Cooley's Cyclopaedia of Practical Receipts Volume I Part 272

5. A fourth 100 gr, of guano is weighed, and exhausted by trituration and digestion with hot water (see 3 _a_); the solution is evaporated to dryness by a gentle heat, and the residuum of the evaporation, after being weighed, is powdered and enclosed in a stout phial with 8 times its volume of alcohol, sp. gr. 825 (63 o. p.); the plant is next securely corked and guarded, and exposed for some time, with agitation, to the heat of 212 Fahr., the whole is then allowed to cool, the contents of the phial filtered, the undissolved portion washed with hot alcohol, and both the filtrate and the 'washings' gently evaporated to dryness, and weighed.

This gives the richness of the sample in UREA, one of the most valuable const.i.tuents of the best guano. Its presence is "a certain proof of its entire soundness." (Ure.)

6. _a._ Another 100 gr. of the guano is taken, and, after being exhausted with water, is dried at 212 Fahr., and weighed; it is then digested with heat in 20 times its weight of borax-water (containing 1% of borax), or in a solution of caustic pota.s.sa, and after a time the whole is thrown on a weighed filter, washed with a little cold distilled water, dried by a heat not higher than that of boiling water, and again carefully weighed. The loss, in grains, indicates the proportion per cent. of URIC ACID.

The accuracy of the result may be verified by adding dilute hydrochloric acid, in slight excess, to the filtrate, collecting the bulky, crystalline precipitate of uric acid which forms, washing it carefully with a little rectified spirit, drying it, and weighing it, as before. This weight, which in general is a very little under that denoted above, is the more accurate of the two. The precipitate is shown to be uric acid by its a.s.suming a rich crimson colour when treated with a little nitric acid, which turns to a rich purple (_murexide_) when it is moistened with ammonia water.

_b._ The quant.i.ty of uric acid last obtained, multiplied by 11012, gives the per-centage of URATE OF AMMONIA.

_Obs._ Amongst the numerous const.i.tuents of guano, none are so valuable in an agricultural point of view as the three substances referred to in the last two sections. Indeed, almost all the ammonia furnished by this substance to the soil, after the latter, manured with it, has been exposed to the air and rain, is derived from the slow decomposition of urea, or urate of ammonia. It is these substances from which the store of latent, or, as Dr Ure terms it, potential ammonia, is derived. The ammonia existing in the guano under the form of carbonate, or of soluble salts (ready formed ammonia), is either soon dissipated in air or is washed away by heavy rains, and, therefore, forms the least valuable and durable portion of this manure. It may be even added artificially, a matter almost impossible with the former. An a.s.say, therefore, for the latent ammonia, or the urea, or the urate of ammonia, any one of them singly, at once furnishes us, as we have already hinted, with evidence of the quality of the guano examined, without the expense and trouble of a complete a.n.a.lysis of this substance. Urea and uric acid are only to be found in the very best samples of guano, and their presence is a positive proof of entire soundness and superior quality. The other valuable portions of guano are pota.s.sa and phosphoric acid (phosphate of lime chiefly); the rest are of little importance. (See 2 _c_, _above_.)

=GUARANA= (Grimault & Co., Paris). 12 migrain powders, each weighing 175 grammes, consisting of guarana, but perhaps also containing an admixture of cocoa seeds, neither prepared nor roasted. (Hager.)

=GUARANA'.= _Syn._ PAULLINIA, BRAZILIAN COCOA. An alimentary and medicinal substance prepared from the seeds of _Paullinia sorbilis_, a Brazilian tree. The dried seeds, deprived of their aril, are pounded and kneaded into a ma.s.s, which is afterwards made into oblong or rounded cakes (GUARANA BREAD). These cakes are used as we use chocolate--mixed with water and sugar, and drank as a beverage. In Brazil this beverage is largely consumed, both on account of its nutritive qualities, and for its stomachic, febrifugal, and aphrodisiac effects. See CHOCOLATE, &c., also _below_.

=GUARANINE'.= A crystalline substance discovered by M. Martius in guarana.

It appears to be identical with caffeine, the active principle of coffee and tea.

=GUD'GEON.= The _Cyprinus gobeo_ (Linn.), a small fresh-water fish, common almost everywhere. The white is considered the best. It was formerly used in medicine.

