Cooley's Cyclopaedia of Practical Receipts Volume I Part 260

=GEN'TIANIN.= _Syn._ GENTIANINE; GENTIANINA, L. A substance obtained by MM. Henry and Caventou from the root of common gentian.

_Prep._ 1. Gentian root (in powder) is digested for 2 or 3 days in cold ether, with agitation, and the filtered tincture evaporated to dryness; the residuum is dissolved in rectified spirit, and the solution is again evaporated; the semi-crystalline ma.s.s is, lastly, redissolved in either alcohol or ether, and crystallised by careful evaporation.

2. (Magendie.) The ethereal extract is exhausted with cold alcohol (rectified spirit), as before, and the resulting tincture is evaporated to dryness; the residuum is dissolved in water, calcined magnesia added in excess, and the whole boiled and filtered; the sediment is digested in ether, and the ethereal tincture allowed to crystallise by slow evaporation.

_Prop., &c._ Gentianin forms golden-yellow needles, scarcely soluble in cold water, but very soluble in alcohol and ether. It is a powerful bitter and stomachic.--_Dose_, 1/2 gr. to 2 gr.

=GER'MAN PASTE.= _Prep._ From pea-meal, 2 lbs.; sweet almonds (blanched), 1 lb.; fresh b.u.t.ter or lard, 1/4 lb.; moist sugar, 5 oz.; hay saffron, 1/2 dr.; beat to a smooth paste, adding cold water q. s., granulate the ma.s.s by pa.s.sing it through a colander, and expose the product to the air in a warm place, until quite hard and dry. The addition of 2 or 3 eggs improves it. Used to feed larks, nightingales, and other insectivorous birds. It will keep good for 12 months in a dry place.

=GER'MAN SILVER.= _Syn._ ALBATA, ARGENTAN, _Electrum_, NICKEL SILVER, TUTENAG, VIRGINIAN PLATE, WHITE COPPER. A well-known alloy, the finer varieties of which nearly equal silver in whiteness and susceptibility of receiving a high polish, whilst they surpa.s.s it in hardness and durability. The following formulae are from the highest authorities, or are the results of actual a.n.a.lysis of the finest commercial samples:--

_Prep._ 1. Copper, 50 parts; nickel, 20 parts; zinc, 30 parts. Very malleable, and takes a high polish.

2. Copper, 50 parts; nickel, 26 parts; zinc, 24 parts. Closely resembles silver; an excellent sample.

3. Copper and zinc, of each 41 parts; nickel, 18 parts. Rather brittle.

4. (M. Gersdorff.) Copper, 50 parts; nickel and zinc, of each 25 parts.

Very white and malleable, and takes a high polish. Recommended as a general subst.i.tute for silver.

5. (Gersdorff.) Copper, 60 parts; nickel and zinc, of each 20 parts. For castings, as bells, candlesticks, &c.

6. (Gersdorff.) Copper, 60 parts; nickel, 25 parts; zinc, 20 parts. For rolling and wire. Very tough and malleable.

7. (Sample made from the ore of Hilburghausen.) Copper, 40-1/2 parts; nickel, 31-1/2 parts; iron, 2-1/2 parts; zinc, 25-1/2 parts. Equal to the best Chinese sample.

8. (Pelouze.) Copper and nickel, equal parts. Recommended by M. Pelouze as superior to any of the alloys containing zinc.

9. (Pelouze.) Copper, 2 parts; nickel, 1 part. Not so white as the last, but more malleable.

10. (White Copper from China.)--_a._ Copper, 30 parts; nickel, 36 parts; zinc, 34 parts.

_b._ (Said to be prepared from native ore.) Copper, 41 parts; nickel, 32 parts; iron, 2-1/2 parts; zinc, 24-1/2 parts. Silvery white, takes a high polish, very sonorous, malleable both cold and at a dull-red heat, and may be rolled into leaves or formed into wire.

11. (White metal spoon, sold as 'German Plate.') Copper, 55 parts; nickel, 24 parts; zinc, 16 parts; tin, 3 parts; iron, 2 parts.

_a.n.a.l._ This may be briefly described as follows:--_a._ 100 gr. of the alloy is digested in nitric acid q. s., diluted with a little water. If the sample is unequally attacked by the acid, and a white external sh.e.l.l is observed which dissolves more slowly than the internal portion, it is 'plated' on those parts with silver. If this silver sh.e.l.l or casing has a polished surface on both sides, the article has been 'electro-plated,' if the contrary is the case, it has most probably been plated in the usual way.

_b._ The solution being completed, heat is applied to expel the excess of acid, and the remainder is largely diluted with distilled water; dilute hydrochloric acid is now dropped in as long as it occasions a precipitate, and the whole, after being moderately heated for a short time, and cooled, is thrown upon a small paper filter; the precipitate on the filter is next washed with distilled water, carefully dried, and ignited in a small porcelain crucible, the filter itself being separately burnt on the cover of the crucible, and the ashes added to its contents prior to ignition.

Every 143-1/2 gr. of the resulting fused chloride is equal to 108 gr. of metallic silver.

