7,120,000 cubic feet of gas used in longest night, say 24th December.
About 2500 persons are employed in the metropolis alone, in this branch
of manufacture.
Between 1822 and 1827 the quantity nearly doubled itself, and that in 5
years.
Between 1827 and 1837 it doubled itself again.
Mr. Kirkham, engineer, obtained a patent, in June, 1837, for an improved
mode of removing the carbonaceous incrustation from the internal
surfaces of gas retorts. He employs a jet or jets of heated atmospheric
air, or other gases containing oxygen, which he impels with force into
the interior of such retorts as have become incrusted in consequence of
the decomposition of the coal. The retort is to be kept thoroughly red
hot during the application of the proposed jets. An iron pipe,
constructed with several flexible joints, leading from a blowing
machine, is bent in such a way as to allow its nozzle end to be
introduced within the retort, and directed to any point of its surface.
I should suppose that air, even at common temperatures, applied to a
retort ignited to the pitch of making gas, would burn away the
incrustations; but hot air will, no doubt, be more powerful.
GAS-HOLDER; a vessel for containing and preserving gas, of which various
forms are described by chemical writers.
GASOMETER, means properly a measurer of gas, though it is employed often
to denote a recipient of gas of any kind. See the article GAS-LIGHT.
GAUZE WIRE CLOTH; is a textile fabric, either plane or tweelled, made of
brass, iron, or copper wire, of very various degrees of fineness and
openness of texture. Its chief uses are for sieves, and safety lamps.
GAY-LUSSITE, is a white mineral of a vitreous fracture, which
crystallizes in oblique rhomboidal prisms; specific gravity from 1·93 to
1·95; scratches gypsum, but is scratched by calcspar; affords water by
calcination; it consists of carbonic acid 28·66; soda, 20·44; lime,
17·70; water, 32·20; clay, 1·00. It is in fact, by my analysis, a
hydrated soda-carbonate of lime in atomic proportions. This mineral
occurs abundantly in insulated crystals, disseminated through the bed of
clay which covers the _urao_, or native sesquicarbonate of soda, at
Lagunilla in Colombia.
GELATINE; (Eng. and Fr.; _Gallert_, _Leim_, Germ.) is an animal product
which is never found in the humours, but it may be obtained by boiling
with water the soft and solid parts; as the muscles, the skin, the
cartilages, bones, ligaments, tendons, and membranes. Isinglass consists
almost entirely of gelatine. This substance is very soluble in boiling
water; the solution forms a tremulous mass of jelly when it cools. Cold
water has little action upon gelatine. Alcohol and tannin (tannic acid,
see GALL-NUTS) precipitate gelatine from its solution; the former by
abstracting the water, the latter by combining with the substance itself
into an insoluble compound; of the nature of leather. No other acid,
except the tannic, and no alkali possesses the property of precipitating
gelatine. But chlorine and certain salts render its solution more or
less turbid; as the nitrate and bi-chloride of mercury, the
proto-chloride of tin, and a few others. Sulphuric acid converts a
solution of gelatine at a boiling heat into sugar. See LIGNEOUS FIBRE.
Gelatine consists of carbon, 47·88; hydrogen, 7·91; oxygen, 27·21. See
GLUE and ISINGLASS.
GEMS, are precious stones, which, by their colour, limpidity, lustre,
brilliant polish, purity, and rarity, are sought after as objects of
dress and decoration. They form the principal part of the crown jewels
of kings, not only from their beauty, but because they are supposed to
comprize the greatest value in the smallest bulk; for a diamond, no
larger than a nut or an acorn, may be the representative sign of the
territorial value of a whole country, the equivalent in commercial
exchange of a hundred fortunes, acquired by severe toils and privations.
Among these beautiful minerals mankind have agreed in forming a select
class, to which the title of _gems_ or _jewels_ has been appropriated;
while the term _precious stone_ is more particularly given to substances
which often occur under a more considerable volume than _fine stones_
ever do.
Diamonds, sapphires, emeralds, rubies, topazes, hyacinths, and
chrysoberyls, are reckoned the most valuable _gems_.
Crystalline quartz, pellucid opalescent or of various hues, amethyst,
lapis lazuli, malachite, jasper, agate, &c., are ranked in the much more
numerous and inferior class of ornamental stones. These distinctions are
not founded upon any strict philosophical principle, but are regulated
by a conventional agreement, not very well defined; for it is impossible
to subject these creatures of fashion and taste to the rigid
subdivisions of science. We have only to consider the value currently
attached to them, and take care not to confound two stones of the same
colour, but which may be very differently prized by the _virtuoso_.