=GUM.= _Syn._ GUMMI, L. The general term for an important cla.s.s of vegetable products. Gums are more or less soluble in cold water, but insoluble in alcohol, ether, and oils. They are obtained from certain plants in amorphous ma.s.ses; most of them exude spontaneously, or on puncturing the bark. The most perfect type of this cla.s.s is the substance called GUM ARABIC, or GUM ACACIA. The gums are employed as demulcents in medicines, and are used as cements, and for giving stiffness and gloss to textile fabrics. Among the vulgar the term is often incorrectly applied to the resins and gum resins.

=Gum Acacia.= _Syn._ GUM ARABIC; ACACIae GUMMI (B. P.); G. ARABIc.u.m, G.

ACACIA, ACACIA (Ph. L.), L. "From various species" (of _Acacia_) "yielding gum" (Ph. L. & E.), chiefly _Acacia arabica_ and _A. vera_. "Whitish or yellowish, transparent or cracked on the surface, and opaque; brittle; it dissolves freely in water." (Ph. L.) It is scentless, and may be bleached by exposure to the sun and air, at the temperature of boiling water. Sp.

gr. 1355. (Ure.) The pure soluble principle of gum Arabic is termed ARABIN (which _see_). BARBARY or MOROCCO GUM, GUM SENEGAL, and EAST INDIA GUM, are inferior commercial varieties of the same substance from other species of _Acacia_ (see _below_).

Powdered gum Arabic (PULVIS ACACIae) is frequently adulterated with flour or farina, or with Senegal or other inferior gums. The first may be detected by agitating a little of the powder with cold water; the pure gum dissolves rapidly, whilst the starch or flour falls to the bottom of the vessel. Or, a little of the powder may be mixed with boiling water, and when cold, tested with tincture of iodine; if it contains starch or flour, the paste will a.s.sume a blue colour. If it contains cherry-tree gum or tragacanth, it will be only partly soluble in cold water, and the paste will be partly coloured, and more or less interspersed with gelatinous clots.

For the detection of dextrin in gum Arabic Hager finds that when some of the adulterated article is placed in a gla.s.s dish, with vertical sides, and a solution of ferric chloride, density 148, diluted with an equal volume of water, is poured over it until the grains are just covered, in the course of a minute or so that particles of gum Arabic will adhere to the bottom of the vessel, whilst the grains of dextrin do not.

Much of the white gum Arabic of the shops is formed by bleaching gum Senegal, by what is called 'Picciotto's process.' The gum is dissolved in water, and sulphurous acid gas pa.s.sed through the solution. The liquid is afterwards boiled to expel the sulphurous acid, a little of which, however, still remains behind. To obtain the gum in a still whiter state, carbonate of baryta is added, and after agitation the mixture is filtered; it is afterwards shaken with gelatinous alumina, again filtered, and evaporated. The product (BLEACHED GUM) is very white, but lacks the peculiar toughness and adhesiveness of the best gum acacia.

=Gum, Barbary.= _Syn._ MOROCCO GUM. An inferior product, consisting of a mixture of several Acacia gums. It is exported from Mogador.

=Gum, Ba.s.sora.= A solution of yellowish gum brought from the neighbourhood of Ba.s.sora. It differs from most gums in being nearly insoluble in water.

The plant yielding it is believed to be a species of _Mimosa_. It contains the principle Ba.s.sORIN, which also exists in gum tragacanth.

=Gum, Bleached.= See GUM ARABIC (_above_).

=Gum, Brit'ish.= _Syn._ DEXTRIN, STARCH GUM. Starch converted by the action of acids, diastase, or heat, into a soluble substance resembling gum.

_Prep._ 1. Malt (crushed small), 1 lb.; warm water, 2 galls.; mix, heat the whole to 145 Fahr., add of potato starch 5 lbs., raise the heat to 160 or 165 Fahr., and mash for about 25 minutes, or until the liquid becomes thin and clear; it must then be instantly run off, and raised to the boiling point to prevent the formation of sugar; after boiling for 3 or 4 minutes the whole must be filtered, and evaporated to dryness by a steam heat.

