or crude sodium carbonate. This is usually done in large cylindrical
revolving furnaces, through, which flames from a fire-grate, or from the
burning of gaseous fuel, pass; the waste heat is utilised for boiling
down "black ash" liquor, obtained by lixiviating the black ash. A
mixture of salt-cake, limestone or chalk (calcium carbonate), and
powdered coal or coal slack is charged into the revolving cylinder;
during the process the mass becomes agglomerated, and the final product
is what is known as a "black-ash ball," consisting chiefly of crude
sodium carbonate and calcium sulphide, but containing smaller quantities
of many other substances. The soda ash or sodium carbonate is obtained
from the black ash by lixiviating with water, and after various
purification processes, the solution is boiled down, as previously
stated, by the waste heat of the black-ash furnace. The alkali is sold
in various forms as soda ash, soda crystals, washing soda, etc.
Caustic soda is manufactured from solution of carbonate of soda by
causticising, that is, treatment with caustic lime or quicklime.
It will have been noticed that one of the chief reagents in the Leblanc
process is the sulphur used in the form of brimstone or as pyrites for
making vitriol in the first stage; this sulphur goes through the entire
process; from the vitriol it goes to form a constituent of the
salt-cake, and afterwards of the calcium sulphide contained in the black
ash. This calcium sulphide remains as an insoluble mass when the
carbonate of soda is extracted from the black ash, and forms the chief
constituent of the alkali waste, which until the year 1880 could be seen
in large heaps around chemical works. Now, however, by means of
treatment with kiln gases containing carbonic acid, the sulphur is
extracted from the waste in the form of hydrogen sulphide, which is
burnt to form vitriol, or is used for making pure sulphur; and so what
was once waste is now a source of profit.
_Ammonia-Soda Process of Alkali Manufacture._--This process depends
upon the fact that when carbonic acid is forced, under pressure, into a
saturated solution of ammonia and common salt, sodium bicarbonate is
precipitated, whilst ammonium chloride or "sal-ammoniac" remains
dissolved in the solution. The reaction was discovered in 1836 by a
Scotch chemist named John Thom, and small quantities of ammonia-soda
were made at that time by the firm of McNaughton & Thom. The successful
carrying out of the process on the large scale depends principally upon
the complete recovery of the expensive reagent, ammonia, and this
problem was only solved within comparatively recent years by Solvay. The
process has been perfected and worked with great success in England by
Messrs. Brunner, Mond, & Co., and has proved a successful rival to the
Leblanc process.
Alkali is also produced to some extent by electrolytic processes,
depending upon the splitting up of a solution of common salt into
caustic soda and chlorine by the use of an electric current.
LECTURE VI
BORIC ACID, BORAX, SOAP
_Boric Acid._--At ordinary temperatures and under ordinary conditions
boric acid is a very weak acid, but like silicic and some other acids,
its relative powers of affinity and combination become very much changed
at high temperatures; thus, fused and strongly heated boric acid can
decompose carbonates and even sulphates, and yet a current of so weak an
acid as hydrogen sulphide, passed through a strong solution of borax,
will decompose it and set free boric acid. Boric acid is obtained
chiefly from Italy. In a tract of country called the Maremma of Tuscany,
embracing an area of about forty square miles, are numerous chasms and
crevices, from which hot vapour and heated gases and springs of water
spurt. The steam issuing from these hot springs contains small
quantities of boric acid, that acid being one of those solid substances
distilling to some extent in a current of steam. The steam vapours thus
bursting forth, owing to some kind of constant volcanic disturbance, are
also more or less laden with sulphuretted hydrogen gas, communicating a
very ill odour to the neighbourhood. These phenomena were at first
looked upon by the people as the work of the devil, and priestly
exorcisms were in considerable request in the hope of quelling them,
very much as a great deal of the mere speech-making at the present time
in England on foreign competition and its evils, and the dulness of
