3. A varnish made by dissolving caoutchouc in rectified petroleum or
naphtha, applied between two surfaces of cloth, as described under
Macintosh’s patent. See CAOUTCHOUC.
4. Vegetable or mineral pitch, applied hot with a brush, as in making
tarpauling for covering goods in ships.
5. A solution of soap worked into cloth, and decomposed in it by the
action of a solution of alum; whence results a mixture of acid fats and
alumina, which insinuates itself among all the woolly filaments, fills
their interstices, and prevents the passage of water.
6. A solution of glue or isinglass, introduced into a stuff, and then
acted upon by a clear infusion of galls, whereby the fibres get
impregnated with an insoluble, impermeable, pulverulent leather.
7. Plaster work is rendered impermeable by mixing artificial or natural
asphaltum with it.
JEWELLERY, _Art of_. See GEM and LAPIDARY.
INCOMBUSTIBLE CLOTH; is a tissue of the fibrous mineral called amianthus
or asbestos. This is too rare to form the object of any considerable
manufacture. Cotton and linen cloth may be best rendered incapable of
taking fire, or burning with flame, by being imbued with a solution of
sal ammoniac.
INCUBATION, ARTIFICIAL. The Egyptians have from time immemorial been
accustomed to hatch eggs by artificial warmth, without the aid of hens,
in peculiar stoves, called _Mammals_. The inhabitants of the village
Bermé, still travel through the most distant provinces of Egypt at
certain seasons of the year, with a portable furnace, heated by a lamp,
and either hatch chickens for sale, or undertake to hatch the eggs
belonging to the natives at a certain rate per dozen. M. de Reaumur
published in France about a century ago, some ingenious observations
upon this subject; but M. Bonnemain was the first person who studied
with due attention all the circumstances of artificial incubation, and
mounted the process successfully upon the commercial scale. So far back
as 1777 he communicated to the Academy of Sciences an interesting fact,
which he had noticed, upon the mechanism employed by chicks to break
their shells; and for some time prior to the French revolution he
furnished the Parisian market with excellent poultry at a period of the
year when the farmers had ceased to supply it. His establishment was
ruined at that disastrous era, and no other has ever since been
constructed or conducted with similar care. As there can be no doubt
however of the practicability and profitableness of the scheme, when
judiciously managed, I shall insert a brief account of his ingenious
arrangements. I had the pleasure of making the acquaintance of this
amiable old man at my first visit to Paris, many years ago, and believe
all his statements to be worthy of credit. Some imitations of his plans
have been made in this country, but how far they have succeeded in an
economical point of view, it is difficult to determine. His apparatus
derives peculiar interest from the fact, that it was founded upon the
principle of the circulation of hot water, by the intestine motions of
its particles, in a returning series of connected pipes; a subject
afterwards illustrated in the experimental researches of Count Rumford.
It has of late years been introduced as a _novelty_ into this country,
and applied to warm the apartments of many public and private buildings.
The following details will prove that the theory and practice of
hot-water circulation were as perfectly understood by M. Bonnemain fifty
years ago, as they are by any of our stove-doctors at the present day.
They were then publicly exhibited at his residence in Paris, and were
afterwards communicated to the world at large in the interesting article
of the _Dictionnaire Technologique_, intitled _Incubation Artificielle_.
The apparatus of M. Bonnemain consisted: 1. of a boiler and pipes for
the circulation of water; 2. of a regulator calculated to maintain an
equable temperature; 3. of a stove-apartment, heated constantly to the
degree best fitted for incubation, which he called the _hatching_ pitch.
He attached to one side a _poussinière_ or chick-room, for cherishing
the chickens during a few days after incubation.