Since it usually happens that the true gems are in a cut and polished
state, or even set in gold or silver, we are thereby unable to apply to
them the criteria of mineralogical and chemical science. The cutting of
the stone has removed or masked its crystalline character, and
circumstances rarely permit the phenomena of double or single refraction
to be observed; while the test by the blowpipe is inadmissible. Hence
the only scientific resources that remain are the trial by electricity,
which is often inconclusive; the degree of hardness, a criterion
requiring great experience in the person who employs it; and, lastly,
the proof by specific gravity, unquestionably one of the surest means of
distinguishing the really fine gems from ornamental stones of similar
colour. This proof can be applied only to a stone that is not set; but
the richer gems are usually dismounted, when offered for sale.
This character of specific gravity may be applied by any person of
common intelligence, with the aid of a small hydrostatic balance. If,
for example, a stone of a fine crimson-red colour, be offered for sale,
as an oriental ruby; the purchaser must ascertain if it be not a
Siberian tourmaline, or ruby spinel. Supposing its weight in air to be
100 grains, if he finds it reduced to 69 grains, when weighed in water,
he concludes that its bulk is equal to that of 31 grains of water, which
is its loss of weight. Now, a real sapphire which weighs 100 grains in
air, would have weighed 76·6 in water; a spinel ruby of 100 grains would
have weighed 72·2 in water, and a Siberian tourmaline of 100 grains
would have weighed only 69 grains in water. The quality of the stone in
question is, therefore, determined beyond all dispute, and the purchaser
may be thus protected from fraud.
The _sard_ of the English jewellers (_Sardoine_, French) is a stone of
the nature of agate, having an orange colour more or less deep, and
passing by insensible shades into yellow, reddish, and brown; whence it
has been agreed to unite under this denomination all the agates whose
colour verges upon brown. It should be remarked, however, that the sard
presents, in its interior and in the middle of its ground, concentric
zones, or small nebulosities, which are not to be seen in the red
cornelian, properly so called. The ancients certainly knew our sard,
since they have left us a great many of them engraved, but they seem to
have associated under the title _sarda_ both the sardoine of the French,
and our cornelians and calcedonies. Pliny says that the _sarda_ came
from the neighbourhood of a city of that name in Lydia, and from the
environs of Babylon. Among the engraved sards which exist in the
collection of antiques in the Bibliothèque Royale of Paris, there is an
Apollo remarkable for its fine colour and great size. When the stone
forms a part of the agate-onyx, it is called sardonyx. For further
details upon Gems, and the art of cutting and engraving them, see
LAPIDARY.
GEOGNOSY, means a knowledge of the structure of the earth; GEOLOGY, a
description of the same. The discussion of this subject does not come
within the province of this Dictionary.
GERMAN SILVER. See the latter end of the article COPPER.
GERMINATION; (Eng. and Fr.; _Das Keimen_, Germ.) is the first sprouting
of a seed after it is sown, or when, after steeping, it is spread upon
the malt floor. See BEER.
GIG MACHINES, are rotatory drums, mounted with thistles or wire teeth
for teazling cloth. See WOOLLEN MANUFACTURE.
GILDING (_Dorure_, Fr.; _Vergoldung_, Germ.); is the art of coating
surfaces with a thin film of gold. For a full discussion of this
subject, see GOLD. Mr. Elkington, gilt toy maker, obtained a patent, in
June, 1836, for gilding copper, brass, &c., by means of potash or soda
combined with carbonic acid, and with a solution of gold. Dissolve, says
he, 5 oz. troy of fine gold in 52 oz. avoirdupois of nitro-muriatic acid
of the following proportions: viz. 21 oz. of pure nitric acid, of spec.
grav. 1·45, 17 oz. of pure muriatic acid, of spec. grav. 1·15; with 14
oz. of distilled water.
The gold being put into the mixture of acids and water, they are to be
heated in a glass or other convenient vessel till the gold is dissolved;
and it is usual to continue the application of heat after this is
effected, until a reddish or yellowish vapour ceases to rise.
The clear liquid is to be carefully poured off from any sediment which
generally appears and results from a small portion of silver, which is
generally found in alloy with gold. The clear liquid is to be placed in
a suitable vessel of stone, pottery ware is preferred. Add to the
solution of gold 4 gallons of distilled water, and 20 pounds of
bicarbonate of potash of the best quality; let the whole boil moderately
for 2 hours, the mixture will then be ready for use.
The articles to be gilded having been first perfectly cleaned from scale
or grease, they are to be suspended on wires, conveniently for a workman
to dip them in the liquid, which is kept boiling. The time required for
gilding any particular article will depend on circumstances, partly on
the quantity of gold remaining in the liquid, and partly on the size and
weight of the article; but a little practice will readily give
sufficient guidance to the workman.
