idea of employing tiles prepared from rock asphalt
for paving purposes is by no means of recent date, as some
may imagine, for as far back as December, 1871, we find
that the pavement in Threadneedle Street was laid with
blocks measuring about 6% by 2% by 13 ins., manufactured
from the impregnated sandstone obtained at Maestu in
Spain. The surface thus formed, however, failed in
places, and after being repaired was finally taken up in
January, 1872, a month and a half after it was laid, and
replaced with compressed rock asphalt powder.
The use of rock asphalt mastic as a paving for either
roadways or footpaths is steadily replacing that of the
compressed rock asphalt powder, and the method of its
employment will be found in the following chapter.
CHAPTER XIII
THE CARRYING OUT OF ROCK ASPHALT MASTIC WORK
OWING to the ease and readiness with which it can be
applied to brick, cement or masonry walls, and to roofs,
whether formed of wood or concrete, rock asphalt mastic
is being recognised more and more as a medium for
dampcoursing, flat roof covering, or lining to tanks and
similar receptacles for liquids.
When it is laid on concrete, care should be taken that
the latter is finished off to a smooth and even surface,
with the necessary falls (for which a slope of 1 ft. in
40 ft. may be taken as a fair average) allowed to the out-
lets or channels. Special attention should be given to
this by the concretor, so that when the asphalter comes
on to the job he can set out his work and ensure that,
after completion, there will be no hollows left where water
can accumulate in wet weather and leave unsightly marks
where it has evaporated in dry weather. The concrete,
to be ready for the covering coat of rock asphalt mastic
should have reached that point (easily recognised by the
experienced asphalter) when the water used in the mixing
of the concrete has so thoroughly bonded the material
that it is taking its final moment of setting into a hard
mass; that is to say, the “initial set ’’ of the concrete,
not the ultimate hardening. If the rock asphalt mastic
is laid on “green * concrete (i.e., not properly set), the
hot material draws the moisture into the asphalt mastic,
causing bubbles which, if pricked, show a clean hole
through the asphalt mastic down to the concrete. On
the other hand, the asphalt mastic does not go down so
well when the concrete has become too dry, as the surface
film of weathered concrete appears to prevent the proper
bond between the two materials.
All channels or gutters should be finished off smoothly
and evenly by the concretor in the same way, the edges
Rock ASPHALT MASTIC work 181
to these, as well as the terminal edges at cornices, etc.,
being finished to a clean, sharp edge or neatly rounded off.
When coke breeze concrete is used, particular care
must be taken that the breeze is clean and properly
burned, as the presence of any small unburned or partially
burnt pieces of coal is deleterious to both concrete and
asphalt work alike, as the tar, pitch or gases from them
will at once blow when the hot asphalt mastic is applied
to the concrete, creating far more blow-holes than are
formed by moisture in ordinary concrete. This entails
considerable extra expense in the making good to these
holes by extra rubbing, etc., not to speak of the
possibility of later trouble by fractures which gradually
develop from this cause and which are almost too small
to locate immediately. This blowing will even occur
under these conditions (as the writer knows from experi-
ence) in the laying of the top coat of the asphalt mastic,
with disastrous results. Free lime also is detrimental to
the longevity of rock asphalt work.
When the asphalt mastic is to be laid upon wooden
roofs, the boarding should not be less than 1 in., closely
cramped together and well nailed to the joists, which
should be well braced so as to make the whole as rigid as
possible, and placed at 12-in. to 15-in. centres, according
to the span of the roof. The necessary fall may be
obtained either by sloping the joists or by nailing taper
pieces upon the latter before the boards are fixed. A
good fall of 1 ft. in 40 ft. should in any case be allowed,
and this fall must be obtained in the timber, not by any
increased thickness of the asphalt layer. Rock asphalt
mastic when laid on boards is successful in most cases,
but it is necessary first to cover the boards with a layer
of clean bituminous felt. Felt which contains tar or
pitch is absolutely detrimental to rock asphalt mastic
and invariably causes trouble later. The risk in laying
the asphalt mastic on boarding is that any shrinkage or
warping of the boards may cause a fracture in the material,
which, being unable to anneal again, may extend into an
open crack, when trouble will arise through leakage.
The weakest part in such work, however, is at the junction
182 NATURAL ROCK ASPHALTS
of the horizontal work with the skirting or vertical work.
Here a movement of the building or the above mentioned
warping of the wood will often drag open the joint in
the asphalt and leave an aperture through which water
readily finds its way, to occasion damage below. Where
the rock asphalt coat finishes into a gutter or over the
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FIG. I.
FIG. 3.
A, Rock Asphalt. B K, Brickwork. LA, Lead Apron.
P, Plaster. L F, Lead Flashing. W J, Wood Joists.
edge of the roof, a lead flashing 4 in. to 6 in. wide should
be used, and the asphalt mastic then worked over it, as
shown in Figs. 1, 2 and 3.
In this case the weak place, either from movement or
from settlement, is at the turn-over, and it is to diminish
the possibility of damage to the rock asphalt coat at this
point that the lead flashing, to which the rock asphalt
adheres quite readily, is used.




ROCK ASPHALT MASTIC WORK 183
The actual laying of the asphalt mastic is an interesting
study from the start, the work being done by skilled work-
men in a gang made up of a layer, a rubber, a potman,
and a labourer, though extra labour is often required
according to the position and the size of the work to be
put in hand. The nature of the rock asphalt mastic as
used for this work has been given in earlier chapters, but
in all cases a proportion of 10 per cent. to 20 per cent. of
clean dry grit is allowed to be added to the asphalt mastic
where the roof about to be covered with it is to be used
later for traffic or promenade purposes, in order to increase
its hardness and its power of resisting friction. This
grit, the type of which varies according to the locality,
between limestone, whinstone, granite, and small pea
gravel, is spread in a thin layer on iron plates and dried
over the asphalt boilers, after which it is added to the hot
material in the pot and well stirred in.
The plant used consists of a two-case, boiler (two or
more of these boilers being used as required, according
to the size of the work to be done) with a pot, usually
having a loose bottom, and a stirrer. Each of these
boilers will contain about 8 to 10 cwt. of the rock asphalt
mastic per operation, and this, when spread, will give
approximately 8 superficial yards of 3-in. work. Besides
the boiler, iron buckets are used for the transference of
the fused material from the cauldron to the spreader,
wooden floats for the spreading and rubbing operations,
gauges, preferably of wood, are required to form the limits
of each bay, the level surface of which is tested from
time to time with a wooden straight-edge. For vertical
work, skirting, channels, etc., certain other minor tools
are also used, but the foregoing are the ones of chief
importance.
The “spreader ’’ is the foreman of the gang, and he is
therefore responsible for the actual putting down of the
work. A skilled man should thoroughly understand the
class of material that he is using, should appreciate any
difficult points which may at times appear to interrupt
the progress of the work and be able to cope with them as
they arise. He should see before he starts operations that
5
184 NATURAL ROCK ASPHALTS
the necessary falls have been allowed for by the principal
contractor (the rock asphalt work should not be put in
hand until such falls are put in to his entire satisfaction),
that the concrete, if he should happen to be laying the
asphalt mastic upon this material, is sufficiently set, that
the work is clean and free from dust and moisture, after
which he then sets out the work so as to be done in a
proper manner. After suitably arranging the gauges so
as to mark the limits of the particular bay that he intends
to put in hand and the thickness of the layer of the
asphalt mastic to be put down, he has the material, after
it has been fused to a suitable consistency in the boiler,
brought to him by the labourer in a special form of iron
bucket out of which it is tipped on to the space before
him, where he then spreads it evenly between the gauges
and brings it to a smooth surface with a wooden float.
The “rubber" follows the layer or “spreader ’’ as the
first man is alternately called, and scatters a fine dust or
sand (which should be of a soft nature, for if it is too
sharp or gritty it scratches the surface of the coat) upon
the hot material. He then rubs the surface until it is
left smooth, taking out at the same time any blow-holes
there may be in it and making them good with fresh
material. The use of the dust in this operation is to
allow the float which is used to rub the asphalt mastic—
hence the name given to the particular workman whose
duty it is to do this—to work freely over it whilst in a
warm state without lifting it in any way, and to leave a
surface over which water will easily run. For this purpose
soft grey sea sand and the dust that is left behind after
the screening of crushed whinstone has been successfully
used by the writer. Much depends, however, on the exact
locality in which the work is being executed and the type
of stone to be found in it, whether a suitable rubbing
dust can be found in the vicinity. The result of this
rubbing of the material is that, owing to the fact that a
certain amount of pressure must necessarily be employed,
any excess of bitumen that may be in the material is
brought to the surface, whilst the body of the rock
asphalt mastic as laid is made more compact. g
ROCK ASPHALT MASTIC WORK 185
The work of the “potman * consists of getting the
material cooked in readiness for the layer, and his duties
are certainly important. Upon his knowledge of the
cooking of the asphalt mastic depends to a very large
extent the ultimate success of the work. He must keep
his pots clean and free from any coating or deposit that
may form on the sides and bottom during the fusing of the
mastic. If this is not done, the lining thus formed in the
pot, acting as it does as a non-conductor of heat, prevents
the proper convection of the heat given out by the fire
below, with the result that the material at the bottom of the
pot is burned and charred before that at the sides is even
melted. Any material thus burnt is worse than useless,
since, if it is laid during the progress of the work, wet easily
percolates through it, owing to the fact that, by being
charred, the bitumen, that is to say, the waterproofing
medium, has become oxidised, leaving a charcoal-like
mass, honeycombed and porous. A clean pot is therefore
most important, and after the day’s work is done, the
pots should be dismantled and the sides chipped with a
cold chisel and hammer, so as to remove all dirt, scale, etc.
Further, the potman must, during the progress of the work,
keep his pots so regulated by constant stirring that the
material comes out of the boilers for use by the layer
uniform in quality, since the bitumen has a tendency to
rise to the surface of the mass and the grit to fall to the
bottom of the pot if the mixture is not carefully watched.
The material, which is imported in blocks weighing
approximately ; cwt. each, is broken up into Small
pieces with a hammer and built up in the pot so that the
heat will circulate through it and cook it evenly and
regularly, and a percentage of bitumen is added. A fire
is then lighted under the boiler, and for this purpose
coke is the best fuel, as it burns when once lighted with a
more even temperature than wood or coal. The time
required to cook the material is from three to four hours,
and the maximum temperature attained should average
between 275° F. and 280° F., as this softens the rock into
a mass of readily worked mastic and allows the natural
moisture in the rock to evaporate without charring it.
186 NATURAL ROCK ASPHALTS
When sufficiently fused, the asphalt mastic will readily
leave the spatula or evaporate spittle. Where the boiler
is set up it is well to place a bunker of sand below the
firebox, so that the heat from the boiler will not cause
any damage below.
The labourer carries the buckets of the molten material
from the boiler, tips them before the spreader as required
by him, and attends upon the other workmen generally.
In order that the mastic shall not stick to the inside of
the bucket, he usually fills into and empties from this
FIG. 4.
A, Rock Asphalt in two layers. B. K, Brickwork. C, Concrete.
C, H, Channel, F, Fillet, D.P.C., Damp Proof Course. S. K, Skirting.
S.P., Stone Parapet. P, Plaster.
article the cinders drawn from the boiler fire before
surrendering it to the potman for re-filling, in order to
coat the interior of the bucket with a deposit of fine ash.
For roofing work the asphalt mastic is laid from # in.
to 1 in. thick in two layers of ; in. Or $ in. respectively.
Wood gauges about 1% ins. wide by $ in. or § in. thick
nominal (the rock asphalt will finish above the thickness
of the gauges, so that these should be a little less than the
required thickness of the layer) are laid to form bays up
to which the work is levelled, these gauges being removed

ROCK ASPHALT MASTIC WORK 187
after the work hardens and relaid as required. When
laying two-coat work great care must be taken to keep -
the under coat thoroughly clean, so that the second or
finishing coat will adhere to it in a proper manner, and
this it will do if the bottom coat is not left exposed too
long before the finishing or top layer is put down. To
ensure that the joints (i.e., the edges of the bays) of the
two coats do not come directly one over the other, the
top bays should be set back some 6 ins. or more from the
outside edge of the bottom layer, thus breaking the joint.
Round the walls a skirting is placed, the usual height of
which is about 6 ins. The material for this work is
applied to the wall with a trowel, and then smoothed up
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A, Rock Asphalt. B.K., Brickwork. C, Concrete.
F, Fillet. P, Plaster.
to an even surface with a tool called a “spatula,” but
before it is put in hand the joint of the brickwork where
the skirting is to terminate should be cut out by the
bricklayer # in. by $ in., in order to allow of the mastic
being tucked into it so as to form a watertight joint with
the brickwork (see Fig. 4).
At the junction of the horizontal work with this skirting
a fillet in asphalt mastic is formed, in order to cement the
vertical and horizontal work together and to strengthen
the joint. Slabs of asphalt mastic of the requisite width
are sometimes made and fixed to the walls with wet
cement, the joints being made good with hot mastic and
then the finishing coat applied, but they are not altogether
satisfactory, and effect no saving in the labour item.





188
NATURAL ROCK ASPHALTS
When the asphalt mastic is to be dressed direct over the
coping, it is usual to finish it in the way shown in Fig. 5.
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If the lights upon the roof are of the sunk “pavement
light ° type, the frame is painted with bitumen and bedded
ROCK ASPHALT MASTIC WORK I89
into the asphalt mastic coat whilst in its soft condition, so
† to * a permanent and waterproof bond (see
ig. 6).
When rock asphalt mastic is to be laid upon a boarded
roof, the boards must first be covered with a suitable felt,
which is nailed into position with butt joints, before the
hot mastic is put down (see Fig. 7). The work is then
carried out in the way just described, but for the skirting,
if this is to be applied to vertical woodwork, such as at
lantern lights, as shown in Fig. 8, it is necessary to use
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EIG. 8. FIG. 9.
A, Rock Asphalt. B.K., Brickwork. F, Fillet. P, Plaster.
S.K, Skirting.
groups of large-headed clout nails, wire netting or
expanded metal of light weight, in order to obtain a
proper key for the asphalt mastic. Wire netting in
particular requires careful fixing, as it is liable to sag.
Where the drainage of rain water is effected by an inside
gutter in conjunction with a Swan neck outlet (Fig. 9), a
lead flange is required to be provided round the outlet
to which the rock asphalt mastic is worked.
For vertical work, where the rock asphalt mastic is to
be used as a lining to a tank, as a vertical dampcourse, or
a similar purpose, the joint of the brickwork should be
cut out as before, every third or fourth course, thus creat-
ing a tie for the asphalt coating. There is a patent brick
upon the market in which a deep groove is cut in the face



I90 NATURAL ROCK ASPHALTS
in such a way that the edges of the recess thus formed
are “herring bone * in character. Designed originally
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to give a bond to plaster work when the latter is placed
directly upon a wall without the intervention of laths,
it is found that they also give a successful bond with rock
asphalt mastic, and so render unnecessary the raggling





















ROCK ASPHALT MASTIC WORK I91
of the brick joints to form a key for vertical work when
they are used.
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Although rock asphalt mastic where used for a lining can
be left without any brick or cement facing (see Fig. 10, a),
when the purpose is merely the storage of water, such as
in the case of a tank or a swimming bath, where it is









192 NATURAL ROCK ASPHALTS
used as a lining for the purpose of checking the entry of
water or dampness, it should be faced up with brick or
concrete, particularly bearing in mind the fact that the
asphalt mastic is a waterproofing material only, and that,
although tough, it will not resist a continuous pressure
unless it is provided with an adequate support or weight.
This matter cannot be too strongly impressed upon the
reader, as the writer has found that there is a tendency
at times on the part of the general contractors to reduce
the thickness of the sustaining walls, from economic
motives, in accordance with the thickness of the coat of
asphalt mastic to be placed upon them, under the mistaken
belief that the added thickness of the latter will com-
pensate for the reduced thickness of the former.
Where necessary, it can also be safely fixed on the out-
side of the walls (the joints being raked in the vertical
work in order to provide the necessary key), across the
top of the footings and then through the floors, any
pressure on the outside of the vertical walls holding it
in its place there. Should any pressure be exerted upon
the layer of rock asphalt mastic from below, such as from
springs or tides, the only remedy is to weight down the
asphalt mastic by covering it with a sufficiently heavy
layer of concrete, the head of water being kept down
during the laying of the asphalt mastic by the sinking of
a sump hole. A concrete inverted floor (Fig. 11), laid
ready to receive the asphalt mastic and then filled to the
required level, considerably strengthens this and is also
more liable to withstand pressure.
For vertical work in extremely wet positions, such as
basements, footings, etc., where it is very difficult to obtain
a proper bond for the asphalt mastic, even by keying at
the brick joints, plates of the asphalt mastic are often
substituted. These are made by first scattering a thin
layer of finely crushed brick upon a suitable flat surface.