_c._ The filtered liquid (see _b_) is next treated with a stream of sulphuretted hydrogen, and the black precipitate is collected, washed, and digested in strong nitric acid; when the solution is complete sulphuric acid is dropped in to precipitate the lead (if any is present); if a precipitate is formed, the whole is evaporated to dryness, and the excess of sulphuric acid expelled by a rather strong heat applied towards the end; the dry ma.s.s is now collected on a filter, washed with a mixture of water and alcohol, dried, and exposed to slight ignition in a porcelain crucible. Every 152 gr. of the resulting dry sulphate is equal to 104 gr.

of lead.

_d._ The liquor filtered from the sulphate of lead, or (in its absence) the nitric solution of the precipitate produced by the sulphuretted hydrogen (see _c_), is next treated with pota.s.sa, &c., as described under the a.n.a.lysis of bra.s.s. Every 40 gr. of the dry protoxide thus obtained represents 32 gr. of pure copper.

_e._ The liquor which was filtered from the precipitate produced by the sulphuretted hydrogen (see _c_) is boiled until it loses its offensive odour, and is then precipitated with carbonate of soda, in slight excess, and again boiled for a few minutes; the precipitate (mixed oxides of nickel and zinc) is collected, washed, and redissolved in dilute acetic or nitric acid, in excess; a current of sulphuretted hydrogen is next pa.s.sed through the solution, the precipitate collected on a filter, washed, redissolved in hydrochloric acid, and the solution again treated with carbonate of soda; the last precipitate (oxide of zinc) is washed, dried, and gently ignited. Every 40 gr. of this oxide is equivalent to 32 gr. of metallic zinc.

_f._ The washings of the precipitated oxides and the liquid filtered from the precipitate occasioned by the sulphuretted hydrogen (see _e_) are mixed together, pure solution of ammonia added in considerable excess, and the mixture agitated for some time; the undissolved portion of the precipitate is then collected on a filter, washed with distilled water, redissolved in dilute nitric acid, again precipitated with solution of pota.s.sa, and this last precipitate (ferric oxide) washed, dried, ignited, and weighed. Every 80 gr. represents 50 gr. of metallic iron.

_g._ The ammoniacal solution filtered from the precipitate of sesquioxide of iron (see _f_) is precipitated with pure solution of pota.s.sa, boiled for a few minutes, and, when cold, thrown on a filter; the precipitate is, lastly, washed with hot water, dried, ignited, and weighed. Every 37-1/2 gr. of the oxide thus obtained is equal to 29-1/2 gr. of metallic nickel.

_Obs._ The manufacture of nickel or German silver has of late acquired an importance which is second only to that of silver plate itself. The superior quality of this alloy, and the graceful patterns which it is often made to a.s.sume in the hands of the accomplished artist cannot fail to have attracted the admiration of the majority of our readers. The value of correct information regarding the preparation of this alloy, and of a ready method of determining the composition of the most improved commercial samples will, therefore, be fully appreciated by every metallurgist who wishes to throw his wares into the arena of public compet.i.tion. Much that is vended under the name of GERMAN SILVER is little better than the BRITANNIA METAL or PLATE PEWTER formerly so plentiful in every establishment in this country. German silver has quite superseded copper as the basis of 'electro-plated goods.'[332]

[Footnote 332: See ELECTROTYPE.]

The union of the metals in the above formulae is effected by heat with the usual precautions. When iron is ordered, it is generally added under the form of 'tin plate.' See ALLOY, BRa.s.s, BRITANNIA METAL, BRONZE, &c.

=GER'MAN TIN'DER.= See AMADOU.

=GERMINA'TION.= The growth or vegetation of a seed by which a young plant is produced. The conditions essential to germination are the presence of warmth, air, and moisture. The most favorable temperature is between 60 and 85 Fahr., according to the habitat of the respective plants. Below 40 Fahr. most of the more perfect seeds either refuse to vegetate, or vegetate slowly and feebly; and at or near the freezing-point none of them undergo this change. At a temperature above 100 Fahr. the young germ is usually injured, and at about 125, if it forms, it soon withers and dies.

See MALTING, SEED, &c.

=GERMS.= The 'germ theory of disease' may be briefly stated to be that which supposes the cause of epidemic and contagious maladies to be due to the agency of specific, inconceivably small germs,--different germs giving rise to different diseases.

These disease germs gaining an entrance by means of air, water, or food into the healthy body, and being possessed of extraordinary powers of increase and subdivision, are supposed to set up the particular disease, and at the same time to multiply to an incredible extent by feeding upon the tissues best suited for their support. Further, they are conceived to be thrown off into the atmosphere from the body of the patient, whence they are conveyed as before described into other healthy animal organism, in which, comporting themselves as in the previous case, they set up a similar disease. See BACTERIA AS ORIGINATORS OF DISEASE.

