=Gluten Choc'olate.= (Gentile's.) A mixture of cocoa and gluten flour. As
a nutritious and appropriate food in diabetes.
=Gluten Flour.= _Prep._ 1. From the waste gluten of the starch works,
washed, dried, and ground.
2. (Gentile's.) From the last, mixed with about an equal weight of wheat
flour.
=GLYC'ERIN.= C_{3}H_{3}O_{3}. _Syn._ GLYCERIN, HYDRATED OXIDE OF GLYCERYL;
GLYCERINUM, L. A sweet syrupy liquid formed during the saponification of
oils and fats.
_Prep._ 1. Olive oil (or other suitable oil), protoxide of lead, and water
are heated together until an insoluble soap of lead (lead plaster) is
formed. The glycerin remains in the aqueous liquid. As this crude solution
of glycerin is produced in great quantities in the manufacture of lead
plaster, the operative chemist has only to purify it. This may be done as
follows:--
The water and washings from lead plaster are mixed together, filtered, and
submitted to the action of a stream of sulphuretted hydrogen to throw down
the lead; the supernatant liquor is decanted from the precipitate,
filtered, and evaporated to the consistence of a syrup in a water bath. To
render it quite pure it is diluted with water, decoloured with a little
animal charcoal, filtered, and again evaporated to the consistence of a
thin syrup, after which it is further evaporated in vacuo, or over
sulphuric acid, until it acquires the sp. gr. 1·265.
2. (M. Bruère-Perrin.) From the sweet liquor of the stearine works (a
product of the process of lime-saponification). The quantity of lime
present in the sample is first determined by means of oxalic acid, and the
proportion of sulphuric acid necessary for its saturation at once
calculated and added; the crude liquor is then concentrated in a
tinned-copper vessel, evaporation being promoted by brisk agitation, until
the sp. gr. sinks to 10° Baumé; it is next cooled and filtered, and
accurately neutralised (if it is required) with carbonate of potassa,
after which it is evaporated to the sp. gr. 24° Baumé; on cooling, it
deposits gelatinous sulphate of potassa; the whole is now filtered, the
deposit on the filter washed with a little very weak spirit and water, the
filtrate and washings mixed together and evaporated, as before, with
agitation, until the sp. gr. 28° Baumé, whilst hot (36° cold), is
attained, when the whole is allowed to cool; the clear liquid is, lastly,
decanted and filtered. In this state it has an amber colour, but may be
rendered colourless and odourless by rediluting it with water, treating it
with animal charcoal, filtering, and again evaporating to a proper
consistence.
3. By saponifying olive oil with caustic alkali, decomposing the resulting
soap with dilute sulphuric or tartaric acid, evaporating the aqueous
portion to dryness (nearly), dissolving out the glycerin with cold
rectified spirit, and filtering and evaporating the solution as before.
4. The residuary liquor of a soap manufactory is evaporated, and treated
with alcohol to dissolve out the glycerin. The spirit is then evaporated
off, the glycerin diluted with water, and finally boiled repeatedly with
animal charcoal until all colour and odour are removed.
_Obs._ The products of the above processes are nearly pure, but that of
Price's patent process, described below, is to be preferred to any of
them.
5. (Commercial.) From sweet stearin-liquor, by precipitating the lime by a
stream of carbonic acid gas, or by a solution of carbonate of soda,
carefully avoiding adding the latter in excess; the liquor is then boiled
a little, filtered, evaporated to a syrupy consistence, and again
filtered. This is the common glycerin of the shops. It may be further
purified as above.
6. (PRICE'S GLYCERIN--Patent dated 1854.) Superheated steam of from 550°
to 600° Fahr.) is introduced into a distillatory apparatus containing palm
oil or other fatty body. The action of the steam effects the decomposition
of the fat, and glycerin and the fatty acids distil over together but no
longer in combination. In the receiver the condensed glycerin, from its
higher specific gravity, sinks below the fatty acids. Sufficient steam
must be supplied, and the temperature nicely regulated. The glycerin is
concentrated by evaporation, and if discoloured, it is redistilled. It is
usually prepared with sp. gr. 1·24, and then contains 94% of anhydrous
glycerin. It can, however, be concentrated to sp. gr. 1·26 when it
contains 98%.
