+--------------------------------+-------+-------+
| |Bombay.|Bengal.|
+--------------------------------+-------+-------+
|Tannin | 54·5 | 48·5 |
|Extractive | 34·0 | 36·5 |
|Mucilage | 6·5 | 8 |
|Insoluble matters, sand and lime| 5 | 7 |
| +-------+-------+
| | 100·0 | 100·0 |
+--------------------------------+-------+-------+
Areka nuts are also found to yield catechu; for which purpose they are
cut into pieces watered in an earthen pot with solution of nitre, and
have a little of the bark of a species of mimosa added to them. The
liquor is then boiled with the nuts, and affords an inspissated
decoction.
Good catechu is a brittle, compact solid, of a dull fracture. It has no
smell, but a very astringent taste. Water dissolves the whole of it,
except the earthy matter, which is probably added during its
preparation. Alcohol dissolves its tannin and extractive. The latter may
be oxidized, and thus rendered insoluble in alcohol, by dissolving the
catechu in water, exposing it for some time to a boiling heat, and
evaporating to dryness.
The tannin of catechu differs from that of galls, in being soluble in
alcohol, and more soluble in water. It precipitates iron of an olive
colour, and gelatine in a mass which gradually becomes brown.
It has been long employed in India for tanning skins, where it is said
to effect this object in five days. I have seen a piece of sole leather
completely tanned by it in this country in ten days, the ox-hide having
been made into a bag, with the hair outside, and kept filled with the
solution of catechu. In India it has also been used to give a brown dye
to cotton goods, and of late years it has been extensively introduced
into the calico print-works of Europe. The salts of copper with sal
ammoniac cause it to give a bronze colour, which is very fast; the
proto-muriate of tin, a brownish yellow; the per-chloride of tin, with
the addition of nitrate of copper, a deep bronze hue; acetate of alumina
alone, a reddish brown, and, with nitrate of copper, a reddish olive
gray; nitrate of iron, a dark brown gray. For dyeing a golden coffee
brown, it has entirely superseded madder; one pound of it being
equivalent to six pounds of this root.
A solution of one part of catechu in ten parts of water, which is
reddish brown, exhibits the following results with--
Acids A brightened shade.
Alkalis A darkened shade.
Proto-sulphate of iron Olive brown precipitate.
Per-sulphate of iron Olive green do.
Sulphate of copper Yellowish brown.
Alum A brightening of the liquor.
Per-nitrate of iron Olive green precipitate.
Nitrate of copper Yellowish brown do.
Nitrate of lead Salmon do.
Proto-nitrate of mercury Milk-coffee do.
Muriate of alumina Brown yellow.
Muriate of tin Do. do.
Per-chloride of tin Do. darker.
Corrosive sublimate Light chocolate do.
Acetate of alumina Brightening of the liquor.
Acetate of copper Copious brown precipitate.
Acetate of lead Salmon coloured do.
Bichromate of potash Copious brown do.
Pure tannin may be obtained from catechu, by treating it with sulphuric
acid and carbonate of lead; but this process has no manufacturing
application.
CATGUT, (_Corde à boyau_, Fr.; _Darmsaite_, Germ.) the name absurdly
enough given to cords made of the twisted intestines of the sheep. The
guts being taken while warm out of the body of the animal, are to be
cleared of feculent matter, freed from any adhering fat, and washed in a
tub of water. The small ends of all the intestines are next to be tied
together, and laid on the edge of the tub, while the body of them is
left to steep in some water, frequently changed, during two days, in
order to loosen the peritoneal and mucous membranes. The bundle of
intestines is then laid upon a sloping table which overhangs the tub,
and their surface is scraped with the back of a knife, to try if the
external membrane will come away freely in breadths of about half the
circumference. This substance is called by the French manufacturers
_filandre_, and the process _filer_. If we attempt to remove it by
beginning at the large end of the intestine, we shall not succeed. This
_filandre_ is employed as thread to sew intestines, and to make the
cords of rackets and battledores. The flayed guts are put again into
fresh water, and after steeping a night, are taken out and scraped clean
next day, on the wooden bench with the rounded back of a knife. This is
called _curing the gut_. The large ends are now cut off, and sold to the
pork-butchers. The intestines are again steeped for a night in fresh
water, and the following day in an alkaline lixivium made by adding 4
ounces of potash, and as much pearlash, to a pail of water containing
about 3 or 4 imperial gallons. This lye is poured in successive
quantities upon the intestines, and poured off again, after 2 or 3
hours, till they be purified. They are now drawn several times through
an open brass thimble, and pressed against it with the nail, in order to
smooth and equalize their surface. They are lastly sorted, according to
their sizes, to suit different purposes.
_Whip-cord_ is made from the above intestines, which are sewed together
endwise by the _filandre_, each junction being cut aslant, so as to make
it strong and smooth. The cord is put into the frame, and each end is
twisted separately; for whip-cord is seldom made out of two guts twisted
together. When twisted it is to be sulphured (see SULPHURING) once or
twice. It may also be dyed black with common ink, pink with red ink,
which the sulphurous acid changes to pink, and green with a green dye
which the colour dealers sell for the purpose. The guts take the dyes
readily. After being well smoothed, the cord is to be dried, and coiled
up for sale.
_Hatter’s cords for bowstrings._--The longest and largest intestines of
sheep, after being properly treated with the potash, are to be twisted
4, 6, 8, 10, or 12 together, according to the intended size of the cord,
which is usually made from 15 to 25 feet long. This cord must be free
from seams and knots. When half dry, it must be exposed twice to the
fumes of burning sulphur; and, after each operation, it is to be well
stretched and smoothed; it should be finally dried in a state of
tension.
_Clockmaker’s cord._--This cord should be extremely thin, and be
therefore made from very small intestines, or from intestines slit up
in their length by a knife fitted for the purpose; being a kind of
lancet surmounted with a ball of lead or wood. The wet gut is strained
over the ball which guides the knife, and the two sections fall down
into a vessel placed beneath. Each hand pulls a section. Clockmakers
also make use of stronger cords made of 2 or more guts twisted together.
_Fiddle and harp strings._--These require the greatest care and
dexterity on the part of the workmen. The treble strings are peculiarly
difficult to make, and are best made at Naples, probably because their
sheep, from their small size and leanness, afford the best raw material.
The first scraping of the guts intended for fiddle-strings must be very
carefully performed; and the alkaline lyes being clarified with a little
alum, are added, in a progressively stronger state from day to day,
during 4 or 5 days, till the guts be well bleached and swollen. They
must then be passed through the thimble, and again cleansed with the
lixivium; after which they are washed, spun, or twisted and sulphured
during two hours. They are finally polished by friction, and dried.
Sometimes they are sulphured twice or thrice before being dried, and are
polished between horse-hair cords.
It has been long a subject of complaint, as well as a serious
inconvenience to musicians, that catgut strings cannot be made in
England of the same goodness and strength as those imported from Italy.
These are made of the peritoneal covering of the intestines of the
sheep; and, in this country, they are manufactured at Whitechapel, and
probably elsewhere in considerable quantity; the consumption of them for
harps, as well as for the instruments of the violin family, being very
great. Their chief fault is weakness; whence it is difficult to bring
the smaller ones, required for the higher notes, to concert pitch;
maintaining at the same time, in their form and construction, that
tenuity or smallness of diameter, which is required to produce a
brilliant and clear tone.
The inconvenience arising from their breaking when in use, and the
expense in the case of harps, where so many are required, are such as to
render it highly desirable to improve a manufacture which, to many
individuals may, however, appear sufficiently contemptible.
It is well known to physiologists, that the membranes of lean animals
are far more tough than of those animals which are fat or in high
condition; and there is no reason to doubt that the superiority of the
Italian strings arises from the state of the sheep in that country. In
London, where no lean animals are slaughtered, and where, indeed, an
extravagant and useless degree of fattening, at least for the purpose of
food, is given to sheep in particular, it is easy to comprehend why
their membranes can never afford a material of the requisite tenacity.