Upon this the asphalt mastic is laid in the ordinary way,
but whilst it is hot, the material is cut into pieces of the
desired size for the particular work. After these have
cooled, the crushed-brick-covered back is coated with a
rich Portland cement mix, and the plates applied to the
ROCK ASPHALT MASTIC WORK I93
wet wall, the joints in which have been previously raked
out in the ordinary way to form a key. The cement in
setting bonds to both the wall and the crushed brick,
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binding the two firmly together. When the wall has been
thus covered, the joints between each plate are raked out
and the cavity carefully pointed with the rock asphalt
mastic. |
Rock asphalt mastic can also be used with advantage
N.R.A. O


194 NATURAL ROCK ASPHALTS
by engineers and surveyors as a damp course for brick or
masonry bridges, etc., but where the idea is to form a road-
way, a layer of sand about 2 ins: thick should be spread
over the surface of the rock asphalt mastic, so as to make
sure that no possible damage can be done to it by the
unloading of ballast, etc. (see Fig. 12).
Where rock asphalt mastic is used as a dampcourse for
heavy buildings or structures, although it is a question
whether, should there be any lateral movement, the
following method of laying the dampcourse would prevent
it, yet it would at least prove that the dampcourse
had not, as a result of its smooth surface, helped such a
movement.
Brick Wall
A
Brick Footings
ite Damp Courše
3. "&.
The cost of this method is naturally more than when
fixed in the usual way, i.e., at one level, but the reader
must understand that in putting forward this suggestion,
the point of view of the *:::: only has been con-
sidered. The idea was conceived through such a move-
ment having taken place in a very heavy building, where
the architect suggested as at least a partial cause that
the dampcourse used (in this case a bituminous one) had
helped this movement. Whether laid in this way or at one
level, however, the mastic can be slightly grooved before
it is quite cold sº as to form a key for the mortar.
By reason of its very durable nature when subjected to
foot traffic, its noiselessness and the ease with which it
can be kept clean, rock asphalt mastic is now largely em-






ROCK ASPHALT MASTIC WORK
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I96 NATURAL ROCK ASPHALTs
ployed as a flooring for warehouses, breweries, factories,
stables, byres and numerous other buildings. In these
cases the material is laid in the same manner as for
roofs, but to a total thickness of 1 to 2 ins., according
to the nature of the traffic it will have to sustain. In
order to give it the requisite hardness to enable it to
withstand the continual wear and tear of handcarts,
barrows, etc., to the top coat of such work can be
advantageously added 15 to 20 per cent. of grit in
the same way as already mentioned for roofing work,
which is to be subjected to traffic. When used in horse
stalls or loose boxes, the fairly smooth surface of the
material has no influence and does not in practice create
the theoretical difficulty of not affording a proper foothold
for the horses. It must be remembered that the animals
are invariably bedded in peat moss litter, straw, sawdust
or similar material, and this is spread in a thick layer over
the bottom of the stall, and so gives the necessary grip
for the feet of the horses. At the entrance to the stable,
however, it is desirable to groove the surface of the asphalt
mastic for this purpose.
An extensive use is now made of the mastic type of
rock asphalt for pavements and such roadways as are
not subjected to much heavy traffic. The method of
carrying out this work is similar to that adopted for
floors as mentioned above (see Fig. 14).
Playgrounds and other open spaces are thus coated
with advantage, whilst a result of the roller skating
movement has been the creation of open-air skating rinks,
the surfaces of which have been formed of the gritted rock
asphalt mastic.
When rock asphalt mastic is used on ironwork, bridges,
etc., the steelwork should be properly cleaned with a
wire brush and a coat of a bituminous solution applied,
as in this case it is necessary to seal the mastic coat
securely down in order to avoid fracture by vibration.
When laid on such structures, even if they are to act as
roadways and the covering to receive the weight of the
traffic, formed of tar macadam or some other material, a
dampcourse of rock asphalt mastic, applied as before
*
ROCK ASPHALT MASTIC WORK 197
described, preserves the steelwork from rot and corrosion.
To allow for contraction and expansion, a joint can be left
at intervals, and this should be half filled with sand and
then on this a layer of bitumen run in, or a narrow strip
of bitumen sheeting placed on edge can be substituted.
Where the ironwork finishes against the abutments or
walls, a lead flashing dipped in bitumen can be used and
the coat of rock asphalt run over it.
If it is necessary to carry the waterproofing material
up the sides of the girder plates, the steelwork should
be well cleaned and painted with a coat of bitumen, and
then a layer of clean bituminous felt or canvas (which
should also be carried about 6 ins. under the horizontal
work) can be stuck on to this, thus supplying the requisite
support for the vertical asphalt mastic work. Whilst
describing the methods to be employed for laying asphalt
mastic direct on to steelwork for bridges one fully realises
the difficulties arising around such work. The questions
of recurrent shock, the effect of vibration, the unequal
distribution of loads, etc., all tend to the conclusion that
a bed of bituminous concrete upon which to lay the rock
asphalt mastic would give the best result, at any rate
until a more general record of the results of tests under
these conditions is available. When ordinary cement
concrete is used as a foundation upon these structures,
it powders with the vibration and the shock, resulting in a
destroyed base and a consequent damaged asphalt mastic
surface. ſ'
Rock asphalt mastic cools off readily in two or three
hours after being laid, and can be used immediately after
for traffic. The present day requirements all tend to a
demand for a cheap material for waterproofing and road
work, and this has brought on to the market many
artificial materials designated “asphalts' but which still
have to prove that the wearing and waterproofing qualities
of the natural rock are possessed by them. The manu-
facturer of artificial asphalt has not wrested from nature
her secret method of blending, which leaves the natural
rock asphalt so impervious to water, naturally elastic, and,
sofar, inimitable for certain purposes to which it is now put.
198 NATURAL ROCK ASPHALTs
Natural rock asphalt mastic, when properly laid with
the best material, has a long life, and the necessity of
demanding lengthy guarantees when the workmanship
and the material is of the best class is absent and should
not, therefore, be encouraged. A knowledge of the nature
of the particular material that is being used and the
method of its application will proclaim its longevity to
the expert. A fair maintenance term of two years should
be sufficient, if the work be placed with a reputable firm of
contractors, and the offer of a lengthy guarantee (such as
fifteen of twenty years) should carry but little weight in
the placing of a contract. In certain work which includes
resistance to water the factor which principally determines
the life of the waterproofing medium is not so much the
durability of the latter as the capacity of the weight
placed upon it to hold back the pressure. In such cases
it is customary for the rock asphalt work to be carefully
examined before being covered in, and then, if it is found
to be satisfactory, for the asphalt contractors to be relieved
of any further responsibility.
It has been recognised abroad that the demand for
lengthy guarantees with this work, whilst of little practical
value, demands the reservation by firms who do large
numbers of extensive contracts, of huge sums which,
from the strictly actuarial point of view, must be kept
locked up in order to cover all possible contingencies.
For this reason the tendency, in the United States
especially, is to be satisfied with a guarantee for such a
period (usually twelve months) as will enable the authori-
ties to discover how the work will withstand all extremes
of weather and traffic. By that time, too, any weak-
nesses that may be in either material or workmanship
will have developed and become recognisable to the
engineer.
The following records are included here, as they speak
for themselves as to the natural elasticity of natural rock
asphalt mastic. In One case, the asphalt mastic was
used as a tank lining, and after the floor of the tank had
been partly covered, a big pressure of water was let on.
This got under the coat of asphalt mastic at the open
ROCK ASPHALT MASTIC WORK 199
edge and lifted it up in the form of bubble which at one
part was 10 to 12 ins. high and had an area of about
15 super ft. The asphalt mastic remained in this position
without any sign of fracture for five or six hours, when it
eventually sank into its normal place again. In another
case a footpath had swollen up considerably from the
rain, and the expansion of the wood blocks exerted such
a pressure on the kerbstone as to cause the asphalt mastic
to camber. When, however, the wood blocks dried out
again, and so withdrew the pressure, the layer of rock
asphalt went back into its place again without damage.
A rock asphalt floor recently inspected by the writer
was of more than usual interest, owing to the fact that,
instead of the customary Portland cement concrete, as
a foundation was used what is best described as a “rock
asphalt concrete,” upon which the finer material was laid
to a smooth finished surface in the ordinary way.
Although being at least forty-five to fifty years old, it
was still in fair condition, though in parts the floor had
been worn down to the bottom layer, some of the larger
aggregate of which was exposed and exhibited gravel
graded from 1 in. downwards.
SPECIMIEN SPECIFICATION FOR ROCK ASPHALT
MASTIC WORK.
The asphalt mastic to be prepared from the natural rock by
an approved mining company, brought to the site of the work
in the original blocks, on the face of which shall be clearly
stamped the brand of the mining company by whom it is
prepared, and laid by skilled workmen.
No sand or gravel to be added unless specially mentioned.
The asphalt mastic to be kept well stirred when being cooked.
Care to be taken that no burnt or charred asphalt mastic is
left amongst the material being laid. To prevent this, the
boilers are not to be left burning overnight. Where grit is
used, it must be well dried on a pan over the boiler before
being mixed with the mastic.
All vertical work to be finished to a smooth and even surface,
and the necessary fillets at angles and base, stops, mitres etc.
to be allowed for.
Where the asphalt mastic turns over into eaves, gutters, or
on to slates, a lead flashing to be provided and fixed by the
plumber before the asphalt mastic is laid.
200 NATURAL ROCK ASPHALTs
The concrete or boarded roof, etc., prepared to receive the
asphalt mastic must be truly laid to falls by the concretor or
carpenter, and in the case of the concrete must be finished
with fine screed to a smooth and even surface. All joints
where skirtings or vertical work are against walls, etc., to be
raked out by the bricklayer and pointed after the asphalt
mastic is fixed. When laid on boards, the felt used as an
underlay to be of a clean nature, free from tar, pitch, or any
other injurious compositions.
The general contractor to provide the use of the necessary
scaffolding etc.
The whole of the work to be left by the asphalter in perfect
order to the satisfaction of the architects.
SPECIMEN QUANTITIES FOR ASPHALT ON
CONCRETE, BRICK WALLS, ETC.
... Super yards. # in. natural rock asphalt mastic as speci-
fied, laid in two layers to break joint on concrete,
finished to a smooth and even surface with the
necessary falls to clear the water readily, measured
elsewhere.
... (Or if on boards.) Do. do. do. in two layers to break
joint, including felt underlay, upon boards laid to
falls measured elsewhere.
... (Or if for vertical work.) Do. do. do. but to vertical
walls, at every fourth course the joints to be raked
by bricklayer to form key for asphalt mastic.
...Lineal feet skirting and fillet against walls or under slates,
(joints to be raked by bricklayer and repointed after
asphalt mastic is fixed).
... Lineal feet. Extra labour only nosing to gutter.
... Lineal feet. Extra labour only to channels.
...Lineal feet. Extra labour only working asphaltmastic
round outlets.
PRICING OF ROCK ASPHALT MASTIC WORK.
BY MEASUREMENT.
Horizontal work at per super yard.
Vertical work at per super yard.
Skirtings, 6 ins, and under at per lineal foot, 1d. per in.
being added for work above this height.
Fillets, extra to skirting, at per lineal foot.
Gutters, by girth, at per lineal foot.
Channels, extra labour only, at per lineal foot.
Eaves or nosings, extra labour only, at per lineal foot.
Rock ASPHALT MASTIC work 201
Outlets through walls, at per outlet.
Cesspools, at per cesspool. -
Felt underlay, at per super yard (though usually included
in the price of the asphalt mastic work).
BY DAYWORK.
LABOUR. MATERIALS.
Asphalter at per hour. Asphalt mastic at per ton.
|Bubber 55 Bitumen ,, CWt.
Potman 3 5 Gravel ,, ton.
Labourer 33 Felt, ,, yard.
Railway fares, etc., at Fuel ,, ton.
actual cost. . Use of plant , day.
CHAPTER XIV
MACADAM ROADS
THE work of J. L. Macadam in revolutionising the
methods until then in vogue for the making up of roads
is too well known, and has already been sufficiently
dilated upon to be gone into in detail here. In brief, the
discovery upon which his system is based was that if
angular fragments of hard stone of suitable size were
bound together under pressure into a compact mass, a
surface would be formed which would be impervious to
water and, above all, extremely durable.
Despite these advantages, however, macadam roads, in
common with all others made up with stone and dirt and
waterbound, have the objectionable feature of creating
dust by reason of the disintegrating action of the vehicular
and pedestrian traffic that passes over their surface, the one
being the result of crushing caused by the pressure, and
the other the result of friction. With the dust also comes
its attendant evil in wet or damp weather of mud, so that,
especially of late years, when rapid motor transit has
caused the raising of the dust in dry weather and the
scattering of the mud in wet weather to become pro-
nounced nuisances, efforts have been, and are still being
made, to at least mitigate this evil, even should its entire
abolition prove impossible. -
To arrive at this result different methods have been
adopted, such as the use of an agglutinating agent or the
surfacing of the road with a hygroscopic compound, but
by far the most successful are the ones which embody the
use of a tar or bitumen as a binder of the road material
itself.
The use of these materials, however, whether as a surface
MACADAM ROADS 208
coat or as a binder, has recently caused an outcry from the
more aesthetic people that this treatment of the roads,
whilst more or less successfully retarding the creation of
the dust evil, is destroying the pleasing (?) whiteness of
the country highways, replacing this with a dismal
uninspiring black. This is incorrect. A tar or a bitu-
minous macadam, when once the excess of the binder,
which invariably forms a kind of varnish on the newly
made surface, is worn off, displays a gray colour
which varies in tint according to the particular stone
that has been used for the aggregate, This, it would be
imagined, is far more restful to the eye than the glaring
whiteness of the untreated roads, especially when this
latter is accompanied with a blinding dust in windy
weather.
Where economy is a dominating factor there is no doubt
that of the two binders mentioned, the first named, being
the cheaper, will always have the preference where
initial economy is essential, and within certain limits this
material is of great value. With regard to this though,
it should be pointed out that the ever increasing demand
for tar, occasioned by its use in the preparation of tar
macadam and the tar spraying of roads, as well as
extended requisitions in those trades in which it is already
used as a raw material, such as the manufacture of dyes,
roofing felts, lining papers, disinfectants, paints, varnishes,
cattle washes, building compounds and the like, is causing
a corresponding steady increase in price, until it is
becoming a moot point whether in the process of time
coal tar and its products will not be equally as expensive
as the true bitumens, unless, of course, the price of the
latter goes up in sympathy.
In any case, it must be borne in mind also that the tar
is produced in the largest quantity at that period of the
year when it is not used upon roads, i.e., during the cold
and wet winter months, whilst during those months in
which the work of road-making and surfacing are most
put in hand the output of tar is extremely limited; in
fact, in many of the country towns in which its use for this
purpose would be especially advantageous, the quantity
204 NATURAL ROCK ASPHALTS
made at that season is practically nil. To the writer's
mind a most inexplicable attitude that is taken up by
the gas committees of some of these small country towns
is the false economy of selling the tar which is made at
their works instead of transferring it to their highways
departments. In order that a mere twenty shillings a ton
may be obtained for their tar—for that is all that is
obtained in the majority of the cases that have been
brought to the notice of the writer—the gas committees
prefer to condemn the ratepayers to the dust-creating,
waterbound highways.
The tar is applied to the roads in two ways, either by
mixing it with the broken metal prior to spreading the
latter, and so forming the well-known tar macadam, or
by spraying the surface of the road itself with the tar in
a hot condition, but the durability of the resultant coat
of tar-bound or tar surfaced material is entirely dependent
upon the quality of the tar which is employed in the work.
To fully appreciate this most important point, it must be
clearly understood that coal tar is not a definite chemical
compound. Instead, it is a mixture of a variety of com-
pounds of the hydrocarbons, hence the wide range in
quality of the different coal tars to be obtained. The
component parts of the tars can, however, be grouped
together for the present purpose under the headings of
(a) gas liquor, (b) light oils, (c) medium oils, (d) heavy
oils, and (e) pitch. Of these, the ones requisite for road
work are (e), (d), and a portion of (c).
The gas liquor is useless, in fact, it is worse than use-
less, for its presence in the crude tar, with which a large
portion of the tarred roads have hitherto been treated,
is the principal cause of the present outcry against river
pollution and the resultant fish destruction which has
been occasioned by the surface water draining from
these roads into the adjacent streams. Under this term
is considered the water and ammoniacal compounds that
have been formed during the destructive distillation of
the coal, the greater part of which are trapped in the gas
producing plant, but an appreciable quantity is still
retained by the crude tar. When the latter is used upon a
MACADAM ROADS 205
road the water evaporates out, and the ammoniacal com-
pounds, being either volatile or soluble, also disappear.
