Libs.
1827. 145,756
1828. 158,109
1829. 153,738
1830. 100,059
1831. 168,329
1832. 138,270
1833. 130,732
1834. 265,490
1835. 352,023
Humboldt states that so long ago as the year 1736, there was imported
into Europe from South America cochineal to the value of 15 millions of
francs. Its high price had for a long time induced dyers to look out for
cheaper substitutes in dyeing red, and since science has introduced so
many improvements in tinctorial processes, both madder and lac have been
made to supersede cochineal to a very great extent. Its price has, in
consequence of this substitution, as well as from more successful modes
of cultivation, fallen very greatly of late years. At present it is only
7_s._ per lib. in London. See SCARLET DYEING.
COCOA, STEARINE, AND ELAINE. Mr. Soames obtained a patent in September
1829, for making these useful articles, by the following process:
He takes the substance called cocoa-nut oil, in the state of lard, in
which it is imported into this country, and submits it to a strong
hydraulic pressure, having made it up in small packages, 3 or 4 inches
wide, 2 feet long, and 1 or 1-1/2 inches thick. These packages are
formed by first wrapping up the said substance in a strong linen cloth,
of close texture, and then in an outward wrapper of strong sail cloth.
The packages are to be placed side by side, in single rows, between the
plates of the press, allowing a small space between the packages for the
escape of the _elaine_.
The temperature at which the pressure is begun, should be from about 50
to 55 degrees, or in summer as nearly at this pitch as can be obtained,
and the packages of the said substance intended for pressure, should be
exposed for several hours previously to about the same temperature. When
the packages will no longer yield their oil or elaine freely at this
temperature, it is to be gradually raised; but it must at no time exceed
65 degrees, and the lower the temperature at which the separation can be
effected, the better will be the quality of the oil expressed.
When the packages are sufficiently pressed, that is, when they will give
out no more oil, or yield it only in drops at long intervals, the
residuum in them is to be taken out and cleansed and purified, which is
done by melting it in a well-tinned copper vessel, which is fixed in an
outer vessel, having a vacant space between, closed at the top, into
which steam is admitted, and the heat is kept up moderately for a
sufficient time to allow the impurities to subside; but if a still
higher degree of purity is required, it is necessary to pass it through
filters of thick flannel lined with blotting paper.
Having been thus cleansed or purified, it is fit for the manufacture of
candles, which are made by the ordinary process used in making mould
tallow candles. Having thus disposed of the stearine, or what is called
the first product, he proceeds with the elaine or oil expressed from it,
and which he calls the second product, as follows: that is to say, he
purifies it by an admixture, according to the degree of its apparent
foulness, of from 1 to 2 per cent. by weight of the sulphuric acid of
commerce, of about 1·80 specific gravity, diluted with six times its
weight of water. The whole is then to be violently agitated by
mechanical means, and he prefers for this purpose the use of a vessel
constructed on the principle of a common barrel churn. When sufficiently
agitated, it will have a dirty whitish appearance, and is then to be
drawn off into another vessel, in which it is to be allowed to settle,
and any scum that rises is to be carefully taken off. In a day or two
the impurities will be deposited at the bottom of the oil, which will
then become clear, or nearly so, and it is to be filtered through a
thick woollen cloth, after which it will be fit for burning in ordinary
lamps and for other uses.
The process of separating the elaine from the stearine, by pressure, in
manner aforesaid, had never before been applied to the substance called
cocoa-nut oil, and consequently no product had heretofore been obtained
thereby from that substance, fit for being manufactured into candles in
the ordinary way, or for being refined by any of the usual modes, so as
to burn in ordinary lamps, both which objects are obtained by this
method of preparing or manufacturing the said substance.
Candles well made from the above material are a very superior article.
The light produced is more brilliant than from the same sized candle
made of tallow; the flame is perfectly colourless, and the wick remains
free from cinder, or any degree of foulness during combustion.
COFFEE. The coffee is the seed of a tree of the family _rubiaceæ_, and
belongs to the Pentandria monogynia of Linnæus. There are several
species of the genus, but the only one cultivated is the _Coffæa
Arabica_, a native of Upper Ethiopia and Arabia Felix. It rises to the
height of 15 or 20 feet; its trunk sends forth opposite branches in
pairs above and at right angles to each other; the leaves resemble those
of the common laurel, although not so dry and thick. From the angle of
the leaf-stalks small groups of white flowers issue, which are like
those of the Spanish jasmine. These flowers fade very soon, and are
replaced by a kind of fruit not unlike a cherry, which contains a yellow
glairy fluid, enveloping two small seeds or berries convex upon one
side, flat and furrowed upon the other in the direction of the long
axis. These seeds are of a horny or cartilaginous nature; they are glued
together, each being surrounded with a peculiar coriaceous membrane.
They constitute the coffee of commerce.
It was not till towards the end of the 15th century that the coffee tree
began to be cultivated in Arabia. Historians usually ascribe the
discovery of the use of coffee as a beverage to the superior of a
monastery there, who, desirous of preventing the monks from sleeping at
their nocturnal services, made them drink the infusion of coffee upon
the report of shepherds, who pretended that their flocks were more
lively after browsing on the fruit of that plant. The use of coffee was
soon rapidly spread, but it encountered much opposition on the part of
the Turkish government, and became the occasion of public assemblies.
Under the reign of Amurath III. the mufti procured a law to shut all the
coffee-houses, and this act of suppression was renewed under the
minority of Mahomet IV. It was not till 1554 under Solyman the Great
that the drinking of coffee was accredited in Constantinople; and a
century elapsed before it was known in London and Paris. Solyman Aga
introduced its use into the latter city in 1669, and in 1672 an Armenian
established the first _café_ at the fair of Saint Germain.
