GLYCEIMM
53
pressure between two iron rollers, by which it iselongated to the extent of half a yard or more. Itis then carefully dried, packed, and sent to market.The common cod— Morrhua vulgaris —yields a poorerkind of isinglass; but the hake only is known to theextensive manufacturers as fit for their purposes.
Hudson’s Bay Isinglass. —This isinglass comes overin the purse form. It is of a light yellow colour,translucent, and free from taste and smell. Theinner lining of the sac, which may be readily strippedoff, is insoluble in water; the remaining membranedissolves in boiling water.
For a long period isinglass has been exported fromCalcutta to China . It is probably the produce of aspecies of Polynemus.
Picked East India isinglass is in small shreds, 2 or3 inches long, and tapering at the extremities. It ishand-picked in India by the natives.
Manilla isinglass has been imported recently asthin cake. It is white and clean, and is equal inquality to Brazilian or Samovey book. The fishwhich yields it is found in the river of Manilla , andon the coasts of the Philippines , Luconia. It issmaller than the Brazilian, but greatly resembles thelump variety of that kind, and the fish is probably anallied species.
Cod sounds , in a dried state, are brought fromScotland , and used as a substitute for foreign isin-glass. They are, however, usually preserved soft bysalting, and dressed for the table.
The properties of isinglass are nearly the same asthose of gelatin.
The more common kinds of isinglass, especiallythe coarse Brazilian, are used by brewers for finingbeer. They are also employed for the clarificationof wines and various other liquids.
Court plaster is formed by brushing a solution ofisinglass, mingled with a little tincture of benzoin,over black sarsenet.
Marine glue, diamond cement, Sfc., are made by dis-solving isinglass in dilute alcohol.
GLYCERIN .—Propemjl alcohol; glycerine, glycerin,French ; glycerin, oelsuss, oelsucker, German ; elaio-saccharum, Latin (C 3 II 8 0 3 or C 3 II 6 (OII) 3 ).— Scheele,its discoverer, termed it the sweet principle of fat.This body is produced from most fixed oils and fatsby the process of saponification. It does not existready formed in the fats, but is formed from them,together with a fatty acid, by addition of the elementsof water, iust as alcohol is produced from acetate ofethyl.
Most fats and oils are mixtures of propenyl ethersof the fatty acids and the acids of the oleic series.When fats are heated with water or with alkalinesolutions, they are converted into glycerin and fattyacids or their alkali salts, namely, soaps.
Glycerin was discovered by Scheele in 1779.He obtained it in the course of making lead plaster.Olive oil, or any of the natural fats, was boiled withlitharge and water till saponification was effected ;He fluid remaining was then decanted, and sulphu-retted hydrogen passed through it till the whole ofdie lead was precipitated as sulphide. After filtra-
tion the liquid was evaporated with great care below212° Fahr., when a viscous fluid remained : this wasglycerin.
Pure glycerin is a colourless, transparent liquid,inodorous, and of a syrupy consistence, possessinga very sweet taste. Its specific gravity is 1-27, at15'°5 C. When exposed to strong winter cold it hasbeen found to solidify to a crystalline mass resemblingsugar-candy, andcomposed of shining octahedral crys-tals about the size of peas, having a strong refractingpower, grating between the teeth, and exhibiting thereactions of pure glycerin. In small quantities thesecrystals melted quickly, but after complete fusionthe glycerin did not again solidify, even when cooledfar below the freezing point of water (Gladstone,Crookes). According to Werner, cold commercialglycerin crystallizes when chlorine gas is passed intoit. Glycerin solidifies at —40° C. to an amorphousmass. When distilled alone it is decomposed for themost part; but when under slight pressure, or in anatmosphere of steam, it distils without decomposition.
Glycerin is soluble in water (which it absorbsfrom the air), alcohol, and chloroform, but is in-soluble in ether. Thrown upon live coals, or heatedin contact with the air, it burns with a blue flame.The alkalies, and so many metallic salts, are dis-solved by it that it ranks next to water as a solvent.
Klever states that 100 parts of glycerin dissolveat 15'°5 C.:—
Parfca by
Weiyht.
Alums. 40
Ammonium carbonate, 20Ammonium chloride,.. 20
Arsenious acid,. 20
Arsenic oxide,. 20
Atropine,. 3
Atropine sulphate,.... 33
Benzoic acid,. 10
Boric acid,. 10
Brucine,. 2*20
Calcium sulphide, .... 5
Oliinchonine sulphate,.. 6*70
Cinchonine,. 0*50
Cupric acetate,. 10
Cupric sulphate,. 30
Iodine,. 1*9
Lead acetate,. 20
Mercuric chloride,.... 7*50
Mercuric cyanide, .... 27
Morphine,. 0*45
Morphine acetate,. 20
Morphine hydrochloride,20Oxalic acid,. 15
1’iirtH byWeight.
Phosphorus,. 0*20
Potassium arsenate,. 50
Potassium bromide,.... 25Potassium chlorate,... 3’50
Potassium cyanide,.... 32Potassium iodide,... . 40
Quinine,. 0*50
Quinine tartrate,. 0*25
Sodium arsenate,. 50
Sodium biborate,. 60
Sodium bicarbonate, .. 8
Sodium carbonate,.... 98
Sodium chlorate. 20
Sulphur, . 0-10
Strychnine,. 0*25
Strychnine nitrate,.... 4
Strychnine sulphate,.. 22*50
Tannic acid,. 50
Tartar emetic,. 5*50
Urea,. 50
Veratrine,. 1
Zinc chloride,. 50
Zinc iodide,. 40
Zinc sulphate,. 35
Glycerin can be obtained from tlie mother liquorof soap factories by adding to it a slight excess ofsulphuric acid, heating the solution with carbon-ate of barium, filtering, and after the filtrate hasbeen concentrated by evaporation, extracting theglycerin with alcohol. On distilling off the spirit,the glycerin remains. It may likewise be readilyprepared by dissolving castor oil in absolute alcoholand passing hydrochloric acid gas through the fluid.The fatty ethers are washed away by water, and theresiduary fluid affords the glycerin in a state ofpurity on evaporation. Any adhering fatty matteris separated by digesting the liquid in ether anddecanting the latter.