2. By exposing dry potato starch, in a stove, to a heat of about 400 Fahr. Yellow and inferior.

3. (M. Payen.) Dry starch, 1 ton, is moistened uniformly with concentrated nitric acid, 4-1/2 lbs. (diluted with), water, q. s., and the paste or dough is made up into small bricks or loaves, and dried in a stove; it is next reduced to coa.r.s.e powder, and exposed in a stove-room for some time to a current of air at 160 to 165 Fahr.; it is next ground, sifted, and exposed, as before, to a heat of about 228 Fahr.; it is, lastly, ground, and pa.s.sed through the 'bolting machine.' Very white and superior. This process has been patented in France by M. Henze.

4. (Pinel.) Water, 100 galls., nitric acid, 1/2 gall., and hydrochloric acid, 1/2 pint, are mixed together, and so much potato starch is mixed as will form a thin paste; in two hours the liquid is drained off, and the solid matter is made up into lumps, which are dried by a gentle heat in a stove-room; they are next coa.r.s.ely pulverised, and the powder is exposed on three successive days to the respective temperatures of 100, 150, and 190 Fahr.; the whole is then sifted, and, lastly, exposed to a heat ranging from 300 to 350 Fahr. Darker coloured than the last. To give it the appearance of gum Arabic, it is made into a paste with water containing 1% of nitric acid, and after being spread on copper plates in layers 3/4 to 1 inch thick, it is exposed to a stove heat ranging from 240 to 300 Fahr.

_Prop., &c._ White; insipid; transparent; friable; soluble in cold water, and in dilute spirit; insoluble in alcohol and ether; its solution yields a precipitate with acetate of lead. Iodine commonly turns commercial dextrin blue, but does not affect the colour of pure dextrin. It is distinguished from ordinary gum by its right-handed polarization of light, and by yielding oxalic but not mucic acid, when treated with nitric acid.

Dextrin is nutritive, emollient, and agglutinant. In France it is largely employed by the pastry-cooks and confectioners, and in medicine as a subst.i.tute for gum. The French surgeons also commonly employ it as a 'stiffening' for the splints used for fractured limbs. In this country it is chiefly used as a fine dressing for muslins, silk, and other textile fabrics, and in calico printing. Recently it has been made up into tear-like ma.s.ses, and sold for gum Arabic, to which, however, it is vastly inferior as an agglutinant. See DEXTRIN.

=Gum, Cherry-tree.= _Syn._ FRUIT-TREE GUM, PLUM-TREE G.; GUMMI CERASI, G.

PRUNI, L. An exudation from the stems of cherry, plum, and some other of the _Rosaceae_. It is only partly soluble in water. It contains CERASIN (which _see_).

=Gum, East India.= This product, which consists of inferior kinds of gum acacia, is chiefly exported from Bombay, having been previously conveyed there from the coast of Arabia. It varies greatly in quality. Some samples are quite unfitted for making gum-water.

=Gum, Insoluble.= See Ba.s.sORA GUM, CHERRY-TREE GUM, and GUM TRAGACANTH.

=Gum, Seed.= _Syn._ GUMMI SEMINUM, L. A species of soluble gum extracted from the seed of the flax (linseed), quince, &c.

=Gum, Senegal.= This product, which is largely exported from Portendie, Sierra Leone, and the French settlements on the Senegal, ranks next in quality to gum acacia, and for many purposes, as calico-printing for instance, it answers equally well. The transparent and light-coloured pieces are frequently picked out and sold as gum Arabic.

=Gum Trag'acanth.= _Syn._ TRAGACANTH, GUM DRAGON; GUMMI TRAGACANTHA, G.

DRACONIS, TRAGACANTHA (Ph. L.), L. The gummy exudation of the _Astragalus verus_, hardened by the air. When digested in water, it swells considerably, a portion is dissolved, and the whole combines to form a thick mucilage. It is totally soluble in boiling water, when some change is supposed to take place in it; a great portion, however, afterwards separates. Sp. gr. 1384. It is chiefly employed in calico-printing, and by shoemakers and lozenge-makers; by the latter to give toughness to the saccharine ma.s.s.

Powdered tragacanth is often adulterated with flour of starch, and not unfrequently with the commoner varieties of gum Arabic. According to M.

Planche, a mixture of pulverised tragacanth and gum Arabic forms, with water, a thinner mucilage than the same quant.i.ty of either of these gums alone. This fraud may be detected as follows:--Make a mucilage of the suspected gum, and add thereto a few drops (2 or 3 to the dr.) of alcoholic tincture of guaiac.u.m, taking care to stir it all the while. If the sample contains any gum Arabic, the mixture, in the course of a few minutes, a.s.sumes a fine blue colour, whilst it does not change colour if the gum tragacanth is pure, 5% of gum arabic can be thus detected. When the quant.i.ty is very small, one to four hours may elapse before the colour is developed. Starch and flour are detected in the manner noticed under GUM ARABIC.