When coffee became somewhat of a necessary of life from the influence of
habit among the people, all the European powers who had colonies between
the tropics, projected to form plantations of coffee trees in them. The
Dutch were the first who transported the coffee plant from Moka to
Batavia, and from Batavia to Amsterdam. In 1714 the magistrates of that
city sent a root to Louis XIV. which he caused to be planted in the
Jardin du Roi. This became the parent stock of all the French coffee
plantations in Martinique.
The most extensive culture of coffee is still in Arabia Felix, and
principally in the kingdom of Yemen, towards the cantons of Aden and
Moka. Although these countries are very hot in the plains, they possess
mountains where the air is mild. The coffee is generally grown halfway
up on their slopes. When cultivated on the lower grounds it is always
surrounded by large trees which shelter it from the torrid sun, and
prevent its fruit from withering before their maturity. The harvest is
gathered at three periods, the most considerable occurs in May, when the
reapers begin by spreading cloths under the trees, then shaking the
branches strongly, so as to make the fruit drop, which they collect, and
expose upon mats to dry. They then pass over the dried berries a very
heavy roller, to break the envelopes, which are afterwards winnowed away
with a fan. The interior bean is again dried before being laid up in
store.
In Demerara, Berbice, and some of our West India islands, where much
good coffee is now raised, a different mode of treating the pulpy fruit
and curing the beans is adopted. When the cherry-looking berry has
assumed a deep-red colour it is gathered, and immediately subjected to
the operations of a mill composed of two wooden rollers, furnished with
iron plates, which revolve near a third fixed roller called the _chops_.
The berries are fed into a hopper above the rollers, and falling down
between them and the chops, they are stripped of their outer skins and
pulp, while the twin beans are separated from each other. These beans
then fall upon a sieve, which allows the skin and the pulp to pass
through, while the hard beans accumulate and are progressively slid over
the edge into baskets. They are next steeped for a night in water,
thoroughly washed in the morning, and afterwards dried in the sun. They
are now ready for the peeling mill, a wooden edge wheel turned
vertically by a horse yoked to the extremity of its horizontal axis. In
travelling over the coffee, it bursts and detaches the coriaceous or
parchment-like skin which surrounds each hemispherical bean. It is then
freed from the membranes by a winnowing machine, in which four pieces of
tin made fast to an axle are caused to revolve with great velocity. Corn
fanners would answer better than this rude instrument of negro
invention. The coffee is finally spread upon mats or tables, picked
clean, and packed up for shipment.
The most highly esteemed coffee is that of Moka. It has a smaller and a
rounder bean; a more agreeable taste and smell than any other. Its
colour is yellow. Next to it in European reputation is the Martinique
and Bourbon coffees; the former is larger than the Arabian and more
oblong; it is rounded at the ends; its colour is greenish, and it
preserves almost always a silver gray pellicle, which comes off in the
roasting. The Bourbon coffee approaches nearest to the Moka from which
it originally sprung. The Saint Domingo coffee has its two extremities
pointed, and is much less esteemed than the preceding.
The coffee tree flourishes in hilly districts where its root can be kept
dry, while its leaves are refreshed with frequent showers. Rocky ground,
with rich decomposed mould in the fissures, agrees best with it. Though
it would grow, as we have said, to the height of 15 or 20 feet, yet it
is usually kept down by pruning to that of five feet for increasing the
production of the fruit, as well as for the convenience of cropping. It
begins to yield fruit the third year, but is not in full bearing till
the fifth, does not thrive beyond the twenty-fifth, and is useless in
general at the thirtieth. In the coffee husbandry, the plants should be
placed eight feet apart, as the trees throw out extensive horizontal
branches, and in holes ten or twelve feet deep to secure a constant
supply of moisture.
Coffee has been analysed by a great many chemists, with considerable
diversity of results. The best analysis perhaps is that of Schrader. He
found that the raw beans distilled with water in a retort communicated
to it their flavour and rendered it turbid, whence they seem to contain
some volatile oil. On reboiling the beans, filtering, and evaporating
the liquor to a syrup, adding a little alcohol till no more matter was
precipitated, and then evaporating to dryness, he obtained 17·58 per
cent. of a yellowish-brown transparent extract, which constitutes the
characteristic part of coffee, though it is not in that state the pure
proximate principle, called _cafeine_. Its most remarkable reaction is
its producing, with both the protoxide and the peroxide salts of iron, a
fine grass green colour, while a dark green precipitate falls, which
re-dissolves when an acid is poured into the liquor. It produces on the
solution of the salts of copper scarcely any effect, till an alkali be
added, when a very beautiful green colour is produced which may be
employed in painting. Coffee beans contain also a resin, and a fatty
substance somewhat like suet. According to Robiquet, ether extracts from
coffee beans nearly 10 per cent. of resin and fat, but he probably
exaggerates the amount. The peculiar substance cafeine contained in the
above extract is crystallizable. It is remarkable in regard to
composition, that after urea and the uric acid, it is among organic
products the richest in azote. It was discovered and described in 1820
by Runge. It does not possess alkaline properties. Pfaff obtained only
90 grains of cafeine from six pounds of coffee beans. There is also an
acid in raw coffee to which the name of _cafeic acid_ has been given.
When distilled to dryness and decomposed, it has the smell of roasted
coffee.
Coffee undergoes important changes in the process of roasting. When it
is roasted to a yellowish brown it loses, according to Cadet, 12-1/2 per
cent. of its weight, and is in this state difficult to grind. When
roasted to a chestnut brown it loses 18 per cent., and when it becomes
entirely black, though not at all carbonised, it has lost 23 per cent.