The light oils are, as their name implies, that portion
of the tar which is volatile at very low temperatures. In
practice, all those oils which evaporate out of the tar at a
temperature below 105°C., are grouped under this heading,
and it is this ready volatility that renders them unfit for
road work, since their presence thins the tar, with the result
that the latter does not coat the stone so well, and their
disappearance after the road has been treated renders the
surface brittle and liable to early segregation, owing to
the additional quantity of pitch that has to be added to
the tar in order to give it the necessary body.
The pitch gives the body to the medium and heavy oils,
but contains a certain percentage of free carbon, the
presence of which, in more than a certain proportion, is
inimical to the sound road. It is for this reason that
specifications for road-making and tarring specially refer
to this subject and declare the maximum of free carbon
which will be permitted in the tar to be used. In gas-
works tar, much less of this free carbon is to be met with
than in blast-furnace tar, whilst water-gas tar is almost
entirely free from it.
To obtain a suitable tar, therefore, it is best that only
a gas-works tar be considered, and that even this should
be first submitted to a refining process. It is possible,
it is true, to purchase tar which has already been distilled,
but this is expensive, and whilst it has the volatile
elements extracted, there is also the possibility that some
of the other oils may have further been taken out for
business purposes and the tar “cut back ’’ again with
the superfluous oils. This abstraction can be readily
detected by the analyst by a suitable comparison of
the quantity of distillate obtained at certain degrees of
temperature, but as this requires an expert to properly
carry through the test it has not been included in the
chapter on analysis.
The road surveyor and engineer are recommended to
purify their own crude tar when it is possible to obtain it
from gas-works in the vicinity. The principal point
206 NATURAL ROCK ASPHALTs
to keep in mind here is to keep the temperature low,
otherwise valuable oils may be lost and the percentage of
free carbon increased by local overheating. In the
majority of instances a proper distilling plant will be out
of the question, but the process can be equally well
carried out in large cauldrons if care is taken to keep the
fires steady and so that the temperature never exceeds
170° C. The practical cessation of ebullition in the caul-
dron at this temperature will show when all the light oils
and water have been driven off, though if it is desired to
make certain of this, a quantity can be heated in a glass
retort to that temperature, and if no distillate is obtained,
it proves that the operation is complete.
When the tar is obtained from one constant source, it
is usually possible to determine in the above manner
exactly how long the cauldron should be heated, and
then it is only necessary to instruct the workman as to
the length of time to continue the operation without any
further trial, though it is always advisable to make
periodical tests in order to check the figure thus obtained
and adopted.
There are now to be had various road-making com-
pounds which, as their names imply, have been prepared
for coal tar, and which give fairly satisfactory results
when properly used. They are to be had in varying
consistencies, so as to be suitable both for surface spraying
and road binding, but they are naturally much more
expensive than water-freed tar itself. In a communica-
tion issued by one of the firms who manufacture these
specialities it is stated that the material they produce
“is prepared from selected crude tars. The oils removed
in the refining process are removed for the purpose and only
to the extent necessary to leave the main product of the
desired test. The amount of oil removed is seldom over
one-fourth of the raw material, and often less than one-
tenth.” This candid statement of the composition of
a well-known road-making compound should be interest-
ing to those highway engineers at present using tar as a
binder.
For tar spraying, of course, only tar is required, but in
MACADAM ROADS 207
the preparation of tar macadam it is customary to add to
this a proportion of pitch in order to give a certain amount
of body to the binder. This pitch, for the same reason
as for the tar, should be one made from a gas-works tar
in preference to one made from a blast furnace tar, and
if it is of the “medium soft' variety there is less chance
of an excess of free carbon than with the “hard” type—
which has undergone a further distillation than the
former—although slightly more is necessary.
The mineral aggregate used for the tar macadam varies
in different localities according to the stone that can be
most economically obtained, but usually it is limestone,
whinstone or granite chippings, though iron slag has also
been used on a fairly large scale with every success.
The particular class of rock which should be employed
depends to a great extent upon the severity of the traffic
which will be passing over the roadway when the tar
macadam is put down. Where, therefore, the traffic is
light, it is infinitely better to have a softer stone than
granite, but if the traffic is very heavy, limestone has a
great tendency, especially in warm weather, to become
marked with the wheel tracks and to become “billowy.”
Slag, it may be added, holds a larger amount of tar than
does limestone, by reason of its porous condition.
It need hardly be mentioned that the more care that is
taken in the choice of the materials and in the work of
intimately mixing them, the better will be the results
afterwards obtained when the tar macadam has been laid.
One of the most imperative requirements in the mixing
operation is a suitable degree of heat. The stone must
be warm and dry, the mixture of tar and pitch must be
hot and of a readily flowing consistency, and the tools
to be used must be similarly heated. Without this heat,
no real bond can be obtained between the stone and the
tar; if the stone is cold, it chills the tar; if the tar is not
sufficiently heated, it cannot penetrate the pores of the
stone to form an adhesive film round each; and if the tools
are cold, the tar clogs, and by sticking to them makes the
proper working of the mass almost impossible.
Mixing machines are to be found on the market for the
208 NATURAL ROCK ASPHALTs
preparation of tar macadam, and if the expense of pur-
chasing one is considered justified, their use can be
throughly recommended as giving an excellent mixture in
a very short space of time. They are extensively adopted
in the United States for the preparation of the material
used for the bituminous roads in that country, and two or
three of the engineering firms there who manufacture
these articles have also inaugurated branches in the
United Kingdom for their production. The American
types are without doubt the most advantageous, for
with them every part of the operation can be done on the
same machine without any loss of time, whilst no perma-
nent firebox or power drives are needed as with the
British types that have come under the notice of the
writer. These machines can be easily adapted by con-
tractors and others who have much concrete work so as
to mix that material also; in fact, in America, where it
is customary to lay the bituminous macadam or cement
upon a foundation of concrete, it is usual first to employ
the machine to prepare the concrete, and then, the founda-
tion being laid, to make the bituminous surface layer in
the same machine, thus effecting an economy in both plant
and labour.
When their use is not permissible by reason of the
small quantity of macadam required at a time, for their
cost is rather high, the mixing must be carried out by hand,
in which case it must be remembered that the smaller
the bulk mixed at each operation, the less possibility there
will be of an uneven mixture. A satisfactory amount,
and one which is very suitable for arranging the propor-
tions of the mixture is a cubic yard of stone at a time,
to which should be added by degrees sufficient of the
pitch and tar mixture to allow of each fragment of rock
being well and properly coated. These proportions will
vary according to the absorptive capacity of the particu-
lar type of rock used and the size to which it is crushed,
whilst the proportion of pitch to tar will depend upon their
respective qualities, and the time of the year in which
the tar macadam is to be laid. Thus a mixture which
is suitable for summer working would consolidate too
MACADAM ROADS 209
rapidly in winter, whilst on the other hand, a material
that would be satisfactorily worked in winter would prove
too soft for summer handling.
The actual operation of making up the material is
as follows:—
The stone is first screened free from dust and then
separated into suitable sizes. The stone thus gauged is
now placed upon a heated iron plate in a shallow layer
and constantly raked, so as to enable it to be well and
evenly heated. In the meantime the tar, which has
previously been freed from water and the light oils, as
mentioned above, is placed in a tar boiler, heated, and the
proper proportion of pitch added, the mass being con-
stantly stirred during the whole time so that the two
materials intimately mingle together. If the shovels to
be used in the mixing are ranged about the fire of the
boiler or used as stirrers for the tar, they will be heated
in readiness for use. A certain amount of caution must
be used in heating the tar, for the sole reason of such
application of heat, it must be understood, is to bring
the tar to a suitable consistency and not to evaporate
any of the oils, those detrimental to the tar macadam
having been already eliminated. Too high a degree of
heat, therefore, only means an unnecessary loss of
material, an inadvisable alteration in the quality of
that material, whist, contrary to the effect of cold, the
heightened temperature causes the binder to become too
thin and so to run off the stone instead of coating it.
The hot stone is piled up in the form of a cone, and a
hollow formed in the apex in which the hot tar is poured.
The mass is then turned well over with the heated shovels
until no stone is left uncoated. Regarding this coating
operation, despite the assertion of certain firms to the
contrary, the writer has still to find a tar macadam in
which the stone can truthfully be said to be impregnated
with the tar. Even if this were possible, the most
probable aggregate to admit of it would be perhaps the
limestone chippings, but with this material the grain is
too close for the purpose, whilst the pitch mingled with
the tar could not penetrate the pores to any appreciable
N.R.A., P
210 NATURAL ROCK ASPHALTS
extent. Should the naturally impregnated limestone be
advanced as controverting this statement, it must be
remembered that this latter material has been proved to
have been impregnated in nearly every instance, whilst
in a powdered and not fragmentary condition. Further
than this, the tar which first enters the pores of the chip-
pings fills them and so obstructs the passage of any
further quantity.
The tar macadam thus made is at first very soft and
should be stored for some time—certain firms recommend
a period of three months—before use, so as to allow it
to mature and to enable the tar, which at first merely
lies on the surface of the stone, to sink deeper into it.
The work of laying a tar macadam road or pavement
should only be carried out in fine weather. If the opera-
tions are attempted in the wet, the rain or dampness
appears to form a kind of emulsion with the oils that are
contained in the tar with the result that, although the
material becomes very pliant and easily spread and
rolled, it never dries or becomes hard and pressure
resisting, but instead, the emulsion formed, in place of
forming a binder between each piece of stone, acts rather
as a lubricant, and so assists their movement with the
result that the tar macadam is easily displaced by traffic
and quickly forms into ugly ruts and holes.
A solid and well-drained foundation, too, is a necessity.
In many cases the ordinary macadam surface existing
upon the road will prove sufficient, but if this is not
suitable, a proper one of hard ballast well rolled must
be provided. It is preferable that this be formed to the
required gradient of the road, as it is much easier to do
this with the foundation than to attempt to taper the
tar macadam surface, particularly so when this bevelling
means the reducing of the thickness of the tar macadam
coat in the gutter, i.e., that portion of the road which
should be the most waterproof of the whole, for whilst
the main surface is practically a water-shedder merely,
the gutters have to act as carriers of the water to the
gullies.
Upon this foundation is spread the first layer of the tar
MACADAM ROADS 211
macadam. This is usually of 4-in. gauged material laid
and rolled, with the interstices filled in with finer tar
macadam, when the whole is steam rolled. The second
layer should be about #-in. in thickness, made up of
§-in. tar macadam and left unrolled ; on this should then
be applied a layer of 2-in. material and rolled into the
§-in. When this is done, 3-in. tar macadam should be
swept with a brush into every crevice or open joint.
As a final coating, a perfect layer of 1%-in. tar macadam
should be applied, and after being rolled once or twice,
finished with a further quantity of the 3-in. material
being swept over its surface, following which the entire
surface is well rolled.
Another method of laying tar macadam is to put the
material down in two layers only. For the bottom layer,
all the crushed stone which passes through a 2-in. ring but
is retained by a 3-in. sieve is used, and the tar macadam
made from this is so laid that when compressed it is some
3%-ins. thick. The top layer consists of the tar macadam
which has been made from the crushed stone which has
passed through the #-in. sieve after the dust has been
extracted from it, and this is spread so as to finish to a
thickness of #-in. when consolidated.
Passing mention may be made, too, of the Gladwell
system of laying tar macadam, which is carried out by
sandwiching a layer of tar macadar.º. between two other
layers of untreated screenings, the idea being that the
compression exerted by the roller and the later traffic
will extract the excess of tar from the centre layer and
press it into the other layers above and below, thus
bonding the whole together.
After the proper preparation of the material itself,
there is no doubt that the life of the road is dependent
upon the care that is taken in properly rolling each
layer of the road surface in order to consolidate the
macadam and to reduce the number of voids in it as
much as possible. Where the material has been prepared
upon the soft side and so shows an excess of the binder,
there is often a difficulty with the macadam sticking to
the roller when the latter is passing over it. This,
P 2
212 NATURAL ROCK ASPHALTS
however, can be prevented quite simply by keeping the
surface of the roller wet or coated with dust.
That a tar macadam road when properly made can be
extremely durable is seen by a certain highway which was
thus surfaced and received a dressing of tar every second
or third year and a new facing of fine tar macadam every
tenth year. This, although laid over thirty years ago,
has proved to be entirely satisfactory, and when broken
up in order to allow of the putting down of tramway
rails, it was found that the main body of the road was
well preserved and it required a considerable amount of
labour to raise the tar macadam, so dense had it become.
The principal causes of failure with tar macadam road.
may be summarised in the following: the omission to
provide a proper drainage of the subsoil underlying the
tar macadam surface; the use of moist or dirty stone
in the preparation of the material; the choice of unsuit-
able sizes of material ; an insufficient rolling of the
respective layers when placed in position; the use of
too large or too small a quantity of tar as the binder;
the unequal distribution of the binder through the tar
macadam ; the careless overheating of the binder when
being boiled in the cauldron; wet, damp, or frosty weather
during the process of laying and compressing. In each
of these cases the rennedy is apparent.
A suitable prepared tar for use in the preparation of tar
macadam has been thus specified: the specific gravity
at 15:5° C. should be approximately 1220, and when
distilled to a tempºrature of 275°C., it should not give off
more than 10 per cent. of distillate, which percentage
should not exceed 25 per cent. when the temperature is
increased to 350° C. When extracted with carbon
bisulphide, benzol and alcohol, the residue of free carbon
that is left behind should not be more than 15 per cent.
by weight.
The idea of Imaking up a road surface with a macadam
bound with tºr seems to have been first acted upon in
Nottingham about the year 1840, though as far back as
1834 Cassel’s patent pitch macadam was on the market.
As a palliative of dust upon highways where, owing to
MACADAM ROADS 213
financial considerations, the adoption of even tar macadam
is impossible, the practice is greatly extending of spraying
the surface of the road with hot tar. Whilst naturally
temporary in effect, and of not so advantageous a charac-
ter as tar macadam itself, there is no doubt that the tar
spraying of road surfaces, besides alleviating the dust evil
—and so receiving the condemnation of the aesthetic soul
who mourns for the lost beauty of the white country road,
the “crime ’’ being equally placed by that person on tar
macadam as well—has a very beneficial effect in pre-
serving the material constituting the macadam road and
so prolonging its life. Although it is still possible to see
the work carried out by manual labour, that is to say,
with one man boiling the tar, a second carrying the hot tarº
from the cauldron in a bucket and emptying it over the
road, where a third brushes it over the surface, the cus-
tomary method now is to use a spraying apparatus, con-
sisting of a reservoir, in which the tar is heated, which
is connected to a spraying pipe at the rear. In order, too,
that the tar, by forcibly impinging upon the surface of the
road, shall penetrate it to a certain extent, certain types
of sprayers have an air compressor attachment, by means
of which the hot tar can be ejected at the desired pressure.
For this work, however, two things are absolutely
essential for. Success, the one being fine, dry and warm
weather, and the other a bone-dry, dust-free road. Dry-
ness is imperative, as otherwise the tar is unable to obtain
a bond with the stone, and dust also forms a very effectual
barrier against proper penetration. The necessity for a
period of fine weather is seen when it is pointed out that
instances have occurred where a road, after being tar
sprayed in the orthodox manner, has been practically
stripped of its newly-formed surface by a heavy rainfall
which has occurred shortly after the completion of the
work. The road is usually cleaned from dust as much as
possible by suitably brushing it, though at least one writer
on this subject has suggested the adoption of a modifica-
tion of the household “vacuum cleaner '' for the work.
A gallon of tar is usually sufficient for 5 to 9 super yards
of roadway, but in order to keep the road in a good con-
214 NATURAL ROCK ASPHALTS
dition it is necessary to renew this tar surface periodically,
so that, although initially low in cost, the continuous
renewal of the work causes the price to augment con-
siderably, approaching, if not actually passing, that of a
properly prepared bituminous roadway.
The permanent utility of tar as a binder for road-making
and, to a minor degree, as a dust preventative is a very
questionable point, whether it is used as the tar macadam
or merely in tar surfacing. A more suitable material
has, therefore, been sought for, and this apparently has
been found in the natural bitumens, the use of which will,
in time, there is little reason to doubt, entirely replace
that of tar except in such instances where initial cost
still dominates.
The various types of bitumen from liquid to solid have
been pressed into service for this purpose, the first for
spraying and surfacing, and the latter as road binders.
For this purpose the main characteristics demanded of
the material besides durability are adhesiveness and
elasticity. The bitumens of paraffin origin show a
great lack of the necessary adhesiveness, and this to
such an extent as to render its main virtue, i.e. that of
bonding the mineral aggregate of the road, almost nil.
Owing to their non-cohesive character when they are
used for road-spraying or surfacing, they usually render
the surface of the road Smeary and greasy, whilst, when
the oils disappear after the inevitable evaporation,
instead of leaving behind them the more solid bitumen,
they disintegrate entirely, and the dust formed on the
roads so treated is accompanied with greasy particles
which occasion even more annoyance than the dust itself.