_Prop._ Pure glycerin is a colourless, odourless, uncrystallisable liquid,
sweet to the taste, and of a syrupy consistence; it mixes with water in
all proportions; it is unctuous and emollient, and softens bodies, like
oil, but without greasing them; it does not evaporate or change in the air
at ordinary temperatures, and is not susceptible of rancidity or
spontaneous fermentation; mixed with yeast and kept in a warm place, it is
gradually converted into propionic acid; a strong heat decomposes it, with
the production of acrolein; it is neutral to test-paper, and possesses
neither basic nor acid properties; it is easily charged with the aroma of
the essential oils, and may be combined with soap, and many other
substances, without undergoing change. Sp. gr., 1·27 (see _above_).
MM. Champion and Pellet recommend the following methods for testing the
purity of glycerin, as being convenient in application, and giving
accurate results.
_Qualitative Test._ The glycerin diluted with twice its weight of water is
treated in the cold.
(1.) With tribasic acetate of lead. If an abundant precipitate be formed,
and rapidly deposited, the presence of a proportion of foreign matters may
be assumed which would make it unsuitable for use in various applications,
such as the manufacture of nitro-glycerin, &c. The crude glycerin obtained
in treating fats with sulphuric acid is frequently thus contaminated.
These foreign matters result from the action of sulphuric acid at a high
temperature (about 110° C.) upon the fatty matter itself or on the
impurities it may contain.
(2.) Glycerin obtained by calcareous saponification, also may contain
oleate of lime. This may be detected with oxalate of ammonia, which throws
down the lime as a clearly perceptible precipitate.
The colour of glycerin is in no way an index of the purity of the product.
In all cases it is useful to be assured of the neutrality of the glycerin.
The preceding tests are suited for glycerins more or less impure, but not
adulterated. According to the authors' experiments the tribasic acetate of
lead separates all the foreign substances due to normal impurity of the
product or alteration in the glycerin during its manufacture. Any addition
of glucose may be detected by Fehlings' solution.
_Quantitative Test._ This test should comprehend the determination of the
water, the foreign organic matter, the lime, and the glycerin.
In the following table the authors have given the density of various
mixtures of water and glycerin, comparatively with the degrees Baumé, and
also the proportions of water corresponding to the densities. They state,
that these determinations have been verified by means of pure anhydrous
glycerin, prepared by keeping glycerin for several hours at a temperature
of 160° C, and terminating the operation _in vacuô_. The density found was
in accord with that given by Berthelot, namely, 1·264.
_Estimation of Organic Matter._ Fifty grams of glycerin diluted with water
are treated with an excess of tribasic acetate of lead, and the
precipitate collected on two tared filters, and the lead compound weighed.
The whole is then calcined, the residue treated with nitric acid, and then
with sulphuric acid, and from the sulphate of lead is calculated the
quantity of oxide of lead, that was in combination with organic matters,
and consequently the proportion of the latter, which rarely exceeds 1 to
1·5 per cent.
Lime may be estimated in the usual manner by oxalate of ammonia.
------------------------------------------------------------------------
Hydrometer | Areometer | Water, | Hydrometer | Areometer | Water,
Weight of | Degrees, | per Cent.| Weight of | Degrees, | per Cent.
Litre. | Baumé. | | Litre. | Baumé. |
-----------------------------------|------------------------------------
1264·0 31·2 0·0 | 1235·0 28·6 11·0
1262·5 31·0 0·5 | 1233·5 28·4 11·5
1261·2 30·9 1·0 | 1232·2 28·3 12·0
1260·0 30·8 1·5 | 1230·7 28·2 12·5
1258·5 30·7 2·0 | 1229·5 28·0 13·0
1257·2 30·6 2·5 | 1228·0 27·8 13·5
1256·0 30·4 3·0 | 1227·0 27·7 14·0
1254·5 30·3 3·5 | 1225·5 27·6 14·5
1253·2 30·2 4·0 | 1224·2 27·4 15·0
1252·0 30·1 4·5 | 1223·0 27·3 15·5
1250·5 30·0 5·0 | 1221·7 27·2 16·0
1249·0 29·9 5·5 | 1220·2 27·0 16·5
1248·0 29·8 6·0 | 1219·0 26·9 17·0
1246·5 29·7 6·5 | 1217·7 26·8 17·5
1245·5 29·6 7·0 | 1216·5 26·7 18·0
1244·0 29·5 7·5 | 1215·0 26·5 18·5
1242·7 29·3 8·0 | 1213·7 26·4 19·0
1241·2 29·2 8·5 | 1212·5 26·3 19·5
1240·0 29·0 9·0 | 1211·2 26·2 20·0
1239·0 28·9 9·5 | 1210·0 26·0 20·5
1237·5 28·8 10·0 | 1208·5 25·9 21·9
1236·2 28·7 10·5 |
------------------------------------------------------------------------
The authors consider that industrially the tribasic acetate of lead might
be used for the removal of organic matter from crude glycerin.