=Gum, Turkey.= Various qualities of gum acacia are sold under this name.

=GUM RES'INS.= _Syn._ GUMMI RESINae, L. Vegetable products in which the properties of gum and resin are combined. They are partly soluble in water, and partly in alcohol. Many of them form a species of emulsion when triturated with the former fluid. The princ.i.p.al gum resins are AMMONIAc.u.m, a.s.sAFTIDA, BDELLIUM, GALBANUM, GAMBOGE, MYRRH, OLIBANUM, OPOPONAX, SAGAPENUM, and SCAMMONY.

=GUN BAR'RELS.= See BROWNING.

=GUN COT'TON.= See PYROXYLIN.

=GUN MET'AL.= An alloy containing 905% of copper and 95% of tin, used for casting pieces of ordnance (erroneously termed 'bra.s.s guns'), also those parts of machinery which are subjected to considerable friction. See ALLOYS, BRONZE, STEREO-METAL, &c.

=GUN'POWDER.= This substance is a mechanical mixture of saltpetre, charcoal, and sulphur. It is seldom prepared on the small scale.

_Prep._ The saltpetre having been trebly refined, by boiling, skimming, filtering, and crystallising, is melted into cakes, which are then brushed to remove any adhering grit or dirt, broken into pieces with a mallet, ground to a fine powder in a mill, and sifted through a fine bolting sieve of bra.s.s wire. The charcoal is that of the alder or willow, and is carefully burnt, as already described, and is then reduced to powder. The sulphur is refined by distillation, and ground to the same fineness as the charcoal and saltpetre. The ingredients are weighed out in the proper proportions, and mixed together in a machine consisting of a wooden drum, having a shaft pa.s.sing through its centre, to which numerous 'flyers' in the shape of knife-blades are attached, the drum and flyers revolving in a contrary direction. When mixed, the charge is carried to the 'incorporating mill,' where it is ground under vertical iron 'mill-stones,' with a small quant.i.ty of distilled water, until the ingredients are thoroughly incorporated. The product of this operation is then pressed into a hard cake, which is next broken into pieces, granulated by means of sieves, and after being 'glazed' by friction, and the dust separated, is dried, with proper precautions, in a stove heated to about 130 by steam pipes.

The proportions of saltpetre, charcoal, and sulphur, used for different kinds of powder, differ very slightly. In 'sporting powders' the proportion of saltpetre is generally from 1 to 3% greater than in the Government powders. In 'miners' powders' it is about 10% less, an excess of sulphur being used. The following are the proportions adopted by European powers:

Saltpetre. Charcoal. Sulphur.

England 75 15 10 France 75 125 125 Austria 75 15 10 Prussia 75 135 115 Russia 7378 1359 1263 Spain 7647 1078 1275 Sweden 76 15 9 (Capt. Jervis-White Jervis.)

_Obs._ The quality of gunpowder is best estimated by actual trial of its power and cleanliness in use. It should be dry, hard, and free from dust; the grains should be of a uniform size, and glossy, and the colour a dark-grey or brownish-grey, not perfectly black. A very little placed on a piece of paper and fired should instantly explode with a flash, and neither leave an appreciable residue on the paper nor burn it. Dried by the heat of boiling water, or in vacuo, it should not lose more than 1/2 to 1% of its weight. Damp powder rapidly 'fouls' the gun. Gunpowder, containing more than 7% of water, does not recover its strength by simply drying it. The sp. gr. ranges between 1795 and 1800.

Karolyi succeeded in a.n.a.lysing the gases of gunpowder which had been fired in conditions closely resembling those which occur in artillery practice.

For this purpose he enclosed a charge of powder in an iron cylinder of such strength that it just burst when the powder was fired by means of the electric spark. This charged cylinder was suspended in a hollow spherical bomb, from which the air was exhausted before firing.

After the explosion had been produced, the gases and the solid residue of the powder were submitted to a.n.a.lysis. The results obtained were the following:[343]

[Footnote 343: 'Phil. Mag.,' 1863.]

1. _Composition of the Powder used._