It is less easy to suggest an adequate remedy; but a knowledge of the
general principle, should this notice meet the eyes of those interested
in the subject, may at least serve the purpose of diminishing the evil
and improving the manufacture, by inducing them to choose in the market
the offal of such carcases as appear least overburthened with fat. It is
probable that such a manufacture might be advantageously established in
those parts of the country where the fashion has not, as in London, led
to the use of meat so much overfed; and it is equally likely, that in
the choice of sheep for this purpose, advantage would arise from using
the Welch, the Highland, or the Southdown breeds, in preference to those
which, like the Lincoln, are prone to excessive accumulations of fat. It
is equally probable, that sheep dying of some of the diseases
accompanied by emaciation, would be peculiarly adapted to this purpose.
That these suggestions are not merely speculative is proved by comparing
the strength of the membranes in question, or that of the other
membranous parts, in the unfattened Highland sheep, with that of those
found in the London markets.
CATHARTINE. The name proposed by MM. Feneulle and Lassaigne for a
chemical principle, which they suppose to be the active constituent of
senna.
CAUSTIC. Any chemical substance corrosive of the skin and flesh; as
potash, called common caustic, and nitrate of silver, called lunar
caustic, by surgeons.
CAVIAR. The salted roe of certain species of fish, especially the
sturgeon. This product forms a considerable article of trade, being
exported annually from the town of Astrachan alone, upon the shores of
the Caspian sea, to the amount of several hundred tons. The Italians
first introduced it into Eastern Europe from Constantinople, under the
name of _caviale_. Russia has now monopolized this branch of commerce.
It is prepared in the following manner:--
The female sturgeon is gutted; the roe is separated from the other
parts, and cleaned by passing it through a very fine searce, by rubbing
it into a pulp between the hands: this is afterwards thrown into tubs,
with the addition of a considerable quantity of salt; the whole is then
well stirred, and set aside in a warm apartment. There is another sort
of caviar, the compressed, in which the roe, after having been cured in
strong brine, is dried in the sun, then put into a cask, and subjected
to strong pressure.
CAWK. The English miner’s name for sulphate of baryta, or heavy spar.
CEDRA, (_Cedrat_, Fr.) is the fruit of a species of orange, citron, or
lemon, a tree which bears the same name. Its peel is very thick, and
covered with an epidermis which encloses a very fragrant and highly
prized essential oil. The preserves flavoured with it are very
agreeable. The citrons are cut into quarters for the dry comfits, but
are put whole into the liquid ones. The liquorist-perfumer makes with
the peel of the _cedra_ an excellent _liqueur_; for which purpose, he
plucks them before they are quite ripe; grates down the peel into a
little brandy, or cuts them into slices, and infuses these in the
spirits. This infusion is distilled for making perfume; but the flavour
is better when the infusion itself is used. See ESSENCES, LIQUORIST,
PERFUMERY.
CELESTINE. Native sulphate of strontia, found abundantly near Bristol,
in the red marl formation. It is decomposed, by ignition with charcoal,
into sulphuret of strontia, which is converted into nitrate by
saturation with nitric acid, evaporation, and crystallization. This
nitrate is employed for the production of the red light in theatrical
fire-works.
CEMENTATION. A chemical process, which consists in imbedding a solid
body, in a pulverulent matter, and exposing both to ignition in an
earthen or metallic case. In this way, iron is cemented with charcoal to
form steel, and bottle glass with gypsum powder, or sand, to form
Reaumur’s porcelain.
CEMENTS. (_Ciments_, Fr.; _Cämente_, _Kitte_, Germ.) Substances capable
of taking the liquid form, and of being in that state applied between
the surfaces of two bodies, so as to unite them by solidifying. They may
be divided into two classes, those which are applied through the agency
of a liquid menstruum, such as water, alcohol, or oil, and those which
are applied by fusion with heat.
The _diamond_ cement for uniting broken pieces of china, glass, &c.
which is sold as a secret at an absurdly dear price, is composed of
isinglass soaked in water till it becomes soft, and then dissolved in
proof spirit, to which a little gum resin, ammoniac, or galbanum, and
resin mastic are added, each previously dissolved in a minimum of
alcohol. When to be applied, it must be gently heated to liquefy it; and
it should be kept for use in a well-corked phial. A glass stopper would
be apt to fix so as not to be removable. This is the cement employed by
the Armenian jewellers in Turkey for glueing the ornamental stones to
trinkets of various kinds. When well made it resists moisture.
Shell-lac dissolved in alcohol, or in a solution of borax, forms a
pretty good cement. White of egg alone, or mixed with finely sifted
quick lime, will answer for uniting objects which are not exposed to
moisture. The latter combination is very strong, and is much employed
for joining pieces of spar and marble ornaments. A similar composition
is used by copper-smiths to secure the edges and rivets of boilers; only
bullock’s blood is the albuminous matter used instead of white of egg.
Another cement in which an analogous substance, the curd or caseum of
milk is employed, is made by boiling slices of skim-milk cheeses into a
gluey consistence in a great quantity of water, and then incorporating
it with quicklime on a slab with a muller, or in a marble mortar. When
this compound is applied warm to broken edges of stoneware, it unites
them very firmly after it is cold.
A cement which gradually indurates to a stony consistence may be made by
mixing 20 parts of clean river sand, two of litharge, and one of
quicklime, into a thin putty with linseed oil. The quicklime may be
replaced with litharge. When this cement is applied to mend broken
pieces of stone, as steps of stairs, it acquires after some time a stony
hardness. A similar composition has been applied to coat over brick
walls, under the name of mastic.
The iron-rust cement is made of from 50 to 100 parts of iron borings,
pounded and sifted, mixed with one part of sal-ammoniac, and when it is
to be applied moistened with as much water as will give it a pasty
consistency. Formerly flowers of sulphur were used, and much more
sal-ammoniac in making this cement, but with decided disadvantage, as
the union is effected by the oxidizement, consequent expansion and
solidification of the iron powder, and any heterogeneous matter
obstructs the effect. The best proportion of sal-ammoniac is, I believe,
one per cent. of the iron borings. Another composition of the same kind
is made by mixing 4 parts of fine borings or filings of iron, 2 parts of
potter’s clay, and 1 part of pounded potsherds, and making them into a
paste with salt and water. When this cement is allowed to concrete
slowly on iron joints, it becomes very hard.
For making architectural ornaments in relief, a moulding composition is
formed of chalk, glue, and paper paste. Even statues have been made with
it, the paper aiding the cohesion of the mass.
Mastics of a resinous or bituminous nature which must be softened or
fused by heat are the following:--
Mr. S. Varley’s consists of sixteen parts of whiting sifted and
thoroughly dried by a red heat, adding when cold a melted mixture of 16
parts of black rosin and 1 of bees’-wax, and stirring well during the
cooling.
Mr. Singer’s electrical and chemical apparatus cement consists of 5 lbs.
of rosin, 1 of bees’-wax, 1 of red ochre, and two table-spoonsful of
Paris-plaster, all melted together. A cheaper one for cementing voltaic
plates into wooden troughs is made with 6 pounds of rosin, 1 pound of
red ochre, 1/2 of a pound of plaster of Paris, and 1/4 of a pound of
linseed oil. The ochre and the plaster of Paris should be calcined
beforehand, and added to the other ingredients in their melted state.
The thinner the stratum of cement that is interposed, the stronger
generally speaking is the junction.
Boiled linseed oil and red lead mixed together into a putty are often
used by coppersmiths and engineers, to secure joints. The washers of
leather or cloth are smeared with this mixture in a pasty state.
The resin mastic alone is sometimes used by jewellers to cement by heat
cameos of white enamel or coloured glass to a real stone, as a ground to
produce the appearance of an onyx. Mastic is likewise used to cement
false backs or doublets to stones to alter their hue.
Melted brimstone either alone, or mixed with rosin and brick dust, forms
a tolerably good and very cheap cement.
Plumber’s cement consists of black rosin one part, brick dust two parts,
well incorporated by a melting heat.