After separation of the precipitate, excess of the lead salt could be
removed by a current of sulphuretted hydrogen, and during the
concentration of the glycerin, the acetic acid set free would be
volatilized with injury to the product. The lead salt might be regenerated
by calcination, and again converted into acetate.[337]
[Footnote 337: 'Moniteur Scientifique,' Quesneville [3], vol. iii, p.
1033.]
The following quantitative test which it is said will detect upon
concentration of the fluids, one-tenth per cent. of glycerin in beer; one
per cent. in sherry, one per cent. in milk, and five per cent. in treacle,
is based upon a fact observed by Iles, viz. that borax when treated with
glycerin, gives to a Bunsen flame the green colour characteristic of
boracic acid. The method of its application as given by Messrs Senier and
Lowe is as follows:--The suspected solution is rendered alkaline by dilute
soda, and a borax bead placed in it for a short time. The bead is then
held in a Bunsen flame, and if the solution contains one per cent. of
glycerin a distinct reaction is observed. Erythrite and glycol give the
same colour.
If a small quantity of glycerin from which the fatty acids have not been
removed, be poured into the palm, and rubbed between the hands, a peculiar
fetid, mouse-like odour will be perceived.
_Uses, &c._ Glycerin is extensively employed as an excipient for medicines
(see GLYCEROLES), also, either alone, or in lotions, baths, &c., as a
soothing emollient, and is added to poultices and dressings instead of
oil, to prevent their hardening. Diluted with water, it often succeeds in
allaying itching and irritation of the skin when all other means fail. As
a cosmetic, either made into a lotion or added to soap (glycerin soap), or
used in small quantities (along with the water employed in washing), it
imparts a healthy clearness and a sensation of softness and coolness to
the skin, which is very agreeable and refreshing. It is the best remedy
known for chapped nipples, hands, lips, &c.; all of which may be prevented
by its use as an article of the toilet. Glycerin is sometimes used as a
sweetening agent, as a substitute for syrup.
Glycerin is employed for a great variety of purposes other than medicinal;
such, for example, as for:--Keeping clay moist for the modeller, for
preventing mustard from drying up, for keeping snuff damp, for the
preservation of fruit, for sweetening liqueurs, wine, beer, and malt
extracts. It is also used as a lubricant for some kinds of machinery, more
especially for watch and chronometer works, because it is unaffected by
contact with the air, does not thicken at a low temperature, and is
without action on such metals as copper, brass, &c. Glycerin is also an
ingredient in copying inks. It renders printing ink soluble in water;
indeed it is an excellent solvent for many substances, including the
Tar-colours (aniline blue, cyanine, aniline violet, and alizarine), and
arsenious acid. It is also added to the pulp of paper in order to render
it soft and pliable. It is said that leather driving-belts made as they
usually are of weakly tanned leather, when kept in glycerin for
twenty-four hours are not so liable to fray. A solution of glycerin in
water is now largely used instead of water alone for the purpose of
filling gas metres, as such a solution does not freeze in winter nor
evaporate in summer. It has also been used for the compasses on board
screw-steamers, in order to protect the inner compass-box, against the
vibrations caused by the motion of the propeller. It is also employed for
the preservation of anatomical preparations, and for mounting microscopic
specimens; as well as for rendering wooden casks impervious to petroleum
or other oils; as well as for the preparation of artificial oil of
mustard, or sulpho-cyan-allyl, which is made by treating glycerin with
iodide of phosphorus, whereby iodide of allyl is formed, which on being
dissolved in alcohol, and next distilled with sulpho-cyanide of potassium,
yields sulpho-cyan-allyl. When treated with concentrated nitric acid,
glycerin yields nitro-glycerin.[338]
[Footnote 338: Wagner's 'Chemical Technology.']