Supposing the articles desired to be gilded be brass or copper buttons,
or small articles for gilt toys, or ornaments of dress, such as earrings
or bracelets, a considerable number of which may be strung on a hoop, or
bended piece of copper or brass wire, and dipped into the vessel
containing the boiling liquid above described, and moved therein, the
requisite gilding will be generally obtained in from a few seconds to a
minute; this is when the liquid is in the condition above described, and
depending on the quality of the gilding desired; but if the liquid has
been used some time, the quantity of gold will be lessened, which will
vary the time of operating to produce a given effect, or the colour
required, all which will quickly be observed by the workman; and by
noting the appearance of the articles from time to time, he will know
when the desired object is obtained, though it is desirable to avoid as
much as possible taking the articles out of the liquid.
When the operation is completed, the workman perfectly washes the
articles so gilded with clean water; they may then be submitted to the
usual process of colouring.
If the articles be cast figures of animals, or otherwise of considerable
weight, compared with the articles above mentioned, the time required to
perform the process will be greater.
In case it is desired to produce what is called a dead appearance, it
may be performed by several processes: the one usually employed is to
dead the articles in the process of cleaning, as practised by
brass-founders and other trades; it is produced by an acid, prepared for
that purpose, sold by the makers under the term “deading aquafortis,”
which is well understood.
It may also be produced by a weak solution of nitrate of mercury,
applied to the articles previous to the gilding process, as is practised
in the process of gilding with mercury, previous to spreading the
amalgam, but generally a much weaker solution; or the articles having
been gilded may be dipped in a solution of nitrate of mercury, and
submitted to heat to expel the same, as is practised in the usual
process of gilding.
It is desirable to remark, that much of the beauty of the result depends
on the well cleaning of the articles, and it is better to clean them by
the ordinary processes, and at once pass them into the liquid to be
gilded. See GOLD, towards the end.
GIN, or _Geneva_, from _Genievre_ (juniper), is a kind of ardent spirits
manufactured in Holland, and hence called Hollands gin in this country,
to distinguish it from British gin. The materials employed in the
distilleries of Schiedam, are two parts of unmalted rye from Riga,
weighing about 54 lbs. per bushel, and one part of malted bigg, weighing
about 37 lbs. per bushel. The mash tun, which serves also as the
fermenting tun, has a capacity of nearly 700 gallons, being about five
feet in diameter at the mouth, rather narrower at the bottom, and 4-1/2
feet deep; the stirring apparatus is an oblong rectangular iron grid,
made fast to the end of a wooden pole. About a barrel, = 36 gallons of
water, at a temperature of from 162° to 168° (the former heat being best
for the most highly dried rye), are put into the mash tun for every
1-1/2 cwt. of meal, after which the malt is introduced and stirred, and
lastly the rye is added. Powerful agitation is given to the magma till
it becomes quite uniform; a process which a vigorous workman piques
himself upon executing in the course of a few minutes. The mouth of the
tun is immediately covered over with canvas, and further secured by a
close wooden lid, to confine the heat; it is left in this state for two
hours. The contents being then stirred up once more, the _transparent_
spent wash of a preceding mashing is first added, and next as much cold
water as will reduce the temperature of the whole to about 85° F. The
best Flanders yeast, which had been brought, for the sake of carriage,
to a doughy consistence by pressure, is now introduced to the amount of
one pound for every 100 gallons of the mashed materials.
The gravity of the fresh wort is usually from 33 to 38 lbs. per Dicas’
hydrometer; and the fermentation is carried on from 48 to 60 hours, at
the end of which time the attenuation is from 7 to 4 lbs., that is, the
specific gravity of the supernatant wash is from 1·007 to 1·004.
The distillers are induced by the scarcity of beer-barm in Holland, to
skim off a quantity of the yeast from the fermenting tuns, and to sell
it to the bakers, whereby they obstruct materially the production of
spirit, though they probably improve its quality, by preventing its
impregnation with yeasty particles; an unpleasant result which seldom
fails to take place in the whiskey distilleries of the United Kingdom.
On the third day after the fermenting tun is set, the wash containing
the grains is transferred to the still, and converted into low wines. To
every 100 gallons of this liquor, two pounds of juniper berries, from 3
to 5 years old, being added along with about one quarter of a pound of
salt, the whole are put into the low wine still, and the fine Hollands
spirit is drawn off by a gentle and well-regulated heat, till the magma
becomes exhausted; the first and the last products being mixed together;
whereby a spirit, 2 to 3 per cent. above our hydrometer proof, is
obtained, possessing the peculiar fine aroma of gin. The quantity of
spirit varies from 18 to 21 gallons per quarter of grain; this large
product being partly due to the employment of the spent wash of the
preceding fermentation; an addition which contributes at the same time
to improve the flavour.