[Illustration: 576 577]
The boiler is represented in vertical section and ground plan, in
_figs._ 576. and 577. It is composed of a double cylinder of copper or
cast-iron _l_, _l_, having a grate _b_ (see plan), an ashpit at _d_
(section). The water occupies the shaded space C, C. _h_, _g_, _g_, _e_,
_e_, are five vertical flues, for conducting the burnt air and smoke,
which first rise in the two exterior flues _e_, _e_, then descend in the
two adjoining flues _g_, _g_, and finally re-mount through the passages
_i_, _i_, in the central flue _h_. During this upwards and downwards
circulation, as shown by the arrows in the section, the products of
combustion are made to impart nearly the whole of their heat to the
water by which they are surrounded. At the commencement, some burning
paper or wood shavings are inserted at the orifice _m_, to establish a
draught in this circuitous chimney. The air is admitted into the ash-pit
at the side, in regulated quantities, through a small square door,
movable round a rod which runs horizontally along its middle line. This
swing valve is acted upon by an expanding bar (see HEAT-REGULATOR),
which opens it more or less, according to the temperature of the stove
apartment in which the eggs are placed.
[Illustration: 578]
D is the upper orifice of the boiler, by which the hotter and
consequently lighter particles of the water continually ascend, and are
replaced by the cooled particles, which enter the boiler near its
bottom, as shown in _fig._ 578. at R. Into further details relative to
the boiler it is needless to enter; for though its form, as designed by
M. Bonnemain, is excellent and most economical of heat for a charcoal
fire, it would not suit one of pit-coal, on account of the obstruction
to the pipes which would soon be occasioned by its soot.
In _fig._ 578. the boiler is shown at R, with the rod which regulates
the air door of the ash-pit. D is a stopcock for modifying the opening
by which the hotter particles of water ascend; G is the water-pipe of
communication, having the heating pipe of distribution attached between
E F, which thence passes backwards and forwards with a very slight slope
from the horizontal direction, till it reaches the _poussinière_ O P Q.
It traverses this apartment, and returns by N N to the orifice of the
boiler H, where it turns vertically downwards, and descends to nearly
the bottom of the boiler, discharging at that point the cooled and
therefore denser particles of water to replace those which continually
issue upwards at D. L R is a tube surmounted with a funnel for keeping
the range of pipes always full of water; and K is a syphon orifice for
permitting the escape of the disengaged air, which would otherwise be
apt to occupy partially the pipes and obstruct the aqueous circulation.
The faster the water gets cooled in the serpentine tubes, the quicker
its circulation will be, because the difference of density between the
water at the top and bottom of the boiler, which is the sole cause of
its movement, will be greater. N represents small saucers filled with
water, to supply the requisite moisture to the heated air, and to place
the eggs, arranged along the trays M M, in an atmosphere analogous to
that under the body of the hen.
When we wish to hatch eggs with this apparatus, the fire is to be
kindled in the boiler, and as soon as the temperature has risen to about
100° F., the eggs are introduced; but only one-twentieth of the whole
number intended, upon the first day; next day, a like number is laid
upon the trays, and thus in succession for twenty days, so that upon the
twenty-first day the eggs first placed may be hatched for the most part,
and we may obtain daily afterwards an equal number of chicks. In this
way, regularity of care is established in the rearing of them.
During the first days of incubation, natural as well as artificial, a
small portion of the water contained in the egg evaporates by the heat,
through the shell, and is replaced by a like quantity of air, which is
afterwards useful for the respiration of the animal. If the warm
atmosphere surrounding the eggs were very dry, such a portion of the
aqueous part of the eggs would evaporate through the pores of the
shells, as would endanger the future life of the chick _in ovo_. The
transpiration from the body of the hen, as she sits upon her eggs,
counteracts this desiccation in general; yet in very dry weather, many
hatching eggs fail from that cause, unless they be placed in moist
decomposing straw. The water saucers N N are therefore essential to
success in artificial incubation.
After the chickens are hatched they are transferred into the nursery, O
Q, on the front side of which there is a small grated trough filled with
millet seed. Small divisions are made between the broods of successive
days, to enable the superintendent to vary their feeding to their age.
In order to supply an establishment of the common kind, where 100 eggs
are to be hatched daily, a dozen of hens would be needed, and 150 eggs
must be placed under them, as only two-thirds in general succeed. At
this rate, 4300 mothers would be required to sit. Now supposing we
should collect ten times as many hens, or 43,000, we should not be able
to command the above number of chickens, as there is seldom a tenth part
of hens in a brooding state. Besides, there would be in this case no
fewer than 720 hens every day coming out with a fresh brood of chickens,
which would require a regiment of superintendents.
