Chapter M: F. Capitaine, who, acting upon a suggestion made by Liebig, some twenty (3)

_b._ The paper filter, with its contents, is next suspended for some time over concentrated sulphuric acid (oil of vitriol) contained in a wide-mouthed bottle or jar, by means of a thread attached to the cork or stopper, care being taken to exclude the external air. The exposure in this way is continued until the guano ceases to diminish in weight, which is ascertained by weighing it at intervals after the first 3 or 4 hours. When this point is arrived at, the filter and its contents are very carefully weighed. The difference between its present weight and its original weight (before the desiccation in _a_), taken in grains, gives the gross quantity of water per cent.

_c._ The dried guano from _b_ is next placed in a weighed, smooth crucible or capsule, and exposed to a low red heat until all the organic matter is completely destroyed, and the whole is reduced to a white ash, which is weighed as soon as it has become cold. This weight, in grains, gives the gross weight per cent. of non-volatile matter (fixed alkaline and earthy chlorides, phosphates, and sulphates); the total loss of weight by combustion denotes the gross per-centage of combustible and volatile matter (urea, uric acid, ammoniacal salts, and organic matter). The latter should not be less than 55 to 60%.

2. _a._ A second 100 gr. of the guano, selected as before, is distilled along with about 75 gr. of fresh-slaked quicklime, and a little water, in a small matrass connected with a tubular, triple bulb-condenser, containing cold distilled water, and immersed in a basin of ice-cold water. (See _engr._) The condenser is charged by plunging one of its extremities into the water, and sucking at the other, until the liquid reaches the level indicated in the margin. A very gentle heat only, cautiously increased, need be employed. After the process is over, the strength of the solution of ammonia found in the condenser is tested, either by taking its density in a small specific-gravity bottle, or by determining its saturating power in the manner described under ALKALIMETRY. This furnishes the per-centage of ready formed ammonia sufficiently accurate for all ordinary purposes, provided proper care is taken.

When extreme accuracy is required, the condenser is charged with a weighed quantity of dilute hydrochloric acid of a known strength, instead of water, and after the process is over, this is tested as before. The quantity of ammoniacal test-liquor (see ALKALIMETRY) now taken to saturate it, deducted from what it would have taken before the exposure in the condenser, gives the per-centage sought.

Another method, giving very accurate results, is to use a rather strong hydrochloric acid (sp. gr. about 1·13) for the condenser; after the operation is over, the contents of the latter are poured into a glass or porcelain capsule, a solution of bichloride of platinum is added, in excess, and the whole is then gently evaporated to dryness; the residuum is rubbed to powder, and exhausted with a mixture of two measures of alcohol and one measure of ether; the undissolved portion is next dried at a heat not exceeding 212° Fahr., and weighed. The weight, in grains, of the ammonia chloride of platinum thus obtained, multiplied by ·0763, gives the per-centage of ready-formed ammonia, as before. When hydrochloric acid is used for the condenser, a simple U-tube and beaker glass may be employed, if a bulb-condenser is not at hand. (See _engr._) The advantages resulting from the use of acid instead of water for the condenser is, that with the former no ammonia can possibly escape being absorbed, whilst little care is required to keep the condenser cool.

_b._ 25 gr. of the guano are next weighed, and after being slightly moistened with a little dilute hydrochloric acid, are thoroughly dried by the heat of boiling water; the dried sample is then mixed in a warm unglazed porcelain mortar with 10 times its weight of a mixture of 2 parts of quicklime to 1 part of hydrate of soda (both quite dry). This mixture is introduced into a combustion tube of hard Bohemian glass, about 16 or 18 inches long, and 3/4 of an inch in diameter (see _engr._) The mortar is rubbed out with a little of the soda-lime mixture, which is also introduced into the tube with that already put there; a little plug of ignited asbestos is then loosely placed over the whole, and the tube is immediately connected with a tubular bulb-condenser, containing moderately strong hydrochloric acid, great care being taken that the joints are made air-tight, which may be determined by the operator sucking a few bubbles out of the apparatus. If, after suction, the liquid remains at a higher level in the furthest bulb (_b_), it is a sign that the connection is sound. This being done, heat is applied to the combustion-tube, by means of spirit-lamps; or, more conveniently, by means of the furnace now usually employed in organic analysis (see _engr._) The tube is next gradually surrounded with red-hot charcoal, by shifting by degrees the screen (_c_), and adding more charcoal, so as to gradually expel the ammonia. The disengagement of gas should take place uninterruptedly, but not too rapidly, in order that the acid may not ascend into the combustion-tube and spoil the experiment. The non-condensable volatile matters which pass off furnish a key to the progress of the operation. The heat is at length increased to a full red. When gas ceases to be evolved, and the mixture in the tube has become quite white, the experiment is at an end. The point (_a_) of the combustion-tube is broken off, and the ammonia which remains in the tube is expelled by sucking gently at the extremity (_b_) of the bulb-condenser. The latter is then disconnected with the apparatus, and emptied into a glass or porcelain capsule, in order to be tested, as directed under 2, _a_. The quantity of ammonia, in grains, thus found, multiplied by 4, gives the WHOLE QUANTITY of AMMONIA per cent., both actual and potential, producible from the sample of guano examined.