trade, the artificial combinations to keep up prices, to reduce wages,
general lamentation, etc., are essayed in the attempt to charm away bad
trade. At length a kind of prophet arose of a very practical character
in the form of the late Count Lardarel, who, mindful of the fact that
the chemist Höffer, in the time of the Grand Duke Leopold I., had
discovered boric acid in the volcanic steam jets, looked hopefully
beyond the exorcisms of the priests and the superstitions of the people
to a possible blessing contained in what appeared to be an unholy
confusion of Nature. He constructed tanks of from 100 to 1000 ft. in
diameter and 7 to 20 ft. in depth, of such a kind that the steam jets
were surrounded by or contained in them, and thus the liquors formed by
condensation became more and more concentrated. These tanks were
arranged at different levels, so that the liquors could be run off from
one to the other, and finally to settling cisterns. Subsequently the
strong liquors were run to lead-lined, wooden vats, in which the boric
acid was crystallised out. Had the industry depended on the use of fuel
it could never have developed, but Count Lardarel ingeniously utilised
the heat of the steam for all the purposes, and neither coal nor wood
was required. Where would that Tuscan boric acid industry have been now
had merely the lamentations of landowners, fears of the people, and
exorcisms of the priests been continued? Instead of being the work of
the arch-enemy of mankind, was not it rather an incitement to a somewhat
high and difficult step in an upward direction towards the attainment,
on a higher platform of knowledge and skill, of a blessing for the whole
province of Tuscany? What was true in the history of that industry and
its development is every whit as true of the much-lamented slackening of
trade through foreign competition or other causes now in this country,
and coming home to yourselves in the hat-manufacturing industry. The
higher platform to which it was somewhat difficult to step up, but upon
which the battle must be fought and the victory won, was one of a higher
scientific and technological education and training. The chemist Höffer
made the discovery of boric acid in the vapours, they would no doubt
take note; but Höffer went no further; and it needed the man of both
educated and practical mind like Count Lardarel to turn the discovery to
account and extract the blessing. In like manner it was clear that in
our educational schemes for the benefit of the people, there must not
only be the scientific investigator of abstract truth, but also the
scientific technologist to point the way to the practical realisation of
tangible profit. Moreover, and a still more important truth, it is the
scientific education of the proprietors and heads we want--educated
capital rather than educated workmen.
_Borax._--A good deal of the Tuscan boric acid is used in France for the
manufacture of borax, which is a sodium salt of boric acid. Borax is
also manufactured from boronitrocalcite, a calcium salt of boric acid,
which is found in Chili and other parts of South America. The crude
boronitrocalcite or "tiza" is boiled with sodium carbonate solution,
and, after settling, the borax is obtained by crystallisation. Borax
itself is found in California and Nevada, U.S.A., and also in Peru,
Ceylon, China, Persia, and Thibet. The commercial product is obtained
from the native borax (known as "tincal") by dissolving in water and
allowing the solution to crystallise. The Peruvian borax sometimes
contains nitre. For testing the purity of refined borax the following
simple tests will usually suffice. A solution of the borax is made
containing 1 part of borax to 50 parts of water, and small portions of
the solution are tested as follows: _Heavy metals_ (_lead_, _copper_,
etc.).--On passing sulphuretted hydrogen into the solution, no
coloration or precipitate should be produced. _Calcium Salts._--The
solution should not give a precipitate with ammonium oxalate solution.
_Carbonates._--The solution should not effervesce on addition of nitric
or hydrochloric acid. _Chlorides._--No appreciable precipitate should
be produced on addition of silver nitrate solution and nitric acid.
_Sulphates._--No appreciable precipitate should be produced on adding
hydrochloric acid and barium chloride. _Iron._--50 c.c. of the solution
should not immediately be coloured blue by 0·5 c.c. of potassium
ferrocyanide solution.