Even the above long list does not exhaust the many useful purposes to
which glycerin is now applied.
=Glycerin Cream for Chilblains.= Equal parts of glycerin, soft soap, and
cherry-laurel water, mixed together.
=Glycerin Cream with Camphor.= Glycerin, 2 parts; camphor, 1 part;
rectified spirit, 1 part. Mix. For chilblains.
=Glycerin Jelly for Microscopic Mounting.= ('Ed. Pharm. Journal.') Soak
any quantity of good clean gelatine in cold water for three or four hours.
Pour off the superfluous water, and melt the gelatine at a gentle heat;
when melted filter through flannel, and to the filtrate add an equal
quantity of Price's gelatin.
The above forms a good firm jelly, requiring little trouble in securing
the cover.
=Glycerin Ointment.= Glycerin, 8 parts; spermaceti, 4 parts; white wax, 1
part; oil of almonds (fixed), 16 parts. Add the glycerin to the melted
ingredients, and stir briskly till cold. For chaps and excoriations.
=GLYCEROLE.= A pharmaceutical preparation, in which glycerin is employed
as the excipient.
=Glycerole of Belladonna.= _Syn._ GLYCERINUM BELLADONNÆ. _Prep._ (Par.
Codex.) Extract of belladonna, 1 oz., glycerole of starch, 10 oz. (by
weight); rub together until perfectly smooth. Glyceroles of hemlock,
henbane, and opium are ordered by the Paris Codex to be prepared in the
same manner.
=Glycerole of Borax.= (B. P.) _Syn._ GLYCERINUM BORACIS, L. 1 of borax in
4-1/2 of glycerin.
=Glycerole of Carbolic Acid.= (B. P.) _Syn._ GLYCERINUM ACIDI CARBOLICI,
L. 1 of acid in 4-1/2 of glycerin.
=Glycerole of Gallic Acid.= (B. P.) _Syn._ GLYCERINUM ACIDI GALLICI, L. 1
of acid in 4-1/2 of glycerin.
=Glycerole of Iodine.= _Syn._ GLYCERINUM CUM IODINIO. _Prep._ (Par.
Codex.) Dissolve 5 parts of iodide of potassium and 1 part of iodine in
their own weight of water, and add to 40 parts of glycerin (by weight).
Applied in skin diseases.
=Glycerole of Iodide of Potassium.= _Syn._ GLYCERINUM POTASSII IODIDI.
_Prep._ (Par. Codex.) Iodide of potassium, 2 parts, glycerole of starch,
15 parts (by weight); dissolve the iodine in its own weight of water, and
add to this glycerole of starch.
=Glycerole of Starch.= (B. P.) _Syn._ GLYCERINUM AMYLI, L. 1 of starch in
8-1/2 of glycerin.
=Glycerole of Tannic Acid.= (B. P.) _Syn._ GLYCERINUM ACIDI TANNICI, L. 1
of acid in 4-1/2 of glycerin.
=Glycerole of Tar.= _Syn._ GLYCERINUM PICIS LIQUIDÆ. _Prep._ (Par. Codex.)
Purified tar, 1 oz. (by weight), glycerole of starch, 3 oz. (by weight).
=GLYCOARNICIN.= A radical cure for gangrene and tubercle (Zeller). 40
grammes clarified honey, with 35 grammes of a tincture of fresh arnica
herb, made with weak brandy. (Hager.)
=GLYCOBLASTOL= (Professor Kletzinsky, Vienna). An extract of the pericarps
of cayenne pepper, made with glycerine, diluted with a little water, and
perfumed with a trace of pleasant-smelling oil containing a suspicion of
patchouli. (Hager.)
=GLYCOCINE.= _Syn._ GLYCOLL. SUGAR OF GELATIN. (C_{2}H_{5}NO_{2}). This is
one of the products of the decomposition of gelatin when boiled with
dilute sulphuric acid; after the acid is removed by means of barium
carbonate, the glycocine may be procured in crystals by evaporating the
solution.