_c._ The quantity of ready-formed ammonia (see 2, _a_) deducted from the quantity last found (see 2, _b_) gives the quantity of LATENT or POTENTIAL AMMONIA that will be slowly developed by the decomposition of the guano in the soil, and become available for the food of plants. This is the most valuable product of this substance as a manure, and can only be obtained in quantity from well-preserved, dry guano.

3. _a._ A third quantity of 100 gr. of the guano, selected as before, is triturated and digested for some time with 12 times its weight of hot distilled water, and the whole being thrown on a filter, the undissolved portion is washed with a little warm distilled water; the solution and 'washings' are then mixed together, and acidulated with nitric acid; a solution of pernitrate of iron is next added, and afterwards solution of ammonia, in excess; the liquid is next heated for a short time, and the bulky reddish-brown precipitate is collected, washed with hot water, dried, ignited, and weighed. The weight, in grains, less the weight of the peroxide of iron in the pernitrate consumed, gives the weight of PHOSPHORIC ACID present in the soluble phosphates contained in the sample. The pernitrate of iron is made by direct solution in hot strong nitric acid, of twice as much pure iron wire as there is phosphoric acid suspected to be present in the liquid. A slight excess will not alter the result. The number of grains of metallic iron used to form the solution, multiplied by 1·4286, gives the weight of the peroxide of iron which is to be deducted from the gross weight of the precipitate.

_b._ The filtrate and 'washings' left from 3 _a_ are mixed, and treated with a little oxalate of ammonia to throw down any lime, and then carefully evaporated to dryness and ignited; the residuum of the ignition, when cold, after being carefully weighed, is treated with the smallest portion of water that will dissolve it; the solution is acidified with hydrochloric acid, and a solution of bichloride of platinum added, in excess; some strong alcohol is next poured in, the precipitate carefully collected on a filter, washed with rectified spirit, dried at 212° Fahr., and weighed. The weight, in grains, multiplied by ·1940, gives the per-centage of POTASSA sought.

_c._ The weight of the potassa multiplied by 1·852, and deducted from the weight of the ignited residuum in 3 _b_ already found (see _above_), gives the quantity of CHLORIDE OF SODIUM or COMMON SALT (nearly).

4. _a._ The insoluble residuum from 3 _a_, dried, and ignited, or the ash from 1 _c_, is digested for 10 or 12 hours in 600 times its weight of water (to which a little common salt or sal-ammoniac may be added), after which the whole is thrown upon a filter; a solution of chloride of barium is then added to the filtrate as long as a precipitate (if any) forms; the latter is collected, washed, dried, ignited, and weighed. The weight, in grains, multiplied by ·5843, denotes the quantity of GYPSUM or SULPHATE OF LIME which has been used to adulterate the sample.

_b._ The insoluble residuum last left on the filter is digested for some time in warm dilute hydrochloric acid; the whole is then thrown upon a filter, and the undissolved portion (SILICA or SAND, with, perhaps, a trace of ALUMINA) is washed, dried, ignited, and weighed. It should not weigh more than 3 to 3-1/2 gr. (3 to 3-1/2%).

_c._ The filtrate and 'washings' from _b_ are next mixed together; the mixed liquid is acidified with dilute sulphuric acid and heated until all the hydrochloric acid is expelled, and the whole reduced to a soft pasty mass; rectified spirit is now poured in, and after active stirring for some time, the mixture is thrown on a filter, and the solid portion washed with a little more rectified spirit; it is then dried, ignited, and weighed. The weight, in grains, multiplied by ·7650, gives the quantity of PHOSPHATE OF LIME per cent. required.