_Soap._--Soap is a salt in the chemical sense, and this leads to a wider
definition of the term "salt" or "saline" compound. Fats and oils, from
which soaps are manufactured, are a kind of _quasi_ salts, composed of a
fatty acid and a chemical constant, if I may use the term, in the shape
of base, namely, glycerin. When these fats and oils, often called
glycerides, are heated with alkali, soda, a true salt of the fatty acid
and soda is formed, and this is the soap, whilst the glycerin remains
behind in the "spent soap lye." Now glycerin is soluble in water
containing dissolved salt (brine), whilst soap is insoluble, though
soluble in pure water. The mixture of soap and glycerin produced from
the fat and soda is therefore treated with brine, a process called
"cutting the soap." The soap separates out in the solid form as a curdy
mass, which can be easily separated. Certain soaps are able to absorb a
large quantity of water, and yet appear quite solid, and in purchasing
large quantities of soap it is necessary, therefore, to determine the
amount of water present. This can be easily done by weighing out ten or
twenty grams of the soap, cut in small pieces, into a porcelain dish and
heating over a gas flame, whilst keeping the soap continually stirred,
until a glass held over the dish no longer becomes blurred by escaping
steam. After cooling, the dry soap is weighed, and the loss of weight
represents the amount of moisture. I have known cases where soap
containing about 83 per cent. of water has been sold at the full market
price. Some soaps also contain more alkali than is actually combined
with the fatty acids of the soap, and that excess alkali is injurious in
washing silks and scouring wool, and is also not good for the skin. The
presence of this free or excess alkali can be at once detected by
rubbing a little phenolphthalein solution on to the freshly-cut surface
of a piece of soap; if free alkali be present, a red colour will be
produced.
LECTURE VII
SHELLAC, WOOD SPIRIT, AND THE STIFFENING AND PROOFING PROCESS
_Shellac._--The resin tribe, of which shellac is a member, comprises
vegetable products of a certain degree of similarity. They are mostly
solid, glassy-looking substances insoluble in water, but soluble in
alcohol and wood spirit. In many cases the alcoholic solutions show an
acid reaction. The resins are partly soluble in alkalis, with formation
of a kind of alkali salts which we may call resin-soaps.
Shellac is obtained from the resinous incrustation produced on the bark
of the twigs and branches of various tropical trees by the puncture of
the female "lac insect" (_Taccardia lacca_). The lac is removed from the
twigs by "beating" in water; the woody matter floats to the surface, and
the resin sinks to the bottom, and when removed forms what is known as
"seed-lac." Formerly, the solution, which contains the colouring matter
dissolved from the crude "stick-lac," was evaporated for recovery of the
so-called "lac-dye," but the latter is no longer used technically. The
seed-lac is bleached by boiling with sodium or potassium carbonate,
alum, or borax, and then, if it is not pale enough, is further bleached
by exposure to sunlight. It is now dried, melted, and mixed with a
certain proportion of rosin or of orpiment (a sulphide of arsenic)
according to the purpose for which it is desired. After further
operations of melting and straining, the lac is melted and spread into
thin sheets to form ordinary shellac, or is melted and dropped on to a
smooth surface to form "button-lac." Ordinary shellac almost invariably
contains some rosin, but good button-lac is free from this substance.
The presence of 5 per cent. of rosin in shellac can be detected by
dissolving in a little alcohol, pouring the solution into water, and
drying the fine impalpable powder which separates. This powder is
extracted with petroleum spirit, and the solution shaken with water
containing a trace of copper acetate. If rosin be present, the petroleum
spirit will be coloured emerald-green.
Borax, soda crystals, and ammonia are all used to dissolve shellac, and
it may be asked: Which of these is least injurious to wool? and why? How
is their action modified by the presence of dilute sulphuric acid in the
wool? I would say that soda crystals and ammonia are alkalis, and if
used strong, are sure to do a certain amount of injury to the fibre of
wool, and more if used hot than cold. Of the two, the ammonia will have
the least effect, especially if dilute, but borax is better than either.