It may also be obtained by heating gelatin with a solution of potash or of
soda. It is, however, most easily separated in a state of purity by
boiling hippuric acid for half an hour with hydrochloric acid; as the
liquid cools benzoic acid is separated in abundance, and glycocine remains
in combination with hydrochloric acid; on the addition of absolute
alcohol, after the solution has been concentrated by evaporation and
super-saturated with ammonia, pure glycocine is deposited in minute
crystals.
Pure glycocine has a sweet taste, inferior to that of cane sugar. It is
soluble in about 400 parts of cold water, less soluble in rectified
spirit, and insoluble in absolute alcohol and in ether. It is not
susceptible of the alcoholic fermentation.
=GLYCYR'RHIZIN.= _Syn._ LIQUORICE SUGAR. An uncrystallisable variety of
sugar obtained from the root of common liquorice (_Glycyrrhiza glabra_).
It is yellow, transparent, soluble in both water and alcohol, and is not
susceptible of the vinous fermentation.
=GLYSTER.= See Enema.
=GNATS and MOS'QUITOES.= Smoke and strong fumes of any kind will drive
away these insects. If you only burn a piece of brown paper in an enclosed
space where they are, they soon after 'settle,' and appear to become so
stupefied as to remain inactive for some time after. In those parts of
the New World where mosquitoes abound, tobacco smoke is commonly had
recourse to in-doors, and large fires made of brush-wood or under-wood
out-of-doors. Old travellers, when compelled to bivouac during the season
in which they are troublesome, are very careful to keep close on the 'lee'
of these fires.
=GOA POWDER.= See ARAROBA.
=GOITRE.= _Syn._ DERBYSHIRE NECK; BRONCHOCELE, TRACHEOCELE; HERNIA
BRONCHIALIS, L. A tumour on the fore part of the neck. It sometimes occurs
in Derbyshire, and is endemic in the Alps and several other mountainous
districts. Iodine and the iodides appear to be the only substances capable
of curing or even arresting the progress of this disease.
There seems little doubt that goitre arises from drinking water rendered
hard by the presence of magnesian and lime salts.
The disease called cretinism, which is a peculiar form of idiocy, is in
some countries more particularly frequently associated with goitre. Both
these maladies prevail in Wurtemberg, Saxony, Silesia, the Tyrol,
Carynthia, Galicia, Austria, and Switzerland. In England, goitre seems
principally confined to the magnesian limestone district extending from
Nottingham to the Tyne; it also prevails in a smaller degree in
Derbyshire, Norfolk, Cambridge, and Somersetshire, where a few scattered
cases of cretinism are to be met with. Goitre is very much more general
than is usually supposed in France. In Asia, it is to be found amongst the
inhabitants of Chinese Tartary, Thibet, and Ceylon, and in India amongst
the dwellers in the valleys and extensive plains that lie at the foot of
the Himalayan mountains.
The disease is likewise known to exist in many parts of Africa; goitre is
also far from uncommon in certain districts of North America; whilst in
South America it is met with amongst the people inhabiting the plateaus of
New Grenada, which comprise localities differing so greatly in climatic
conditions, as deep and humid valleys, and arid plains almost or entirely
destitute of verdure.
Goitre is a disease that may be very rapidly and readily set up. Bally
says he has known certain waters in Switzerland produce it even in eight
or ten days; and the French medical journals contain many similar
instances of its early development.
=GOLD.= Au. _Syn._ AURUM; OR, Fr.; GOLD, Ger.) Gold is the most valuable
and, probably, the longest known of all the metals. From the remotest
period it has been esteemed for its beauty and permanence, and has been
taken as the standard measure of value amongst all civilised nations. An
account of the uses of gold in the arts, and its influence on society in
all ages, as a symbol of wealth and an article of ornament and utility,
would embrace the whole history of mankind. At the present day it alike
contributes to the conveniences, comforts, and luxuries of life; as often
exciting the baser passions of the human heart as promoting the cause of
benevolence and virtue.
Gold is found almost invariably in the metallic state. It occurs as gold
dust in the sands of various rivers, and in the alluvial soil of
auriferous districts, from both of which it is obtained by the simple
process of washing. Traces of it are constantly found in the iron and
other pyrites of the more ancient rocks. Sometimes it occurs beautifully
crystallised in the cubic form, associated with quartz, oxide of iron, and
other substances, in regular veins. In the gold fields of California and
Australia lumps of nearly pure gold have been discovered in abundance
during the last few years. In the former country a mass of gold weighing
28 pounds was found, whilst in our own colonies one weighing 106 pounds
was dug out of a quartz rock, near Bathurst. The latter contained upwards
of 91% of pure gold, and nearly 8-1/2% of silver; being as pure as the
English sovereign, or, in trade language, '22 carats fine.'