_d._ The filtrate from _c_ is diluted with water, and after being boiled for a few minutes, ammonia is added in slight excess, followed by a solution of sulphate of magnesia (previously mixed with as much sal-ammoniac as will prevent ammonia producing a precipitate in it), slowly dropped in as long as it disturbs the liquor; the whole is now allowed to rest for 10 or 12 hours, when the precipitate is collected on a filter, and washed with water alkalised with ammonia, as long as the filtering liquid is rendered turbid by chloride of barium; it is next dried, submitted to intense ignition for some time in a covered platinum crucible, and, when cold, carefully weighed. The weight, in grains, multiplied by ·6429, indicates the per-centage of PHOSPHORIC ACID in the insoluble phosphates (phosphates of lime, magnesia, &c.) in the sample examined.

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 constituents 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 potassa, 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 assuming 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 quantity of uric acid last obtained, multiplied by 1·1012, gives the per-centage of URATE OF AMMONIA.

_Obs._ Amongst the numerous constituents 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 assay, 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 analysis 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 potassa 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 1·75 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 mass, 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 class 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 masses; most of them exude spontaneously, or on puncturing the bark. The most perfect type of this class 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; ACACIÆ GUMMI (B. P.); G. ARABICUM, 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. 1·355. (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 ACACIÆ) 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 assume 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 glass dish, with vertical sides, and a solution of ferric chloride, density 1·48, 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 passed 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, Bassora.= A solution of yellowish gum brought from the neighbourhood of Bassora. 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 BASSORIN, 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 coarse 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 passed through the 'bolting machine.' Very white and superior. This process has been patented in France by M. Henzé.

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 coarsely 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 substitute 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 masses, 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 _Rosaceæ_. 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 BASSORA 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. 1·384. It is chiefly employed in calico-printing, and by shoemakers and lozenge-makers; by the latter to give toughness to the saccharine mass.

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 quantity 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 guaiacum, taking care to stir it all the while. If the sample contains any gum Arabic, the mixture, in the course of a few minutes, assumes 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 quantity 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 RESINÆ, 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 principal gum resins are AMMONIACUM, ASSAF[OE]TIDA, 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 90·5% of copper and 9·5% of tin, used for casting pieces of ordnance (erroneously termed 'brass 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 brass 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 passing 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 quantity 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 12·5 12·5
Austria 75 15 10
Prussia 75 13·5 11·5
Russia 73·78 13·59 12·63
Spain 76·47 10·78 12·75
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 1·795 and 1·800.

Karolyi succeeded in analysing 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 analysis. The results obtained were the following:[343]

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

1. _Composition of the Powder used._

Ordnance Powder. Small Arms Powder.
Nitre 73·78 77·15
Sulphur 12·80 8·63
{Carbon 10·88 11·78
Charcoal. {Hydrogen 0·38 0·42
{Oxygen 1·82 1·79
{Ash 0·31 0·28
------ ------
99·97 100·05

2. _Products of Combustion by Weight._

Ordnance Powder. Small Arms Powder.
{ Nitrogen 9·77 } { 10·06 }
{ Carbonic anhydride 17·39 } { 21·79 }
Gaseous. { Carbonic oxide 2·64 } { 1·47 }
{ Hydrogen 0·11 } 30·58 { 0·14 } 34·18
{ Sulph. hydrogen 0·27 } { 0·23 }
{ Marsh gas 0·40 } { 0·49 }

{ Ammonic sesquicarbonate 2·68 } { 2·66 }
{ Potassic sulphate 36·95 } { 36·17 }
{ " carbonate 19·40 } { 20·78 }
Solid. { " hyposulphite 2·85 } 69·25 { 1·77 } 65·14
{ " sulphide 0·11 } { 0·00 }
{Charcoal 2·57 } { 2·60 }
{Sulphur 4·69 } { 1·16 }
Loss. 0·17 0·68
------ ------
100·00 100·00

3. _Products of Combustion by Volume in 100 of Gas._

Ordnance Powder. Small Arms Powder.
Nitrogen 37·58 } { 35·33 }
Carbonic anhydride 42·74 } { 48·90 }
Carbonic oxide 10·19 } { 5·18 }
Hydrogen 5·93 } 100 { 6·90 } 100
Sulphuretted hydrogen 0·86 } { 0·67 }
Marsh gas 2·70 } { 3·02 }

It will be seen from the above figures that in addition to the generation of a considerable amount of carbonic anhydride (carbonic acid) by the combustion of gunpowder, there is liberated at the same time a large quantity of solid matter, in the form of sulphate and carbonate of potash, sulphide of potassium, sulphur, charcoal, &c. This will explain why the air of mines is so prejudicial to the health of the miner, particularly when he is engaged in blasting operations, these being carried on in a more or less confined space. See AIR, VITIATED.