The cement of dihl for coating the fronts of buildings consists of
linseed oil, rendered dry by boiling with litharge, and mixed with
porcelain clay in fine powder, to give it the consistence of stiff
mortar. Pipe-clay would answer equally well if well dried, and any
colour might be given with ground bricks, or pottery. A little oil of
turpentine to thin this cement aids its cohesion upon stone, brick, or
wood. It has been applied to sheets of wire cloth, and in this state
laid upon terraces, in order to make them water tight; but it is little
less expensive than lead.
The bituminous or black cement for bottle corks consists of pitch
hardened by the addition of rosin and brick-dust.
In certain localities where a limestone impregnated with bitumen occurs,
it is dried, ground, sifted, and then mixed with about its own weight of
melted pitch, either mineral, vegetable, or that of coal tar. When this
mixture is getting semifluid, it may be moulded into large slabs or
tiles in wooden frames lined with sheet iron, previously smeared over
with common lime mortar, in order to prevent adhesion to the moulds,
which, being in movable pieces, are easily dismounted so as to turn out
the cake of artificial bituminous stone. This cement is manufactured
upon a great scale in many places, and used for making Italian terraces,
covering the floors of balconies, flat roofs, water reservoirs, water
conduits, &c. When laid down, the joints must be well run together with
hot irons. The floor of the terrace should be previously covered with a
layer of Paris plaster or common mortar, nearly an inch thick, with a
regular slope of one inch to the yard. Such bituminous cement weighs 144
pounds the cubic foot; or a foot of square surface, one inch thick,
weighs 12 pounds. Sometimes a second layer of these slabs or tiles is
applied over the first, with the precaution of making the seams or
joints of the upper correspond with the middle of the under ones.
Occasionally a bottom bed, of coarse cloth or gray paper, is applied.
The larger the slabs are made, as far as they can be conveniently
transported and laid down, so much the better. For _hydraulic_ cements,
see MORTAR.
CERASIN. The name given by Dr. John to those gums which swell, but do
not dissolve in water; such as gum tragacanth. It is synonymous with
BASSORINE, which see.
CERATE from _cera_, _wax_. An unguent, of rather a stiff consistence,
made of oil, or lard and wax, thickened occasionally with pulverulent
matters.
CERINE. A substance which forms from 70 to 80 per cent. of bees’-wax. It
may be obtained by digesting wax, for some time, in spirit of wine, at a
boiling temperature. The _myricine_ separates, while the _cerine_
remains dissolved, and may be obtained from the decanted liquor by
evaporation. Cerine is white, analogous to wax, fusible at 134° F.,
hardly acted upon by hot nitric acid, but is readily carbonized by hot
sulphuric acid. When treated with caustic alkaline lye, it is converted
into margaric acid and _ceraïne_.
CERIUM. A peculiar metal discovered in the rare mineral, called
_cerite_, found only in the copper mine of Bastnaes, near Riddarhytta,
in Sweden. Cerium, extracted from its chloride by potassium, appears as
a dark red or chocolate powder, which assumes a metallic lustre by
friction. It does not conduct electricity well, like other metals; it is
infusible; its specific gravity is unknown. It has been applied to no
use in the arts.
CERUSE. A name of white lead. See LEAD.
CETINE. The name given by Chevreul to spermaceti.
CHAINWORK is a peculiar style of textile fabric, to which hosiery and
tambouring belong. See HOSIERY.
CHALK. (_Craie_, Fr.; _Kreide_, Germ.) A friable carbonate of lime,
white, opaque, soft, dull, or without any appearance of polish in its
fracture. Its specific gravity varies from 2·4 to 2·6. It usually
contains a little silica, alumina, and oxide of iron. It may be purified
by trituration, and elutriation. The siliceous and ferruginous matters
subside first, and the finer chalky particles floating in the
supernatant liquid, may be decanted with it, and obtained by subsidence.
When thus purified, it is called _whitening_ and Spanish white, in
England; _schlemmkreide_, in Germany; _blanc de Troyes_, and _blanc de
Meudon_, in France. Pure chalk should dissolve readily in dilute
muriatic acid, and the solution should afford no precipitate with water
of ammonia.
CHALK--_Black_. A mineral, called also _drawing-slate_.
CHALK--_French_. _Steatite_, or soap stone; a soft magnesian mineral.
CHALK--_Red_. A clay coloured with the peroxide of iron, of which it
contains about 17 per cent.
CHARCOAL. The fixed residuum of vegetables exposed to ignition out of
contact of air. In the article CARBON, I have described the general
properties of charcoal and the simplest mode of making it. I shall here
detail the best systems of manufacturing this product upon the continent
of Europe.
[Illustration: 272 273 274]
To carbonize wood under a movable covering, the plan of _meiler_, or
heaps, is employed very much in Germany. The wood is arranged either in
horizontal layers, or in nearly vertical ones, with a slight slope, so
as to form conical rounded heaps of different sizes. The former are
called lying _meiler_, _fig._ 272.; the latter standing _meiler_,
_figs._ 273. and 274. Both are distributed in much the same way.
[Illustration: 275]
In districts where the wood can be transported into one place by means
of rivers, or mountain slides, a dry flat space must be pitched upon,
screened from storms and floods, which may be walled round, having a
slight declivity made in the ground, towards the centre. See _fig._ 275.
Into this space the tarry acid will partially fall, and may be conducted
outwards, through a covered gutter beneath, into a covered tank. The
mouth of the tank must be shut, during the coaking, with an iron or
stone slab, luted with clay. A square iron plate is placed over the
inner orifice of the gutter, to prevent it being choked with coal ashes.
_Fig._ 275. represents a walled _meiler_ station; _a_, the station; _b_,
the gutter; _c_, the tank, which is covered with the slab _d_; _e_, a
slab which serves to keep the gutter clear of coals. The cover of the
heaps is formed of earth, sand, ashes, or such other matter as may be
most readily found in the woods. They should be kindled in the centre.
From 6 days to 4 weeks may be required for charring a heap, according to
its size; hard wood requiring most time; and the slower the process, the
better and greater is the product, generally speaking.
[Illustration: 276 277]
Charring of wood in mounds (_Haufe_ or _liegende werke_) _figs._ 276.
and 277. differs from that in the _meiler_, because the wood in the
_haufe_ is successively charred, and the charcoal is raked out by little
and little. The product is said to be greater in this way, and also
better. Uncleft billets, 6 or 8 feet long, being laid over each other,
are covered with ashes, and then carbonized. The station is sometimes
horizontal, and sometimes made to slope. The length may be 24 feet, the
breadth 8 feet; and the wood is laid crosswise. Piles are set
perpendicularly to support the roof, made of boughs and leaves, covered
with ashes. Pipes are occasionally laid within the upper part of the
mounds, which serve to catch and carry off some of the liquid products
into proper tanks.
[Illustration: 278 279]
_Fig._ 278. is a vertical section, and _fig._ 279. a half bird’s-eye
view, and half cross section, at the height of the pit-bottom, of
Chabeaussière’s kiln for making wood charcoal. _a_ is the oven; _b_,
vertical air-pipes; _c c_, horizontal flues for admitting air to the
kiln; _d d_, small pits which communicate by short horizontal pipes _e
e_, with the vertical ones; _f_, the sole of the kiln, a circle of
brickwork, upon which the cover or hood _h_ reposes; _i_, a pipe which
leads to the cistern _k_; _l_, the pipe destined for carrying off the
gaseous matter; _m m_, holes in the iron cover or lid.
The distribution of the wood is like that in the horizontal _meilers_,
or heaps; it is kindled in the central vertical canal with burning fuel,
and the lid is covered with a few inches of earth. At the beginning of
the operation all the draught flues are left open, but they are
progressively closed, as occasion requires. In eight kilns of this kind,
500 _decasters_ of oak wood are carbonized, from which 16,000
hectolitres of charcoal are obtained, equal to 64,000 pounds French,
being about 25 per cent.; besides tar and 3000 velts of wood vinegar, of
from 2° to 3°. _Baumé_.