_Artificial Incubation, by means of Hot Mineral Waters._--This curious
process is described very briefly in a letter by M. D’Arcet. The
following are extracts from this letter:--
“In June, 1825, I obtained chickens and pigeons at Vichy, by artificial
incubation, effected through the means of the thermal waters of that
place. In 1827 I went to the baths of Chaudes-Aigues, principally for
the purpose of doing the same thing there. Finding the proprietor a
zealous man, I succeeded in making a useful application of this source
of heat to the production of poultry.
“The advantage of this process may be comprehended, when it is known
that the invalids who arrive at Vichy, for instance in the month of May,
find chickens only the size of quails; whereas, by this means, they may
be readily supplied six months old.
“The good which may be done by establishing artificial incubation in
places where hot springs exist, is _incalculable_; it may be introduced
into these establishments without at all interfering with the medical
treatment of patients, since the hatching would go on in winter, at a
time when the baths for other purposes are out of use.
“There is no other trouble required in breeding chickens, by means of
hot baths, than to break the eggs at the proper time; for, when the
apartments are closed, the whole of the interior will readily acquire a
sufficiently elevated and very constant temperature.”
In addition to these details by M. D’Arcet, a letter was received from
M. Felgeris, the proprietor of the baths at Chaudes-Aigues (Cantal), in
which he describes the success he had in following M. D’Arcet’s process.
This consists in putting the eggs into a small basket, suspending it in
one of the stove-rooms heated by the hot mineral water, and turning
round the eggs every day. The very first trial was attended with
success, and no failure was experienced in four repetitions of it.
INDIGO. This invaluable blue dye-stuff, for which no tolerable
substitute has been found, was known to the ancients as a pigment under
the name of _indicum_, whence its present denomination. In modern
Europe, it first came into extensive use in Italy, but, about the middle
of the 16th century, the Dutch began to import and employ it in
considerable quantities. Its general introduction into the dye-houses of
both England and France was kept back by absurd laws, founded upon an
opinion that it was a fugitive substance, and even prejudicial to the
fibre of wool. See DYEING, p. 413.
The plants which afford this dye-drug grow in the East and West Indies,
in the middle regions of America, in Africa, and Europe. They are all
species of the genera _Indigofera_, _Isatis_, and _Nerium_.
The following are cultivated:--_Indigofera tinctoria_ affords in Bengal,
Malabar, Madagascar, the Isle of France, and St. Domingo, an article of
middling quality, but in large quantity. The _indigofera disperma_, a
plant cultivated in the East Indies and America, grows higher than the
preceding, is woody, and furnishes a superior dye-stuff. The Guatimala
indigo comes from this species. _Indigofera Anil_ grows in the same
countries, and also in the West Indies. The _Indigofera Argentea_, which
grows also in Africa; it yields little indigo, but of an excellent
quality. _Indigofera Pseudotinctoria_, which is cultivated in the East
Indies, furnishes the best of all: the _Indigofera Glauca_ is the
Egyptian and Arabian species. There are also the _cærulea_, _cinerea
erecta_, _hirsuta_, _glabra_, and several others. The _Nerium
tinctorium_ of the East Indies affords some indigo; as does the _Isatis
tinctoria_, or Woad, in Europe; and the _Polygonum tinctorium_.
The districts of Kishenagar, Jessore, and Moorshedabad, in Bengal,
ranging from 88° to 90° E.L. and 22-1/2° to 24° N.L., produce the finest
indigo. That from the districts about Burdwan and Benares is of a
coarser or harsher grain. Tyroot, in lat. 26°, yields a tolerably good
article. The portion of Bengal most propitious to the cultivation of
indigo lies between the river Hoogly and the main stream of the Ganges.