For the above instructive details of the manufacture of genuine
Hollands, I am indebted to Robert More, Esq., formerly of Underwood,
distiller, who after studying the art at Schiedam, tried to introduce
that spirit into general consumption in this country, but found the
palates of our gin-drinkers too much corrupted to relish so pure a
beverage.
GINNING, is the name of the operation by which the filaments of cotton
are separated from the seeds. See COTTON MANUFACTURE.
GLANCE COAL, or anthracite, of which there are two varieties, the
_slaty_ and the _conchoidal_. See ANTHRACITE.
GLASS (_Verre_, Fr.; _Glas_, Germ.); is a transparent solid formed by
the fusion of siliceous and alkaline matter. It was known to the
Phenicians, and constituted for a long time an exclusive manufacture of
that people, in consequence of its ingredients, natron, sand, and fuel,
abounding upon their coasts. It is probable that the more ancient
Egyptians were unacquainted with glass, for we find no mention of it in
the writings of Moses. But according to Pliny and Strabo, the glass
works of Sidon and Alexandria were famous in their times, and produced
beautiful articles; which were cut, engraved, gilt, and stained of the
most brilliant colours, in imitation of precious stones. The Romans
employed glass for various purposes; and have left specimens in
Herculaneum of window-glass, which must have been blown by methods
analogous to the modern. The Phenician processes seem to have been
learned by the Crusaders, and transferred to Venice in the 13th century,
where they were long held secret, and formed a lucrative commercial
monopoly. Soon after the middle of the 17th century, Colbert enriched
France with the blown mirror glass manufacture.
Chance undoubtedly had a principal share in the invention of this
curious fabrication, but there were circumstances in the most ancient
arts likely to lead to it; such as the fusing and vitrifying heats
required for the formation of pottery, and for the extraction of metals
from their ores. Pliny ascribes the origin of glass to the following
accident. A merchant-ship laden with natron being driven upon the coast
at the mouth of the river Belus, in tempestuous weather, the crew were
compelled to cook their victuals ashore, and having placed lumps of the
natron upon the sand, as supports to the kettles, found to their
surprise masses of transparent stone among the cinders. The sand of this
small stream of Galilee, which runs from the foot of Mount Carmel, was
in consequence supposed to possess a peculiar virtue for making glass,
and continued for ages to be sought after and exported to distant
countries for this purpose.
Agricola, the oldest author who has written technically upon glass,
describes furnaces and processes closely resembling those employed at
the present day. Neri, Kunckel, Henckel, Pott, Achard, and some other
chemists, have since then composed treatises upon the subject; but Neri,
Bosc, Antic, Loysel, and Allut, in the Encyclopédie Méthodique, are the
best of the elder authorities.
The window-glass manufacture was first begun in England in 1557, in
Crutched Friars, London; and fine articles of flint-glass were soon
afterwards made in the Savoy House, Strand. In 1635 the art received a
great improvement from Sir Robert Mansell, by the use of coal fuel
instead of wood. The first sheets of blown glass for looking glasses and
coach windows were made in 1673 at Lambeth, by Venetian artisans
employed under the patronage of the Duke of Buckingham.
The casting of mirror-plates was commenced in France about the year
1688, by Abraham Thevart; an invention which gave rise soon afterwards
to the establishment of the celebrated works of St. Gobin, which
continued for nearly a century the sole place where this highly prized
object of luxury was well made. In excellence and cheapness, the French
mirror-plate has been, however, for some time rivalled by the English.
The analysis of modern chemists, which will be detailed in the course of
this article, and the light thrown upon the manufacture of glass in
general by the accurate means now possessed of purifying its several
ingredients, would have brought the art to the highest state of
perfection in this country, but for the vexatious interference and
obstructions of our excise laws.
The researches of Berzelius having removed all doubts concerning the
acid character of silica, the general composition of glass presents now
no difficulty of conception. This substance consists of one or more
salts; which are silicates with bases of potash, soda, lime, oxide of
iron, alumina, or oxide of lead; in any of which compounds we can
substitute one of these bases for another, provided that one alkaline
base be left. Silica in its turn may be replaced by the boracic acid,
without causing the glass to lose its principal characters.
Under the title glass are therefore comprehended various substances
fusible at a high temperature, solid at ordinary temperatures,
brilliant, generally more or less transparent, and always brittle. The
following chemical distribution of glasses has been proposed.
1. Soluble glass; a simple silicate of potash or soda; or of both these
alkalis.