344 CONSIDERATION OF CARBON COMPOUNDS. 



Fats and fat oils. All true fats are compound ethers of the tri- 

 atomic alcohol glycerin, in which the three replaceable hydrogen atoms 

 of the hydroxyl are replaced by three univalent radicals of the higher 

 members of the fatty acids. For instance : 



OH 



Glycerin = C 3 H 5 .(OH) 3 or C 3 H 5 rlOH 



\OH 

 Stearicacid = C 18 H 35 O.OH or C 18 H 35 O\ O 



H/ 



(C 18 H 35 O).0 



Stearin or tristearin = C 3 H 5 .(C 18 H 35 O) 3 .O 3 or C 3 H 5 :_ (C 18 H 35 O).O 



\(C 18 H 35 0).0 



While all natural fats are glycerin in which the three hydrogen 

 atoms are replaced, we may by artificial means introduce but one or 

 two acid radicals, thus forming : 



(C 18 H 35 0)0 (C 18 H 35 0)0 



Monostearin = C 3 H 5 _OH Distearin = C 3 H 5 ^_(C 18 H 35 O)O 



\OH \(OH) 



Fats are often termed glycerides ; stearin being, for instance, the 

 glyceride of stearic acid. 



The principal fats consist of mixtures of palmitin, C 3 H 5 .(C 16 H 31 O) 3 . 

 O,, stearin, C 3 H 6 .(C 18 H 35 O) 3 .O 3 , and olein, C 3 H 5 .(C 18 H 33 O) 3 .O 3 . 

 Stearin and palmitin are solids, olein is a liquid at ordinary tem- 

 perature ; the relative quantity of the three fats mentioned determines 

 its solid or liquid condition. The liquid fats, containing generally 

 olein as their chief constituent, are called fatty oils or fixed oils in 

 contradistinction to volatile or essential oils. 



All fats, when in a pure state, are colorless, odorless, and tasteless 

 substances, which stain paper permanently ; they are insoluble in 

 water, difficultly soluble in cold alcohol, easily soluble in ether, disul- 

 phide of carbon, benzene, etc. The taste and color of fats are due to 

 foreign substances, often produced by a slight decomposition which 

 has taken place in some of the fat. All fats are lighter than water, 

 and all solid fats fuse below 100 C. (212 F.) ; fats can be distilled 

 without change at about 300 C. (572 F.), but are decomposed at a 

 higher temperature with the formation of numerous products, some 

 of which have an extremely disagreeable odor, as, for instance, 

 acrolein, C 3 H 4 O, an aldehyde which in composition is equal to 

 glycerin minus two molecules of water : 



C 3 H 5 (HO) 3 - - 2H 2 = C 3 H 4 0. 



Some fats keep without change when pure ; since they contain, 

 however, impurities generally, such as albuminous matter, etc., they 