It is often found that the instances where the spraying
of roads with a liquid bitumen has been brought into
discredit, have arisen simply from the use of an unsuitable
material of this character.
With a true liquid bitumen, on the other hand, its
intense affinity for finely divided mineral matter, which has
been remarked upon in earlier chapters, causes it to be
quickly absorbed by loose macadam or screenings, and
these will not release it later on. Unless, therefore, the
MACADAM ROADS 215
liquid bitumen is sprayed in excess, there will be no
“ bleeding ” of the road so treated, but as the more
volatile elements evaporate out, the more solid bitumen
left behind, being already closely combined with the
mineral, still holds it firmly together to form a coherent
dustless surface. If a road is consistently treated in this
manner, it results in the gradual formation of a bituminous
macadam surface of an excellent character. Care, how-
ever, must be taken in the operation of spraying that
the liquid is spread evenly over the surface, for its peculiar
characteristic is that it will not spread over the road but
lie where it is applied. Again, the road must be carefully
freed from dust, with which the material will incorporate
to form lumps, whilst if the bitumen is spread in excess,
it will result in the formation of soft spots in the road
surface. It is therefore suggested that the liquid bitumen
be spread over a good foundation consisting of a thin, loose,
but even layer of crushed stone passing through a 1-inch
ring, and after this a top course of similar screenings
should be rolled in which, by binding with the bitumen
thus spread, will result in a surface very similar to the
usual bituminous macadam. -
Even for road surfaces made of concrete this idea can
be adopted with advantage, as by this means the concrete
foundation is rendered good for all time, whilst the wearing
course serves the purpose of carrying all classes of traffic
without rubbing, ravelling or creating a dust. It must
be understood, however, that to obtain a satisfactory
result, the liquid bitumen must not be sealed up in the
body of the road, as in this case it would merely lie dormant,
developing no strength, but acting more as a lubricant
to the road metal than as a binder. It must be so used
that its strength can develop by the evaporating out of it
of the lighter oils.
In new roads, however, the principal method of employ-
ing bitumen is in the form of a bituminous macadam.
This material is formed in much the same way as the tar
macadam type, in batch-mixing machines, with the sole
difference that a suitable bitumen is substituted for the
tar. It is difficult to define the most suitable proportions
216 NATURAL ROCK ASPHALTS
of bitumen and aggregate, for this material, as so much
depends upon the type of the stone that is used and the
widely varying qualities of bitumen that are employed.
The best results, however, will be obtained by combining
such proportions that the entire aggregate will be coated
with bitumen in an amount which is equal to that which
the material would hold after compaction, without any
excess being forced to the surface. Whilst the proportions
may be adjusted either by volume or by weight, it is perhaps
advisable if only the former were used. To see the reason
of this, it is only necessary to call to mind the variations in
the specific gravities of both mineral aggregate and
bitumen. Thus the maximum variation in road-making
rocks is from 2:00 to 3-65, so that if rocks of extreme
character were crushed to the same size and mixed with,
say, 6 per cent. by weight of a given bitumen, a varia-
tion would be obtained in the number of gallons of the
latter of 45 to 81 per cent. per cubic yard of rock. If
the variation in the bitumens is still further taken into
consideration, the proportioning by weight would show
even greater differences in the volume proportions.
(From a paper by Prevost Hubbard on the bituminous
content of bituminous aggregates).
Before laying the bituminous macadam, the surface
of the existing road is scarified and upon it is placed a
bottom course 4 ins, deep of crushed stone graded between
1} to 2% ins. This is rolled to the standard depth and
upon it is then laid the bituminous macadam consisting
of crushed stone graded from 14 in. to 4 in., mixed with
a suitable bitumen in a hot condition. When this has
sufficiently cooled, so that the weight of the roller will not
push the material out of its place, it is rolled to a firm
surface, free from any irregularities. On this is applied
a seal coat of bitumen, which, as soon as spread, is covered
with grit of pea size. The whole is now well rolled with
the heavy roller until the grit is firmly bonded into the
bitumen forming the seal coat.
As an alternative to the mixing method of preparing a
bituminous macadam, the material is sometimes made up
in what is known as the “penetration * method, though
MACADAM ROADS 217
it must be confessed that this latter does not appear to
give anything like the satisfactory results obtained with
the former. In this case, too, the sub-grade is first scarified
and a 2-in. layer of coarse stone applied, rolled and shaped
to the camber of the finished road. A further layer of
the same stone is now put down 3 ins, thick, into which
after being rolled, is sprayed a hot bitumen by means of
a pressure sprayer, about 1% gallons being used per Super
yard. Immediately after this application, a coating of
pea stone is spread upon the hot bitumen and the whole
rolled. A second spraying of about ; gallon per square
yard is now applied, following which a sufficient amount
of pea stone is put down to form a good wearing surface.
The adoption of this class of work in the United
Kingdom is still in its infancy, so that as yet it is impossible
to give any definite figures or results of its use. In the
United States highways and roads thus formed are giving
gratifying results, but as Dr. Sommer, of the Barber
organisation, remarked to the writer during a conversation
this summer, both weather conditions and subsoil are
entirely different here and will necessitate a great
modification in the type of bitumen used, in order to
successfully combat them. -
CHAPTER XV
OTHER USES OF BITUMEN
ONE of the most important uses of bitumen after the
paving industry is that for the impregnation of felts for
roofing, waterproofing, insulating and similar purposes.
This is in reality the outcome of the gradual perfecting
of the older tar impregnated felts, so that a short resumé
of the entire history of this industry may not be out of
place here.
Scandinavia is the birthplace of this material, and it
was invented there in the eighteenth century by the
Swedish naval adviser, Dr. Faxe. His methods, although
brought up to date, as may be expected, are still in use
at the present time there.
Naturally the first roofs covered by him with this
material proved to be very defective, for the idea of
impregnating the felt with a waterproofing compound
had not then been thought of. Instead, the method
adopted was to lay the unimpregnated felt upon the
sarking boards, to which it was fixed with short-headed
nails, in shingle fashion, the felt being made at this time
in flat sheets some 30 to 40 ins. wide and of varying
lengths, not in the long rolls as we have it now. When
the roof was completely covered in this way, the felt was
then painted with hot wood tar in order to make it
watertight. A natural consequence of this was that the
tar only partially penetrated the fibres of the felt, and
the thin coat of tar thus formed was soon destroyed by
the action of the weather. Following this, the felt itself
became swollen up with the absorption of rain and was
the victim of the first strong gale that came along. For
OTHER USES OF BITUMEN 219
this reason the crude idea found but very little use at
that time.
In Germany Dr. Gilly, of the Office of Works, appre-
ciated the value of the method and so he interested himself
in its perfection. In his book “The Art of Public
Buildings ’’ he strongly recommended its use to the
German public, particularly for agricultural buildings.
His efforts were frustrated, however, by the intervention
of the Napoleonic wars at the commencement of the
nineteenth century, as the result of which all trace of
roofs covered in this way in Germany seem to have been
lost, and it was not until the early forties that we again
find any interest taken in them there. About the year
1842, Herr Büsscher, the founder of the firm of Büsscher
and Hoffmann, in Eberswalde, came from Sweden, and
having asked for and obtained from the Swedish govern-
ment the necessary instructions for the preparation and
laying of roofing felt as carried on in that country, he
covered his premises in Eberswalde with this material.
He only appears to have made sufficient felt for his
personal requirements, for we find that it was only after
another firm in the same town, Messrs. Ebert Bros.,
had prepared it in bulk for sale that their example was
followed by Büsscher. It was now that the first improve-
ment in the manufacture of the roofing felt was made, for
whereas the Swedish method had been to paint the unim-
pregnated roofing felt after it had been fixed in position
on the roof, the idea suggested itself to the German
manufacturers of impregnating the sheet, a process which
was at first carried out immediately before the sheets were
placed in position on the roof, and then later in the factory
itself before the sheets were sent out. With the increas-
ing use and competition between manufacturers came
improvements both in the material and in the methods
of manufacture, so that, with more and more satisfactory
results to offer, this method of roof covering came to be
better appreciated by the general public, and so came more
and more into vogue.
Instead of the expensive wood tar which was at first
used as the impregnating compound, a substitute was
220 NATURAL ROCK ASPHALTs
found at this juncture in the coal tar which was formed
as a by-product in the gas-works. As here this material
was looked upon as an extremely troublesome, undesirable
and worthless article it was readily and freely sold to the
roofing felt manufacturers at nominal prices. As yet,
however, the method of manufacture was merely to steep
the square of unimpregnated felt into a cauldron of hot
tar until it was thoroughly soaked. When this was done,
the sheet was taken out of the tank, the Superfluous
surface tar drained off and the felt allowed to dry in the
open air. The idea of extracting this excess of tar by
means of press rollers was only thought of at a later date,
when it was begun to manufacture the felt in rolls instead
of sheets.
No article has been more misconceived, perhaps, than
the raw felt, i.e., the unimpregnated article, that is used
in the manufacture of roofing felt. By many, even
amongst those who should know better, it is spoken of
in a disparaging manner as “paper,” and its possibilities
discounted accordingly. The true raw felt as used by the
reputable firms of roofing felt manufacturers is, however,
a loosely woven felt prepared from woollen fibres, and
though the process through which it goes may in some
respects be comparable to that seen in the ordinary paper
mill, the resultant material is quite distinct. Like paper,
though, it lends itself to an easy adulteration, but the
true type is prepared from woollen fibre only. This
adulteration is done in two ways: either the quality of
the fibre is reduced by intermixing with it a quantity of
vegetable fibres, or else, since this material is always sold
by weight by the manufacturers to the makers of roofing
felts, by the addition of “ loadings ’’ of mineral matter
such as chalk, gypsum, whiting, alumina, etc. All these
methods of cheapening are to the detriment of the finished
roofing felt, and as showing how completely in the hands
of the makers of this material the manufacturers of
roofing felts are, it may be stated that there is only one
firm of roofing felt producers in the United Kingdom who
prepare their own raw felt.
In order to show how completely dependent upon the
OTHER USES OF BITUMEN 221
quality of the raw felt the prepared product is, it should
be remembered that vegetable fibres rapidly decay with
constant exposure to all weathers, whilst of the “loadings”
chalk in particular forms an additive compound with tar,
which, being soluble in water, is dissolved out with heavy
rains and leaves behind it open pores in the roofing felt
through which damp and rain readily penetrate.
These adulterants are all readily recognisable by
certain chemical tests, but as this is too wide a subject
to admit of adequate treatment here, the reader who is
desirous of going more fully into the matter is referred
to a work on “Roofing and Waterproofing Felts,” which
the writer hopes to produce shortly, and in which the
manufacture and use of these articles will be thoroughly
dealt with.
In brief, upon the quality of the raw felt is essentially
dependent the life of the finished roofing felt, and this
quality is itself dependent upon the quantity of vegetable
fibre and “ loadings ’’ that is used in the process of
manufacture.
The different thicknesses of the raw felt are known to
the trade under particular numbers, and these numbers
relate to the area of the material in a certain fixed weight.
The usual varieties range upwards as follows, though
any special one can be prepared by the manufacturers
if it is specially ordered :—

Number. Thickness. Area in 50 kilogrammes.
00 or 50 2°00 m ms. 50 square metres.
0 or 60 1°75 ,, 60 , , ,,
I or 75 1°66 , , 75 ,, 92
II or 90 l‘40 , 90 ,, 33
III or 120 1:00 ,, 120 ,, 35
IV Or, 150 under 100 mms. 150 ,, 95
and so on. These thicknesses and areas are, of course,
only approximate, and depend to a very great extent
upon the material from which the raw felt is made and
the amount of moisture and loadings that it contains.
222 NATURAL ROCK ASPHALTS
A first-class raw felt should show an approximate
composition somewhat as follows:—
Moisture .. tº º tº tº . . . . . 5 to 10 °lo
sh .. tº e ge e tº § tº tº ... 0-5 °lo
Wool fibre . . tº tº tº º tº gº ... 89.5 to 94.5 °lo
The amount of this last can be ascertained by treating
a dried sample with caustic potash in a solution of which
the wool fibre dissolves out.
In the early stages of the manufacture of roofing felt,
this raw felt, or “fibre ‘’as it is now usually termed by its
users, in order to prevent any confusion with the finished
impregnated felt, was made in sheets. These were
immersed in heated tar, drained and air-dried. The
operation was done by filling a suitable tank about three
parts full of tar and then heating this to the requisite
temperature by means of a fire-box below the tank. Into
this hot tar were then laid singly, one on the top of the
other, as many sheets of “fibre ‘’ as the tank would hold.
The tar was kept heated and the sheets were left in it
until they were all thoroughly impregnated, a process
which usually occupied several hours, during which time
care had to be taken that the topmost sheet was always
kept covered with the liquid. The sheets were then lifted
out by means of iron tweezers and placed upon a draining
table preparatory to being hung up to dry, and their place
in the tank filled with a further number of unimpregnated
sheets after the volume of the tar in the tank had been
replenished. After the impregnated felt had been drained
of all its superfluous tar it was then hung up to dry, or in
fine weather laid out in the open, first one and then the
other side being exposed until the whole was thoroughly
dry. Following this, the sheets would be made up into
piles in the store in readiness for use or for despatch in that
form. It was then made only in one thickness, and of this
a hundred sheets of about 0.7 metres square weighed
50 kgs. and cost in the early fifties about 16s.
As time went on the manufacture of the fibre became
more perfected, with the result that instead of the material
being made up in sheets, it was manufactured in long rolls.
OTHER USES OF BITUMEN 228
From this the natural consequence was the alteration of
the method of impregnation so as to fit in with this modifi-
cation. Various means were tried from time to time to
bring about a satisfactory result, but all of them with but
Varying degrees of success. The first difficulty was that
the full length of the roll could not be laid out flat in the
tank, as this would necessitate the requisition of too large
a tank. Then it was also found that as long as the fibre
remained in the tar the saturation by the liquid loosened
the texture of the material, so that it was very easily torn,
and therefore demanded a very careful and skilful hand-
ling. Again, it was further discovered that when the
raw felt was placed in the tank in its rolled up state as
received from the manufacturers, it was not properly
impregnated by the tar, which merely soaked through the
Outer piles and left the inner ones untouched.
At first the rolls of the fibre were cut into shorter
lengths of 10 to 15 metres, and these again rolled up loosely,
so that a definite air space was left between each ply. As
the weight of the roll would cause each ply, even although
thus loosely rolled up, to press upon each other, and so
prevent a regular impregnation, they were immersed in
the tank in an upright position by being first stood upon
a perforated board in the centre of which was fixed an
upright rod which, by being passed through the centre of
the roll of fibre, held the latter in position and at the same
time acted as a kind of handle, since by means of it the
roll could be raised and lowered into the tank as required.
After the fibre had been completely saturated the roll
was taken out of the tank and placed upon the draining
table, from which the excess of tar ran back again into
the tank. Following this the roll was opened out either
in the open air or, when the condition of the weather
precluded this, in a drying room, and after being
thoroughly air-dried, it was finally rolled up again
and stood upon its end in the stock room ready for
despatch.
The next advance in the manufacture of the tarred felt
was to do away with the troublesome and lengthy work
entailed with the air-drying of the finished material, and
224 NATURAL ROCK ASPHALTS
to avoid this, and also to prevent the felt from sticking
together when it was finally rolled up, the makers began
to scatter sand over its surface. By doing this, it was
discovered that further advantages had been unconsciously
obtained for the felt, for the weight became appreciably
increased, the material became apparently thicker, and
hence, to the popular mind, stronger—a fallacy that still
holds at the present time among many buyers—whilst
the surface offered a much more pleasing aspect when
the felt was laid upon a roof than the hitherto monotonous
black colour of the older type.
Nor did the progress of the manufacturing methods stop
here. The time required for the final operation having
been so appreciably reduced in this way, it was then
desired to cut down the period taken up by the draining
of the felt after impregnation. For this, however, two
successive steps are traceable. The first idea was to
scrape the felt as it was being extracted from the tank.
By this time the method of upright immersion had been
replaced by that of rolling the length of fibre around a reel
which was then lowered horizontally into the boiling tar.
In this case the difficulty of merely impregnating the
surface of the roll, as the result of the adjacent plies pressing
upon each other, was again met with and obviated in
this instance by the use of a pair of waxed cords which
were rolled on the reel together with the fibre in such a
way as to separate each ply. In order to form a still
greater space between the latter, the cords were knotted
at regular intervals of about 3 ins, and a free access to
the entire surface of the fibre on both sides was thus secured
for the tar.
The scraping operation was effected by fixing two iron
rods across the tank, so that an aperture was left between
them, and after the fibre had been suitably saturated,
the free end of the roll was passed through this slit. As
the impregnated fibre was drawn from the tank, each
side was thus scraped by these rods and the superfluous
tar immediately flowed back again into the tank. By
this means, not only was the excess of tar scraped off,
but the certain amount of pressure that was necessarily
* OTHER USES OF BITUMEN 225
exerted by the rods upon the surface of the felt resulted
in the material becoming closer in texture, since the fibres
which had been loosened by the liquid were thus firmly
compressed together, and the resultant impregnated felt,
therefore, became tougher.