[Illustration: 280]
At Crouy upon the Ourcq, near Meaux, there is a well constructed kiln
for making turf-charcoal. It resembles most nearly a tar-kiln. In _fig._
280. _a_ is the cylindrical coaking place, whose surrounding walls are
heated by the flame which passes through the intermediate space _b_. The
place itself is divided by partitions of fire tiles into three stages,
through the apertures in which the flames of the fire _c c_, rise, and
heat the exterior of the coaking apartment. In order to confine the
heat, there is in the enclosing walls of the outer kiln a cylindrical
hollow space _d_, where the air is kept stagnant. Through the apertures
left in the upper end at _e_, the turf is introduced; they are then shut
with an iron plate _f_, which is covered with ashes or sand. The
fire-place opens above this aperture, and its outlet is provided with a
moveable iron cover _g_, in which there is a small hole for the issue of
the gases. The sole of the kiln consists of a cast iron slab _h_, which
may be raised by means of a hook _i_ upon it. This is drawn back after
the carbonization is completed, whereby the charcoal falls from the
coaking space into a subjacent vault. The volatile products are carried
off by the pipe _k_, and led into the condensing cistern; the gases
escaping to the fire-place where they are burned. The iron slab is
protected from the corrosion of the acid vapours by a layer of coal
ashes.
CHICA is a red colouring principle made use of in America by some Indian
tribes to stain their skins. It is extracted from the _bignonia chica_
by boiling its leaves in water, decanting the decoction, and allowing it
to settle and cool, when a red matter falls down, which is formed into
cakes and dried. This substance is not fusible, and, when burned,
diffuses the same odour as animal bodies do. It is insoluble in cold
water, very soluble in alcohol and ether, but, after the evaporation of
these liquids, it is recovered unchanged. Fats and unctuous oils both
dissolve it. It is soluble in carbonated and caustic alkaline lyes, from
which it is precipitated by the acids without alteration. An excess of
alkali, however, speedily decomposes it. Nitric acid transforms it into
oxalic acid, and a bitter matter. Chlorine makes it white.
The savages mix this pigment with the fat of the cayman or alligator,
and rub their skins with the mixture. It may probably be turned to
account in the arts of civilized nations.
CHIMNEY. (_Cheminée_, Fr.; _Schornstein_, Germ.) Chimney is a modern
invention for promoting the draught of fires and carrying off the smoke,
introduced into England so late as the age of Elizabeth, though it seems
to have been employed in Italy 100 years before. The Romans, with all
their luxurious refinements, must have had their epicurean cookery
placed in perpetual jeopardy from their kitchen fires, which, having no
vent by a vertical tunnel in the walls, discharged their smoke and
frequently their flames at the windows, to the no small alarm of their
neighbours, and annoyance of even the street passengers.
Chimneys in dwelling houses serve also the valuable purpose of promoting
salubrious circulation of air in the apartments, when not foolishly
sealed with anti-ventilating stove-chests.
The first person who sought to investigate the general principles of
chimney draughts, in subserviency to manufacturing establishments, was
the celebrated Montgolfier. As the ascent of heated air in a conduit
depends upon the diminution of its specific gravity, or, in other words,
upon the increase of its volume by the heat, the ascensional force may
be deduced from the difference between the density of the elastic fluid
in the interior of the chimney, and of the external air; that is,
between the different heights of the internal and external columns of
elastic fluid supposed to be reduced to the same density. In the latter
case, the velocity of the gaseous products of combustion in the interior
of the chimney is equal to that of a heavy body let fall from a height
equal to the difference in height of the two aerial columns.
To illustrate this position by an example, let us consider the simple
case of a chimney of ventilation for carrying off foul air from a
factory of any kind; and suppose that the tunnel of iron be incased
throughout with steam at 212 degrees Fahr. Suppose this tunnel to be 100
yards high, then the weight of the column of air in it will be to that
of a column of external air 100 yards high, assumed at 32° F. inversely
as its expansion by 180°; that is, as 1000 is to 1·375; or as 72·727 is
to 100. The column of external air at 32° being 100 yards, the internal
column will be represented by 72·727; and the difference = 27·27, will
be the amount of unbalanced weight or pressure, which is the effective
cause of the ventilation. Calculating the velocity of current due to
this difference of weight by the well-known formula for the fall of
heavy bodies, that is to say, multiplying the above difference, which is
27·27, by the constant factor 19·62, and extracting the square root of
the product; thus, √(19·62 × 27·27) = 23·13 will be the velocity in
yards per second, which, multiplied by 3, gives 69·39 feet. The quantity
of air which passes in a second is obtained of course by multiplying the
area or cross section of the tunnel by this velocity. If that section is
half a yard, that is = a quadrangle 2-1/4 feet by 2, we shall have 23·13
× 0·5 = 11·565 cubic yards, = 312-1/4 cubic feet.
The problem becomes a little more complicated in calculating the
velocity of air which has served for combustion, because it has changed
its nature, a variable proportion of its oxygen gas of specific gravity
1·111, being converted into carbonic acid gas of specific gravity 1·524.
The quantity of air passed through well-constructed furnaces may, in
general, be regarded as double of what is rigorously necessary for
combustion, and the proportion of carbonic acid generated, therefore,
not one half of what it would be were all the oxygen so combined. The
increase of weight in such burned air of the temperature of 212°, over
that of pure air equally heated, being taken into account in the
preceding calculation, will give us about 19 yards or 57 feet per second
for the velocity in a chimney 100 yards high incased in steam.
Such are the deductions of theory; but they differ considerably from
practical results, in consequence of the friction of the air upon the
sides of the chimneys, which varies likewise with its form, length, and
quality. The direction and force of the winds also exercise a variable
influence upon chimney furnaces differently situated. In chimnies made
of wrought iron, like those of steam boats, the refrigeration is
considerable, and causes a diminution of velocity far greater than what
occurs in a factory stalk of well-built brick work. In comparing the
numbers resulting from the trials made on chimneys of different
materials and of different forms, it has been concluded that the
obstruction to the draught of the air, or the deduction to be made from
the theoretical velocity of efflux, is directly proportional to the
length of the chimneys and to the square of the velocity, and inversely
to their diameter. With an ordinary wrought-iron pipe, of from 4 inches
to 5 inches diameter, attached to an ordinary stove, burning good
charcoal, the difference is prodigious between the velocity calculated
by the above theoretical rule, and that observed by means of a
stop-watch, and the ascent of a puff of smoke from a little tow, dipped
in oil of turpentine thrust quickly into the fire. The chimney being 45
feet high, the temperature of the atmosphere 68° Fahr., the velocity per
second was,--
Trials. By theory. By experiment. Mean temperature
of chimney.
1 26·4 feet 5 feet 190° Fahr.
2 29·4 5·76 214
3 34·5 6·3 270
To obtain congruity between calculation and experiment, several
circumstances must be introduced into our formulæ. In the first place,
the theoretical velocity must be multiplied by a factor, which is
different according as the chimney is made of bricks, pottery, sheet
iron, or cast iron. This factor must be multiplied by the square root of
the diameter of the chimney (supposed to be round), divided by its
length, increased by four times its diameter. Thus, for pottery, its
expression is 2·06√(D/(L + D)); D being the diameter, and L the length
of the chimney.
A pottery chimney, 33 feet high, and 7 inches in diameter, when the
excess of its mean temperature above that of the atmosphere was 205°
Fahr., had a pressure of hot air equal to 11·7 feet, and a velocity of
7·2 feet per second. By calculating from the last formula, the same
number very nearly is obtained. In none of the experiments did the
velocity exceed 12 feet per second, when the difference of temperature
was more than 410° Fahr.
Every different form of chimney would require a special set of
experiments to be made for determining the proper factor to be used.
This troublesome operation may be saved by the judicious application of
a delicate differential barometer, such as that invented by Dr.
Wollaston; though this instrument does not seem to have been applied by
its very ingenious author in measuring the draughts or ventilating
powers of furnaces.
