CHEMISTRY. 



many seeds, and in the cellular tissue of animals, 

 are all normal compound ethers of glycerine, con- 

 stituted like triacetine ; such compounds are called 

 'glycerides.' As triacetine is formed by the union 

 of glycerine and acetic acid and the simultaneous 

 separation of water, so we can reverse the process, 

 and by heating triacetine with a large quantity of 

 superheated steam, add water to it, and obtain 

 glycerine and acetic acid. The fats and oils 

 treated in the same way yield glycerine and one 

 or more ' fatty or oily acids.' A similar decom- 

 position takes place, but much more readily, when 

 the fat or oil is treated with caustic potash or 

 caustic soda. In this case, of course, we obtain, 

 not the acid, but its potash or soda salt, and as 

 the potash and soda salts of the fatty and oily 

 acids are soaps, this process is called 'saponifica- 

 tion,' or soap-making ; and a fat or oil is said to be 

 'saponified' when it is treated with a caustic 

 alkali. In order to separate the soap thus pro- 

 duced from the glycerine formed at the same time, 

 common salt is added to the liquid, when the soap, 

 being insoluble in brine, separates as a curdy 

 solid, leaving the glycerine dissolved. ' Hard 

 soap ' has soda, ' soft soap ' potash, as base. 



The most important 'glycerides' are stearine, 

 palmitine, oleine, and linoleine, which are normal 

 compound ethers of glycerine and stearic, palmitic, 

 oleic, and linoleic acids, respectively. Stearine 

 and palmitine are white solids, melting at 160 F. 

 and 142 F. respectively. Oleine and linoleine are 

 liquids. The ordinary fats, such as suet, lard, 

 tallow, &c. are mixtures of stearine, palmitine, and 

 oleine in various proportions ; the harder and less 

 fusible containing most stearine ; the softer and 

 more fusible containing most oleine. Olive-oil 

 contains palmitine and oleine ; almond-oil, oleine 

 with a small quantity of palmitine. Linoleine 

 occurs in linseed-oil, poppy-oil, hemp-seed oil, and 

 other 'drying oils;' when exposed to the air, it 

 absorbs oxygen, and is converted into a solid 

 varnish. Castor-oil consists almost entirely of 

 ricinoleine, the glyceride of ricinoleic acid. The 

 composition of these fatty and oily acids is given 

 in the following table : 



Palmitic Acid Ci 6 H3 2 O a . 



Stearic Acid 

 Oleic Acid 

 Linoleic Acid 

 Ricinoleic Acid 



ORGANIC ACIDS. 



We have already mentioned a considerable 

 number of organic acids namely, acetic, lactic, 

 formic, valerianic, oxalic, stearic, palmitic, oleic, 

 linoleic, and ricinoleic. We shall here name, and 

 very shortly describe a few more. 



Succinic Acid, C 4 H 8 O 4 , a dibasic acid, obtained 

 Iby the distillation of amber, by the oxidation of 

 fatty acids, and by the reduction of malic and of 

 t;irtaric acids. 



Malic Acid, C 4 H O 6 , a dibasic acid, obtained 

 from the juice of sour apples, currants, rowan- 

 berries, rhubarb, &c. 



Tartaric Acid, C 4 H 6 O fl , a dibasic acid. Acid 

 tartrate of potash, C 4 H 6 KO 6 , occurs in the juice of 

 the grape. This salt is somewhat sparingly 

 soluble in water, and still less soluble in dilute 

 alcohol ; it is therefore deposited as a crystalline 

 crust when the grape-juice is fermented. This 



crust, which contains, besides bitartrate ot potash, 

 tartrate of lime, and colouring-matter, is called 

 tartar or argol. Purified by recrystallisation, it is 

 known as cream of tartar. Tartaric acid is ob- 

 tained from it by first converting it into tartrate of 

 lime, and decomposing this by sulphuric acid. 

 Tartar emetic is prepared by dissolving antimoni- 

 ous oxide (Sb 2 O 3 ) in a solution of cream of tartar. 



Citric Add, C 6 H 8 O 7 , a tribasic acid, occurs in 

 the juice of the orange, lemon, citron, and, along 

 with malic acid, in the currant, gooseberry, rasp- 

 berry, and many other fruits. It is prepared by 

 neutralising the acid juice with lime, and decom- 

 posing the citrate of lime by means of sulphuric 

 acid. 



When citric acid is heated, it loses water, and is 

 converted into aconitic acid, C 6 H 6 O 6 , a tribasic 

 acid, also obtained from the aconite plant, whence 

 its name. 



Benzoic Add, QHgOj, a monobasic acid, is con- 

 tained in gum-benzoin, and is obtained from it by 

 sublimation. Oil of bitter almonds is a mixture of 

 prussic acid and benzoic aldehyd (C r H 6 O). Ben- 

 zoic acid when distilled with lime yields benzol, 

 C 6 H 6 ; thus, C r H 6 2 + CaO,H 2 O = C 6 H 6 + 

 CaO,CO 2 + H 2 O. 



Gallic Add, C^HQO,, a monobasic acid obtained 

 by the fermentation of the tannin of nut-galls. It 

 produces, when mixed with solutions of ferric salts, 

 a deep blue-black precipitate, which is the basis of 

 ordinary writing ink. With ferrous salts, it pro- 

 duces a white precipitate, which becomes black, 

 owing to oxidation, when exposed to the air. 



Tannin or Tannic Add. This name is applied 

 to a number of substances occurring in nut-galls, 

 oak-bark, catechu, kino, cinchona bark, &c. and 

 having the property of forming an insoluble com- 

 pound with gelatine. 



Uric Add, C 5 H 4 N 4 O 3 , a dibasic acid, occurs as 

 urate of soda, and urate of ammonia in the excre- 

 ments of birds and reptiles, in small quantity in 

 the urine of other animals, in some urinary calculi, 

 and in the ' chalk-stones ' which form in the joints 

 of gouty persons. Urate of ammonia forms a 

 large part of guano. 



Prussic Add or Hydrocyanic Add. If nitrogen 

 gas is passed through a heated mixture of charcoal 

 and caustic potash, carbonic oxide, hydrogen, 

 and a substance having the composition KCN, 

 are formed, thus : 



2KHO + 40 + N, = 2KCN + 2CO + H r 



The potassium in this compound may be replaced 

 by other metals, thus : KCN + AgNO 3 = AgCN 

 + KNO 3 , and KCN + HC1 = HCN + KG. 

 There is thus a series of compounds in which the 

 group CN acts as a monad salt- radical plays, in 

 fact, the part of Cl. This radical is called cyano- 

 gen, and its compounds, cyanides. HCN is 

 hydrocyanic (or prussic) acid ; KCN, cyanide of 

 potassium ; and so on. Almost all cyanogen com- 

 pounds are prepared from the substance known 

 as ' yellow prussiate of potash,' or ' ferrocyanide 

 of potassium.' This salt has the composition 

 4KCN,Fe(CN) 2 , and may be regarded as a com- 

 pound of cyanide of potassium and ferrous cyanide. 

 It is formed by fusing animal refuse containing 

 nitrogen (such as dried blood, parings of horn, 

 hide, &c.) along with caustic potash and iron, 

 exhausting the mass with water in the presence of 

 air, and concentrating the clear solution, when the 



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