=GHEE.= A sort of b.u.t.ter used by the natives of India. _Prep._ Milk is boiled in large earthen pots for an hour or two, then allowed to cool, a little curdled milk called 'dhye' being added, in order to make the whole coagulate. After a lapse of some hours the contents of each to the depth of 5 or 6 inches are removed and placed in a larger earthenware utensil, in which they are churned by means of a piece of split bamboo for about half an hour; then hot water is poured in, and the churning continued for half an hour longer, after which time the b.u.t.ter is found to be formed.

When this becomes rancid, it is melted in an earthen vessel, and boiled until all the water has evaporated; after which a little salt or betel-leaf is put into it, and finally it is poured off into suitable vessels in which it can be preserved from the air. Bottles are commonly used for this purpose. See b.u.t.tER.

=GHER'KINS.= _Syn._ GIR'KINS. Small cuc.u.mbers adapted for pickling. See PICKLES.

=GILD'ING.= _Syn._ DORURE, Fr. The art or process of covering the surfaces of bodies with a thin film of gold, for the purpose of increasing their durability or improving their appearance. For the sake of brevity we shall briefly notice the leading varieties of gilding, and their applications, in alphabetical order.

GILDING, BURNISHED. This is distemper gilding to which a 'face' has been given with the 'burnisher.' It is chiefly employed for the polished portions of the frames of pictures and mirrors, the more prominent parts of statuettes, &c.

GILDING, CHEMICAL. Those varieties in which the film of gold is formed on the surface through the agency of chemical affinity, in opposition to mechanical gilding, in which the gold is made to adhere by the intervention of some glutinous substance.

GILDING, COLD. The articles (copper or bra.s.s) to be gilded, after being softened, annealed, and polished in the usual manner, are rubbed with a little gilding powder by means of a piece of cork moistened with a solution of salt in water; after which the work is burnished with a piece of hemat.i.te or polished steel. (See _below_.)

GILDING, DISTEMPER. This is applied to wood, plaster, marble, &c. It is commonly performed in this country by giving the wood, first, a coating of good size, and next, several successive coats of size thickened with finely powdered whiting, Spanish white, or plaster of Paris until a good face is produced; observing to let each coat become quite dry, and to rub it perfectly smooth with fine gla.s.s paper, before the application of the following one. When the proper 'face' is obtained, the surface is thinly and evenly gone over with gold size, and when this is nearly dry, the gold leaf is applied, and afterwards burnished with an agate or dog's tooth.

The process, as adopted by the Parisian artists, who greatly excel in this species of gilding, is very complicated, and is divided into at least 17 distinct operations, each of which they declare to be essential to its excellence.

GILDING, ELECTRO-. See ELECTROTYPE.

GILDING, GRECIAN. In this variety sal-ammoniac and corrosive sublimate, equal parts, are dissolved in nitric acid, and a solution of gold made with this menstruum; after slight concentration the liquid is applied to the surface of silver, which immediately becomes black, but on being heated exhibits a rich gilded surface.

GILDING, j.a.pANNER'S. The surface is covered with oil size thinned with spirits of turpentine, and gold, in powder, is gently dabbed on with a puff of wash leather. This gives the appearance of 'frosted gold.' A coating of varnish is next given, followed by exposure to a gentle heat in the 'stove.'

GILDING, LEAF. This term is commonly applied to the gilding of paper, vellum, &c., by applying leaf gold to the surface, previously prepared with a coating of gum water, size, or white of egg. It is usually burnished with an agate or dog's tooth.

GILDING, MECHANICAL. See CHEMICAL GILDING (_above_).

GILDING, MERCURIAL. See WASH GILDING (_below_).

GILDING, OIL. This species of gilding may be divided into several operations. The following are the abridged instructions of a Parisian artist on the subject:--1. The surface is prepared by a coating of white lead in drying oil.--2. Another coat is given, made with calcined white lead or ma.s.sicot, ground in linseed oil and turpentine. 3 or 4 coats of this mixture are often given, at intervals of at least 23 hours, observing to carefully smooth off each coat with pumice stone or shave gra.s.s before the application of the following ones.--3. The 'Gold Colour,' or paint, is next applied. It is usually very adhesive gold size, or the bottom of the pot or dish in which painters wash their brushes. For this purpose it is thoroughly ground and strained.--4. When the gold colour becomes partially dry and sufficiently tenacious, the gold leaf is applied, and pressed on with a wad of cotton-wool or a soft brush. It is now left for several days to harden.--5. A coat of spirit varnish is next given, and the object is cautiously pa.s.sed over a chafing-dish of charcoal, observing to avoid stopping the motion of the piece whilst doing so, as the work would then become discoloured and blistered.--6. The work is 'finished off' with pale oil varnish. For out-door gilding and common work the varnishing process is generally omitted. This species of gilding is applied to woodwork, plaster, metal, &c.

GILDING, VARNISH. This is a mere variety of oil gilding, applied to equipages, furniture, mirror and picture frames, &c., the surface being highly varnished and polished before it receives the size or gold colour; and after the gilding has become quite dry, a coat of spirit varnish, fumed with the chafing dish as above, is applied, followed by 2, 3, or more coats of the best copal varnish, at intervals of 3 or 4 days each.