736 FATTY ACIDS. [App. 



It is found in the solid excrements, and is formed readily by the de- 

 composition, through putrefaction, of impure leucin, ammonia being at 

 the same time evolved; hence its occurrence in urine when that fluid 

 contains leucin, as in cases of acute atrophy of the liver. 



Caproic acid. C 6 H u O . OH. 



Caprylic C 8 H 15 O.OH. 



Capric (Rutic) acid C 10 H 19 O . OH. 



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

 varying proportions in the faeces from a meat diet. The first is an oily 

 fluid, slightly soluble in water, the others are solids and scarcely soluble 

 in water ; they are soluble in all proportions in alcohol and aether. 

 They may be prepared from butter, and separated by the varying solu- 

 bilities of their barium salts. 



Laurostearic acid. C 12 H 23 . OH. 

 Myristic C U H 27 O. OH. 



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

 They present no points of interest, 



Palmitic acid. C 16 H 31 . OH. 

 Stearic C 18 H 35 O.OH. 



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

 bodies, the former melting at 62 Q, 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, aether, 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 l : this 

 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, intermediate to the above two, is not now 

 admitted, since Heintz 2 has shewn that it is really a mixture of palmitic and stearic 

 acid. Margaric acid possesses the anomalous melting point of 59'9 C. A mixture 

 of 60 parts stearic and 40 of palmitic acids, melts at 60-3. 



1 Heintz, Annal. d. Phy*. it. Chcm. Ed. 92, S. 588. 2 Op. cit. - 