At this stage the felt was withdrawn from the tank
by hand, and the next idea was to effect such extraction
mechanically by means of rollers. Immediately this was
done, it was observed that these rollers must also exert
pressure upon the felt in order to obtain the requisite
grip upon it, and it therefore naturally followed that in
place of the scraping rods, the rollers were brought forward
immediately above the tank and made to act in the
double capacity of drainers and extractors. This method
is the one which is still adopted in the different types
of impregnating machines used in the modern processes.
Attention was now turned to the impregnating operation
itself. The first alteration to be put in hand here was that
instead of reeling the fibre before immersion, one end only
of the fibre was fixed to the reel, which was then lowered
into the hot tar, and only after this had been done was the
remainder of the roll of fibre reeled upon it. By this
means, of course, the fibre came in contact with the
impregnating fluid before being rolled up, and the Satur-
ating thus commenced continued during the length of time
that the roll was permitted to remain in the tank.
Of late years though, efforts have been made with the
greatest success both in Germany and the United States—
the process being installed in certain English factories,
after the experience of the first two mentioned countries
had proved its value—whereby the entire operation of
impregnating, draining, Sanding, and rolling up can be
carried out without a stop. Mechanical power has been
most effectively employed to replace the older hand labour,
so that in the modern machine capable of turning out as
many as 500 to 1,000 rolls of the finished felt, each
15 yds. long by 1 yd. wide, only five workmen are really
needed. Two of these attend the beginning of the machine,
where a huge reel of the fibre is mounted and runs con-
stantly at a steady rate into the impregnating tank.
N.R.As Q
226 NATURAL ROCK ASPHALTS
When one reel is finished, its end is “stitched ” to the
beginning of a second reel with metal slips so that no
stoppage of the machine is necessary. By suitably
placing in the tank a set of immersing rollers, which
having a rotary motion of their own exert no tension
on the fibre as it passes over them in the impregnating
fluid, the material is passed backwards and forwards
through the liquid until it has been immersed for such a
length of time that previous tests have shown to be
requisite for the proper impregnation of the fibre. As,
for instance, a heavy fibre will need a much longer time
for the impregnating fluid to properly penetrate it than
would a lighter one, the speed at which these immersing
rollers rotate can be reduced according to the particular
class of felt that may be in the process of preparation
at the time being.
From this tank the wet fabric automatically passes on
to a set of press rollers which, after extracting the excess
of the impregnating fluid and suitably compressing the
fibre, conveys it, in the case of the more modern types
of machines, into a small coating tank in which the
impregnated felt, whilst passing through a less fluid mass
than is to be found in the impregnating tank, receives a
surface coat of a much tougher material which, being
deposited in a hot condition at a time when the impreg-
nating compound is also warm, obtains the requisite bond
with it, and so prevents the possibility of it peeling off
when exposed. From this coating tank the felt proceeds
through a further set of press rollers, after which it is
drawn below sand “hoppers ” in such a way that each
side is alternately sanded. Journeying on, the felt thus
sanded is passed through a cooling chamber, and from
thence it goes through a guillotine arrangement, the
cutting edge of which drops mechanically every 12 or
15 yds. as the case may be. Automatic rolling-up
arrangements terminate the machine, from which the rolls
of impregnated felt pass down an incline which transfers
them into the store quite ready for immediate despatch,
though it is to the advantage of the felt if it is allowed
to mature for not less than a fortnight before being used.
OTHER USES OF BITUMEN 227.
Of the squad of workmen mentioned above, the
remaining three are employed, one to watch the progress
of the felt through the machine and to regulate the fall
of sand from the hoppers—the sand being filled auto-
matically into the hoppers from the sand drier and screen
by means of a suitable elevator and conveyor— and the
other two to attend the rolling up of the prepared and
finished material, to place upon it the different coloured
paper bands which denote the particular quality of the
felt then being prepared, and to transfer it to the store.
But the mechanical arrangement is not the only portion
of the work that can show such a remarkable progress.
The impregnating material itself has been greatly modified.
At first, as we have already seen, crude tar was the liquid
used, but it was found by experience that the felt prepared
from this had the very unsatisfactory attribute of
becoming brittle with any length of exposure and, there-
fore, cracked with the warping of the Sarking boards
upon which it was laid. Inquiry into the cause of this
resulted in the discovery that the exposure of the felt
to atmospheric conditions caused the volatile light oils
of the tar to evaporate out of it, leaving the material
both brittle and porous. As a temporary expedient it
was then the custom to periodically paint the felt with
a fresh supply of tar so as to renew the flexibility of the
material, but even this merely masked and did not really
correct the weakness. To obviate this, therefore, the
crude tar was replaced with distilled tar in which all the
light oils had been previously extracted, or with prepared
tar in which the light, medium, and some of the heavy
oils were first extracted, and then the pitch thus obtained
“cut back ’’ or remixed with the medium oils. The
reason of this was to obtain the heavy (anthracene) oils
which had an extensive employment in other trades,
particularly in the manufacture of artificial indigo, and
then, by regulating the amount of the oils used in the
“cutting back ’’ operation, to obtain an impregnating
compound which would have a suitable body for this par-
ticular impregnating work. When distilled tar only is
used, it is usual to obtain the necessary body, especially
Q 2
228 NATURAL ROCK ASPHALTS
for the coating operation, by mixing in with it a sufficient
quantity of pitch.
The so-called “sheet asphalts,” now so extensively
used for both roofing and dampcoursing, are in reality
this class of felt in which the impregnating compound is
the distilled or the prepared tar.
No matter with what type of impregnating material,
however, the tarred felts always have the inherent weak-
ness of gradually losing their flexibility, and so of becoming
liable to crack, hence the necessity of periodically tarring
or “varnishing ” all roofs covered with this material in
order to replace the volatile elements which have been
lost, and also to fill up the pores in the felt that have been
formed by the evaporating out of these oils. The next
progressive step, therefore, was to find some alternative
impregnating compound which would not develop this
weakness upon exposure, and for this purpose are now
largely used such materials as stearin pitch, petroleum
pitch, cotton seed oil, etc., but by far the best results
have been secured by the adoption of bitumen, with the
use of which was created that type of roofing felts now
so widely known as “ready roofings.” Of these, however,
only three of the many brands to be found in the United
Kingdom are actually manufactured in Great Britain,
the remainder, although marketed through English firms,
being imported principally from the United States.
The felts prepared from materials other than coal tar
and pitch are naturally much more expensive, but this
initial expense is more than outbalanced by their
durability and the entire absence of any maintaining cost,
for with even the “ asphalt ’’ roofing felts it is absolutely
essential for the well being of the covering to coat it with
tar varnish when laid and to renew this protective coat
periodically. With the advent of the bituminous felts,
the necessity for the coat of sand, too, is done away with,
its place being usually taken by powdered French chalk,
mica, or even asbestos, so that the same thickness of fibre
shows a much thicker roofing felt when made into the
sanded material than when used for the “ready roofings.”
The writer mentions this, as he has found that too much
OTHER USES OF BITUMEN 229
stress is laid upon the gross thickness of the sanded felt
and not sufficient upon the net thickness of the impreg-
nated fibre only, which, after all, is the essential part of
the roofing. In a like way, too much attention is paid to
the keeping up of the weight of the felt, a matter which
is easily adjusted by the use of an additional quantity
of sand on the surface, and at times it is almost impossible
to get the consumer to grasp the fact that the durability
and the water tightness of the felt cannot be gauged by
weight, unless the weight which is taken into consideration
is that of the felt without the sand. -
The “ready roofings ’’ are made in two operations, the
first the impregnation of the felt, and the second, the
coating of the felt thus formed. A similar type of machine
to that used for the continuous manufacture of the tarred
felts is employed in this case too, so that the entire pro-
cess of rolling the fibre into the thin impregnating bitumen,
saturating the fibre, extracting and compressing the
impregnated felt, passing this into the coating tank,
extracting and surfacing this with mineral, rolling up, etc.
is done on the one machine consecutively. For the
impregnating material, a thin flowing consistency is
given by means of heat to the fluxed bitumen in order that
the fibre shall be thoroughly saturated with it. The
coating compound is a much thicker type, for its duty is
not to impregnate, but to lay thickly upon the surface
of the saturated felt, obtaining the bond requisite to
prevent it from peeling off, by adhering to the bitumen
saturating the pores. Its purpose is to hermetically seal
the fluxed bitumen in the fibre, and by thus preventing
any possibility of the latter drying out, it results in the
felt permanently retaining its flexibility. As, of course,
this coating of bitumen must also possess a certain amount
of elasticity, it is customary to use the so-called “rubber *
bitumens, usually “cut back ’’ gilsonites, for this purpose,
although, for the sake of cheapness blown petroleum
residues are often used in the lower grade classes.
The fibres usually employed for these roofings are
numbers 100 for the one-ply, 90 for the two-ply, and
60 for the three-ply roofings. The term “plies' as used
230 NATURAL ROCK ASPHALTS
in this manner is not very happy, since it would imply
that the thicker varieties are composed of two or more
layers of the thinner one combined together, which,
however, is not the case. Immediately the felt has been
coated, it is then dusted with either French chalk, mica
or asbestos, in order to absorb any small quantities of
the fluxing oils that may show upon the surface, and also
to prevent the felt from sticking when rolled up. The
mica gives a white glistening appearance to the surface,
whilst the French chalk leaves a quiet neutral grey finish.
The use of the asbestos is to exhibit an absolutely fire-
proof surface when laid, though its value is more apparent
than real. The British made felt is put up in rolls con-
taining 15 sq. yds., and it is now usual in packing up a
roll of this material to also include with it the necessaries
for its use—the cement for the joints, and the nails and
caps, these being packed up in circular tins or boxes, which
fit into the centre of the roll.
The material, as its name implies, is used in the covering
of roofs of buildings of all descriptions, whether temporary
or permanent, sloping, segmental or flat. Although very
suitable for temporary roofs or even for the sloping and
segmental roofs of more or less permanent structures,
the writer does not agree with its use for flat work, although
it is now employed for this purpose in England to a fairly
large extent, and his belief is also held by various other
gentlemen intimately concerned with the manufacture
and use of such felts.
The weak point in work of this description is at the
joints. The work is usually carried out with a single
layer of felt, an overlapping joint being made at the seams,
which are then sealed with a bituminous mastic and nailed.
Now with the intense heat of summer this mastic must
soften, and, further, the felt itself expands; with the cold
evenings comes the corresponding hardening of the one
and contraction of the other. This continuous movement,
although imperceptible, can only have but one result, the
weakening of the joint, which is usually only some two
or three inches broad. Again, the felt is left entirely
unprotected, and so is easily cut and damaged by traffic,
OTHER USES OF BITUMEN 231
for flat roofs at the present day are nothing if not utilitarian,
and the writer has seen them put to the most varied and
multitudinous of uses, from a drying lawn to a skating rink.
Besides this, too, in wet weather there is always a mass
of water lying directly upon them, so that when any weak
spots are occasioned by the motion mentioned, or by
sharp objects brought in contact with the felt, whether
flying slates from adjoining buildings in stormy weather,
or hob nails in the boots of the promenaders, this water
soon finds them out and works its way below, doing great
damage to both the structure and its contents alike. If
a flat roof is to be covered in this way, two layers at least
of the felt should be put down, but as this would then
bring the cost of the work up to approximately that for
the more superior methods of flat roof covering, such as
rock asphalt, vulcanite, etc., this recommendation will
scarcely be carried out, for in the majority of cases this
method is adopted only because of the initial economy
effected.
When laid on a sloping or segmental roof, there is the
option of running the layers either from gable to gable
or from eave to eave. Both methods are in use, as the
difference in their respective values is more theoretical
than real. However, the writer personally much prefers
the latter, since by this means the rain draining from the
roof has a clear run from ridge to eave, whilst with the
first method there is invariably a hollow every three feet
where the overlapping of the two adjacent sheets occurs
to form the seam, and in which water is trapped.
In either way the method of carrying out the work is
the same. The sheets of felt are first unrolled out flat
on the roof so as to attain the same temperature as it,
and thus prevent any stretching after the covering has
been finally placed in position and fixed, as this would
cause the sheet to sag and wrinkle. This done, it is then
cut into suitable lengths, and these laid on the sarking
boards in the places they are to take. At each joint of
the felt, whether where two lengths adjoin or where two
pieces are joined to form a complete length, an overlap
of from 3 to 4} ins. is made. Whilst this is being put in
282. NATURAL ROCK ASPHALTS
hand by one workman, another is engaged in melting the
cement to a fairly watery consistency, in which state it
is painted between the laps with a broad stiff brush, and
then the upper lap is firmly pressed down into the lower
one. After this the joints are again gone over and nailed
with either specially made broad-headed, dome-shaped
nails, or, which is more usual, with galvanized broad-headed
nails and washers, the nails being spaced about 2 ins. apart.
The heads of these are customarily given a coat of cement,
so as to prevent them rusting in damp weather. At the
eaves the felt is tucked under the edge of the boarding and
close nailed there in a similar way. Where any projections
occur in the roof, such as chimneys, ventilators, lantern
lights, or party walls, a wood angle fillet is fitted at the
base of the projection, up which the felt is dressed and
close nailed at the apex. To protect the junction of
the felt and the wall, a top flashing is used, preferably
of metal, which is wedged into a raggle cut into the wall
for the purpose and then dressed over the felt.
Despite the manufacturers’ assurances to the contrary,
it is always advisable to give the surface of the felt a
protective coat of asphalt varnish, and to renew this
periodically. With the felt which has been finished with
French chalk (which it has been omitted to state must be
thoroughly brushed away from the felt at the seams before
the application of the cement, since, if present, it prevents
the proper adhesion of the cement with the felt), a neutral
grey roof covering is the result when first laid—if it is not
provided with the suggested protective coat—but this
gradually changes to a dull black. Many occupants and
owners of felt covered structures prefered to see a coloured
roof rather than this, and the desired effect is easily
obtained by the use of a paint made from a non-fugitive
colour, whether mineral or otherwise. The usual solvents
used for these paints have a solvent action on bitumen,
so that a paint thus applied has a partial bond to the
bitumen which coats the felt through the medium of its
solvent and so is not washed away. Certain coloured
bituminous felts for this purpose are to be met with on
the market, but the method just mentioned gives equally
OTHER USES OF BITUMEN 233
satisfactory results, whilst it has the further advantage
that the paint coat possesses a similar protective action
to the felt as would the layer of asphalt varnish.
Bituminous products allied to the roofing felts are
the bituminous sheetings and the bituminous damp-
courses. A slight amount of confusion is occasionally
found with the use of the first named term, since it is
employed by certain manufacturing firms to refer to a
material which is practically identical with the bituminous
roofing felt, except for the fact that it does not receive
the second coat of bitumen, but consists merely of the
impregnated fibre. Besides this the term is also seen
used to designate a thinner quality of the bituminous
dampcourse.
The first type of bituminous sheeting is used principally
as an insulator against cold and damp, so that the question
of the probable effect of heat upon it is negligible. In
any case the method of using it eliminates the possibility
of exposure to any outside influence, so that the protective
coat given to the roofing felt is unnecessary here. Some
American types of this material are to be found which have
been sized, but, although this additional operation gives
the product a more finished appearance, it cannot be said
that any important practical advantage is to be derived
from it.
The bitumen dampcourse is, however, quite a distinct
material. In fact it may be regarded as a layer of more
or less pure bitumen through the middle of which runs a
sheet of jute cloth or, as it is now sometimes made, a thin
sheet of laminated lead. The advantages of its use as
described by “Specification ” are that “it is absolutely
impervious, apparently indestructible, and yields to
settlement without fracture. Perfectly watertight joints
can also be made between vertical and horizontal damp
proofing.” A weakness in this material that is not always
understood as much as it might be is the fact that as the
mortar used in the wall in which it is placed can only
obtain a very slight bond with the bitumen, there is
always the tendency to create a movement of the upper
portion of the wall resting upon it.
234 NATURAL ROCK ASPHALTS
The recent adoption of lead as a core for this material
is entirely unnecessary, and from the manufacturers’
catalogues it would appear that the strong point in support
of its use for this purpose is the longevity of the metal.
Be this as it may, the thinness of the laminated lead
which is actually used in this article reduces its practical
value to a minimum, whilst as regards durability, a refer-
ence to the earlier pages of this book, which refer to the
ancient uses of bitumen, will show that the use of the
latter for waterproofing and dampcoursing, besides being
much older than that of lead, can still be found in erec-
tions which were built many centuries earlier than the
date of the ancient Greek use of lead which is brought
forward in support of its use in the bitumen dampcourse.
