7 GEIC ACID. 



yaviy U that which U used when it is nfcnmnry to change the 

 direction of the original motion, either angularly on the game plane, or 

 at a different elevation, in a perpendicular or angular direction. Some- 

 time* bevilled gearing u formed by cutting the teeth of the wheel* 

 upon portions of cone* working into one another ; or by means of 

 teeth cut upon the path of a screw, working into a worm cut upon the 

 upright shaft. 



Perhaps it ought to be added, that the periods of revolution of the 

 different kind* of gearing, whether fixed or moveable, straight or 

 bevilled, are quite as often ejual, or synchronous, as they are slower or 

 faster. When the periods of revolution are synchronous, the wheels 

 are, of course, of equal diameters. 

 BIC ACID. [GELS.] 



GEIX, a name given to Inimut.'m common with ulmin, liumic acid, 

 ulmie acid, hiimni, and yeie acid. This substance is obtained from 

 common mould, which when boiled with alkalies, and the solution 

 filtered and treated with acids, yields a brown deposit, which has the 

 above names. Mulder states that the substance contains 2J to 7 per 

 cent, of nitrogen. These substances appear to be vegetable matters in 

 a state of decay. 



The name y<in has also been given to a bitter non-azotieed matter 

 found in the rout of the Gmm urbanum. Its composition is not 

 known. 



GELATIN. The physiological relations of gelatin, and its value as 

 an article of food, have already been described. [GELATIN, in NAT. i 1 1 - r. 

 Div.] The present article will, therefore, merely contain a description 

 of its manufacture fur commerce, and the chemical action of various 

 substances upon it. 



Tarings of the hoofs and horns, the crushed bones, and the cuttings 

 of the hides of animals, are placed in cast-iron cylinders, and subjected 

 to the action of steam at ordinary or at a more or loss increased 

 pressure ; a strong solution of gelatin in hot water ia thus produced, 

 which is poured out on to polished slabs of tin, marble, Ac., to solidify, 

 and the resulting sheets afterwards cut into shreds by machinery. If 

 the gelatin is required for dietetic purposes, great care is observed in 

 the selection and cleaning of the materials from which it is to be 

 obtained. Some makers bleach it with sulphurous acid, flavour it with 

 various essences, well dry and powder it to render it more rapidly 

 soluble in water, and one patentee even takes the trouble to dry it in 

 vacuo. Gelatin of a common description is used in pharmacy for 

 making captula, little bags intended to contain active medicinal pre- 

 parations of nauseous taste and odour ; also for coating pills. Sheet 

 gelatin, coloured, is now largely used as an ornamental envelope for 

 confectionary, &c., and in the fabrication of toys and other small 

 articles. 



Gelatin softens and swells up in cold writer, but does not dissolve. 

 It ia also insoluble in alcohol, ether, and the fixed and essential oils. 

 Boiling water dissolves it in considerable quantity. If a sheet of 

 tolerably soft gelatin be printed upon, and then immersed in spirit of 

 wine, a considerable but equal contraction takes place ; and the print 

 transferred to stone furnishes impressions 'similar to the original, but 

 much reduced in size. By printing upon a sheet of very dry gelatin, 

 and afterwards immersing in water, the converse of the above result ia 

 obtained. 



Chlorine acts upon gelatin, forming with it a white compound, from 

 which the gelatin may be reproduced unchanged on the addition of 

 ammonia. Nitric acid converts gelatin into oxalic acid, and other pro- 

 ducts. Sulphuric acid transforms it into leuciu, a kind of sugar called 

 glycocin, and into some other products. Acetic acid dissolves gelatin ; 

 strong alkalies decompose it. Its aqueous solution is precipitated by 

 bichloride of platinum, corrosive sublimate, infusion of galls, or any 

 liquid containing tannin, but is not rendered even turbid by solution 

 of ferrocyanidc of potassium, a test by which gelatin is at once dis- 

 tinguished from albumen. 



From the difficulty of obtaining gelatin in an absolutely definite 

 condition, its true chemical composition is somewhat uncertain. The 

 formula usually adopted for it is C,,H M N,0, ; this nearly agrees with 

 the following per centagc results obtained by Mulder : 



Carbon 50-40 - 



Hydrogen . . 6'64 



Nitrogen 18-34 



Oxygen (including trace of sulphur) . . 24-(i 



ciKLATIXE AND GLUE. 



100-00 



riELATIXE AND GLUE. These nearly-allied substances may 

 conveniently be noticed together, in relation to their manufacture and 

 uses. 



GeJaiinc. Gelatine is used partly as an agent in food, and partly as 

 * cement. Much of it exists in the bones of animals; and it adonis 

 one evidence of the improved processes of modern times, that so valu- 

 able a substance is now saved which used formerly to be wasted. Tin- 

 jelly can be obtained by the action of heat on the organised tissue of 

 bones, tendons, ligaments, sinews, skin, and serous membrane, whiUt 

 in contact with water. Isinglass is nothing more than a purer kind 

 of gelatine. All gelatines dissolve more or less in hot water, and form 

 a translucent jelly. Gelatine and tannin form leather, a fact which 

 explains the rationale of the tanning process. 