Schrader has analyzed roasted coffee comparatively with raw coffee, and
he found in the first 12-1/2 per cent. of an extract of coffee, soluble
in water and alcohol, which possesses nearly the properties of the
extract of the raw coffee, although it has a deeper brown colour, and
softens more readily in the air. He found also 10·4 of a blackish brown
gum; 5·7 of an oxygenated extract or rather _apothème_ soluble in
alcohol, insoluble in water; 2 of a fatty substance and resin; 69 of
burnt vegetable fibre, insoluble. On distilling roasted coffee with
water, Schrader obtained a product which contained the aromatic
principle of coffee; it reddened litmus paper, and exhaled a strong and
agreeable odour of roasted coffee. If we roast coffee in a retort, the
first portions of the aromatic principle of coffee condense into a
yellow liquid in the receiver; and these may be added to the coffee
roasted in the common way, from which this matter has been expelled and
dissipated in the air.
Chenevix affirmed that by the roasting of coffee a certain quantity of
tannin possessing the property of precipitating gelatine is generated.
Cadet made the same observation, and found, moreover, that the tannin
was most abundant in the lightly roasted coffee, and that there was
nearly none of it in coffee highly roasted. Payssé and Schrader, on the
contrary, state that solution of gelatine does not precipitate either
the decoction of roasted coffee or the alcoholic extract of this coffee.
Runge likewise asserts that he could obtain no precipitate with
gelatine; but he says that albumen precipitates from the decoction of
roasted coffee the same kind of tannin as is precipitated from raw
coffee by the acetate of lead, and set free from the lead by
sulphuretted hydrogen. With these results my own experiments agree.
Gelatine certainly does not disturb clear infusion of roasted coffee,
but the salts of iron blacken it.
Schrader endeavoured to roast separately the different principles of
coffee, but none of them exhaled the aromatic odour of roasted coffee
except the horny fibrous matter. He therefore concludes that this
substance contributes mainly to the characteristic taste of roasted
coffee, which cannot be imitated by any other vegetable matter, and
which, as we have seen, should be ascribed chiefly to the altered cafeic
acid. According to Garot we may extract the cafeine without alteration
from roasted coffee by precipitating its decoction by subacetate of
lead, treating the washed precipitate with sulphuretted hydrogen, and
evaporating the liquid product to dryness.
Of late years, much ingenuity has been expended in contriving various
forms of apparatus for making infusions of coffee for the table. I have
tried most of them, and find, after all, none so good as a _cafetière à
la Belloy_, the coffee _biggin_, with the perforated tin plate strainer,
especially when the filtered liquor is kept simmering in a close vessel,
set over a lamp or steam pan. The useful and agreeable matter in coffee
is very soluble: it comes off with the first waters of infusion, and
needs no boiling.
To roast coffee rightly we should keep in view the proper objects of
this process, which are to develop its aroma, and destroy its toughness,
so that it may be readily ground to powder. Too much heat destroys those
principles which we should wish to preserve, and substitutes new ones
which have nothing in common with the first, but add a disagreeable
empyreumatic taste and smell. If, on the other hand, the rawness or
greenness is not removed by an adequate heat, it masks the flavour of
the bean, and injures the beverage made with it. When well roasted in
the sheet iron cylinders set to revolve over a fire, it should have a
uniform chocolate colour, a point readily hit by experienced roasters,
who now manage the business very well for the principal coffee dealers
both of London and Paris, so far as my judgment can determine. The
development of the proper aroma is a criterion by which coffee roasters
frequently regulate their operations. When it loses more than 20 per
cent. of its weight, coffee is sure to be injured. It should never be
ground till immediately before infusion.
COKE, is carbonized pitcoal. See CHARCOAL; and PITCOAL at the end.
COLCOTHAR OF VITRIOL, (_Rouge d’Angleterre_, Fr.; _Rothes Eisenoxyd_,
Germ.) is the brown-red peroxide of iron, produced by calcining sulphate
of iron with a strong heat, levigating the resulting mass, and
elutriating it into an impalpable powder. A better way of making it so
as to complete the separation of the acid, is to mix 100 parts of the
green sulphate of iron with 42 of common salt, to calcine the mixture,
wash away the resulting sulphate of soda, and levigate the residuum. The
sulphuric acid in this case expels the chlorine of the salt in the form
of muriatic acid gas, and saturates its alkaline base produced by the
chemical reaction; whence an oxide will be obtained free from acid, much
superior to what is commonly found in the shops. The best sort of
polishing powder called _jewellers’ red rouge_ or plate powder is the
precipitated oxide of iron prepared by adding solution of soda to
solution of copperas, washing, drying, and calcining the powder in
shallow vessels with a gentle heat, till it assumes a deep brown red
colour. See IRON.
COLOPHANY, black rosin, the solid residuum of the distillation of
turpentine, when all the oil has been worked off.
COLOURING MATTER. (_Matière colorante_, Fr.; _Farbstoff_, Germ.) See
DYEING, the several dye-stuffs and pigments.
COLUMBIUM, a peculiar metal extracted from a rare mineral brought from
Haddam in Connecticut. It is also called Tantalium from the mineral
_tantalite_ and _yttrotantalite_, found in Sweden. It has hitherto no
application to the arts. It combines with two successive doses of
oxygen; by the second it becomes an acid.
COLZA, is a variety of cabbage, the _brassica oleracea_, whose seeds
afford, by pressure, an oil much employed in France and Belgium for
burning in lamps, and for many other purposes. This plant requires a
rich but light soil; it does not succeed upon either sandy or clayey
lands. The ground for it must be deeply ploughed and well dunged. It
should be sown in July, and be afterwards replanted in a richly manured
field. In October it is to be planted out in beds, 15 or 18 inches
apart. Colza may also be sowed in furrows 8 or 10 inches asunder.
Land which has been just cropped for wheat is that usually destined to
colza; it may be fresh dunged with advantage. The harvest takes place in
July, with the sickle, a little before the seeds are completely ripe,
lest they should drop off. As the seed is productive of oil, however,
only in proportion to its ripeness, the cut plants are allowed to
complete their maturation, by laying them in heaps under airy sheds, or
placing them in a stack, and thatching it with straw.