The jute cloth which is used in the ordinary types of
this material is generally a 10-Oz. Hessian. Cloths of
lighter weights than this are unable to give the requisite
support to the heavy coat they have to carry, whilst the
heavier and closer woven ones prevent the interbinding
of the bitumen on the two sides, with the result that the
latter is liable to peel away from the jute backing.
The bitumen which is employed in its manufacture
is of very varying types, although the Trinidad epure
was originally the only one used, since at that time the
more flexible rubbery types were not on the market.
Now, however, but few of the possible kinds are not used,
including blown petroleum residues and other substitutes.
With this bitumen is usually mixed a quantity of mineral
matter in a very fine pulverulent condition, very often a low
grade French chalk, though lamp black and other non-
gritty powders are sometimes used. Like roofing felt, the
manufacture was originally carried on by hand, the thickly
flowing hot bitumen being brushed over each side of the
tautly stretched jute cloth, though now the coating is
done by mechanical methods. Some firms add a quantity
of rock asphalt powder to the mixture—sometimes up to
33% per cent.—but although this toughens the material
considerably, until it is almost like stone, it causes it to
entirely lose its flexibility, which is its most necessary
feature. Its uses are principally as a dampcourse for
OTHER USES OF BITUMEN 235
buildings and as a lining for reservoirs and liquid con-
taining tanks, though upon occasion it is found, but
with doubtful success—since the quality of the bitumen
most in use in its preparation differs greatly from that
used in the bituminous roofing felts, not to speak of the
difference in the process of manufacture itself—acting
as a roofing.
The procedure of using this material is slightly modified
from that of laying the roofing felt. In this case, the
cement for the joints is not required, as the necessary bond
between the two overlapping sheets is effected by the bitu-
men itself. The margin of the material that is to form the
seam is carefully cleaned of the French chalk with which
it is usual to coat this product also, and of the paper which
is used by some firms as a temporary backing for the
purpose of preventing the plies from sticking when rolled
up. The sheets are then placed in position and the flame
of a blow lamp played between the edges so as to fuse
the bitumen there. Immediately the bitumen is in a
suitable condition, the upper lap is pressed firmly upon
the lower one and the joint then dressed with a jointing
iron. When used for vertical work, the necessary hold
to the vertical structure is obtained by the use of special
wall ties. These are made in two parts, one of which is
built into the supporting wall in such a way as to leave a
screw portion projecting. This is forced through the
material and the hole made good by fusing the bitumen
around it and pressing upon it an iron washer. When
this has been done, the second portion of the wall tie is
fixed to the screw and afterwards built into the retaining
wall, which it is usual to erect in front of damproofing
work of this description.
The fact of bitumen being used largely in the manufac-
ture of black varnishes and japans has been repeatedly
referred to in the earlier chapters. For this purpose it
is of course necessary that the bitumen shall be perfectly
pure, without any mineral matter, and shall be of such a
type that it will not soften or become liquid at such
extremes of heat to which it may be subjected when in
use, or become brittle at the maximum degree of cold
236 NATURAL ROCK ASPHALTS
with which it may have to contend, but it should always
remain elastic and flexible. The particular type that best
fulfils these requirements is the American gilsonite when
cut back with a suitable flux, though the material obtained
from the Dead Sea and in Syria generally is still largely
used by the more conservative firms manufacturing these
materials. *
These bituminous varnishes, enamels and paints are of
inestimable value for all kinds of outside work, but
especially so for exposed iron and steel work, since their
flexibility allows them to stretch and to contract with the
corresponding expansion and contraction of the metal work
without the protecting film of bitumen becoming weakened
in any way. Their success has, as might be expected,
caused the creation of cheaper substitutes with coal tar
bases, but as these crack, flake and become oxidised with
the continuous exposure to the atmosphere, the results
of their adoption are, to say the least, unsatisfactory.
The bituminous paints are specially valuable for the
protection of steel work on ships or similar marine
structures which are subjected to the action of salt sea
spray for lengthy periods, whilst, since bitumen is proof
against most acids and alkalies, it is extremely useful to
protect metal work that may be exposed to atmospheres
in which these active agents are found. Although these
bituminous paints are usually black in colour, at least
one firm has recently placed upon the market a coloured
bituminous paint which, the makers affirm, does not
contain more than 5 per cent. of colouring matter.
Bitumen for varnish making should be practically
entirely soluble in carbon bisulphide, chloroform, and oil
of turpentine. It should have a conchoidal fracture
showing a bright resinous lustre. It should not flow into
a modified shape when left upon a sloping surface as does
coal tar pitch, but should retain its sharpness of angle
even when immersed in boiling water. If the bitumen has
been adulterated with coal tar pitch, it has a much less
brilliant fracture, and shows a metallic rather than a
resinous lustre. Whilst pure bitumen has a smooth and
homogeneous appearance and feel, the adulterated
OTHER USES OF BITUMEN 237
specimen shows up granular and pasty, nor will the latter
allow itself to be drawn out into even threads like the
pure variety.
Another very extensive use to which this material is
now put is the insulation of electric cables. For the origin
of this idea in the United Kingdom, the credit must be
given to the late W. O. Callender, the founder of the
celebrated firm of Callenders’ Cable and Construction
Co., Ltd., and who, during his business career, was inti-
mately interested in certain of the continental rock
asphalt companies. For this work a long fibred flexible
bitumen is desirable, and particular attention should be
taken in the choice of a suitable type so as to prevent all
possibility of the troublesome and expensive task of
tracing and repairing an underground fracture or weakness
at a later date. It is with regret that the writer has
noticed at times, particularly when the work of conduit
insulation has been in the hands of smaller firms, the
adoption of adulterated bitumens, if not actually artificial
ones. Such material can only have the one result of
occasioning the development of weaknesses in the work at
a later date, and this does not tend to enhance the
reputation of the firm who has carried it out. It must be
confessed, too, that the adoption of such material is often
the result of an insufficient knowledge of the material
being handled, the question of price playing a very im-
portant part in its choice.
With the ever increasing use of reinforced concrete for
constructional purposes, efforts have been, and are still being,
made to overcome the inherent capacity of this material
to absorb moisture. Two distinct methods have been
adopted, the one being to coat the surface of the concrete
structure when erected with a damp resisting compound,
and the other to blend into the concrete itself a compound
which, by filling up its pores and any minute voids that
may be in it, will thus prevent the entry of water. Both
methods are claimed to have special advantages and their
drawbacks, and, whilst the use of an external coat of a
bituminous paint is used by some firms for the facing
method, it is of interest to note that attempts have been
238 NATURAL ROCK ASPHALTS
successfully made to blend into the concrete during the
operation of mixing, a quantity of asphaltic oil which,
whilst, so it is affirmed, not affecting the strength of the
concrete in any way, is able to thoroughly waterproof it.
A few years ago a British patent was granted for a method
of waterproofing concrete with a compound having as its
base the heavy tar oils, but the writer has not been able
to ascertain whether the idea has been used to any great
extent, whilst, having in mind the quality possessed by
coal tar products of gradually oxidising, he is inclined
to doubt the lasting nature of such a method.
Owing to the fact that its flexible nature enables it to
withstand vibration, use has been made of bitumen in
the foundations of such pieces of machinery as steam
hammers or high speed engines, where it is desirable to
reduce the amount of vibration otherwise transmitted to
their immediate surroundings. This is usually done by
making up the foundation with a bituminous concrete,
using just sufficient bitumen to coat the aggregate and
to fill the voids, without making the material too soft to
withstand the pressure that will later be brought to bear
upon it. On the continent it is the custom to include in
this material a quantity of the naturally impregnated
asphalt rock, as this materially assists in the absorption of
both pressure and vibration. After the material has been
placed in position, it is then bricked in, or else walled in
with concrete, and covered over with a layer of the last
named, so as to protect the bitumen from any droppings
of oil or grease which, as will be understood from earlier
chapters, have a solvent effect upon it.
In a similar way bitumen is also used for insulating
purposes in ice chambers, cold storage rooms and the
like, owing to the fact that it is able to retain its flexibility
under intense cold. For this purpose, the aggregate
which is bound together by the bitumen is composed of
crushed cork, and slabs of the bitumen bound cork are
thus made under the influence of heat and pressure, in
varying thicknesses.
The foregoing is but a brief mention of a few of the many
uses to which bitumen is now put, and it shows how limit-
OTHER USES OF BITUMEN 239
less are the possibilities of this material if its properties
are carefully considered. That its use other than as a
paving material is not new, is seen by the fact that over
fifty years ago, “bituminised paper pipes '' were made and
used for the purpose of gas mains in the north of England.
As, however, illuminating gas has a certain amount of
action upon bitumen—as is found even in the modern
asphalt pavements when a leakage of gas occurs below
such a surface—it must be concluded that the experiment
then made could not have been a lasting success, especially
so as the writer, despite careful inquiries in the district,
has not been able to find any trace of their present
existence in the towns in which they were originally laid
down, so that the suggestion then thrown out by the local
newspaper that “there is every probability that they will
speedily come into general use ’’ was apparently not
realised.
INDEX
Acquafr EDDA mines, 165
Adulteration of bitumen, 143
of rock asphalt, 123
Advantages of rock asphalt for
paving, 170
Aesthetic effect of bitumen on
roads, 213
African deposits, 90
Albanian bitumen, 71
American deposits, 92
Analysis of bitumen, 134
of rock asphalt, 153
of tar, 150
Ancient uses, 34
Application of juman to roads,
14
of tar to roads, 212
Aristotle, 42
Arsenic in rock asphalt, 79
Ash content, 143
Asphalt, definition of, 7
derivation of, 34
felt, 228
Asphaltene, 139
Austria-Hungary, deposits in, 73
BARBADOAN bitumen, 114
Bentheim deposit, 90
Bermudez bitumen, 106
lake, description of, 108
Biblical references, 38
Bill of quantities, specimen, 200
Binder, bitumen as a, 214
tar as a, 203
Bitumen, dampcourse, 233
definition of, 7
deposits of, 63
derivation of, 34
geology of, ll
industrial application,
218
of intercalation, 160
N.R, As
Bitumen, of porous penetration,
159
spraying, 217
uses of, 218 *
Bituminised paper pipes, 239
Bituminous macadam, 215
paint, 236
sands, 73
sheetings, 233
Bºing property of rock asphalt
l
Bleeding of bituminous roads, 215
Blocks, rock asphalt mastic, 131
Brick, patent for vertical work,
189
Bridges, rock asphalt on, 193
British imports, 33
CABLE insulation, 237
Californian bitumen, 116
Calphonium, 161
Canadian bitumen, 118
Carbene content, 149
Carbon, fixed, 140
free, 142
Cº. of failure in tar macadam,
2
Characteristics of bitumen for road
making, 214
of rock asphalt, 23
Chemical composition of bitumen,
156, tests, 134
Coal tar, 150
Colour test, 145 -
Coloured bituminous paint, 132
rock asphalt mastic, 132
* to roofing felts,
Component parts of coal tar, 204
Compressed rock asphalt roads,
170
rock asphalt tiles, 125
R.
242
INDEX
Concrete for rock asphalt work,
170
Constitution of rock asphalt, 21
Cooking rock asphalt mastic, 125
Crappe, 80
Cuban bitumen, 111
DAMPCOURSE, rock asphalt as, 194
Dead Sea, 65
Definitions, 7
Deposits of bitumen, 63
of rock asphalt, 76
Description of Bermudez lake, 108
of Trinidad lake, 93
Determination of flash point, 148
of ignition point,
148
of melting point,
141
of moisture in bitu-
men, 137
Diodorus, 41
Disadvantages of rock asphalt as
paving, 170
Discovery of rock asphalt, 47
Dºgator for rock asphalt,
l
Dust prevention, 212
EGYPT, deposits of bitumen in, 90
Egyptian uses of bitumen, 40
Elaterite, 116
Encyclopaedia Britannica, 2
Evaporation test, 149
Expansion, joint in rock asphalt,
191
Extraction of bitumen from rock
asphalt, 61
Eyrinis, Dr., 47
FAILURE in tar macadam, causes
of, 212
Felt, bituminous, 228
tarred, 222
Felts for roofing, 218
Fibre for roofing felts, 220
Fixed carbon, 142
Flash point, determination of, 148
Flashings in rock asphalt work 182
Foot traffic, effect of, 175
Foundations for rock asphalt, 170
for tar macadam, 210
Free carbon, 149
French deposits, 81
Fugitiveness of tar as a binder, 214
GALLENSTEIN, 73
Geology of bitumen, 11
of rock asphalt, 17
German deposits, 76
Gilsonite, 117
Glance pitch, 116
Grahamites, 117
Greek fire, 43
Grooved brick for vertical work,
189
Guarantees, 198

HERODOTUS, 37
Historical references, 34
Homer, 37
Hydraulic asphalt powder, 132
Prº for asphalt tiles,
5
IDENTIFICATION of bitumen, 143
of artificial sub-
stitutes, 142
Ignition point, determination of,
Impregnation of felts, 222
types of, 160
Impure bitumen, analysis of, 143
Intercalation, bitumen of, 160
Invention of tarred felts, 218
Ironwork, rº, asphalt mastic on,
l
preservation of, 236
Italian deposits, 87
rock asphalt for road
making, 165
JEWISH pitch, 41
Josephus, 41
KATRAN, 72
Rir, 72
INDEX
243
LAKES, bitumen, 93
Laying bitumen dampcourse, 235
bituminous macadam, 216
rock asphalt mastic, 183
powder, 171
tiles, 173
tar macadam, 218
tºy guarantees, undesirable,
Limmer rock asphalt, 76
Liquid bitumens, 73
Lobsann rock asphalt, 51
MACADAMS, 8
Maltha, 8
Malthenes, 149
Manjak, 115
Manufacture of tar macadam, 209
Maracaibo bitumen, 110
Mastic, rock asphalt, 125
Mastication test, 152
Mºs point, determination of,
l
Methods of analysis, 134
Mexican bitumen, 116
Mineral aggregates, 207
Mixing machines, 208
Moisture, determination of, 146
Moulds for rock asphalt mastic,
128
NATURAL bitumen, identification,
142
Noah's Ark, 35
Nomenclature, 1
North American deposits, 116
OLD material, use of, 129
PAINT, bituminous, 236
Paraffin content, 150
Paving, rock asphalt mastic as, 196
powder tiles,
173
Pechelbronn bitumen, 79
Penetration test, 147
Peru, bitumen deposits in, 110
Petrolene, 139
Philosopher's stone, 44
Physical tests, 23
Pissasphaltum, 2
Pitch, definition of, 7
lands, 103
tests for, 152
Pliny, 42
Porous, penetration, bitumen of,
Potman, 185
Powder, rock asphalt, 57
Preparation of samples, 135
Pressure, asphalt subject to, 159
Prevention of dust, 202
Pricing of asphalt mastic work,
200
Purification of bitumen, 101
Pyro-bitumens, 9
QUANTITIES, specimen bill of, 100
Quarrying rock asphalt, 122
READY roofings, 228
References, biblical, 38
historical, 34
Regularity of impregnation, 164
Roadmaking with rock asphalt,
170
with asphalt tiles,
173
bitumen for, 214
Rock asphalt as paving, 170
discovery of, 47
geology of, 7 j .
mastic, 125
mining, 120
powder, 123
preparation of, 123
quarrying of, 122'
segregation of, 159
substitutes for, 130
tests for, 154
tiles, 125
Roof covering with felt, 231
with rock asphalt,
186
Roofing felt, 218
fibre for, 221
manufacture of, 222
Rubber, 184
Russian deposits, 72
º
*d
244
INDEX
SABLONNIERE, de la, 51
Samples, preparation of, 135
Sands, bituminous, 73
Sassenay, Count, 52
Seyssel rock asphalt, 81
Shale oil, 112
Sheet asphalt, 8
Sicilian rock asphalt, 88
Skirtings in rock asphalt work, 187
Slabs, rock asphalt for wet walls, .
192
Solubility of bitumen, 156
Sources of bitumen, 63
Spanish deposits, 90
Specific gravity of bitumen, 157
test for, 151
Specification of bitumen, 30
of rock asphalt, 32
Specimen bill of quantities, 200
specification, 199
Spreader, 183
Stables, rock asphalt in, 196
Stinkstein, 73
Strabo, 41
Substitutes for bitumen, 145
for rock asphalt, 130
Sulphur content, 157
Sulphuric acid, action on bitumen,
144
Sumerians, 35
Swiss rock asphalt, 79
Syrian bitumen, 67
TACITUs, 41
Tar, 204
Tar macadam, 209
spraying, 213
Tests, 134
Texan bitumen, 116
Tiles, rock asphalt mastic, 131
powder, 125
Tower of Babel, 37
Traffic, foot 174
vehicular, 174
Trinidad epure, 98
lake, description of, 93
bitumen, 99
land bitumen, 102
Types of impregnation, 160
TJINTAHITE, 117
Undesirability of lengthy guaran-
tee, 198
Use of old material, 129
Uses of bitumen, 218
of rock asphalt, 170
Utah, bitumen in, 117
VAL DE TRAVERS rock asphalt, 79
Vehicular traffic, 174
Venezuelan bitumen, 106
Vertical work in rock asphalt, 189
in bitumen, 235
Worwohler rock asphalt, 77
WATER BOUND roads, 202
Wearing coefficient, 160
Wurtzilite, 117
XENOPHON, 41
{
univ. of MichioAN,
is”
*-‘.