Without touching in this article on the chemistry of gelatine as an 

 article of food, we may mention that gelatine is nourishing as a 

 but not alone ; for it is wanting in flesh-making elements. The 1 

 Samuel Bentham, a person of great ingenuity, drew the attention of 

 the Admiralty, in 1 >-'.', to the advantage and economy of supplying 

 the navy with gelatine procured from bones, by a process invented by 

 D'Aroet long before, and much practised in France. Frviu-h workmen. 

 and some of the inmates of French hospitals, are frequently *i 

 with soup made from bone-gelatine at a cost of one farthing per put : 

 and it could be made sufficiently strong to be portable when cold for one 

 halfpenny. Bentham proposed that the bones of salt beef should not 

 be thrown away, as at present, on shipboard. If the joint-! were de- 

 prived of the bone before the meat is shipped, the good beef could be 

 packed in a small space, and thereby economise stowage on board ; 

 while the bones would be available as a source of gelatine. Beef bones 

 contain 30 per cent, of gelatine, and 10 per cent, of fat, which can be 

 extracted by processes easily managed. The gelatine could be flavoured 

 and dried, and would be very valuable as an article of ship diet The 

 meat also could be more easily and perfectly salted, and could ! . 

 rolled up like Hamburg beef before being put into the casks. Bentham, 

 calculating on the lu.sU furnished by the French chemists, asserted 

 that the bones which arc stripped of their meat every day in London, 

 would furnish gelatine sufficient for one small basin of soup to every 

 one of the inhabitants, young and old. He impressed his views, on the 

 Admiralty, but without success ; and we believe bone-gelatine does 

 not yet form an element in the dietary of the British navy. The 

 French adopt the system much more extensively than ourselves. On 

 the large scale, the gelatine ia extracted by steam, and sometimes a 

 little muriatic acid is employed to remove the phosphate of lime. 

 Even /ocri! bones have been made to yield gelatine. 



The power of obtaining gelatine from bones being once understood, 

 the variety of applications becomes very considerable. Bone-gi 

 for divers purposes, ia bleached with sulphuric acid or animal charcoal. 

 It may be tinted blue by sulphate of indigo or juice of blue-berries ; 

 green, by the juice of spinach; or red by that of beetroot. Cake 

 gelatine is made by the French from the cuttings of the skins used in 

 kid-glove making. Nelson's patent gelatine is obtained from glue- 

 pieces or cuttings from the hides and skins of animals. In IP: 

 it, the fragments are freed from hair, wool, flesh, and fat ; then i-; 

 for several hours in a solution of caustic soda ; then placed in c 

 vessels at a temperature of C0 or 70 Fahr. ; next washed to expel the 

 alkali ; then exposed to the vapours of burning sulphur ; and thru 

 dissolved in water at a temperature of ISO" Fahr. After tl. 

 solution is strained into settling vessels, where it is kept for several hours 

 at a temperature of 110 Fahr. It ia then poured to tlie depth of half 

 an inch upon a cooling slab, and the resultant cake of jelly 

 further processes, is prepared into one of two kinds, opaque or trans- 

 parent both intended 'as substitutes for isinglass. Hattray's patent 

 gelatine is another kind, produced in a somewhat similar way 

 waste glove-pieces. Swinburne's patent gelatine is made from tin- 

 cuttings of calves' skins. What is called rough gelatine in mode frm 

 the spongy insides of the horns and ribs of oxen, and the softer parts 

 of the skulls and other bones, also from sheep's bones the preparation 

 requiring, of course, a good deal of cleaning, steeping, boiling, steaming, 

 evaporating, &c. 



Glue. This thicker kind of gelatine is prepared from fthe clippings 

 of hides, hoofs, &c , obtained at the tan-yard. The first operation is to 

 wash this refuse in lime-water, and afterwards to boil it in water, and 

 skim the solution, which, is then rendered clear by being strained 

 through baskets, and evaporated by a gentle heat to a proper degree of 

 thickness. It is finally cooled in wooden vessels, cut into thin 

 portions, and dried upon coarse net-work. When properly prepared, 

 glue is of a deep brown colour, translucent, and free from spots and 

 clouds. When required for use, it is broken into pieces, and steeped 

 for about twenty-four hours in cold water, by which it swells and 

 softens. When gently heated in a water-lath, such as the common 

 glue-pot is, it is applied by means of a brush to the various kii 

 work Ifor which it is used. The adhesion depends upon the evapora- 

 tion of the water. Mr. Tucker patented a process, in 1856, for 

 glue without the use of a netting. He pours the boiled mass into 

 separate pans disposed on racks in a drying chamber ; heat ia a ; 

 at a temperature of 140 or 160 Fahr., and fans are then rot.it 

 current of air through the chamber. Another propos 

 drying ia to pass the glue into a vessel fitted with a horizontal 

 eylimliT, kept heated by steam within or by a steam jacket on the out- 

 side; the lower half of the cylinder dips into the glue, ami r< 

 at a slow rate, the surface take up a thin film of the glue, wlii.-h 

 quickly solidifies and dries ; a film is thus formed and dried at each 

 revolution of the cylinders. 



Besides the application of gelatine to food, and that of glue as a 

 cement, both are used in very numerous ways in the mechanical art*. 

 Glue ond treacle make a peculi.-ir elastic substance very useful for 

 printers' hiking-rollers. Gelatine casts, and gelatine moulds for casts, 

 are now very common especially the latter, on account of the ease 

 with which the casts can be taken out of them. The ytl<ii',,,< art of Paris 

 make sheets of exquisitely fine gelatine, dyed to the molt brilliant 

 colours. These sheets can be applied to many useful purposes ,- they 

 can be u.:ed 09 a layer on the surface of an engraving or woven material 