In the East Indies, after having ploughed the ground in October,
November, and the beginning of December, they sow the seed of the indigo
plant in the last half of March and the beginning of April, while the
soil being neither too hot nor too dry, is most propitious to its
germination. A light mould answers best; and sunshine, with occasional
light showers, are most favourable to its growth. Twelve pounds of seeds
are sufficient for sowing an acre of land. The plants grow rapidly, and
will bear to be cut for the first time at the beginning of July, nay, in
some districts, so early as the middle of June. The indications of
maturity are the bursting forth of the flower buds, and the expansion of
the blossoms; at which period the plant abounds most in the dyeing
principle. Another indication is taken from the leaves; which, if they
break across, when doubled flat, denote a state of maturity. But this
character is somewhat fallacious, and depends upon the poverty or
richness of the soil. When much rain falls, the plants grow too rapidly,
and do not sufficiently elaborate the blue pigment. Bright sunshine is
most advantageous to its production.
The first cropping of the plants is the best; after two months a second
is made; after another interval, a third, and even a fourth; but each of
these is of diminished value. There are only two croppings in America.
Two methods are pursued to extract the indigo from the plant; the first
effects it by fermentation of the fresh leaves and stems; the second, by
maceration of the dried leaves; the latter process being most
advantageous.
1. _From the recent leaves._--In the indigo factories of Bengal, there
are two large stone-built cisterns, the bottom of the first being nearly
upon a level with the top of the second, in order to allow the liquid
contents to be run out of the one into the other. The uppermost is
called the fermenting vat, or the steeper; its area is 20 feet square,
and its depth 3 feet; the lowermost, called the beater or beating vat,
is as broad as the other, but one third longer. The cuttings of the
plant, as they come from the field, are stratified in the steeper, till
this be filled within 5 or 6 inches of its brim. In order that the
plant, during its fermentation, may not swell and rise out of the vat,
beams of wood and twigs of bamboo are braced tight over the surface of
the plants, after which water is pumped upon them till it stands within
three or four inches of the edge of the vessel. An active fermentation
speedily commences, which is completed within 14 or 15 hours; a little
longer or shorter, according to the temperature of the air, the
prevailing winds, the quality of the water, and the ripeness of the
plants. Nine or ten hours after the immersion of the plant, the
condition of the vat must be examined; frothy bubbles appear, which rise
like little pyramids, are at first of a white colour, but soon become
gray-blue; and then deep purple-red. The fermentation is at this time
violent, the fluid is in constant commotion, apparently boiling,
innumerable bubbles mount to the surface, and a copper-coloured dense
scum covers the whole. As long as the liquor is agitated, the
fermentation must not be disturbed; but when it becomes more tranquil,
the liquor is to be drawn off into the lower cistern. It is of the
utmost consequence not to push the fermentation too far, because the
quality of the whole indigo is deteriorated; but rather to cut it short,
in which case there is, indeed, a loss of weight, but the article is
better. The liquor possesses now a glistening yellow colour, which, when
the indigo precipitates, changes to green. The average temperature of
the liquor is commonly 85° Fahr.; its specific gravity at the surface is
1·0015; and at the bottom 1·003.
As soon as the liquor has been run into the lower cistern, ten men are
set to work to beat it with oars, or shovels 4 feet long, called
_busquets_. Paddle wheels have also been employed for the same purpose.
Meanwhile two other labourers clear away the compressing beams and
bamboos from the surface of the upper vat, remove the exhausted plant,
set it to dry for fuel, clean out the vessel, and stratify fresh plants
in it. The fermented plant appears still green, but it has lost three
fourths of its bulk in the process, or from 12 to 14 per cent. of its
weight, chiefly water and extractive matter.