The influence of a little sulphuric acid in the wool would be in the
direction of neutralising some of the ammonia or soda, and shellac, if
dissolved in the alkalis, would be to some extent precipitated on the
fibre, unless the alkali, soda or ammonia, were present in sufficient
excess to neutralise that sulphuric acid and to leave a sufficient
balance to keep the shellac in solution. Borax, which is a borate of
soda, would be so acted on by the sulphuric acid that some boric acid
would be set free, the sulphuric acid robbing some of that borax of its
soda. This boric acid would not be nearly so injurious to wool as
carbonate of soda or ammonia would.
The best solvent for shellac, however, in the preparation of the
stiffening and proofing mixture for hats, is probably wood spirit or
methylated spirit. A solution of shellac in wood spirit is indeed used
for the spirit-proofing of silk hats, and to some extent of felt hats,
and on the whole the best work, I believe, is done with it. Moreover,
borax is not a cheap agent, and being non-volatile it is all left behind
in the proofed material, whereas wood spirit or methylated spirit is a
volatile liquid, _i.e._ a liquid easily driven off in vapour, and after
application to the felt it may be almost all recovered again for re-use.
In this way I conceive the use of wood spirit would be both more
effective and also cheaper than that of borax, besides being most
suitable in the case of any kind of dyes and colours to be subsequently
applied to the hats.
_Wood Spirit._--Wood spirit, the pure form of which is methyl alcohol,
is one of the products of the destructive distillation of wood. The wood
is distilled in large iron retorts connected to apparatus for condensing
the distillation products. The heating is conducted slowly at first, so
that the maximum yield of the valuable products--wood acid (acetic acid)
and wood spirit--which distil at a low temperature, is obtained. When
the condensed products are allowed to settle, they separate into two
distinct layers, the lower one consisting of a thick, very dark tar,
whilst the upper one, much larger in quantity, is the crude wood acid
(containing also the wood spirit), and is reddish-yellow or
reddish-brown in colour. This crude wood acid is distilled, and the wood
spirit which distils off first is collected separately from the acetic
acid which afterwards comes over. The acid is used for the preparation
of alumina and iron mordants (see next lecture), or is neutralised with
lime, forming grey acetate of lime, from which, subsequently, pure
acetic acid or acetone is prepared. The crude wood spirit is mixed with
milk of lime, and after standing for several hours is distilled in a
rectifying still. The distillate is diluted with water, run off from any
oily impurities which are separated, and re-distilled once or twice
after treatment with quicklime.
_Stiffening and Proofing Process._--Before proceeding to discuss the
stiffening and proofing of hat forms or "bodies," it will be well to
point out that it was in thoroughly grasping the importance of a
rational and scientific method of carrying out this process that
Continental hat manufacturers had been able to steal a march upon their
English rivals in competition as to a special kind of hat which sold
well on the Continent. There are, or ought to be, three aims in the
process of proofing and stiffening, all the three being of equal
importance. These are: first, to waterproof the hat-forms; second, to
stiffen them at the same time and by the same process; and the third,
the one the importance of which I think English hat manufacturers have
frequently overlooked, at least in the past, is to so proof and stiffen
the hat-forms as to leave them in a suitable condition for the
subsequent dyeing process. In proofing the felt, the fibres become
varnished over with a kind of glaze which is insoluble in water, and
this varnish or proof is but imperfectly removed from the ends of the
fibres on the upper surface of the felt. The consequence is a too slight
penetration of the dyestuff into the inner pores of the fibres; indeed,
in the logwood black dyeing of such proofed felt a great deal of the
colour becomes precipitated on the outside of the fibres--a kind of
process of "smudging-on" of a black pigment taking place. The subsequent
"greening" of the black hats after a short period of wear is simply due
to the ease with which such badly fixed dye rubs off, washes off, or
wears off, the brownish or yellowish substratum which gradually comes to
light, causing a greenish shade to at length appear. If we examine under
the microscope a pure unproofed fur fibre, its characteristic structure
is quite visible. Examination of an unproofed fibre dyed with logwood
black shows again the same characteristic structure with the dye inside
the fibre, colouring it a beautiful bluish-grey tint, the inner cellular
markings being black. A proofed fur fibre, on the other hand, when
examined under the microscope, is seen to be covered with a kind of
translucent glaze, which completely envelops it, and prevents the
beautiful markings showing the scaly structure of the fibre from being
seen. Finally, if we examine microscopically a proofed fibre which has
been dyed, or which we have attempted to dye, with logwood black, we
find that the fibre presents an appearance similar to that of rope which
has been drawn through some black pigment or black mud, and then dried.