The cabbage stalks are thrashed with flails, the seeds are winnowed,
sifted, spread out in the air to dry; then packed away in sacks, in
order to be subjected to the oil mill at the beginning of winter. The
oil-cake is a very agreeable food to cattle, and serves to fatten them.
It is reckoned to defray the cost of the mill.
Colza impoverishes the soil very much, as do, indeed, all the plants
cultivated for the sake of their oleaginous seeds. It must not,
therefore, be come back upon again for six years, if fine crops be
desired. The double ploughing which it requires, effectually cleans the
ground. See OILS, UNCTUOUS.
COMB, the name of an instrument made of a thin plate either plane or
curved of wood, horn, tortoise-shell, ivory, bone, or metal, cut out
upon one or both of its sides or edges, into a series of somewhat long
teeth, not far apart; which is employed for disentangling, laying
parallel and smooth the hairs of man, horses, or other animals.
A thin steel saw bow, mounted in an iron or wooden handle, is the
implement used by the comb-maker to cut the bone, ivory, and wood into
slices of from a twelfth to a quarter of an inch thick, and of a size
suitable to that of the comb. The pieces of tortoise-shell as found in
commerce are never flat, or, indeed, of any regular curvature, such as
the comb must have. They are therefore steeped in boiling water
sufficiently long to soften them, and set to cool in a press between
iron or brass moulds, which impart to them the desired form which they
preserve after cooling. After receiving their outline shape, and
curvature, by proper flat files or fine rasps, the place of the teeth is
marked with a triangular file, and then the teeth themselves are cut out
with a double saw, composed of two thin slips of tempered steel, such as
the main-spring of a watch, notched with very fine sharp teeth. These
slips are mounted in a wooden or iron stock or handle, in which they may
be placed at different distances to suit the width of the comb teeth. A
comb-maker, however, well provided in tools, has an assortment of double
saws set at every ordinary width. The two slips of this saw have their
teeth in different planes, so that when it begins to cut, the most
prominent slip alone acts, and when the teeth of this one have fairly
entered into the comb, the other parallel blade begins to saw. The
workman, meanwhile, has fixed the plate of tortoise-shell or ivory
between the flat jaws of two pieces of wood, like a vice made fast to a
bench, so that the comb intended to be cut is placed at an angle of 45°
with the horizon. He now saws perpendicularly, forming two teeth at a
time, proceeding truly in the direction of the first tracing.
A much better mode of making combs is to fix upon a shaft or arbour in a
lathe a series of circular saws, with intervening brass washers or discs
to keep them at suitable distances; to set in a frame like a vice, in
front of these saws, the piece of ivory or horn to be cut; and to press
it forward upon the saws at an angle of 45 degrees, by means of a
regulated screw motion. When the teeth are thus cut, they are smoothed
and polished with files, and by rubbing with pumice stone and tripoli.
Mr. Bundy, of Camden Town, obtained a patent so long ago as 1796, for an
apparatus of that kind, which had an additional arbour fitted with a
series of circular saws, or rather files, for sharpening the points of
the comb teeth.
More recently, Mr. Lyne has invented a machine in which, by means of
pressure, two combs are cut out at once with chisels from any tough
material, such as horn or tortoise-shell, somewhat softened at the
moment by the application of a heated iron to it. The piece of horn is
made fast to a carriage, which is moved forwards by means of a screw
until it comes under the action of a ratchet-wheel, toothed upon a part
of its circumference. The teeth of this wheel bring a lever into action,
furnished with a chisel or knife, which cuts out a double comb from the
flat piece, the teeth of which combs are opposite to each other. By this
means no part of the substance is lost, as in sawing out combs. The same
carriage may be used, also, to bear a piece of ivory in the hard state
towards a circular saw, on the principles above explained, with such
precision, that from 80 to 100 teeth can be formed in the space of one
inch by a proper disposition of the tool.
Bullocks’ horns, after the tips are sawed off, are roasted in the flame
of a wood fire, till they are sufficiently softened; when they are slit
up, pressed in a machine between two iron plates, and then plunged into
a trough of cold water, whereby they are hardened. A paste of quicklime,
litharge, and water is used to stain the horn to resemble
tortoise-shell. See HORN.
COMBINATION (_Combinaison_, Fr.; _Verbindung_, Germ.); a chemical term
which denotes the intimate union of dissimilar particles of matter, into
a homogeneous looking compound, possessed of properties generally
different from those of the separate constituents.
COMBUSTIBLE (Eng. and Fr.; _Brennstoff_, Germ.); any substance which
exposed in the air to a certain temperature, consumes spontaneously with
the emission of heat and light. All such combustibles as are cheap
enough for common use go under the name of Fuel; which see. Every
combustible requires a peculiar pitch of temperature to be kindled,
called its _accendible_ point. Thus phosphorus, sulphur, hydrogen,
carburetted hydrogen, carbon, each takes fire at successively higher
heats.
COMBUSTION (Eng. and Fr.; _Verbrennung_, Germ.) results in common cases
from the mutual chemical reaction of the combustible, and the oxygen of
the atmosphere, whereby a new compound is formed; the heat and light
evolved being most probably produced by the rapid motions of the
particles during the progress of this combination.
COMPOUND COLOURS. If the effects of the colouring particles did not vary
according to the combinations which they form, and the actions exercised
upon them by the different substances present in a dyeing bath, we might
determine with precision the shade which ought to result from the
mixture of any two colours, or of the ingredients affording these
colours separately. Though the chemical action of the mordants, and of
the liquor in the dye-bath often changes the results, yet theory may
always predict them within a certain degree. It is not the colour
appropriate to the dye-stuffs which is to be considered as the
constituent part of compound colours, but that which they must assume
with a certain mordant and dye-bath. Our attention ought therefore to be
directed principally to the operation of the chemical agents employed.
1. The mixture of blue and yellow dyes produces green. D’Ambourney,
indeed, says that he has extracted a fast green from the fermented juice
of the berries of the buckthorn (_rhamnus frangula_), but no dyer would
trust to such a colour.