_Prep._ This consists merely in the separation of the gold and its
subsequent purification. Formerly, the auriferous sulphides, if very poor,
were first roasted, then fused into 'mattes' and again roasted; they were
next melted with lead, and the alloy thus obtained was refined by
cupellation. When the ores were very rich, the preliminary calcination and
fusion were omitted, and the alloy of lead at once formed. This method (by
fusion) does not answer well with auriferous copper pyrites or ores very
poor in gold. At the present time the method of amalgamation is
principally followed. When a 'vein-stone' is to be wrought for gold, it is
reduced to powder (on the small scale by hand, on the large scale in
stamping mills), and is shaken in a suitable apparatus with water and
mercury; an amalgam of gold is formed, which is then separated from the
mixture, and its mercury removed by distillation. The gold is next cast
into 'ingots.'
_Refining._--Gold obtained by the first method usually contains a little
copper and silver, and frequently tin or iron. Tin may be removed by
adding a little corrosive sublimate or nitre to the gold melted in a
crucible. The process by amalgamation commonly leaves no other alloy than
silver. This metal is removed either in the 'dry way,' by fusing the gold
with sulphur or sulphide of antimony; or in the 'wet way,' by 'quartation'
and 'parting.' At the Royal Mint, "when gold ingots contain a certain
quantity of silver" (say 2% or 3%), "instead of leaving it, as formerly,
to constitute a part of the standard alloy, it pays to extract it, and to
substitute copper in its place. To get the silver out of the said ingots,
they are melted with about 3 parts of silver--the resulting alloy is
granulated and boiled with sulphuric acid--the gold remains untouched, and
all the silver is dissolved and converted into sulphate.... The sulphate
of silver is then decomposed by the immersion of copper plates; the
silver is precipitated in a fine, crystalline powder, washed, pressed into
masses, and melted, and so affords PURE SILVER, which is afterwards made
standard by alloying it with copper, and is used for coinage. The
resulting sulphate of copper (which exists in the solution) is then
crystallised, and sold." (Brande.) "By first exhausting the gold with
nitric acid, and then boiling it in sulphuric acid, some two or three
thousandth part of silver which escaped the action of the nitric acid is
dissolved out, and perfectly pure gold is obtained." (Ure.)
By a foreign invention, patented in 1851 by Mr W. E. Newton, the
operations of 'separations' and 'refining' are conducted by one process.
The argentiferous substance, whether in the state of ore or bullion, is
reduced to a granulated or spongy state, by fusion along with zinc, or
some other metal cheaper than silver, and the zinc is subsequently
removed, by digesting the resulting granulated, laminated, or pulverulent
alloy, in dilute sulphuric acid, or other acid. The zinc, &c., is
recovered by the usual means. This process, carefully conducted, produces
metal of great ductility and purity, containing 99% to 99-1/2% of pure
gold.
Chemically pure gold is obtained by dissolving the metal in
nitro-hydrochloric acid, adding a solution of protosulphate of iron, and
collecting and washing the precipitate. In this state it is a brown
powder, which acquires a metallic lustre by friction or heat.
_Prop._ The most marked properties of gold are its rich yellow colour, its
ductility, malleability, insolubility in all menstrua except 'aqua regia'
(nitro-hydrochloric acid), aqueous chlorine, and hydrofluoric acid, and
its very slight affinity for oxygen. It melts at a bright red heat (2316°
Fahr.--Daniell), and the fused metal has a brilliant green colour. It
forms compounds with chlorine, iodine, oxygen, sulphur, &c. Sp. gr. of
native gold, 13·3 to 17·7; of pure gold, 19·3 (average); its greatest
density is 19·5.
