112 Progress of Foreign Science. 



is such as to exert a happy influence on young chemists who are 

 engaged in organic analysis, by pointing out the steps to be fol- 

 lowed when the object is to inquire if an organic matter should be 

 regarded as a species of an immediate principle, or as a combina- 

 tion of several species, and by compelling them moreover to under- 

 take trials which they would otherwise be apt to neglect. 



Comparative examination of the Acids of Butter., of the phocenic 

 and hircic Acids. — In the state of hydrate, the acids of butter and 

 phocenic acid enter into ebullition at a higher temperature than that 

 of boiling water. They may be distilled over without alteration. 

 At 9° C. below zero, the phocenic, butyric, and caproic acids are 

 liquid, whilst at 15° C. above zero, the capric acid is in the form of 

 small needles. 



All these acids are colourless, and more or less odorous. The 

 butyric and phocenic acids have a much stronger aromatic odour 

 than the caproic and capric acids. The smells of the first two are 

 a little similar ; but it is impossible to confound them after they 

 have been once felt. The odours of the caproic and capric acids 

 resemble somewhat that of sweat ; but the capric acid is distin- 

 guishable from the caproic by something, which reminds one of 

 the odour of a he-goat. All these acids have a burning taste, 

 and a saccharine after-taste, like that of the nitric and muriatic 

 ethers. At 25° C. the density of the butyric acid is 0.9675, that of 

 phocenic acid 0.932, that of caproic acid 0.923, and that of capric 

 acid 0.910 at 18°. 



They differ extremely in regard to their solubility in water. The 

 butiric acid dissolves in it in all proportions, and the combination 

 which results from 2 parts of acid and 1 of water, is denser than 

 the latter liquid. The other acids are much less soluble. 



100 of water dissolve 5.50 of phocenic acid ; 

 1.50 caproic acid; 

 0.12 capric acid. 



Alkohol dissolves the four acids in every proportion ; and the 

 solutions of the butyric and phocenic acids have an ethereous 

 odour of the rennet apple, even when no sensible quantity of ether 

 can be detected. 



Butyric acid unites to hog's lard, and communicates to it the 

 taste and smell of butter, but this aromatized fat soon loses its 

 smell by exposure to air. 



The composition of these three acids is in volume ; 



Butyric acid. Phocenic. Caproic. 



Oxygen .... 3 3 3 



Carbon .... 8 10 12 



Hydrogen ... 11 14 19 



The salts formed by the acids of butter and the phocenic acid, 

 exhale, in the moist state, the smell peculiar to their acid, espe- 

 cially when slightly heated, or brought into contact with carbonic 