2. The mixture of red and blue produces violet, purple, _columbine_
(dove-colour), pansy, amaranth, lilac, mallow, and a great many other
shades, determined by the nature and tone of the red and blue
dye-stuffs, as well as their relative proportions in the bath.
3. The mixture of red and yellow produces orange, _mordoré_, cinnamon,
_coquelicot_, brick, capuchin; with the addition of blue, olives of
various shades; and with duns instead of yellows, chestnut, snuff, musk,
and other tints.
4. Blacks of the lighter kinds constitute grays; and, mixed with other
colours, produce _marrone_ (marroons), coffees, damascenes. For further
details upon this subject, see CALICO PRINTING, DYEING, as also the
individual colours in their alphabetical places.
CONCRETE. The name given by architects to a compact mass of pebbles,
sand and lime cemented together, in order to form the foundations of
buildings. Semple says that the best proportions are 80 parts of
pebbles, each about 7 or 8 ounces in weight, 40 parts sharp river sand,
and 10 of good lime; the last is to be mixed with water to a thinnish
consistence, and grouted in. It has been found that Thames ballast, as
taken from the bed of the river, consists nearly of 2 parts of pebbles
to 1 of sand, and therefore answers exceedingly well for making
concrete; with from one-seventh to one-eighth part of lime. The best
mode of making concrete, according to Mr. Godwin, is to mix the lime,
previously ground, with the ballast in a dry state; sufficient water is
now thrown over it to effect a perfect mixture, after which it should be
turned over at least twice with shovels, or oftener; then put into
barrows, and wheeled away for use instantly. It is generally found
advisable to employ two sets of men to perform this operation, with
three in each set; one man to fetch the water, &c., while the other two
turn over the mixture to the second set, and they, repeating the
process, turn over the concrete to the barrow-men. After being put into
the barrows, it should at once be wheeled up planks, so raised as to
give it a fall of some yards, and thrown into the foundation, by which
means the particles are driven closer together, and greater solidity is
given to the whole mass. Soon after being thrown in, the mixture is
observed usually to be in commotion, and much heat is evolved with a
copious emission of vapour. The barrow-load of concrete in the fall
spreading over the ground, will form generally a stratum of from 7 to 9
inches thick, which should be allowed to set before throwing in a
second.
Another method of making concrete, is first to cover the foundation with
a certain quantity of water, and then to throw in the dry mixture of
ballast and lime. It is next turned and levelled with shovels; after
which more water is pumped in, and the operation is repeated. The former
method is undoubtedly preferable.
In some cases it has been found necessary to mix the ingredients in a
pug-mill, as in mixing clay, &c. for bricks. For the preparation of a
concrete foundation, as the hardening should be rapid, no more water
should be used than is absolutely necessary to effect a perfect mixture
of the ingredients. Hot water accelerates the induration. There is about
one-fifth of contraction in volume in the concrete, in reference to the
bulk of its ingredients. To form a cubical yard of concrete, about 30
feet cube of ballast and 3-1/2 feet cube of ground lime must be
employed, with a sufficient quantity of water.
CONGELATION (Eng. and Fr.; _Gefrierung_, Germ.); the act of freezing
liquids. Many means are supplied by chemistry of effecting or promoting
this process, but they do not constitute any peculiar art or
manufacture. See ICE-HOUSE.
COOLING OF FLUIDS. In Mr. Derosnes’s method, the cooling agents employed
are a current of atmospheric air, and warm water of the same or nearly
the same temperature as that of the vapours which are to be operated
upon.
_Fig._ 295. represents merely a diagram of the general features of an
apparatus constructed upon the principles proposed to be employed,
which will serve to explain the nature of this improvement.
[Illustration: 295]
Let A be the source of the vapours, or the vessel, boiler, alembic, or
closed pan that contains the liquid or syrup to be evaporated or
concentrated. The pipe B, through which the vapour passes as it rises in
the boiler, is surrounded by another tube C, of larger diameter, closed
at both ends. A pump D, draws from the reservoir E, warm water, which
water has been heated by its previous and continual passage through the
apparatus in contact with the surface of the vapour pipes. This pump
forces the water by the pipe F, into the annular space or chamber
between the pipes B and C, in which chamber, by its immediate contact
with the pipe B, it acquires the temperature of the vapours intended to
be refrigerated. The pipe G conveys the water from the pipe C, into the
annular colander or sieve H, which has a multitude of small holes
pierced through its under part, and from whence the warm water descends
in the form of a continued shower of rain. To the end of the pipe B, a
distiller’s worm I I, is connected, which is placed beneath the colander
H. The entire length of the worm-pipe should be bound round with linen
or cotton cloth, as a conductor of the heat, which cloth will be
continually moistened by the rain in its descent from the colander. As
this water has been heated in passing along the tube C, the shower of
rain descending from the colander will be at a higher temperature than
that of the atmosphere, and, consequently, by heating the surrounding
air as it descends, a considerable upward draft will be produced through
the coils of the worm-pipe.
If the colander and the worm-pipe are enclosed within a chimney or
upright tube, as K K, open at top and bottom, a current of ascending air
will be produced within it by the descending shower of hot water,
similar in effect to that which would be produced in a chimney
communicating with a furnace, or to that of the burner of an argand
lamp. Consequently, it will be perceived that in opposition to the
descending rain, a strong upward current of air will blow through that
part of the cylinder K K, which is beneath the colander. When the air
first enters the lower aperture of the chimney or tube K, it is of the
same temperature and moisture as the external atmosphere; but in its
passage up the tube it meets with a warmer and damper atmosphere, caused
by the heat given out from the hot fluid continually passing through the
pipes, and by the hot shower of rain, and also by the steam evolved from
the surfaces of the coils of the worm, which are continually wetted by
the descending rain, the evaporation being considerably augmented by the
cloth bound round the worm-pipe, retaining the water as it descends in
drops from coil to coil.