The liquor in the lower vat must be strongly beaten for an hour and a
half, when the indigo begins to agglomerate in flocks, and to
precipitate. This is the moment for judging whether there has been any
error committed in the fermentation; which must be corrected by the
operation of beating. If the fermentation has been defective, much froth
rises in the beating, which must be allayed with a little oil, and then
a reddish tinge appears. If large round granulations are formed, the
beating is continued, in order to see if they will grow smaller. If they
become as small as fine sand, and if the water clears up, the indigo is
allowed quietly to subside. Should the vat have been over fermented, a
thick fat-looking crust covers the liquor, which does not disappear by
the introduction of a flask of oil. In such a case the beating must be
moderated. Whenever the granulations become round, and begin to subside,
and the liquor clears up, the beating must be discontinued. The froth or
scum diffuses itself spontaneously into separate minute particles, that
move about the surface of the liquor; which are marks of an excessive
fermentation. On the other hand, a rightly fermented vat is easy to
work; the froth, though abundant, vanishes whenever the granulations
make their appearance. The colour of the liquor, when drawn out of the
steeper into the beater, is bright green; but as soon as the
agglomerations of the indigo commence, it assumes the colour of Madeira
wine; and speedily afterwards, in the course of beating, a small round
grain is formed, which, on separating, makes the water transparent, and
falls down, when all the turbidity and froth vanish.
The object of the beating is threefold: first, it tends to disengage a
great quantity of carbonic acid present in the fermented liquor;
secondly, to give the newly developed indigo its requisite dose of
oxygen by the most extensive exposure of its particles to the
atmosphere; thirdly, to agglomerate the indigo in distinct flocks or
granulations. In order to hasten the precipitation, lime-water is
occasionally added to the fermented liquor in the progress of beating,
but it is not indispensable, and has been supposed capable of
deteriorating the indigo. In the front of the beater a beam is fixed
upright, in which three or more holes are pierced a few inches in
diameter. These are closed with plugs during the beating, but, two or
three hours after it, as the indigo subsides, the upper plug is
withdrawn to run off the supernatant liquor, and then the lower plugs in
succession. The state of this liquor being examined, affords an
indication of the success of both the processes. When the whole liquor
is run off, a labourer enters the vat, sweeps all the precipitate into
one corner, and empties the thinner part into a spout which leads into a
cistern, alongside of a boiler, 20 feet long, 3 feet wide and 3 deep.
When all this liquor is once collected, it is pumped through a bag for
retaining the impurities, into the boiler, and heated to ebullition. The
froth soon subsides, and shows an oily looking film upon the liquor. The
indigo is by this process not only freed from the yellow extractive
matter, but is enriched in the intensity of its colour, and increased in
weight. From the boiler the mixture is run, after two or three hours,
into a general receiver called the _dripping vat_, or table, which, for
a factory of twelve pairs of preparation vats, is 20 feet long, 10 feet
wide, and 3 feet deep; having a false bottom, 2 feet under the top edge.
This cistern stands in a basin of masonry (made water tight with Chunam
hydraulic cement), the bottom of which slopes to one end, in order to
facilitate the drainage. A thick woollen web is stretched along the
bottom of the inner vessel, to act as a filter. As long as the liquor
passes through turbid, it is pumped back into the receiver. Whenever it
runs clear, the receiver is covered with another piece of cloth to
exclude the dust, and allowed to drain at its leisure. Next morning the
drained magma is put into a strong bag, and squeezed in a press. The
indigo is then carefully taken out of the bag, and cut with a brass wire
into bits, about 3 inches cube, which are dried, in an airy house, upon
shelves of wicker work. During the drying, a whitish efflorescence comes
upon the pieces, which must be carefully removed with a brush. In some
places, particularly on the coast of Coromandel, the dried indigo lumps
are allowed to effloresce in a cask for some time, and when they become
hard they are wiped and packed for exportation.
From some experiments it would appear that the gas disengaged during the
middle period of the fermentation is composed in 100 parts of 27·5
carbonic acid, 5·8 oxygen, and 66·7 azote; and towards its end, of 40·5
carbonic acid, 4·5 oxygen, and 55·0 azote. The fermenting leaves
apparently convert the oxygen of the atmosphere into carbonic acid gas,
and leave its azote; besides the quantity of carbonic acid which they
spontaneously evolve. Carburetted hydrogen does not seem to be
disengaged. That the liquor in the beating vat absorbs oxygen from the
air in proportion as the indigo becomes flocculent and granular, has
been ascertained by experiment, as well as that sunshine accelerates the
separation of the indigo blue. Out of 1000 parts of the fermented liquor
of specific gravity 1·003, the blue precipitate may constitute 0·75 of a
part. Such a proportion upon the great scale is however above the
average, which is not more than 0·5. When lime water is added, an
extractive matter is thrown down, which amounts to from 20 to 47 parts
in 1000 of the liquor. It has a dark brown tint, a viscid appearance, an
unpleasant smell, and a bitter taste. It becomes moist in damp air, and
dissolves in water without decomposition. It is precipitated by lime,
alkalis, infusion of galls, and acetate of lead. All indigo contains a
little lime derived from the plant, even though none has been used in
its preparation.