=Gunpowder, Schultze.= The subjoined account of Schultze gunpowder is a transcription of a report communicated to the editor of the 'Field' newspaper by Mr F. Toms, A.I.C., F.C.S. After referring to a previous communication on the same subject Mr Toms proceeds as follows:--I have carried out some further experiments, with the aid (by Dr Frankland's kind permission) of apparatus more suited to my requirements than that previously at my disposal; and I now proceed to lay before you the results of these experiments, and the conclusions to which they have led me, respecting the powders formerly received and the new Schultze powder, with a sample of which you have since favoured me.

The main constituent of the Schultze gunpowder, as you are aware, is wood fibre, which, having first been purified, is then subjected to the action of strong nitric acid (intensified by mixture with sulphuric acid), and thus is converted into a kind of nitro-cellulose or pyroxylin, the ordinary form of which is gun-cotton. The wood fibre undergoes no change in appearance by this treatment; but a change takes place in its chemical composition, which may thus be exemplified:

CELLULOSE NITRO-CELLULOSE
(unconverted cotton or (cotton or wood fibre treated
wood fibre). with nitric acid).
Carbon 6 parts 6 parts.
Oxygen 5 " 5 "
Hydrogen 10 " 7 " or more.
Nitroxyl (NO_{2}) none 3 " or less.

It will thus be seen that the sole difference between gun-cotton or Schultze powder and ordinary cotton or wood fibre is, that some of the hydrogen is abstracted and has its place supplied by nitroxyl--a substance contained in nitric acid, and composed of one part of nitrogen united with two parts of oxygen. Under the most favorable circumstances, it is possible to replace _three_ of the ten parts of hydrogen by three of the nitroxyl, when the substance produced is explosive, and is called from its composition _tri_-nitro-cellulose. This is the purest form of gun-cotton. If weaker acid is used, less hydrogen is displaced, and the product is called _di_-nitro-cellulose or _mono_-nitro-cellulose, according as it contains _two_ or only _one_ part of nitroxyl. These derivatives are either feebly explosive or not explosive at all. Such are the compounds known as photographic collodion and soluble gun cotton--the latter name distinguishing it from pure gun-cotton, which is not soluble in a mixture of ether and alcohol.

The Schultze powder contains both the explosive and the non-explosive varieties of nitro-cellulose.

If the wood fibre, after being carefully purified according to the method described in Schultze's patent of 1864, were thoroughly desiccated and allowed to cool out of contact with air, and then dipped in acid of the strength mentioned in the specification, there seems no theoretical reason why an explosive powder containing at least 90% of true tri-nitro-cellulose should not be produced. As, however, I find on experiment that nothing like that per-centage is arrived at, I can only conclude that, in order to moderate the violence of the explosion, the Schultze Company secure the formation of a large per-centage of "soluble" or less explosive nitro-compounds by merely air-drying their wood.

If this supposition be generally true, it seems probable that the sample of Schultze powder supplied by Messrs Blissett may owe its extra explosive force to exceptional care being taken, during the interval between the drying and the dipping, to prevent the absorption of moisture--with the addition, perhaps, of an increased length of exposure to the action of the acid.

That some such variation of the ordinary procedure was carried out seems evident from the different proportions of soluble and insoluble gun-cotton in the specimens of Schuitze powder supplied by Messrs Blissett and Messrs Bland; for it was found that on the washed wood fibre from each being submitted to the action of a mixture of alcohol and ether, about one half of the former powder and two thirds of the latter were dissolved out. This shows that while the "Blissett" specimen contained about one half its weight of insoluble or explosive nitro-cellulose, the "Bland" contained only about one third--a difference which confirms the result obtained by analysis as stated below.