SEP II 1913
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BRADBURY, AGNEW, & Co. LD., PRINTERs, LoNDON AND TONBRIDGE.
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*I
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*I
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*I
*I
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Coombs, H. A. Gear Teeth. (Science Series No. 120)... 16mo, o 50
Cooper, W. R. Primary Batteries. . . . . . . . . . . . . . . . . . . . . . . 8vo, *4 oo
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Crosskey, L. R. Elementary Prospective. . . . . . . . . . . . . . . . . 8vo, I oo
Crosskey, L. R., and Thaw, J. Advanced Perspective. . . . . . 8vo, I 50
Culley, J. L. Theory of Arches. (Science Series No. 87.)16mo, o 50
Davenport, C. The Book. (Westminster Series.) . . . . . . . . 8vo, *2 oo
Davies, D. C. Metalliferous Minerals and Mining. . . . . . . . . 8vo, a 5 od
Earthy Minerals and Mining. . . . . . . . . . . . . . . . . . . . . . . 8vo, 5 od
Davies, E. H. Machinery for Metalliferous Mines. . . . . . . . 8vo, 8 oo
Davies, F. H. Electric Power and Traction . . . . . . . . . . . . . 8vo, *2 oo
Dawson, P. Electric Traction on Railways. . . . . . . . . . . . . . 8vo, *9 oo
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Del Mar, W. A. Electric Power Conductors. . . . . . . . . . . . . . 8vo, *2 oô
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De Roos, J. D. C. Linkages. (Science Series No. 47.)... 16mo, o 50
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Dinger, Lieut. H. C. Care and Operation of Naval Machinery
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Dixon, D. B. Machinist's and Steam Engineer’s Practical Cal-
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Doble, W. A. Power Plant Construction on the Pacific Coast.
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Dodd, G. Dictionary of Manufactures, Mining, Machinery, and
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Dorr, B. F. The Surveyor's Guide and Pocket Table-book.
- I6mo, mor, 2 oo
Down, P. B. Handy Copper Wire Table. . . . . . . . . . . . . . . 16mo, *I oo
Draper, C. H. Elementary Text-book of Light, Heat and
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—— Heat and the Principles of Thermo-dynamics. . . . . . . I2mo, I 50
Duckwall, E. W. Canning and Preserving of Food Products.8vo, *5 oo
Dumesny, P., and Noyer, J. Wood Products, Distillates, and
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Duncan, W. G., and Penman, D. The Electrical Equipment of
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Duthie, A. L. Decorative Glass Processes. (Westminster
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Eissler, M. The Metallurgy of Gold. . . . . . . . . . . . . . . . . . . . . 8vo, 7 5o
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Ekin, T. C. Water Pipe and Sewage Discharge Diagrams. . folio, *3 oo
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Erfurt, J. Dyeing of Paper Pulp. Trans. by J. Hubner...8vo, *7 5o
Erskine-Murray, J. A. Handbook of Wireless Telegraphy... 8vo, *3 50
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Ewing, A. J. Magnetic Induction in Iron. . . . . . . . . . . . . . . . 8vo, *4 oo
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Fairley, W., and Andre, Geo. J. Ventilation of Coal Mines.
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Fairweather, W. C. Foreign and Colonial Patent Laws . . .8vo, *3 oo
Fanning, T. T. Hydraulic and Water-supply Engineering.
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Fauth, P. The Moon in Modern Astronomy. Trans. by J.
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Fay, I. W. The Coal-tar Colors . . . . . . . . . . . . . . . . . . . . . . 8vo (In Press.)
Fernbach, R. L. Glue and Gelatine. . . . . . . . . . . . . . . . . . . . . 8vo, *3 oo
Fischer, E. The Preparation of Organic Compounds. Trans.
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Fiske, Lieut. B. A. Electricity in Theory and Practice . . . .8vo, 2 50
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Flynn, P. J. Flow of Water. (Science Series No. 84.)... 16mo, o 5o
Hydraulic Tables. (Science Series No. 66.). . . . . . . . I6mo, o 5o
Foley, N. British and American Customary and Metric Meas—
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Foster, Gen. J. G. Submarine Blasting in Boston (Mass.)
Harbor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4to, 3 50
Fowle, F. F. Overhead Transmission Line Crossings . . . . 12mo, " *I 50
— The Solution of Alternating Current Problems.
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Handbook of Mineralogy. (Science Series No. 86.)... 16mo, o 5o
Francis, J. B. Lowell Hydraulic Experiments. . . . . . . . . . . . 4to, I5 Oo
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Furnell, J. Paints, Colors, Oils, and Warnishes. . . . . . . . . . . 8vo, *I oo
Gant, L. W. Elements of Electric Traction. . . . . . . . . . . . . . 8vo, *2 50
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Geerligs, H. C. P. Cane Sugar and Its Manufacture . . . . . . . 8vo, *5 od
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Gas Lighting. (Science Series No. 1 II.). . . . . . . . . . . . . 16mo, o 50
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— House Drainage. (Science Series No. 63.). . . . . . . . . Iómo, o 50
Sanitary Drainage of Buildings. (Science Series No. 93.)
Iómo, o 5o
Gerhardi, C. W. H. Electricity Meters. . . . . . . . . . . . . . . . . .8vo, *4 oo
Geschwind, L. Manufacture of Alum and Sulphates. Trans.
by C. Salter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8vo, *5 oo
Gibbs, W. E. Lighting by Acetylene . . . . . . . . . . . . . . . . . . I2mo, *I 5o
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Text-books.). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . *I 5o
Gibson, A. H. Hydraulics and Its Application. . . . . . . . . . . . 8vo, *5 oo
Water Hammer in Hydraulic Pipe Lines. . . . . . . . . . . I2mo, *2 oo
Gilbreth, F. B. Motion Study. A Method for Increasing the
Efficiency of the Workman. . . . . . . . . . . . . . . . . . . I2mo, *2 oo
Gillmore, Gen. Q. A. Limes, Hydraulic Cements and Mortars.
- 8vo, 4 oo
— Roads, Streets, and Pavements. - - - - - - - - - - - - - - - - - - I2mo, 2 Oo
Golding, H. A. The Theta-Phi Diagram. . . . . . . . . . . . . . . I2mo, *r 25
Goldschmidt, R. Alternating Current Commutator Motor .8vo, *3 oo
Goodchild, W. Precious Stones. (Westminster Series.). . .8vo, *2 oo
Goodeve, T. M. Textbook on the Steam-engine. . . . . . . . . I2mo, 2 OO
Gore, G. Electrolytic Separation of Metals. . . . . . . . . . . . . . . 8vo, *3 5o
Gould, E. S. Arithmetic of the Steam-engine..... ” e - - - - I2mo, I oo
Calculus. (Science Series No. II2.). . . . . . . . . . . . . . . Iómo, o 50
High Masonry Dams. (Science Series No. 22.). . . . . Iómo, o 50
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Series.). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Iómo, o 50
Grant, J. Brewing and Distilling. (Westminster Series.) 8vo (In Press.)
Gray, J. Electrical Influence Machines, , , , . . . . . . . . . . . . I2mo, 2 oo
14 D. VAN NOSTRAND COMPANY’s SHORT-TITLE CATALOG
Greenwood; E. Classified Guide to Technical and Commercial
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Gregorius, R. Mineral Waxes. Trans. by C. Salter. . . . . I2mo, *3
Griffiths, A. B. A Treatise on Manures. . . . . . . . . . . . . . . . I2mo, 3
— Dental Metallurgy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8vo, *3
Gross, E. Hops. . . . . . . . . . . . . . . . . . . . . . . . -------------- 8vo, *4
Grossman, J. Ammonia and its Compounds. . . . . . . . . . . . 12mo, *1
Groth, L. A. Welding and Cutting Metals by Gases or Electric-
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Grover, F. Modern Gas and Oil Engines. . . . . . . . . . . . . . . . 8vo, *2
Gruner, A. Power-loom Weaving. . . . . . . . . . . . . . . . . . . . . . 8vo, *3
Güldner, Hugo. Internal-Combustion Engines. Trans. by
H. Diedrichs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4to, *Io
Gunther, C. O. Integration. . . . . . . . . . . . . . . . . . . . . . . . . . 12mo, *r
Gurden, R. L. Traverse Tables . . . . . . . . . . . . . . . folio, half mor. 7
Guy, A. E. Experiments on the Flexure of Beams. . . . . . . . . 8vo, *1
Haeder, H. Handbook on the Steam-engine. Trans. by H. H.
OO
OO
OO
50
50
25
OO
OO
OO
OO
25
50
25
P. Powles. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I2mo, 3 Oo
Hainbach, R. Pottery Decoration. Trans. by C. Slater. . I2mo, *3 oo
Hale, W. J. Calculations of General Chemistry. . . . . . . . . 12mo, *I oo
Hall, C. H. Chemistry of Paints and Paint Vehicles..... 12mo, *2 oo
Hall, R. H. Governors and Governing Mechanism. . . . . . 12mo, *2 oo
Hall, W. S. Elements of the Differential and Integral Calculus
x * 8vo, *2 25
Descriptive Geometry . . . . . . . . . . 8vo volume and 4to atlas, *3 50
Haller, G. F., and Cunningham, E. T. The Tesla Coil. . . . . 12mo, *I 25
Halsey, F. A. Slide Valve Gears.... . . . . . . . . . . . . . . . . . . I2mo, I 50
— The Use of the Slide Rule. (Science Series.). . . . . . . I6mo, o
Worm and Spiral Gearing. (Science Series.). . . . . . . 16mo, o
Hamilton, W. G. Useful Information for Railway Men... 16mo, I
Hammer,W. J. Radium and Other Radioactive Substances, 8vo, *I
Hancock, H. Textbook of Mechanics and Hydrostatics. . . . .8vo, I
Hardy, E. Elementary Principles of Graphic Statics. . . . . I2mo, "I
Harper, W. B. Utilization of Wood Waste by Distillation. 4to, *3
I
3
3
3
Harrison, W. B. The Mechanics' Tool-book..... . . . . . . . . 12mo,
Hart, J. W. External Plumbing Work... . . . . . . . . . . . . . . . 8vo, *
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— Principles of Hot Water Supply. . . . . . . . . . . . . . . . . . . . 8vo, *
50
50
OO
OO ,
50
50
OO
50
OO
OO
OO
D. VAN NOSTRAND COMPANY’s short-TITLE CATALOG 15
Hart, J. W. Sanitary Plumbing and Drainage. . . . . . . . . . . 8vo,
Haskins, C. H. The Galvanometer and Its Uses... . . . . . . 16mo,
Hatt, J. A. H. The Colorist. . . . . . . . . . . . . . . . . . . square I2mo,
Hausbrand, E. Drying by Means of Air and Steam. Trans.
by A. C. Wright. . . . . . . . . . . . . . . . . . . . . . . . . . . . I2mo,
Evaporing, Condensing and Cooling Apparatus. Trans.
by A. C. Wright. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8vo,
Hausner, A. Manufacture of Preserved Foods and Sweetmeats.
Trans. by A. Morris and H. Robson. . . . . . . . . . . . . 8vo,
Hawke, W. H. Premier Cipher Telegraphic Code. . . . . . . . . 4to,
— roo,ooo Words Supplement to the Premier Code. . . . . . 4to,
Hawkesworth, J. Graphical Handbook for Reniforced Concrete
Design. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4to,
Hay, A. Alternating Currents . . . . . . . . . . . . . . . . . . . . . . . . . 8vo,
Principles of Alternate-current Working. . . . . . . . . . . 12mo,
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Heap, Major D. P. Electrical Appliances. . . . . . . . . . . . . . . . 8vo,
Heaviside, O. Electromagnetic Theory. Two volumes.
8vo, each,
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Vol. I. Thermodynamics and the Mechanics. . . . . . . . 8vo,
Vol. II. Form, Construction and Working. . . . . . . . . . . 8vo,
——- Abridged edition of above volumes (Elementary)
*3
I
* I
*2
*5
*3
*5
OO
50
50
OO
OO
OO
OO
OO
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50
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50
50
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8vo (In Preparation)
— Notes on Elementary Kinematics. . . . . . . . . . . . 8vo, boards,
Graphics of Machine Forces. . . . . . . . . . . . . . . . . 8vo, boards,
Hedges, K. Modern Lightning Conductors. . . . . . . . . . . . . . . 8vo,
Heermann, P. Dyers’ Materials. Trans. by A. C. Wright.
I2mo,
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Cotton. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8vo,
Henrici, O. Skeleton Structures. . . . . . . . . . . . . . . . . . . . . . . . 8vo,
Hermann, F. Painting on Glass and Porcelain. . . . . . . . . . . 8vo,
Hermann, G. The Graphical Statics of Mechanism. Trans.
by A. P. Smith..... . . . . . . . . . . . . . . . . . . . . . . . . . I2mo,
Herzfeld, J. Testing of Yarns and Textile Fabrics. . . . . . . . 8vo,
* I
*I
3
*2
*2
OO
OO
OO
50
Hildebrandt, A. Airships, Past and Present.... . . . . . . . . . . 8vo,
*3
*3
OO
50
3 50
OO
5O
50
16 D. VAN NOSTRAND COMPANY’s SHORT-TITLE CATALOG
Hildenbrand, B. W. Cable-Making. (Science Series No. 32.)
Iómo, o 50
Hildrich, H. Short History of Chemistry. . . . . . . . . . . . . . . . . . (In Press.)
Hill, J. W. The Purification of Public Water Supplies. New
Edition..... . . . . * * * . . . . . . . . . (In Press.)
Interpretation of Water Analysis. . . . . . . . . . . . . . . . . . . . . (In Press.)
Hiroi, I. Plate Girder Construction. (Science Series No. 95.)
16mo, o 50
— Statically-Indeterminate Stresses... . . . . . . . . . . . . . . . 12mo, *2 oo
Hirshfeld, C. F. Engineering Thermodynamics. (Science
Series.).... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I6mo, o 50
Hobart, H. M. Heavy Electrical Engineering.. . . . . . . . . . . . 8vo, *4 50
— Electricity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8vo, *2 oo
Electric Trains... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8vo, *2 5o
Hobbs, W. R. P. The Arithmetic of Electrical Measurements
I2mo, O 50
Hoff, J. N. Paint and Warnish Facts and Formulas. . . . . 12mo, *I 50
Hoff, Com.W. B. The Avoidance of Collisions at Sea. 16mo, mor., o 75
Hole, W. The Distribution of Gas. . . . . . . . . . . . . . . . . . . . . . 8vo, *7 50
Holley, A. L. Railway Practice. . . . . . . . . . . . . . . . . . . . . . . folio, I2 oo
Hölmes, A. B. The Electric Light Popularly Explained.
I2mo, paper, O 50
Hopkins, N. M. Experimental Electrochemistry. . . . . . . . . . 8vo, *3 oo
Model Engines and Small Boats. . . . . . . . . . . . . . . . . . . I2mo, I 25
Hopkinson, J., Shoolbred, J. N., and Day, R. E. Dynamic
Electricity. (Science Series No. 71.). . . . . . . . . . . I6mo, o 50
Horner, J. Engineers' Turning. . . . . . . . . . . . . . . . . . . . . . . . 8vo, *3 50
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— Toothed Gearing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I2m.0, 2 25
Houghton, C. E. The Elements of Mechanics of Materials.12mo, *2 oo
Houllevigue, L. The Evolution of the Sciences. . . . . . . . . . .8vo, *2 oo
Howe, G. Mathematics for the Practical Man. . . . . . . . . . 12mo, *I 25
Howorth, J. Repairing and Riveting Glass, China and Earthen-
* Ware- - - - - - - . . . . . . . . . . . . . . . . . . . . . . . . . . . 8vo, paper, *o 50
Hubbard, E. The Utilization of Wood-waste..... . . . . . . . .8vo, *2 50
Humber, W. Calculation of Strains in Girders... . . . . . . . 12mo, 2 50
Humphreys, A. C. The . Business Features of Engineering
Practice. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8vo, * 1 25
Hurst, G. H. Handbook of the Theory of Color. . . . . . . . . . 8vo, *2 50
D. VAN NOSTRAND COMPANY'S SHORT-TITLE CATALOG 17
Hurst, G.H. Dictionary of Chemicals and Raw Products...8vo, *3 oo
— Lubricating Oils, Fats and Greases. . . . . . . . . . . . . . . . . . 8vo, *3 oo.