The atmosphere within the tube being of a higher temperature than
without, a current of air constantly ascends and escapes at the upper
aperture K, and its place is supplied by fresh air from the surrounding
atmosphere, entering the tube below. The fresh air thus admitted at the
bottom of the tube being cold and dry, will be suited to take up the
heat and moisture within, because the water within the tube being in a
state of dispersion as rain, presents to the air many points, or a very
extended surface, and also because it is of a higher temperature than
the air; and, besides, cold dry air is continually renewed, and a source
of warmth is furnished by the latent caloric to the steam, as fast as it
is evolved. Thus a portion of the descending rain, or water, is
evaporated, and the effect of this evaporation is to subtract caloric
not only from the water held in contact with the coils of the worm-pipe
by the cloth enveloping it, but also from the hot vapours which pass
through the worm. This process of evaporation has, therefore, a cooling
power, which is but slight in the lower part of the chimney or tube K;
because the temperature of the water, or rain, and of the worm, at this
part, are of a lower temperature; but its refrigerating power increases
as it rises towards the colander, and there it acquires its maximum of
intensity, so that at any point between the lower aperture of the
cylinder and the colander, the current of air is always a little cooler
than the atmosphere of the region through which it passes (that is, at
its maximum); and in passing this region of higher temperature, it is
not only put in equilibrium of temperature, but also made to take up an
additional quantity of aqueous vapours, which equalises the new
temperature it acquires with its capacity of saturation. The cooling
caused by the evaporation acts in an incessant and progressive manner
from the lower aperture of the cylinder to the under side of the
colander; and this cooling not only acts as an agent of the evaporation
which the current of air cools, but it refrigerates also, because it
becomes warmed in abstracting caloric from the vapours or liquids
passing through the worm; and this refrigeration acts also incessantly
and progressively from the lower part of the tube or chimney to the
colander.
The patentee states, in conclusion, that “the velocity or force of the
current of air that passes through the chimney or tube K, can be
accelerated by artificial means, either by conducting the air and vapour
passing from the upper aperture of the cylinder into the chimney or
flues of a furnace, or by means of a revolving, forcing, or exhausting
fan, or ventilator, or any other contrivance which will produce an
increased current of air, but which it is not necessary to be
particularly described, as I only wish to explain the principles of a
simple apparatus, constructed in any convenient form; and I would
remark, that the area of the lower aperture through which the air is
introduced into the chimney or tube K, and also the area of the upper
aperture, or that through which it passes to the atmosphere, should be
in accordance with the effect intended to be obtained.
“It is further to be remarked, that in order to obtain from this
apparatus the best effect, the velocity of the current of air must be
itself a maximum; and as the speed or velocity of the current of air is
owing to and determined by the excess of the temperature of the
descending water, or rain, and of the coils of the worm to that of the
exterior atmosphere, it ensues that the temperature of the water, or
rain, must be a maximum. But this excess of temperature is a maximum
only when the source of the rain is at the same temperature as the
vapours to be condensed: if less warm, it would attract less air; or, if
warmer, it would augment the temperature of the vapours intended to be
condensed. Consequently, the shower of water employed in the tube K, as
the agent for cooling, bestows its maximum of effect when it is as warm
as the vapours to be condensed; therefore, I may express this
proposition, viz., ‘That in refrigerating with water, less of it may be
expended when it is warm than when it is cold, and that the least
quantity of water will be evaporated when it is as warm as the aqueous
or spirituous vapours upon which it is to operate.’
“This proposition may appear strange, nevertheless it is conformable to
the laws of nature; and appears only strange, because until now warm
water has not been employed with currents of air for refrigerating.
“Hence it is necessary to raise the temperature of the water in the
colander to the temperature of the vapours to be condensed: therefore, I
cause the lukewarm water, pumped from the reservoir E, to circulate in
the chamber C. In this circulation it also begins to act as a
refrigerating medium, taking up a portion of heat from the vapours that
pass through the pipe B, and afterwards it acts as a further condenser
in the cylinder, in the way described. Finally, the portion of this
water that is still in the fluid state, after having fallen down from
coil to coil, arrives lukewarm to the inclined surface L, which conducts
it into the reservoir E, from whence it is pumped up into the chamber C,
as before described.
“The tube or chimney K, may have more or less altitude; the higher it is
the greater is the current produced. The force or velocity of the
current of air can be governed by the areas of the introduction and exit
apertures. If the cylinder rises only to the height of the sieve, the
effect is much less than when it is prolonged beyond this height. I
would further remark, that if the cylinder was removed, a slight effect
might be produced, provided that a current of air be preserved in the
cylindrical space limited by the coils of the worm, and also if the
current was produced between the coils; or a central passage might be
formed in an apparatus of another shape than that above described.
“I have only shown the application of the worm, because intending only
to explain the principles of this method of condensing and
refrigerating.
“The small quantity of water wasted in this manner of condensation,
(that is, that portion passed off to the atmosphere in the form of
vapours, at the upper aperture of the cylinder K,) may be replaced by a
small stream of cold water, which may be brought to the apparatus, and
perhaps most conveniently introduced into the reservoir E, or into the
chamber between the pipes B and C. When operating upon aqueous vapours,
the waste of water is always less in weight than that of the vapours
liquefied. When this apparatus is applied to the purposes of
distillation, the end of the worm should terminate in a vessel M, which
is to receive the produce of the condensation. It will be seen that this
improved process is applicable to various purposes, where condensation
or refrigeration is required; for instance, in the boiling or
concentration of sugar; to condensing and refrigerating distilled
vapours, or steam, or saline liquids, either in vacuum or not; to
cooling brewers’ worts; and to the refrigeration of other liquors, or
any other processes, when it may be required.”