The _soluble_ gun-cotton, ordinarily non-explosive, may, however, be rendered explosive by saturating it with bodies rich in oxygen, which promote the decomposition and complete the combustion of the fibre. Nitre is used for that purpose, because it parts with its oxygen readily; and nitrate of baryta is also used, because, being more stable than the nitre, it renders the combustion more gradual than would be the case if nitre were alone employed. When both are used, the nitre, I should think, would start, and the nitrate of baryta continue and finish the combustion of the powder. The amount used is, I suppose, the result of calculation and experiment; but a powder containing little true tri-nitro-cellulose should require more of these salts than one containing much tri-nitro-cellulose; and an excess of the salts would lower the rate of burning of the powder.

I will now give my analysis in full of the three powders, viz.--(1) the ordinary powder issued last season, being part of a supply obtained from Messrs Bland, gunmakers, of the Strand; (2) some powder furnished by Messrs Blissett, of Holborn, and alluded to in their letter in the 'Field' of Jan. 19th last, as having damaged a gun made by them; and (3) some of the new powder of 1878, as used at the 'Field' trial of explosives in May last.

1877 1878
Bland's. Blissett's. Trial or
New.

Moisture, per cent. 2·18 2·39 2·97
{Nitrate of baryta, per cent. 21·50 16·59 22·32
Extracted { " potash, per cent. 11·46 10·46 6·47
by water. {Yellow coloured organic
{substance, trace of chlorides,
{&c., undetermined

{The converted wood fibre }
Insoluble { (nitro-cellulose) then }
in water. { remaining contained the } 5·0 6·0 2·95
{ following per-centage of }
{ mineral matter }

The converted wood fibre (after allowing for extraneous mineral matter) possessed the following per-centage composition. I place for comparison Professor Abel's determination of the composition of tri-nitro-cellulose, and two of the impurities found along with it, in a parallel column.

Bland's. Blissett's. Trial or New. Tri-nitro- Impurities.
Cellulose.
Carbon 28·75 28·07 28·12 24·24 29·20 30·50
Hydrogen 3·49 3·65 3·54 2·36 -- 2·91
Nitrogen 10·80 15·60 11·66 14·14 11·85 --
Oxygen 56·06 52·68 56·68 59·26 -- --

These powders exploded at a temperature of about 190° C. (374° F.), the different samples varying but slightly. Pure gun-cotton is stated by Professor Abel to explode at 150° C. (302° F.); and black powders are said, by different authorities, to explode at various temperatures between 500° and 600° F., according to the variation in their composition and manufacture.

In addition to the difference in chemical composition of these Schultze powders, I would point out that there is a difference in density--the Blissett being heaviest, the Bland next, and the New the lightest of the three. I think this fact also has some bearing on the violence of the explosion. In black powders, I believe, a dense powder, speaking generally, is stronger than a lighter one; and the Schultze patent states that hard woods make more explosive powders--not, I take it, because the composition is thereby altered, but because a denser powder is produced. It would appear to me, from the above analyses, that the new trial powder should contain rather more explosive force than the Bland variety, though considerably less than the Blissett. The result may, however, be modified by the difference in density of the powders; and your practical experiments will show how far this agrees with the results of the shooting.

I have hitherto only spoken of the explosive force of the powder; now I will touch on another point--its tendency to spontaneous decomposition. Knowing that, in the case of gun-cotton, its stability is injured by a small proportion of resin and other organic impurities, and by the presence of free mineral acids. I did not expect to find this powder (made from a less pure kind of cellulose, from which also it must be somewhat difficult to wash all traces of acid) equal in stability to gun-cotton; and on subjecting the three kinds of Schultze powder to the Government 'heat test' of 150° F. (with a minimum of 10 minutes' duration), it was found that the

New or Trial (1878) Powder stood the test 12 m.
'Bland's' sample " 8 "
'Blissett's' sample " 7 "

This shows that the 'new' powder is very stable, as it stood the test for two minutes beyond the Government minimum, while the other two samples were a good way below it. The officials at Waltham Abbey would accept no gun-cotton which did not stand the test for ten minutes; and I have seen the best gun-cotton stand it for fifteen.

Whether the loose granulated condition of the Schultze powder, when stored, is sufficient to neutralise this inferiority in purity, and render a sample of Schultze, which only stands the test of seven minutes, as little liable to spontaneous combustion as gun-cotton which stands the test for ten minutes, there is at present no evidence to show.