It is quite plain that no lustrous appearance or good "finish" can be
expected from such material. Now how did the Continental hat
manufacturers achieve their success, both as regards dyeing either with
logwood black or with coal-tar colours, and also getting a high degree
of "finish"? They attained their object by rubbing the proofing varnish
on the inside of the hat bodies, in some cases first protecting the
outside with a gum-varnish soluble in water but resisting the
lac-varnish rubbed inside. Thus the proofing could never reach the
outside. On throwing the hat bodies, thus proofed by a logical and
scientific process, into the dye-bath, the gums on the outer surface are
dissolved and removed, and the dye strikes into a pure, clean fibre,
capable of a high degree of finish. This process, however, whilst very
good for the softer hats used on the Continent, is not so satisfactory
for the harder, stiffer headgear demanded in Great Britain. What was
needed was a process which would allow of a through-and-through proofing
and stiffening, and also of satisfactory dyeing of the stiffened and
proofed felt. This was accomplished by a process patented in 1887 by Mr.
F.W. Cheetham, and called the "veneering" process. The hat bodies,
proofed as hard as usual, are thrown into a "bumping machine" containing
hot water rendered faintly acid with sulphuric acid, and mixed with
short-staple fur or wool, usually of a finer quality than that of which
the hat bodies are composed. The hot acid water promotes in a high
degree the felting powers of the short-staple wool or fur, and, to a
lesser extent, the thinly proofed ends of the fibres projecting from
the surfaces of the proofed hat-forms. Thus the short-staple wool or fur
felts itself on to the fibres already forming part of the hat bodies,
and a new layer of pure, unproofed wool or fur is gradually wrought on
to the proofed surface. The hat-forms are then taken out and washed, and
can be dyed with the greatest ease and with excellent results, as will
be seen from the accompanying illustration (see Fig. 15). This
successful invention emphasises the value of the microscope in the
study of processes connected with textile fibres. I would strongly
advise everyone interested in hat manufacturing or similar industries to
make a collection of wool and fur fibres, and mount them on microscope
slides so as to form a kind of index collection for reference.
[Illustration: FIG. 15.
1. Natural wool fibre unproofed.
2. Wool fibre showing proof on surface, filling up the cells
and rendering the same dye-proof.
3. Fur fibre from surface of veneered felt, showing dye
deposited in cells and on the surface, bright and lustrous.
4. Wool fibre as in No. 2, with dye deposited on surface of
proof.
5. Section of proofed and veneered body, showing unproofed
surface.
6. Section of proofed body without "veneer."]
LECTURE VIII
MORDANTS: THEIR NATURE AND USE
The name or word "mordant" indicates the empiricism, or our old friend
"the rule of thumb," of the age in which it was first created and used.
It serves as a landmark of that age, which, by the way, needed
landmarks, for it was an age of something between scientific twilight
and absolute darkness. _Morder_ in French, derived from the Latin
_mordere_, means "to bite," and formerly the users of mordants in dyeing
and printing believed their action to be merely a mechanical action,
that is, that they exerted a biting or corroding influence, serving to
open the pores of the fabrics, and thus to give more ready ingress to
the colour or dye.