If into one leg of this differential syphon, water be put, and fine
spermaceti oil into the other, we shall have two liquids, which are to
each other in density as the numbers 8 and 7. If proof spirit be
employed instead of water, we shall then have the relation of very
nearly 20 to 19. I have made experiments on furnace draughts with the
instrument in each of these states, and find the water and oil syphon to
be sufficiently sensible: for the weaker draughts of common fire-places
the spirits and oil will be preferable barometric fluids.
To the lateral projecting tube of the instrument, as described by Dr.
Wollaston, I found it necessary to attach a stop-cock, in order to cut
off the action of the chimney, while placing the syphon, to allow of its
being fixed in a proper state of adjustment, with its junction line of
the oil and water at the zero of the scale. Since a slight deviation of
the legs of the syphon from the perpendicular, changes very considerably
the line of the level, this adjustment should be made secure by fixing
the horizontal pipe tightly into a round hole, bored into the chimney
stalk, or drilled through the furnace door. On gently turning the
stop-cock, the difference of atmospherical pressure corresponding to the
chimney draught, will be immediately indicated by the ascent of the
junction-line of the liquids in the syphon. This modification of
apparatus permits the experiment to be readily rectified by again
shutting off the draught, when the air will slowly re-enter the syphon;
because the projecting tube of the barometer is thrust into the
stop-cock, but not hermetically joined; whereby its junction line is
allowed to return to the zero of the scale in the course of a few
seconds.
Out of many experiments made with this instrument, I shall content
myself with describing a few, very carefully performed at the breweries
of Messrs. Trueman, Hanbury, and Buxton, and of Sir H. Meux, Bart., and
at the machine factory of Messrs. Braithwaite; in the latter of which I
was assisted by Captain Ericsson. In the first trials at the breweries,
the end of the stop-cock attached to the differential barometer was
lapped round with hemp, and made fast into the circular peep-hole of the
furnace door of a wort copper, communicating with two upright parallel
chimneys, each 18 inches square, and 50 feet high. The fire was burning
with fully its average intensity at the time. The adjustment of the
level being perfect, the stop-cock orifice was opened, and the junction
level of the oil and water rose steadily, and stood at 1-1/4 inches,
corresponding to 1·25/8 = 0·156 of 1 inch of water, or a column of air
10·7 feet high. This difference of pressure indicates a velocity of 26
feet per second. In a second set of experiments, the extremity of the
stop-cock was inserted into a hole, bored through the chimney stalk of
the boiler of a Boulton and Watt steam-engine of twenty-horse power. The
area of this chimney was exactly 18 inches square at the level of the
bored hole, and its summit rose 50 feet above it. The fire-grate was
about 10 feet below that level. On opening the stop-cock, the junction
line rose 2-1/4 inches. This experiment was verified by repetition upon
different days, with fires burning at their average intensity, and
consuming fully 12 lbs. of the best coals hourly for each horse’s power,
or nearly one ton and a third in twelve hours. If we divide the number
2-1/4 by 8, the quotient 0·28 will represent the fractional part of 1
inch of water, supported in the syphon by the unbalanced pressure of the
atmosphere in the said chimney; which corresponds to 19-1/4 feet of air,
and indicates a velocity in the chimney current of 35 feet per second.
The consumption of fuel was much more considerable in the immense grate
under the wort copper, than it was under the steam-engine boiler.
In my experiments at Messrs. Braithwaite’s factory, the maximum
displacement of the junction line was 1 inch, when the differential oil
and water barometer was placed in direct communication with a chimney 15
inches square, belonging to a steam boiler, and when the fire was made
to burn so fiercely, that, on opening the safety-valve of the boiler,
the excess of steam beyond the consumption of the engine, rushed out
with such violence as to fill the whole premises. The pressure of
one-eighth of an inch of water denotes a velocity of draught of 23·4
feet per second.
In building chimneys, we should be careful to make their area rather too
large than too small; because we can readily reduce it to any desired
size, by means of a sliding register plate near its bottom, or a damper
plate applied to its top, adjustable by wires or chains, passing over
pulleys. Wide chimneys are not so liable as narrow ones to have their
draught affected by strong winds. In a factory, many furnace flues are
often conducted into one vertical chimney stalk, with great economy in
the first erection, and increased power of draught in the several fires.
Vast improvements have been made in this country, of late years, in
building stalks for steam boilers and chemical furnaces. Instead of
constructing an expensive, lofty scaffolding of timber round the
chimney, for the bricklayers to stand upon, and to place their
materials, pigeon-holes, or recesses, are left at regular intervals, a
few feet apart, within the chimney, for receiving the ends of stout
wooden bars, which are laid across, so as to form a species of temporary
ladder in the interior of the tunnel. By means of these bars, with the
aid of ropes and pulleys, every thing may be progressively hoisted, for
the building of the highest engine or other stalks. An expert
bricklayer, with a handy labourer, can in this way raise, in a few
weeks, a considerable chimney, 40 feet high, 5 feet 8 inches square
outside, 2 feet 8 inches inside at the base, 28 inches outside, and 20
inches inside at the top. To facilitate the erection, and at the same
time increase the solidity of an insulated stalk of this kind, it is
built with three or more successive plinths, or recedures, as shown in
_fig._ 281. It is necessary to make such chimneys thick and substantial
near the base, in order that they may sustain the first violence of the
fire, and prevent the sudden dissipation of the heat. When many flues
are conducted into one chimney stalk, the area of the latter should be
nearly equal to the sum of the areas of the former, or at least of as
many of them as shall be going simultaneously. When the products of
combustion from any furnace must be conducted downwards, in order to
enter near the bottom of the main stalk, they will not flow off until
the lowest part of the channel be heated by burning some wood shavings
or straw in it, whereby the air syphon is set agoing. Immediately after
kindling this transient fire at that spot, the orifice must be shut by
which it was introduced; otherwise the draught of the furnace would be
seriously impeded. But this precaution is seldom necessary in great
factories, where a certain degree of heat is always maintained in the
flues, or, at least, should be preserved, by shutting the damper plate
of each separate flue, whenever its own furnace ceases to act. Such
chimneys are finished at top with a coping of stone-slabs, to secure
their brickwork against the infiltration of rains, and they should be
furnished with metallic conducting rods, to protect them from explosions
of lightning.
When small domestic stoves are used, with very slow combustion, as has
been recently proposed, upon the score of a misjudged economy, there is
great danger of the inmates being suffocated or asphyxied, by the
regurgitation of the noxious burned air. The smoke doctors who recommend
such a vicious plan, from their ignorance of chemical science, are not
aware that the carbonic acid gas, of coke or coal, must be heated 250°
F. above the atmospheric air, to acquire the same low specific gravity
with it. In other words, unless so rarefied by heat, that gaseous poison
will descend through the orifice of the ash-pit, and be replaced by the
lighter air of the apartment. Drs. Priestley and Dalton have long ago
shown the co-existence of these two-fold crossing currents of air, even
through the substance of stone-ware tubes. True economy of heat, and
salubrity, alike require vivid combustion of the fuel, with a somewhat
brisk draught inside of the chimney, and a corresponding abstraction of
air from the apartment. Wholesome continuous ventilation, under the
ordinary circumstances of dwelling houses, cannot be secured in any
other way. Were these mephitic stoves, which have been of late so
ridiculously puffed in the public prints, generally introduced, the
faculty would need to be immediately quadrupled to supply the demand
for medical advice; for headaches, sickness, nervous ailments, and
apoplexy, would become the constant inmates of every inhabited mansion.
The phenomena of the grotto of Pausilippo might then be daily realised
at home, among those who ventured to recline upon sofas in such
carbonated apartments; only instead of a puppy being suffocated _pro
tempore_, human beings would be sacrificed, to save two-penny worth of
fuel _per diem_.
[Illustration: 281]
The figures upon the preceding page represent one of the two chimneys,
recently erected at the Camden Town station, for the steam boilers of
the two engines of 60 horse-power each, belonging to the London and
Birmingham Railway Company. These engines draw their train of carriages
up the inclined plane of Hampstead Hill. The chimneys were designed by
Robert Stephenson, Esq., engineer to the Company, executed by William
Cubitt, Esq., of Gray’s Inn Road,--and do equal honour to both
gentlemen, being probably the most elegant and substantial specimens of
this style of architecture in the world. In the section, _fig._ 281.,
A represents a bed of _concrete_, 6 feet thick, and 24 feet square.