To carry out this 'heat test' properly, some practice is required; so, in order to put the matter beyond doubt, I called in the assistance of my friend Mr Arthur Linnell, F.C.S., chemist to the Gun-Cotton Company, Stowmarket, a gentleman who uses the test daily, and who carried out the above three experiments strictly after the manner adopted by himself and by the Government officials.

In addition to Mr Linnell's experiments, I noted that the aqueous extract of 'Blissett' was very faintly acid; that when heated in a chest at 195° F. moist blue litmus was very quickly reddened.

I think this serious defect (want of stability) is due to want of care in the washing; and I base this opinion on the following facts:

(1) The 'Bland' and 'Blissett' samples (the powders of least stability) are of a deeper tint than the 'new' (due to the soluble yellow impurity before mentioned). By continued washing in warm water they become pale, like the more carefully prepared new powder, and the yellow substance is dissolved away. Hence the lighter colour of the 'new' (and most stable) indicates it has less of this organic impurity.

(2) Sulphuric and nitric acids are used in the dipping of the powder, but should be entirely washed out, as they promote spontaneous decomposition. If left in, the sulphuric acid will, when the salts are added, decompose the nitrate of baryta, forming insoluble baric sulphate and free nitric acid.

On experiment I ascertained that the abnormally large quantity of mineral matter or ash (5 and 6 per cent.) found in the insoluble part of the 'Bland' and 'Blissett' powders _is_ due to baric sulphate, and I think the acidity of the aqueous extract is due to the nitric acid thus set free.

Had this baric sulphate been present in the new powder, I should have thought it was purposely formed in all to prevent access of moisture; but, not finding this substance in this carefully prepared sample, I attribute its presence in the other cases to carelessness on the part of the workmen.

I should state that all these powders consisted of a granulated and consolidated pulp. This improvement must, I think, have considerable advantages over the sawdust form previously adopted by the Schultze Company in as much as it facilitates a more thorough purification being carried out, and produces a more homogeneous and equal powder. It is possible, too, that working with pulp may be of advantage, inasmuch as the company may now, by varying the pressure in forming the cake, obtain grains of any required density.

In conclusion, I may say that, in my opinion the most difficult task which the Schultze Company have had to encounter is that of obtaining uniformity of strength in their explosive; and the 'Blisset' sample of their powder may he looked upon as an experimental batch in which (by altering the mode of procedure in some such manner as I have indicated) they made a powder with a large per-centage of tri-nitro-cellulose, thus producing a more rapidly burning substance, and consequently a more violent explosion.

Taking all things into consideration, I think the Schultze Company, in manufacturing a nitro-explosive which gives the uniformity of shooting power shown in your recent experiments, have worked out a most troublesome problem with remarkable success. The difficulty of obtaining such results is evidenced by the fact that so many inventions of a somewhat similar character have been abandoned for sporting purposes from a deficiency in this respect.

But, however difficult it may be to manufacture a powder giving uniform shooting, it is evidently possible, with suitable care to produce (as the 'new' Schultze shows) a wood powder which is perfectly safe and stable, as far as spontaneous decomposition is concerned. The company, therefore, if they have not already done so, ought to take means to prevent powder of the low stability of the 'Bland' and 'Blissett' samples being again issued from their works.

P.S.--Since writing the above I have examined cursorily a sample of the 'Dittmar' wood powder, an American variety of 'Schultze,' used by Captain Bogardus in some of his recent shooting competitions. The powder is somewhat darker in tint, and of slightly larger grain, than the Schultze. In density it is intermediate between 'Bland's' and the 'new' powder; and the charge in a twenty-bore cartridge was forty-two grains. This powder would seem to be made from solid cubes of wood (not a pulped mass like the present 'granulated' Schultze, or of sawdust splinters like the old so-called 'cube' Schultze). It contains no nitrate of baryta, but has a small quantity of nitrate of potash and soda. Possessing, as it would seem, therefore, a much smaller proportion of oxidizing salts than the English Schultze, it should contain, to make up for this loss of force, a larger proportion of explosive pyroxylin; but this is a point I have not experimentally determined. ('Field,' August 3rd, 1878, No. 1336, p. 143.)

=Gunpowder, White.= _Syn._ BLASTING POWDER. _Prep._ 1. See BLASTING POWDER, No. 3.