Soaps. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8vo, *5 oo
— Textile Soaps and Oils. . . . . . . . . . . . . . . . . . . . . . . . . . . . 8vo, *2 50
Hurst, H. E., and Lattey, R. T. Text-book of Physics. . . . . 8vo, *3 oo
Hutchinson, R. W., Jr. Long Distance Electric Power Trans-
mission. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12mo, *3 oo
Hutchinson, R. W., Jr., and Ihlseng, M. C. Electricity in
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Hutchinson, W. B. Patents and How to Make Money Out of
Them. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I2mo, I 25
Hutton, W. S. Steam-boiler Construction. . . . . . . . . . . . . . . 8vo, 6 oo
— Practical Engineer’s Handbook. . . . . . . . . . . . . . . . . . . . . 8vo, 7 oo
The Works’ Manager’s Handbook. . . . . . . . . . . . . . . . . . 8vo, 6 oo
Hyde, E. W. Skew Arches. (Science Series No. 15.)... . . 16mo, o 50
Induction Coils. (Science Series No. 53.). . . . . . . . . . . . . . . 16mo, o 50
Ingle, H. Manual of Agricultural Chemistry. . . . . . . . . . . . . 8vo, *3 oo
Innes, C. H. Problems in Machine Design. . . . . . . . . . . . . 12mo, *2 oo
Air Compressors and Blowing Engines. . . . . . . . . . . . . . 12mo, *2 oo
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The Fan. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12mo, *2 oo
Isherwood, B. F. Engineering Precedents for Steam Machinery
8vo, 2 50
Iwatts, E. B. Railway Management at Stations. . . . . . . . . . . 8vo, *2 50
Jacob, A., and Gould, E. S. . On the Designing and Construction
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Jamieson, A. Text Book on Steam and Steam Engines. . . . 8vo, 3 oo
Elementary Manual on Steam and the Steam Engine. 12mo, I 50
Jannettaz, E. Guide to the Determination of Rocks. Trans.
by G. W. Plympton..... . . . . . . . . . . . . . . . . . . . . . I2mo, I 50
Jehl, F. Manufacture of Carbons. . . . . . . . . . . . . . . . . . . . . . 8vo, *4 oo
Jennings, A. S. Commercial Paints and Painting. (West-
minster Series.) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8vo (In Press.)
Jennison, F. H. The Manufacture of Lake ‘Pigments . . . . . 8vo, *3 oo
Jepson, G. Cams and the Principles of their Construction...8vo, *I 5o
—- Mechanical Drawing. . . . . . . . . . . . . . . . . . . . . .8vo (In Preparation.)
Jockin, W. Arithmetic of the Gold and Silversmith. . . . . 12mo, *I oo
18 D. VAN NOSTRAND COMPANY'S SHORT-TITLE CATALOG
Johnson, G. L. Photographic Optics and Color Photography
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Johnson, W. H. The Cultivation and Preparation of Para
Rubber. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8vo, *3 oo
Johnson, W. McA. The Metallurgy of Nickel. . . . . . . . . (In Preparation.)
Johnston, J. F. W., and Cameron, C. Elements of Agricultural
Chemistry and Geology. . . . . . . . . . . . .* * * * * * * * * * 12mo, 2 6o
Joly, J. Radioactivity and Geology. . . . . . . . . . . . . . . . . . . 12mo, *3 oo
Jones, H. C. Electrical Nature of Matter and Radioactivity
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Jones, M. W. Testing Raw Materials Used in Paint. . . . . 12mo, *2 oo
Jones, L., and Scard, F. I. Manufacture of Cane Sugar. . . . . 8vo, *5 oo
Joynson, F. H. Designing and Construction of Machine Gear-
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Jüptner, H. F. V. Siderology: The Science of Iron... . . . . . 8vo, *5 oo
Kansas City Bridge. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4to, 6 oo
Kapp, G. Alternate Current Machinery. (Science Series No.
96.). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I6mo, o 50
— Dynamos, Motors, Alternators and Rotary Converters.
Trans. by H. H. Simmons....... . . . . . . . . . . . . . . .8vo, 4 oo
Electric Transmission of Energy. ... . . . . . . . . . . . 12mo, 3 50
Keim, A. W. Prevention of Dampness in Buildings . . . . . . 8vo, *2 oo
Keller, S. S. Mathematics for Engineering Students.
I2mo, half leather,
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Kelsey, W. R. Continuous-current Dynamos and Motors.
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Kemble, W. T., and Underhill, C. R. The Periodic Law and the
Hydrogen Spectrum. . . . . . . . . . . . . . . . . . . . 8vo, paper, *o 50
Kemp, J. F. Handbook of Rocks. . . . . . . . . . . . . . . . . . . . . . . 8vo, *I 50
Kendall, E. Twelve Figure Cipher Code. . . . . . . . . . . . . . . . . 4to, *I5 od
Kennedy, A. B. W., and Thurston, R. H. Kinematics of
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Kennedy, A. B. W., Unwin, W. C., and Idell, F. E. Compressed
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D. VAN NOSTRAND COMPANY’s SHORT-TITLE CATALOG 19
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Kennelly, A. E. Electro-dynamic Machinery. . . . . . . . . . . . , 8vo, I 50
Kent, W. Strength of Materials. (Science Series No. 4.1.). 16mo, o 50
Kershaw, J. B. C. Fuel, Water and Gas Analysis. . . . . . . .8vo, *2 50
Electrometallurgy. (Westminster Series.). . . . . . . . . . .8vo, *2 oo
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Kingdon, J. A. Applied Magnetism. . . . . . . . . . . . . . . . . . . . 8vo, *3 oo
Kinzbrunner, C. Alternate Current Windings. . . . . . . . . . . . 8vo, *I 5o
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Kirkbride, J. Engraving for Illustration. . . . . . . . . . . . . . . . .8vo, *I 50
Kirkwood, J. P. Filtration of River Waters. . . . . . . . . . . . . . 4to, 7 50
Klein, J. F. Design of a High speed Steam-engine . . . . . . . 8vo, *5 oo
Physical Significance of Entropy. . . . . . . . . . . . . . . . . . . . 8vo, *I 50
Kleinhans, F. B. Boiler Construction. . . . . . . . . . . . . . . . . . . 8vo, 3 oo
Knight, Capt. A. M. Modern Steamship . . . . . . . . . . . . . . . . . 8vo, *7 50
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Knott, C. G., and Mackay, J. S. Practical Mathematics. . .8vo, 2 oo
Koester, F. Steam-Electric Power Plants. . . . . . . . . . . . . . . . 4to, *5 oo
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Koller, T. The Utilization of Waste Products. . . . . . . . . . . . 8vo, *3 50
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Larrabee, C. S. Cipher and Secret Letter and Telegraphic
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La Rue, B. F. Swing Bridges. (Science Series No. Io'ſ.). 16mo, o 50
Lassar-Cohn, Dr. Modern Scientific Chemistry. Trans. by M.
M. Pattison Muir. . . . . . . . . . . . . . . . . . . . . . . . . . . I2m.0,
Latimer, L. H., Field, C. J., and Howell, J. W. Incandescent
Electric Lighting. (Science Series No. 57.). . . . .16mo, o 50
Latta, M. N. Handbook of American Gas-Engineering Practice.
2 OO
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Leask, A. R. Breakdowns at Sea. . . . . . . . . . . . . . . . . . . . . I2mo, 2 OO
Triple and Quadruple Expansion Engines. . . . . . . . . . I2mo, 2 OO
Refrigerating Machinery . . . . . . . . . . . . . . . . . . . . . . . . I2mo, 2 oo
Lecky, S. T. S. “Wrinkles’’ in Practical Navigation . . . . .8vo, *8 oo
Le Doux, M. Ice-Making Machines. (Science Series No. 46.)
* I6mo, o 50
Leeds, C. C. Mechanical Drawing for Trade Schools. oblong, 4to,
High School Edition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . *I 25
Machinery Trades Edition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . *2 oo
Lefévre, L. Architectural Pottery. Trans. by H. K. Bird and
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Lehner, S. Ink Manufacture. Trans. by A. Morris and H.
Robson. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8vo, *2 50
Lemstrom, S. Electricity in Agriculture and Horticulture.
º - 8vo, *I 50
Le Van, W. B. Steam-Engine Indicator. (Science Series No.
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Lewes, W. B. Liquid and Gaseous Fuels. (Westminster Series.)
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Livermore, V. P., and Williams, J. How to Become a Com-
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Livingstone, R. Design and Construction of Commutators. 8vo, *2 25
Lobben, P. Machinists' and Draftsmen's Handbook . . . . . . 8vo, 2 50
Locke, A. G. and C. G. Manufacture of Sulphuric Acid . . . . . 8vo, Io oo
Lockwood, T. D. Electricity, Magnetism, and Electro-teleg-
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Electrical Measurement and the Galvanometer . . . . . 12mo, I 50
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Loring, A. E. A. Handbook of the Electromagnetic Telegraph.
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Power Plants: their Design, Efficiency, and Power Costs.
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Lupton, A., Parr, G. D. A., and Perkin, H. Electricity as Applied -
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Maguire, Wm. R. Domestic Sanitary Drainage and Plumbing . .
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Mallet, A. Compound Engines. Trans. by R. R. Buel. . . .
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Markham, E. R. The American Steel Worker. . . . . . . . . . I2mo, 2 50
Marlow, T. G. Drying Machinery and Practice. ... . . . . . . . .8vo, *5 oo
Marsh, C. F. Concise Treatise on Reinforced Concrete. . . . 8vo, *2 50
Marsh, C. F., and Dunn, W. Reinforced Concrete. . . . . . . . 4to, *5 oo
Manual of Reinforced Concrete and Concrete Block Con-
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Marshall, W.J., and Sankey, H. R. Gas Engines. (Westminster
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Massie, W. W., and Underhill, C. R. Wireless Telegraphy and
Telephony. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12mo, *I oo
Matheson, D. Australian Saw-Miller’s Log and Timber Ready
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Mathot, R. E. Internal Combustion Engines . . . . . . . . . . . . 8vo, *6 oo
Maurice, W. Electric Blasting Apparatus and Explosives .. 8vo, *3 50
Shot Firer’s Guide. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8vo, *I 50
Maxwell, J. C. Matter and Motion. (Science Series No. 36.)
I6mo, o 50
Maxwell, W. H., and Brown, J. T. Encyclopedia of Municipal
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Mayer, A. M. Lecture Notes on Physics.. . . . . . . . . . . . . . . . 8vo, 2 oo
D. VAN NOSTRAND COMPANY'S SHORT-TITLE CATALOG 23
McCullough, R. S. Mechanical Theory of Heat. . . . . . . . . . . 8vo, 3 50
McIntosh, J. G. Technology of Sugar. . . . . . . . . . . . . . . . . . .8vo, *4 50
Industrial Alcohol. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8vo, *3 oo
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Vol. II. Warnish Materials and Oil Warnish Making....... *4 oo
Vol. III.------. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (In Preparation.)
McKnight, J. D., and Brown, A. W. Marine Multitubular
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McMaster, J. B. Bridge and Tunnel Centres. (Science Series
No. 20.). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I6mo, o 5o
McMechen, F. L. Tests for Ores, Minerals and Metals. . . 12mo, *I oo
McNeill, B. McNeill’s Code. . . . . . . . . . . . . . . . . . . . . . . . . . . . 8vo, *6 oo
McPherson, J. A. Water-works Distribution . . . . . . . . . . . . 8vo, 2 5o
Melick, C. W. Dairy Laboratory Guide. . . . . . . . . . . . . . . . 12mo, * 1 25
Merck, E. Chemical Reagents; Their Purity and Tests. . . .8vo, *I 5o
Merritt, Wm. H. Field Testing for Gold and Silver. I6mo, leather, I 5o
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Michell, S. Mine Drainage. . . . . . . . . . . . . . . . . . . . . . . . . . . . 8vo, Io oo
Mierzinski, S. Waterproofing of Fabrics. Trans. by A. Morris
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Miller, E. H. Quantitative Analysis for Mining Engineers. .8vo, *I 5o
Miller, G. A. Determinants. (Science Series No. 105.). 16mo,
Milroy, M. E. W. Home Lace-making. . . . . . . . . . . . . . . . 12mo, * I oo
Minifie, W. Mechanical Drawing. . . . . . . . . . . . . . . . . . . . . . . 8vo, *4 oo
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Modern Meteorology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I2m O, I 50
Monckton, C. C. F. Radiotelegraphy. (Westminster Series.)
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Monteverde, R. D. West Pocket Glossary of English-Spanish,
Spanish-English Technical Terms. . . . . . 64mo, leather, *I oo
Moore, E. C. S. New Tables for the Complete Solution of
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Moreing, C. A., and Neal, T. New General and Mining Tele-
graph Code. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8vo, *5 oo
Morgan, A. P. Wireless Telegraph Construction for Amateurs.
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24 D. WAN NOSTRAND COMPANY'S SHORT-TITLE CATALOG
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Moses, A. J., and Parsons, C. I. Elements of Mineralogy. , 8vo, *2 50
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Munby, A. E. Chemistry and Physics of Building Materials.
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Murphy, J. G. Practical Mining. . . . . . . . . . . . . . . . . . . . . . I6mo, I oo
Murray, J. A. Soils and Manures. (Westminster Series.). 8vo, *2 oo
Naquet, A. Legal Chemistry. . . . . . . . . . . . . . . . . . . . . . .. . . I2mo, 2 OO
Nasmith, J. The Student’s Cotton Spinning. . . . . . . . . . . . . . 8vo, 3 oo
Neilson, R. M. Aeroplane Patents. . . . . . . . . . . . . . . . . . . . . . 8vo, *2 oo
Nerz, F. Searchlights. Trans. by C. Rodgers. . . . . . . . . . . .8vo, *3 oo
Neuberger, H., and Noalhat, H. Technology of Petroleum.
Trans. by J. G. McIntosh. . . . . . . . . . . . . . . . . . . . . . 8vo, *Io oc
Newall, J. W. Drawing, Sizing and Cutting Bevel-gears.
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Nicol, G. Ship Construction and Calculations. . . . . . . . . . . . 8vo, *4 50
Nipher, F. E. Theory of Magnetic Measurements. . . . . . . I2mo, I Oo
Nisbet, H. Grammar of Textile Design. . . . . . . . . . . . . . . . . .8vo, *3 oo
Nolan, H. The Telescope. (Science Series No. 51.). . . . . Iómo, o 50
Noll, A. How to Wire Buildings... . . . . . . . . . . . . . . . . . . .12mo, I 5o
Nugent, E. Treatise on Optics . . . . . . . . . . . . . . . . . . . . . . . I2mo, I 50
O'Connor, H. The Gas Engineer's Pocketbook. . . 12mo, leather, 3 5o
Petrol Air Gas. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12mo, *o 75
Ohm, G. S., and Lockwood, T. D. Galvanic Circuit. Trans. by
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Olsen, J. C. Text book of Quantitative Chemical Analysis . .8vo, *4 oo
Olsson, A. Motor Control, in Turret Turning and Gun Elevating.
(U. S. Navy Electrical Series, No. 1.) . . . . 12mo, paper, *o 5o
Oudin, M. A. Standard Polyphase Apparatus and Systems . .8vo, *3 oo
Palaz, A. Industrial Photometry. Trans. by G. W. Patterson,
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*
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D, VAN NOSTRAND COMPANY's SHORT-TITLE CATALOG 25
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Parr, G. D. A. Electrical Engineering Measuring Instruments.
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Parry, E. J. Chemistry of Essential Oils and Artificial Per-
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Parry, E. J., and Coste, J. H. Chemistry of Pigments . . . . . . 8vo, *4 5o
Parry, L. A. Risk and Dangers of Various Occupations. . . . .8vo, *3 oo
Parshall, H. F., and Hobart, H. M. Armature Windings . . . . 4to, *7 5o
Electric Railway Engineering. . . . . . . . . . . . . . . . . . . . . . 4to, *Io oo
Parshall, H. F., and Parry, E. Electrical Equipment of Tram-
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Parsons, S. J. Malleable Cast Iron. . . . . . . . . . . . . . . . . . . . . . 8vo, *2 50
Passmore, A. C. Technical Terms Used in Architecture . . .8vo, *3 50
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Patton, H. B. Lecture Notes on Crystallography . . . . . . . . . 8vo, * 1 25
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Perrine, F. A. C. Conductors for Electrical Distribution . . . 8vo, *3 5o
Perry, J. Applied Mechanics. . . . . . . . . . . . . . . . . . . . . . . . . . 8vo, *2 50
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Plattner's Manual of Blowpipe Analysis. Eighth Edition, re-
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>k
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Practical Iron Founding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I2mo, I 50
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Calorimeter Tables. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8vo, I oo
Preece, W. H. Electric Lamps. . . . . . . . . . . . . . . . . . . . . . . . . . (In Press.)
Prelind, C. Earth and Rock Excavation. . . . . . . . . . . . . . . . . 8vo, *3 oo
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Prescott, A. B. Organic Analysis. . . . . . . . . . . . . . . . . . . . . . . 8vo, 5 od
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