I have inserted the specification of this patent _verbatim_. M. Derosne
has busied himself during a long life with a prodigious number of
ingenious little contrivances for clarifying and boiling syrups,
distillation, &c., but he has in this invention taken a bolder flight,
having secured the exclusive privilege of condensing vapours, and
cooling liquors, with hot water, in preference to cold. No man at all
versant in the scientific doctrines, or the practical applications of
caloric, will ever seek to meddle with his monopoly of such a scheme. He
may find, perhaps, some needy coppersmith ready to espouse that or any
other equally foolish project, provided a productive job can be made of
it, against credulous customers.
For some rational methods of cooling liquors, and condensing vapours,
see REFRIGERATION, STILL, and SUGAR.
COPAL, a resin which exudes spontaneously from two trees, the _Rhus
copallinum_, and the _Elæocarpus copalifer_, the first of which grows in
America, and the second in the East Indies. A third species of copal
tree grows on the coasts of Guinea, especially on the banks of some
rivers, among whose sands the resin is found. It occurs in lumps of
various sizes and of various shades of colour, from the palest greenish
yellow to darkish brown. I found its specific gravity to vary in
different specimens from 1·059 to 1·071, being intermediate in density
between its two kindred resins, animé and amber. Some rate its specific
gravity so high as 1·139, which I should think one of the errors with
which chemical compilations teem. Copal is too hard to be scratched by
the nail, whence the excellence of its varnish. It has a conchoidal
fracture, and is without smell or taste. When exposed to heat in a glass
retort over a spirit lamp it readily melts into a liquid, which being
further heated boils with explosive jets. A viscid oily-looking matter
then distils over. After continuing the process for some time, no
succinic acid is found in the receiver, but the copal blackens in the
retort. Anhydrous alcohol boiled upon it, causes it to swell, and
transforms it by degrees into an elastic viscid substance. It is not
soluble in alcohol of 0·825 at the boiling point, as I have ascertained.
Copal dissolves in ether, and this ethereous solution may be mixed with
alcohol without decomposition. Caoutchoucine acts very slightly upon it
by my experiments, even at the boiling temperature of this very volatile
fluid; but a mixture of it with alcohol of 0·825 in equal parts
dissolves it very rapidly in the cold into a perfectly liquid varnish.
Alcohol holding camphor in solution also dissolves it, but not nearly so
well as the last solvent. According to Unverdorben, copal may be
completely dissolved by digesting one part of it for 24 hours with one
part and a half of alcohol (probably anhydrous), because that portion of
copal which is insoluble in alcohol, dissolves in a very concentrated
solution of the soluble portion. Oil of petroleum and turpentine
dissolve only 1 or 2 per cent. of raw copal. By particular management,
indeed, oil of turpentine may be combined with copal, as we shall
describe under the article VARNISH.
Fused copal possesses different properties from the substance in its
solid state; for it then may be made to combine both with alcohol and
oil of turpentine.
Unverdorben has extracted from the copal of Africa, five different kinds
of resin, none of which has however been applied to any use in the arts.
The ultimate constituents of copal by my analysis are, carbon 79·87,
hydrogen 9·00, oxygen 11·1; being of hydrogen 7·6 in excess above the
quantity necessary to form water with the oxygen. Of copal and animé,
551,166 libs. were imported in 1835.
COPPER is one of the metals most anciently known. It was named from the
island of Cyprus, where it was extensively mined and smelted by the
Greeks. It has a reddish brown colour inclining to yellow; a faint but
nauseous and rather disagreeable taste; and when rubbed between the
fingers it imparts a smell somewhat analogous to its taste. Its specific
gravity is from 8·8 to 8·9. It is much more malleable than it is
ductile; so that far finer leaves may be obtained from it than wire. It
melts at the 27th degree of Wedgewood’s pyrometer, and at a higher
temperature it evaporates in fumes which tinge the fire of a bluish
green. By exposure to heat with access of air, it is rapidly converted
into black scales of peroxide. In tenacity it yields to iron; but
surpasses gold, silver, and platinum, considerably in this respect.
In mineralogy, the genus copper includes about 13 different species, and
each of these contains a great many varieties. These ores do not possess
any one general exterior character by which they can be recognized; but
they are readily distinguished by chemical re-agents. Water of ammonia
digested upon any of the cupreous ores in a pulverized state, after they
have been calcined either alone or with nitre, assumes an intense blue
colour, indicative of copper. The richest of the ordinary ores appear
under two aspects; the first class has a metallic lustre, a copper red,
brass yellow, iron gray, or blackish gray colour, sometimes inclining to
blue; the second is without metallic appearance, has a red colour,
verging upon purple, blue, or green, the last tint being the most usual.
Few copper ores are to be met with, indeed, which do not betray the
presence of this metal by more or less of a greenish film.
1. _Native copper_, occurs in crystals, branches and filaments, its most
common locality being in primitive rocks. It is found abundantly in
Siberia, at the mines of Tourinski, in those of Hungary, of
Fundo-Moldavi in Gallicia, of Fahlun in Sweden, of Cornwall, &c. The
gangues of native copper are granite, gneiss, mica-slate, clay-slate,
quartz, carbonate or fluate of lime, sulphate of barytes, &c. The most
remarkable masses of native copper hitherto observed were; first, one in
Brazil, 14 leagues from Basa, which weighed 2616 pounds; and secondly,
another which Dr. Francis-le-Baron discovered in America to the south of
Lake Superior. It was nearly 15 feet in circumference.
2. _Sulphuret of Copper, the vitreous ore of Brochant._ The texture of
this ore is compact: its fracture, conchoidal, surface sometimes dull;
colour, iron black or lead gray, often bluish, iridescent, or reddish
from a mixture of protoxide. It is easily melted even by the heat of a
candle; but more difficult of reduction than protoxide. This ore yields
to the knife, assuming a metallic lustre when cut. Its density varies
from 4·8 to 5·34. Its composition according to Klaproth is 78·5 copper,
18·5 sulphur, with a little iron and silica. Its equivalent constitution
by theory is 80 copper + 20 sulphur = 100; whence 78·5 of metal should
be associated with 19·6 of sulphur. This ore is therefore one of the
richest ores, and forms very powerful veins, which likewise contain some
orange protoxide. It is to be found in all considerable copper
districts; in Siberia, Saxony, Sweden, and especially Cornwall, where
the finest crystals occur.
