CHEMICAL BASIS OF THE ANIMAL BODY. 119 



Caproic acid. C 5 H U . COOH. 

 Caprylic acid. C 7 H 15 . COOH. 

 Capric (Rutic) acid. C 9 H 19 . COOH. 



These three occur together (as fats) in butter, and are contained in 

 varying proportions in the faeces from a meat diet and the first two in 

 sweat. The first is an oily fluid, slightly soluble in water, the others 

 are solids and scarcely soluble in water ; they are soluble in all propor- 

 tions in alcohol and in ether. They may be prepared from butter, and 

 separated by the varying solubilities of their barium salts. 



Laurie or Laurostearic acid. C U H 23 .COOH. 

 Myristic acid. C^H^ . COOH. 



These occur as neutral fats in spermaceti, in butter and other fats. 

 They present no points of interest. 



Palmitic acid. C 15 H 31 . COOH. 

 Stearic acid. C^H^ . COOH. 



These are solid, colourless when pure, tasteless, odourless, crystalline 

 bodies, the former melting at 62 C., the latter at 69 '2 C. In water 

 they are quite insoluble ; palmitic acid is more readily soluble in cold 

 alcohol than stearic : both are readily dissolved by hot alcohol, ether, or 

 chloroform. Glacial acetic acid dissolves them in large quantity, the 

 solution being assisted by warming. They readily form soaps with the 

 alkalis, also with many other metals. The varying solubilities of their 

 barium salts afford the means of separating them when mixed 1 : this 

 method may also be applied to many others of the higher members 

 of this series. 



These acids in combination with glycerin (see below), together with 

 the analogous compound of oleic acid, form the principal constituents of 

 human fat. As salts of calcium they occur in the faeces and in 

 ' adipocire,' and probably in chyle, blood and serous fluids, as salts of 

 sodium. They are found in the free state in decomposing pus, and in 

 the caseous deposits of tuberculosis. 



The existence of margaric acid, as obtained from natural fats, intermediate to 

 the above two, is not now admitted, since Heintz has shown 2 that it is really a 

 mixture of palmitic and stearic acids. Margaric acid possesses the anomalous 

 melting point of 59*9 C. A mixture of 60 parts stearic acid and 40 of palmitic 

 acid, melts at 60'3. A true margaric acid may however be prepared by replacing 

 the group OH in cetyl-alcohol (C^H^ . OH) by the group COOH. 



1 Heintz, Poggendorff's Annal. d. Phys. u. Chem. Bd. xcn. S. 588. 



2 Op.cit. 