2. Yellow prussiate of potash and white sugar, of each 1 part; chlorate of potassa, 2 parts; powder each separately, and mix them well, but carefully, with a bone or wooden knife. It may be granulated like gunpowder, by making the powder into a paste with a little water, and pressing the mass through a parchment sieve.[344]

[Footnote 344: See the precautions noticed under BLASTING POWDER, page 230.]

=GUN'JAH.= See HEMP (Indian).

=GUT.= _Syn._ FISHING GUT, SILKWORM G. This is obtained from the _Bombyx mori_ (Linn.) or silkworm caterpillar. _Prep._ The silkworms, when just ready to spin, are steeped in strong vinegar for 12 hours in warm weather, or 2 or 3 in cold weather, and are then broken in half, and stretched out as far as possible on a board, furnished with slits or pegs to hold them; in this state they are allowed to dry in the sun or a warm place.

_Obs._ Used by anglers. The worms may be known to be going to spin by refusing food, and by having a fine silken thread hanging from the mouth.

=GUT'TA PERCHA.= The concrete juice of the _Isonandro Gutta_, a tree growing only in the Malayan Archipelago, and of other species of the same genus. The stem of the gutta-percha tree grows to the diameter of 5 or 6 feet, and on being notched yields a milky juice, which, after exposure to the air for some time, solidifies, forming the gutta percha of commerce. It arrives in this country in irregular blocks of some pounds in weight, usually containing a large portion of impurities in the form of pieces of wood, stones, and earth. To prepare this crude product for manufacturing into useful articles, the blocks are first cut into slices, and then torn into shreds. These are softened by hot water, and kneaded in a 'masticator,' the stones, earth, and other impurities, being gradually washed away by water. After several hours the gutta percha is found to be kneaded into a perfectly homogeneous mass, which is rolled or drawn into sheets, bands, or tubes, as required.

_Prop., &c._ Gutta percha is a tough, inelastic substance, becoming soft and plastic at 212° Fahr., at which temperature two pieces may be firmly welded together. It is one of the best insulators of electricity, is impervious to moisture, and resists the action of acids and alkalies to a great extent. Its best solvents are benzol, chloroform, bisulphuret of carbon, rectified mineral naphtha, and rectified oil of turpentine. All these dissolve it readily. According to the analysis of Payen, the purified gutta percha of commerce consists of 75 to 828 of chemically pure gutta percha, which is insoluble in ether and alcohol, and a white and a yellow resin, soluble in boiling alcohol.

_Uses._ These are numerous and varied. No substance, perhaps, with the exception of caoutchouc, has been 'tortured' to so many different purposes. Its perfect plasticity when warm, and its capability of receiving the most delicate impressions, render it invaluable in many cases where india rubber would be useless. Beautiful mouldings, picture frames, and a number of ornamental articles, are made from it. To the chemist and photographer it is of great use as a material for making bottles, carboys, photographic baths, and voltaic battery cells. One of the most important uses to which it has been applied is for enclosing the metallic wires used for telegraphic purposes. Its indestructibility by water, its plasticity, and high insulating power, have rendered it particularly valuable for this purpose. At the International Exhibition of 1862 the Gutta Percha Company exhibited one mile of covered wire perfectly insulated, which was hardly thicker than common sewing cotton. Gutta percha may be rolled into thin transparent sheets, which, being perfectly impervious to moisture, are well adapted for surgical purposes. Again, a solution of gutta percha in chloroform forms an excellent dressing for incised wounds, and a protection for abraded surfaces, burns, &c. It is used in the same way as collodion.

=Gutta Percha, Purified.= Dr Cattell, of London, has succeeded in purifying gutta percha so perfectly from all extraneous matter, that it presents the appearance of ivory. The raw material is dissolved in a certain solvent, and the solution most carefully filtered until it leaves on evaporation the gutta percha in a pure milk-white condition.

=GYP'SUM.= This is native sulphate of lime. When baked, to deprive it of water, and ground, it forms PLASTER OF PARIS. Gypsum is an excellent manure for certain soils.

=HAARBALSAM, Vegetabilischer--Vegetable Hair Balsam= (Joh. Andr. Hauschild, Leipsic). A decoction of burdock root, containing a little spirit and coloured green with indigo. (König.) Hager analysed a turbid brownish fluid, which deposited a brown precipitate on standing, and when filtered consisted of a decoction of burdock root with 20 per cent. of spirit.