_Tests._ Metallic gold is characterised by its yellow colour, insolubility
in nitric acid, and its ready solubility in aqua regia, forming a rich
yellow or amber-coloured liquid, which stains the skin purple. Solutions
of gold exhibit the following reactions:--Protosulphate of iron gives a
brown precipitate, which acquires a metallic lustre when
rubbed;--Protochloride of tin (preferably containing a little perchloride)
gives a violet, purple, or blackish precipitate, insoluble in hydrochloric
acid;--Sulphuretted hydrogen and hydrosulphide, of ammonia give a black
precipitate, insoluble in simple acids;--Ammonia gives a reddish-yellow
precipitate ('fulminating gold'), with tolerably concentrated solutions,
either at once or on boiling the liquid;--Liquor of potassa gives a
reddish-yellow precipitate with neutral solutions of gold, insoluble in
excess.
_Estim._ 1. In the dry way;--
The quantity of gold in an ALLOY is usually estimated by 'assaying' the
sample. Before proceeding to the assay, it is necessary to form some
estimate of the quantity of other metals (copper or silver, or both) in
the specimen to be examined, in order to employ the proper proportion of
lead in the 'cupellation.' The experienced assayer commonly does this by
the 'assay of the touch,' and, in certain cases, by a rough preliminary
assay. The quantity of lead employed may be about 16 times the weight of
the copper present in the sample, and when the alloy contains silver an
additional allowance of lead, equal to 1/10th of its weight, is made on
that account. When no silver is present, or it is not required to be
estimated, a much larger proportion of lead may be employed. The weight
taken for the assay ('assay pound') is usually 12 or 6 gr. The alloy and
dose of lead being accurately weighed and separately wrapped in small
pieces of paper, the assay may be at once proceeded with.
[Greek: a]. CUPELLATION. This operation, the most important of the whole,
has been already described. Unlike silver, gold will bear the highest heat
of the furnace without 'vegetating,' 'fuming,' or being absorbed by the
cupel. The loss of weight gives the amount of copper in the alloy.
[Greek: b]. QUARTATION. The cupelled sample is fused with three times its
weight of pure silver (called the 'witness'), by which the gold is reduced
to one fourth of the mass, or less, and in this state may be easily
removed.
[Greek: g]. PARTING. The alloy, after quartation, is hammered or rolled
out into a thin strip or leaf, curled into a spiral form, and boiled for a
quarter of an hour, in a small flask, with about 2-1/2 to 3 oz. of nitric
acid (sp. gr. 1·3); and the fluid being poured off, it is again boiled in
a similar manner with 1-1/2 to 2 oz. more of nitric acid (sp. gr. 1·2),
after which the gold is carefully collected, washed in pure water, and
dried. When the operation of 'parting' is skilfully conducted, and the
acid not too strong, the metal preserves its spiral form; otherwise, it
falls into the state of flakes or powder. The second boiling or digestion
is technically termed the 'reprise.' The loss of weight by 'parting,'
after deducting that of the 'witness,' corresponds to the quantity of
silver originally in the specimen.
[Greek: d]. ANNEALING. This consists in putting the pure gold obtained by
the last process into a small porous crucible or cupel, and heating it to
redness in the muffle.
[Greek: e]. WEIGHING. This must be done with the utmost accuracy. The
weight, in grains troy, doubled or quadrupled, as the case may be, gives
the number of carats fine of the alloy examined, without calculation.
According to the 'OLD FRENCH METHOD' of assaying gold, the following
quantities are taken:--For the assay pound, 12 gr.; fine silver, 30 gr.;
lead, 108 gr. These having been cupelled together, the (perfect) button
is rolled into a leaf (1-1/2 × 5 inches), twisted on a quill, and
submitted to parting with 2-1/2 oz. and 1-1/2 oz. of nitric acid, sp. gr.
1·16 (20° Baumé). The remainder of the process is similar to that above
described. Two assays are made in the same manner, with a third on pure
gold or gold of a known fineness; and no conclusion is drawn, unless the
assay of the latter comes out accurately, and that of the first two
correspond to each other.
For alloys containing platinum, which usually consist of copper, silver,
platinum, and gold, the method of assaying is as follows:--The alloy is
'cupelled' in the usual way, the loss of weight expresses the amount of
copper; and the button, made into a riband and treated with sulphuric
acid, indicates, by the portion dissolved, that also of the silver
present. By submitting the residuum to quartation, the platinum becomes
soluble in nitric acid. The loss after digestion in this menstruum
expresses the weight of that metal, and the weight of the portion now
remaining is that of the pure gold. Gold containing palladium may be
assayed in the same manner.