3. _Copper Pyrites_, resembles in its metallic yellow hue, sulphuret of
iron; but the latter is less pale, harder, and strikes fire more easily
with steel. It presents the most lively rainbow colours. Its specific
gravity is 4·3. It contains generally a good deal of iron; as the
following analysis will show; copper 30, sulphur 37, iron 33, in 100
parts. According to Hisinger, the Swedish pyrites contains 63 of copper,
12 of iron, and 25 of sulphur. These ores occur in primitive and
transition districts in vast masses and powerful veins; and are commonly
accompanied with gray copper, sulphuret of iron, sparry iron, sulphurets
of lead, and zinc.
4. _Gray Copper_, has a steel gray colour, more or less deep, either
shining or dull; fracture uneven; a distinct metallic lustre; difficult
of fusion at the blowpipe; it communicates to glass of borax a
yellowish-red colour. Its density in crystals is 4·86. Its composition
is very variable; consisting essentially of copper, iron, antimony, and
sulphur. The exploration of this ore is profitable, in consequence of
the silver which it frequently contains. It occurs in primitive
mountains; and is often accompanied with red silver ore, copper pyrites,
and crystallized quartz.
5. _Protoxide of Copper_, or _red oxide of Copper_: its colour is a deep
red, sometimes very lively, especially when bruised. It is friable,
difficult of fusion at the blowpipe, reducible on burning charcoal,
soluble with effervescence in nitric acid, forming a green liquid. Its
constitution when pure, is 88·9 copper + 11·1 oxygen = 100.
6. _Black oxide of Copper_, is of a velvet black, inclining sometimes to
brown or blue; and it acquires the metallic lustre on being rubbed. It
is infusible at the blowpipe. Its composition is, copper 80 + oxygen 20;
being a true peroxide.
7. _Hydrosilicate of Copper_, consists essentially of oxide of copper,
silica, and water. Its colour is green; and its fracture is conchoidal
with a resinous lustre, like most minerals which contain water. Its
specific gravity is 2·73. It is infusible at the blowpipe alone, but it
melts easily with borax.
8. _Dioptase Copper_, or _Emerald Malachite_; a beautiful but rare
cupreous mineral, consisting of oxide of copper, carbonate of lime,
silica, and water in varying proportions.
9. _Carbonate of Copper_, _Malachite_; is of a blue or green colour. It
occurs often in beautiful crystals.
10. _Sulphate of Copper_, _Blue Vitriol_, similar to the artificial salt
of the laboratory. The blue water which flows from certain copper mines,
is a solution of this salt. The copper is easily procured in the
metallic state by plunging pieces of iron into it.
11. _Phosphate of Copper_, is of an emerald green, or verdigris colour
with some spots of black. It presents fibrous or tuberculous masses with
a silky lustre in the fracture. It dissolves in nitric acid without
effervescence, forming a blue liquid; melts at the blowpipe, and is
reducible upon charcoal, with the aid of a little grease, into a
metallic globule. Its powder does not colour flame green, like the
powder of muriate of copper.
12. _Muriate of Copper_, is green of various shades; its powder imparts
to flame a remarkable blue and green colour. It dissolves in nitric acid
without effervescence; and is easily reduced before the blowpipe. Its
density is 3·5. By Klaproth’s analysis it consists of oxide of copper
73, muriatic acid 10, water 17.
13. _Arseniate of Copper._ It occurs in beautiful blue crystals. Before
the blowpipe it melts exhaling fumes of a garlic odour, and it affords
metallic globules when in contact with charcoal. See more upon the ores
at the end of this article.
In the article METALLURGY, I have described the mode of working certain
copper mines; and shall content myself here with giving a brief account
of two cupreous formations, interesting in a geological point of view;
that of the copper slate of Mansfeldt, and of the copper veins of
Cornwall.
The curious strata of bituminous schist in the first of these
localities, are among the most ancient of any which contain the exuviæ
of organised bodies not testaceous. From among their tabular slabs the
vast multitudes of fossil fish were extracted, which have rendered the
cantons of Mansfeldt, Eisleben, Ilmenau, and other places in Thuringia
and Voigtland so celebrated. Many of the fish are transformed into
copper pyrites. Here, also, have been found the fossil remains of the
lizard family, called _Monitors_.
Such is the influence of a wise administration upon the prosperity of
mines, that the thin layer of slate in this formation, of which 100
pounds commonly contain but one pound and a half of copper, occasionally
argentiferous, has been for several centuries the object of smelting
works of the greatest importance to the territory of Mansfeldt and the
adjoining country.
The frequent derangements which this metallic deposit experiences, led
skilful directors of the under-ground operations at an early period to
study the order of superposition of the accompanying rocks. From their
observations, there resulted a system of facts which have served to
guide miners, not only in the country of Mansfeldt, but over a great
portion of Germany, and in several other countries where the same series
of rocks, forming the immediate envelope of the cupreous schists, were
found to occur in the same order of superposition.
_Of the English copper works._--The deposits of copper in Cornwall occur
always as veins in granite, or in the schistose rocks which surround and
cover it; and hence, the Cornish miners work mostly in the granite or
greenish clay slate; the former of which they call _growan_, the latter
_killas_. But tin is sometimes disseminated in small veins in porphyry
or _elvan_, which itself forms great veins in the above rocks. No
stratification has been observed in Cornwall.
The copper veins are abundant in the killas and rare in the granite; but
most numerous near the line of junction of the two rocks. The different
kinds of mineral veins in Cornwall may be classed as follows:--