B, brick footings set in cement; the lower course 19 feet square.
C, Bramley-fall stone base, with a chain of wrought iron let into it.
D, a portion, 15 feet high, curved to a radius of 113 feet, built
entirely of Malm paviours, (a peculiarly good kind of bricks.)
E, shaft built of Malm paviours in mortar.
F, ditto, built from the inside, without exterior scaffolding.
G, the cap ornamented, (as shown in the plan alongside,) with Portland
stone, the dressings being tied together with copper cramps and an iron
bond.
[Illustration: 282]
_Fig._ 282. represents the mouldings of the top, upon an enlarged scale.
[Illustration: 283]
_Fig._ 283., a plan of the foundation, ditto.
[Illustration: 284]
_Fig._ 284., ditto, at the level of the entrance of the flue, as seen in
[Illustration: 285]
_Fig._ 285., the elevation of the chimney.
[Illustration: 286]
_Fig._ 286., plan at the ground level I, in _fig._ 281. and 285.
K, _fig._ 281., the lightning conducting rod.
CHINTZ is a peculiar style of fast-printed calico, in which figures of
at least five different colours are impressed upon a white or light
coloured ground.
CHLORATE OF POTASH, commonly called oxymuriate of potash. This
interesting saline compound has become the object of a pretty extensive
manufacture, in consequence of its application to make matches for
procuring instantaneous light, and a detonating powder for fire-arms. It
may be prepared both in the humid and dry way.
Having made a strong solution of purified potash, or carbonate of
potash, with from two to three parts of water, we pass through it in a
Woulfe’s apparatus a current of chlorine gas, till it ceases to absorb
any more. Chloride of potash and chloride of potassium alone are formed
as long as there is an excess of alkali in the solution; but afterwards
in the further reaction of the materials, the chloride passes into the
state of a chlorate, and, as such, precipitates from the solution.
During the first half of the operation, that is, till the potash be
about one half saturated with chlorine, as indicated by litmus paper
ceasing to be darkened and beginning to be blanched, only the chloride
of potassium or muriate of potash falls. The process should be
interrupted at this point in order to remove the salt, to wash it, to
add the washings to the liquor, and then to transmit the gas freely
through the solution. As the operation advances, less muriate of potash
is formed, and at length nothing but the pure chlorate is separated in
crystals. When finally the bubbles of gas pass through without being
sensibly absorbed, the process is known to be completed; the liquid may
then be allowed to settle, and be poured off from the crystals of
chlorate of potash, which are purified from the muriate by dissolving
them in three times their weight of boiling water, and filtering the
solution while hot. On its cooling, the chlorate will separate in
pearly-looking crystalline plates. It may be rendered quite pure by a
second crystallization, in which state it does not affect solution of
nitrate of silver.
The above potash lye usually gets a reddish tint in the course of the
process in consequence of a little manganesic acid coming over with the
chlorine, but it gradually loses this colour as the saturation becomes
complete, when the solution turns yellow. The tubes for conveying the
gas should be of large diameter, if they be plunged into the saline
solution, because the crystallization which takes place in it is apt to
choke them up. This inconvenience may however be obviated by attaching
to the end of the glass tube, a tube of caoutchouc terminated in a small
glass funnel, or simply the neck of a caoutchouc bottle with a part of
its body, whose width will not be readily closed with a saline crust.
The residuary lixivium may be used against another operation, or it may
be evaporated down to half its bulk and set aside to crystallize,
whereby some more chlorate will be obtained, mixed indeed with muriate
and carbonate, from which however it may be separated by a second
crystallization. In general the pure chlorate obtained does not exceed
one tenth the weight of the potash employed; because in thus treating
potash with chlorine, five-sixths of it are converted into muriate of
potash and only one sixth into chlorate, and a part of the latter
adheres to the muriate, or is lost in the mother waters of the
crystallizations.
The chlorate of potash may be more conveniently manufactured, like that
of lime, in the dry way. St. Romer patented at Vienna the following
method for that purpose in 1821:--Ten pounds of crystallised peroxide of
manganese are to be finely pulverised, mixed with ten pounds of
plumbago, and thirty pounds of common salt, and put into the leaden
retort represented in _fig._ 287. p. 287. From the middle of the
helmet-shaped lid of this vessel, a lead tube, two feet long and two
inches wide, conducts to the receiver, which is a square earthen pan,
hard glazed both within and without, of the same capacity with the
retort. The end of the tube must be made fast to a frame at the height
of six inches above the bottom of the receiver. Upon its inner sides
four inches apart, brackets are to be fixed for supporting a series of
laths or shelves of white wood, on which a number of little paper or
paste-board boxes are to be laid. In these boxes ten pounds of the
purest carbonate of potash, prepared from tartar, are to be spread. The
receiver must now be covered with a lid made tight by a water lute.
Twenty pounds of concentrated sulphuric acid previously diluted with
sixteen pounds of water, and then cooled, are to be poured upon the
mixed materials in the retort, the lid immediately secured, with the
tube adjusted in the receiver. The whole must be allowed to operate
spontaneously without heat for twelve hours. At the end of this time the
retort is to be surrounded with a water bath and steadily heated during
twelve hours, and then left to cool for six hours. The apparatus must
now be opened, the cakes of chlorate of potash removed, and freed from
muriate by solution and crystallization.
M. Liebig proposes the following process for obtaining chlorate of
potash:--
Heat chloride of lime in water till it ceases to destroy vegetable
colours. In this case a mixture of chloride of calcium and chlorate of
potash is obtained. This is to be dissolved in hot water, and to the
solution concentrated by evaporation, chloride of potassium is to be
added, and then suffered to cool. After cooling, a quantity of crystals
of chlorate of potash is obtained, which are to be redissolved and
crystallized again to purify them. M. Liebig considers that this will be
a cheap process for obtaining chlorate of potash. From 12 ounces of
chloride of lime, of so bad a quality that it left 65 per cent. of
insoluble matter, he obtained an ounce of chlorate of potash.
The only difficulty to overcome in this process is, from the chloride of
lime not being so easily decomposed by heat as is generally supposed; a
solution of it may be kept boiling for an hour without losing its
bleaching power. The best method is to form a thin paste with chloride
of lime and water, and then to evaporate it to dryness. If it be
required to prepare it by passing chlorine into cream of lime, it is
advantageous to keep it very hot.
The chlorate of potash which separates from the solution by
crystallization, has not the form of scales which it usually possesses,
but is prismatic: whether this is occasioned by some admixture has not
been ascertained; but on re-crystallizing, it is obtained in the usual
form.
The solution ought not merely to be left to cool, in order to procure
crystals, for the crystallization is far from being terminated even
after complete cooling; crystals continue to be deposited for 3 or 4
days.
The following modification of the process for making chlorate of potash
is that of M. Vée. A solution of chloride of lime marking 18° or 20°
Baumé, is to be set upon the fire in a lead or cast iron pot, and when
it begins to get hot, there is to be dissolved in it, a quantity of
chloride of potassium sufficient to raise the hydrometer 3 or 4 degrees.
It must be then concentrated as quickly as possible till it marks 30° or
31°, taking care that it does not boil over by the sudden extrication of
oxygen. The concentrated liquor is set aside to crystallize in a cool
place; where a deposit of chlorate of potash forms, mixed with chloride
of potassium. The mother waters being evaporated to the density of 36°,
afford another crop of crystals, after which they may be thrown away.
The salts obtained at the first crystallization are to be re-dissolved,
and the solution being brought to 15° or 16° is to be filtered, when it
will afford upon cooling pure chlorate of potash.