2. _Indigo from dried leaves._--The ripe plant being cropped, is to be
dried in sunshine from 9 o’clock in the morning till 4 in the afternoon,
during two days, and threshed to separate the stems from the leaves,
which are then stored up in magazines till a sufficient quantity be
collected for manufacturing operations. The newly dried leaves must be
free from spots, and friable between the fingers. When kept dry, the
leaves undergo in the course of 4 weeks, a material change, their
beautiful green tint turning into a pale blue-gray, previous to which
the leaves afford no indigo by maceration in water, but subsequently a
large quantity. Afterwards the product becomes less considerable.
The following process is pursued to extract indigo from the dried
leaves. They are infused in the steeping vat with six times their bulk
of water, and allowed to macerate for two hours with continual stirring
till all the floating leaves sink. The fine green liquor is then drawn
off into the beater vat, for if it stood longer in the steeper, some of
the indigo would settle among the leaves and be lost. Hot water, as
employed by some manufacturers, is not necessary. The process with dry
leaves possesses this advantage, that a provision of the plant may be
made at the most suitable times, independently of the vicissitudes of
the weather, and the indigo may be uniformly made; and moreover, that
the fermentation of the fresh leaves, often capricious in its course, is
superseded by a much shorter period of simple maceration.
The process for obtaining indigo from the _Nerium_ is altogether the
same, but hot water has been generally applied to the dried leaves. For
woad, hot water must be employed, and also lime water as a precipitant,
on account of the small proportion of indigo in the plant. Dilute
muriatic acid is digested upon the woad indigo to remove the lime,
without which no dye could be precipitated. According to the warmth of
the summer and the ripeness of the plant, from 2 to 5 ounces of indigo
may be obtained from 100 pounds of the dried woad, or upon an average 4
ounces to the hundred weight.
The indigo found in European commerce is imported from Bengal,
Coromandel, Madras, the Mauritius, Manilla, and Java in the Eastern
hemisphere; from Senegal, Caraccas, Guatimala, Brazil, (South Carolina
and Louisiana in small quantity), and formerly from the West India
islands, especially St. Domingo. Its quality depends upon the species of
the plant, its ripeness, the soil and climate of its growth, and mode of
manufacture. The East Indian and Brazilian indigo comes packed in
chests, the Guatimala in ox-hides, called _surons_.
The organ which affords the indigo is confined entirely to the pellicle
of the leaves, and exists in largest quantity at the commencement of
maturation while the plant is in flower. The indigofera is remarkable
for giving a blue tinge to the urine of cows that feed upon its leaves.
According to some manufacturers, the plants should be cut down in dry
weather, an hour or two before sunset, carried off the field in bundles,
and immediately spread upon a dry floor. Next morning the reaping is
resumed for an hour and a half, before the sun acts too powerfully upon
vegetation; and the plants are treated in the same way. Both cuttings
become sufficiently dry by three o’clock in the afternoon, so as to
permit the leaves to be separated from the stems by threshing. They are
now thoroughly dried in the sunshine, then coarsely bruised, or
sometimes ground to powder in a mill, and packed up for the operations
of manufacture.
In the spring of 1830 I subjected a variety of specimens of indigo to
comparative analyses, by dissolving a few grains of each in strong
sulphuric acid, diluting the solutions with an equal volume of water,
and determining the resulting shade of colour in a hollow prism of plate
glass, furnished with a graduated scale. The following are the results,
compared to the shade produced by a like weight of absolute indigo.