=Haarbalsam Mailandischer--Mailand's Hairbalsam= (Kreller, Nuremberg). Beef marrow, 40 parts; cinchona extract, 5 parts; balsam of Peru, 1 part; storax, 1 part; oil of bergamot, 1 part; oil of lemons, 1/2 part. (Hager.)

=Haarbalsam Ostindischer--East Indian Hairbalsam= (Dr Ayer). Contains sugar of lead, sulphur, glycerin, oil of lavender, and water.

=Haarbalsam= (J. F. Sehwarzlose Söhne, Berlin). A brownish-yellow spirituous aromatic fluid, having nearly the composition of eau de Cologne, with liquid storax, carbonate of potash, and a fat--perhaps derived from cantharides. (Hager.)

=Haarbalsam= (A. Marquart, Leipsic). A mixture of 83 grammes water perfumed with eau de Cologne, with 12 grammes glycerin, 4·25 grammes milk of sulphur, and 1·2 gramme lead nitrate.

=HAD'DOCK.= A small sea-fish, allied to the cod, and esteemed an excellent article of food. It is the _Gadus æglefinus_ of Linnæus. Split, smoked, and dried, it is common in the smaller shops of London.

=HÆMATEM'ESIS.= In _pathology_, vomiting of blood. See STOMACH AFFECTIONS.

=HÆM'ATITE.= _Syn._ HEMATITE. In _mineralogy_, one of the most important iron ores. Two kinds are distinguished, the red, which is an anhydrous peroxide of iron, and the brown, which is the hydrated peroxide.

=HÆMATOCRYS'TALLIN.= A crystalline substance obtained by the action of oxygen and afterwards carbonic acid on the 'clot' of blood.

=HÆMATOS'IN.= _Syn._ HÆMATIN, RED PIGMENT OF BLOOD. The red colouring principle of the blood. It is not known in a state of purity. It differs from the other animal principles in containing, as an essential ingredient, the sesquioxide of iron.

=HÆMATOX'YLIN.= A principle obtained by Chevreul from common logwood (_Hæmatoxylon campechianum_), and on which its colour appears to depend.

_Prep._ 1. Infuse logwood chips in water, at a temperature of about 130° Fahr., for 12 hours, filter, and evaporate to dryness in a water bath; digest the residuum in rectified spirit for 24 hours, again filter and evaporate; then add a little water; again gently evaporate and set aside the solution in a cold place that crystals may form; these must be washed in rectified spirit and dried.

2. Digest powdered hard extract of logwood in rectified spirit, and proceed as last.

3. Powdered logwood is mixed with sand and digested for several days in pure ether; the resulting liquid is filtered, evaporated to a syrup, and set aside to crystallise.

_Prop., &c._ Brilliant reddish-white or straw-yellow crystals, soluble in boiling water, forming an orange-red solution which turns yellow as it cools, but resumes its former colour on being heated. Alkalies in excess change its colour successively into purple, violet, and brown; acids brighten it; with the metallic oxides it forms compounds having a blue, purple, or violet colour.

=HÆMOP'TYSIS.= In _pathology_, spitting of blood. It generally arises from extreme fulness of the blood-vessels of the lungs, or the rupture of blood-vessels, as a consequence of ulceration; but sometimes it is induced by excessive exertion or external violence. Depletion, aperients, acidulous and astringent drinks, and nauseants, are the usual remedies. Acetate of lead, in small doses, has been recommended for this affection. When this substance is given, it should be accompanied with a sufficient quantity of free acetic acid, to prevent its being converted into the poisonous carbonate of lead in the system.

=HÆM'ORRHAGE.= _Syn._ HEMORRHAGE; HÆMORRHAGIA, L. A bleeding or flow of blood. Bleeding may be divided into active, passive, and accidental.--Active hæmorrhage is that arising from a full state of the vessels, or plethora.--Passive hæmorrhage, from general debility of the system, and of the blood-vessels in particular.--Accidental hæmorrhage, from external violence, as blows, wounds, &c. The first generally requires depletion, and the second the usual treatment to establish the general health and vigour of the body. The bleeding from wounds, if extensive, should be arrested by tying the ruptured blood-vessels; or where this cannot be done, and in less important cases, by the application of styptics, as creasote, sulphate of iron, infusion of galls, compound tincture of benzoin, &c.