Chlorate or oxymuriate of potash has a cooling, somewhat unpleasant and
nitrous taste. It does not bleach. At 60° F. 100 parts of water dissolve
six parts of it, and at its boiling point or 220°, sixty parts. When
heated to dull ignition in a glass retort it gives out 39·15 per cent.
of its weight of oxygen, and becomes thereby chloride of potassium. When
strongly triturated in a mortar it crackles, throws out sparks, and
becomes luminous. It deflagrates upon red-hot cinders like nitre: when
triturated along with sulphur, or phosphorus, it detonates with great
violence, not without danger to the hands of the operator, if they be
not protected by a thick glove. Similar detonations may be produced with
cinnabar or vermillion, sulphuret of potassium, sugar, volatile oils,
&c.; but they can be effected only by the smart blow of a heated hammer
and anvil. A mixture of sugar or starch with chlorate of potash is
readily inflamed by a drop of sulphuric acid, and this experiment is the
basis of the preparation of the oxygenated matches, as they have been
commonly called. The following formula forms a good paste for tipping
the said matches, made of narrow slips of either wood or card. Thirty
parts of the chlorate in fine powder are to be mixed gently with a
spatula upon paper with ten parts of flowers of sulphur well levigated,
eight of sugar, five of gum arabic, and enough of vermillion to give the
whole a rose tint. We begin by mixing tenderly together the sugar, the
gum, and the salt previously pulverised; we then add as much water as
shall reduce the mixture to a thin paste, and lastly introduce the
sulphur; after which all must be well incorporated. The points of the
matches, either previously tipped with sulphur or not, are to be dipped
in that paste, so as to get coated with a little of it, and are lastly
laid in a warm place till they become thoroughly dry. To kindle one of
them, it must be touched with strong sulphuric acid, which for this
purpose is usually kept in a small well-stoppered phial, and thickened
with amianthus. Aspen is reckoned the best wood for matches.
Of late years a detonating priming for fire-arms has been much used with
the percussion locks. The simplest formula for making it is to take ten
parts of gunpowder, to lixiviate it with water, and to mix the residuum,
while moist, with five parts and a quarter of chlorate of potash,
reduced to an extremely fine powder. The paste may be made pretty thin,
for the salt is sparingly soluble in the cold water, and it mixes best
when tolerably fluid. This powder when dry is dangerous to handle, being
very apt to explode. But this danger is guarded against by letting fall
a drop of the paste into each copper percussion cap, and leaving it to
dry there. In the detonation of this powder, besides muriate of potash,
there are generated a little sulphate of potash and chlorine gas, which
rust the metal very fast. For which reason fulminate of mercury is now
preferred by many sportsmen as a detonating powder. See FULMINATE.
CHLORATES, compounds of chloric acid with the salifiable bases. The only
acid belonging to this class of any manufacturing importance is the
following:
CHLORIC ACID; the acid constituent of the preceding salt; it consists of
one equivalent prime of chlorine = 35·476, + 5 of oxygen, = 40·065; of
which the sum 75·535 is the prime equivalent of the acid.
CHLORINE; the most energetic of the undecompounded bodies, or chemical
elements as they are usually called, exists, under ordinary
circumstances, as a greenish yellow gas, but, when exposed to a pressure
of 4 atmospheres, it becomes a yellow transparent liquid. In the first
state, its density compared to air, reckoned 1·000, is 2·47; in the
second, its density compared to water, 1·000, is 1·33. No degree of
cold, hitherto tried, has liquefied the gas when dry. It is obtained by
putting into a glass retort a mixture of 3 parts of common salt, with 2
parts of peroxide of manganese, and pouring upon it 2 parts of sulphuric
acid diluted with its own weight of water; or, more conveniently, by
pouring moderately strong muriatic acid upon peroxide of manganese in a
retort; and in either case applying the gentle heat of a spirit lamp or
a water bath, while the beak of the retort is plunged under brine upon
the shelf of the pneumatic trough. The gas issues, and may be received
in the usual way into inverted glass jars, or phials; but the first
which comes over being mixed with the air of the retort, must be
rejected. It has a peculiar smell, and irritates the nostrils most
violently when inhaled, as also the windpipe and lungs. It is eminently
noxious to animal life, and, if breathed in its undiluted state, would
prove instantly fatal. It supports the combustion of many bodies, and
indeed spontaneously burns several without their being previously
kindled. The resulting combinations are called chlorides, and act most
important parts in many manufacturing processes.
Water absorbs, at the ordinary temperature of the atmosphere, about
double its volume of chlorine, and acquires the colour, smell, and taste
of the gas, as well as its power of destroying or bleaching vegetable
colours. When this aqueous chlorine is cooled to 36° F. dark yellow
crystalline plates appear in it of the hydrate of chlorine, which are
composed in 100 parts of 27·7 chlorine, and 72·3 water. If these
crystals be heated to about 45° they liquefy, and the gas flies off.
Chlorine has a powerful affinity for hydrogen, not only combining with
it rapidly in the gaseous, but seizing it in many of its liquid and
solid combinations, as in volatile oils, which it inflames, and in
yellow wax, cotton, and flax, which it whitens. The compound of chlorine
and hydrogen gases is muriatic acid gas. Manganese, when mixed with
liquid muriatic acid, as in the above process, abstracts the hydrogen,
and lets the chlorine gas go free. When chlorine is passed into water,
it decomposes some of it, seizes its hydrogen to form a little muriatic
acid, and enables its oxygen to unite either with the chlorine, into
chlorous acid, or with the remaining water, and to constitute oxygenated
water. Hence, aqueous chlorine, exposed to the sunbeam, continually
evolves oxygen, and, ere long, becomes muriatic acid.
This watery compound acts in a powerful way upon coloured vegetable
fibres, extracting their hydrogen or colouring element by the twofold
affinities of the chlorine and oxygen for it.
Hence chlorine, as a bleaching agent, requires to be tempered by the
quiescent affinity of some alkaline base, potash or lime. Malaria, or
morbific and putrescent miasmata, consist chiefly of hydrogenous matter
as their basis, and are best counteracted by chlorine, where it can be
conveniently applied.
_Chlorides of Potash, Soda, and Lime._--These are the most important
preparations through which chlorine exercises its peculiar powers upon
the objects of manufactures. When a weak solution of caustic potash or
soda is saturated with chlorine, it affords a bleaching liquor which is
still used by some bleachers and calico-printers for their most delicate
processes; but the price of the alkalis has led to the disuse of these
chlorides as a general means, and has occasioned an extensive employment
of chloride of lime. Upon the manufacture of this interesting compound I
made an elaborate series of experiments several years ago, and published
the results in the 13th volume of Brande’s Journal, for April 1822. I
have no reason to suppose, from any thing that has been published since,
that the processes there described have been essentially improved, or
that any errors, either theoretical or practical, of any moment, exist
in that memoir. I shall therefore first present my readers with a brief
abstract of it, and then make such observations as subsequent inquiries
suggest.
In the researches which I made, at many different times, upon the nature
of the chloride of lime, I generally sought to combine the information
flowing from both synthesis and analysis; that is, I first converted a
known portion of hydrate of lime into bleaching-powder, and then
subjected this chloride to analysis.
Two hundred grains of the atomic proto-hydrate of pure lime were put
into a glass globe, which was kept cold by immersion in a body of water
at 50°. A stream of chlorine, after being washed in water of the same
temperature in another glass globe, connected to the former by a long
narrow glass tube, was passed over the calcareous hydrate. The globe
with the lime was detached from the rest of the apparatus from time to
time, that the process might be suspended as soon as the augmentation of
weight ceased. This happened when the 200 grains of hydrate, containing
151·9 of lime, had absorbed 130 grains of chlorine. By one analytical
experiment it was found, that dilute muriatic acid expelled from 50
grains of the chloride, 20 grains of chlorine, or 40 per cent.; and by
another, from 40 grains, 16·25 of gas, which is 40·6 per cent. From the
residuum of the first 39·7 grains of carbonate of lime were obtained by
carbonate of ammonia; from that of the second, 36·6 of ignited muriate
of lime. The whole results are therefore as follows:--
+--------+----------+-------------+------------+------+
| |Synthesis.|1st Analysis.|2d Analysis.| Mean.|
| +----------+-------------+------------+------+
|Chlorine| 39·39 | 40·00 | 40·62 | 40·31|
|Lime | 46·00 | 44·74 | 46·07 | 45·50|
|Water | 14·60 | 15·26 | 13·31 | 14·28|
| | ------ | ------ | ------ |------|
| | 100·00 | 100·00 | 100·00 |100·00|
+--------+----------+-------------+------------+------+
Though the heat generated by the action of the dilute acid had carried
off in the analytical experiments a small portion of moisture with the
chlorine, yet their accordance with the synthetic experiment is
sufficiently good to confirm the general results. The above powder
appears to have been a pure chloride, without any mixture of muriate.
But it exhibits no atomic constitution in its proportions.
To 200 grains of that hydrate of lime 30 grains of water being added,
the powder was subjected to a stream of chlorine in the above way, till
saturation took place. Its increase of weight was 150 grains.
It ought to be remarked, that in this and the preceding experiment,
there was no appreciable pneumatic pressure employed to aid the
condensation of the chlorine. In the last case, we see that the addition
of 30 grains of water has enabled the lime to absorb 20 grains more of
chlorine, being altogether a quantity of gas nearly equal to that of the
dry lime. Thus, an atom of lime seems associated with 7/9 of an atom of
chlorine. Analysis by muriatic acid confirmed this composition. It gave
Chlorine 39·5 = 51·8 cubic inches.
Lime 39·9
Water 20·6
-----
100·0
-----
A great variety of apparatus has been at different times contrived for
favouring the combination of chlorine with the slacked lime for the
purposes of commerce. One of the most ingenious forms, is that of a
cylinder, or barrel, furnished with narrow wooden shelves within, and
suspended on a hollow axis by which the chlorine was admitted, and round
which the barrel was made to revolve. By this mode of agitation, the
lime-dust being exposed on the most extensive surface, was speedily
impregnated with the gas to the requisite degree. Such a mechanism I saw
at MM. Oberkampf and Widmer’s celebrated _fabrique de toiles peintes_,
at Jouy, in 1816. But this is a costly refinement, inadmissible on the
largest scale of British manufacture. The simplest, and, in my opinion,
the best construction for subjecting lime-powder to chlorine, is a large
chamber 8 or 9 feet high, built of siliceous sandstone, having the
joints of the masonry secured with a cement composed of pitch, resin,
and dry gypsum in equal parts. A door is fitted into it at one end,
which can be made air-tight by strips of cloth and clay lute. A window
on each side enables the operator to judge how the impregnation goes on
by the colour of the air, and also gives light for making the
arrangements within at the commencement of the process. As water lutes
are incomparably superior to all others where the pneumatic pressure is
small, I would recommend a large valve or door on this principle to be
made in the roof, and two tunnels of considerable width at the bottom of
each side wall. The three covers could be simultaneously lifted off by
cords passing over a pulley, without the necessity of the workman
approaching the deleterious gas, when the apartment is to be opened. A
great number of wooden shelves, or rather trays, 8 or 10 feet long, 2
feet broad, and 1 inch deep, are provided to receive the riddled slacked
lime, containing generally about 2 atoms of lime to 3 of water. These
shelves are piled one over another in the chamber, to the height of 5 or
6 feet, cross bars below each keeping them about an inch asunder, that
the gas may have free room to circulate over the surface of the
calcareous hydrate.
The alembics for generating the chlorine, which are usually nearly
spherical, are in some cases made entirely of lead, in others of two
hemispheres, joined together in the middle, the upper hemisphere being
lead, the under one cast-iron. The first kind of alembic is enclosed for
two-thirds from its bottom, in a leaden or iron case, the interval of
two inches between the two being destined to receive steam from an
adjoining boiler. Those which consist below of cast-iron, have their
bottom directly exposed to a very gentle fire; round the outer edge of
the iron hemisphere a groove is cast, into which the under edge of the
leaden hemisphere fits, the joint being rendered air-tight by Roman or
patent cement. In this leaden dome there are four apertures, each
secured by a water-lute. The first opening is about 10 or 12 inches
square, and is shut with a leaden valve, with incurvated edges, that fit
into the water channel at the margin of the hole. It is destined for the
admission of a workman to rectify any derangement in the apparatus of
rotation, or to detach hard concretions of salt from the bottom.
The second aperture is in the centre of the top. Here a tube of lead is
fixed, which descends nearly to the bottom, and down through which the
vertical axis passes. To its lower end the cross bars of iron, or of
wood, sheathed with lead, are attached, by whose revolution the
materials receive the proper agitation for mixing the dense manganese
with the sulphuric acid and salt. The motion is communicated either by
the hand of a workman applied from time to time to a winch at top, or it
is given by connecting the axis with wheel work, impelled by a stream of
water or a steam-engine. The third opening admits the syphon-formed
funnel, through which the sulphuric acid is introduced; and the fourth
is the orifice of the eduction-pipe.
Manufacturers differ much from each other in the proportion of their
materials for generating chlorine. In general, 10 cwt. of salt are mixed
with from 10 to 14 cwt. of manganese, to which mixture, after its
introduction into the alembic, from 12 to 14 cwt. of sulphuric acid are
added in successive portions. That quantity of oil of vitriol must,
however, be previously diluted with water, till its specific gravity
becomes about 1·6. But, indeed, this dilution is seldom actually made,
for the manufacturer of bleaching-powder almost always prepares his own
sulphuric acid for the purpose, and therefore carries its concentration
no higher in the leaden boilers than the density of 1·65, which from my
table of sulphuric acid, indicates 1/4th of its weight of water, and
therefore 1/3d more of such acid must be used.
The fourth aperture, I have said, admits the eduction pipe. This pipe is
afterwards conveyed into a leaden chest or cylinder, in which all the
other eduction pipes also terminate. They are connected with it simply
by water-lutes, having a hydrostatic pressure of 2 or 3 inches. In this
general _diversorium_ the chlorine is washed from adhering muriatic
acid, by passing through a little water, in which each tube is immersed,
and from this the gas is let off by a pretty large leaden tube, into the
combination room. It usually enters in the top of the ceiling, whence it
diffuses its heavy gas equally round.
Four days are required, at the ordinary rate of working, for making good
marketable bleaching-powder. A more rapid formation would merely
endanger an elevation of temperature, productive of muriate of lime, at
the expense of the bleaching quality. But skilful manufacturers use here
an alternating process. They pile up, first of all, the wooden trays
only in alternate shelves in each column. At the end of two days the
distillation is intermitted, and the chamber is laid open. After two
hours the workman enters, to introduce the alternate trays covered with
fresh hydrate of lime, and at the same time rakes up thoroughly the
half-formed chloride in the others. The door is then secured, and the
chamber, after being filled for two days more with chlorine, is again
opened, to allow the first set of trays to be removed, and to be
replaced by others, containing fresh hydrate, as before. Thus the
process is conducted in regular alternation; thus, to my knowledge,
very superior bleaching-powder is manufactured, and thus the chlorine
may be suffered to enter in a pretty uniform stream. But for this
judicious plan, as the hydrate advances in impregnation, its faculty of
absorption becoming diminished, it would be requisite to diminish
proportionately the evolution of chlorine, or to allow the excess to
escape to the great loss of the proprietor, and, what is of more
consequence, to the great detriment of the health of the workmen.
The manufacturer generally reckons on obtaining from one ton of
rock-salt, employed as above, a ton and a half of good bleaching-powder.
But the following analysis of the operation will show that he ought to
obtain two tons.
When a mixture of sulphuric acid, common salt, and black oxide of
manganese are the ingredients used, as by the manufacturer of
bleaching-powder, the absolute proportions are, upon the oxygen scale of
equivalents:--
1 atom muriate of soda 7·5 29·70 100·0
1 atom peroxide of manganese 5·5 21·78 73·3
2 atoms oil of vitriol 1·846 12·25 48·52 163·3
------ ------
25·25 100·00