20 THE FAT OF MILK. 



solutions are unaffected. Alkaline permanganate oxidises it to 

 carbon dioxide ; Johnstone states that oxalic acid is formed from 

 butyric acid by the action of alkaline permanganate, but other 

 observers are unanimous in denying this. 



The salts of butyric acid are all soluble in water. When 

 ignited they leave a residue of the carbonate of the metal (except 

 the silver and mercury salts, which leave metallic silver and no 

 residue, respectively). The calcium salt has the following 

 solubility : 



100 parts of water at C. dissolve 19-4 parts. 



20 17-6 



,,60-85 15-0 

 100 15-8 



A cold saturated solution is precipitated by heat. It crystal- 

 lises in rhombic needles from cold solutions, and in rhombic 

 prisms from hot solutions. 



The barium salt is much used for determining the molecular 

 weight of the acid ; it cannot be dried at 100 C. without slight 

 loss of butyric acid, but is quite permanent at 90 C. One 

 thousand parts of absolute alcohol dissolve 11-7 parts at 30 

 and 2-45 parts at 14 according to Luck, who has used this 

 method of separating it from barium formate, acetate, etc. 



Silver butyrate crystallises by cooling a hot solution in needles, 

 but by spontaneous evaporation in monoclinic prisms. 100 parts 

 of water at 16 dissolve 0-413 part. 



Both the acid and calcium salt form molecular compounds 

 with calcium chloride. 



Butyric acid occurs in the free state in perspiration and as 

 ethyl salt in the oils of Hemcleum giganteum and H. spondylium, 

 hexyl butyrate being also present in the latter ; the oil from the 

 seeds of the parsnip (Pastinaca saliva) consists chiefly of octyl 

 butyrate. Ethyl butyrate is a volatile liquid of a smell recalling 

 the odour of pine apples. 



Caproic Acid, CH 3 .CH 2 .CH 2 .CH 2 .CH 2 COOH. Kcefoed has 

 proved that the caproic acid of the fat of milk is normal. This 

 acid is an oily liquid with an unpleasant goat-like smell. It 

 boils at 205 C., solidifies at 18 C., and melts at 1-5. Its 

 density at is 0-9446 according to Zander. 



It hardly mixes with water, is extracted by ether from an 

 aqueous solution, and possesses considerable solubility in the 

 mixed higher fatty acids of milk fat. From a dilute aqueous 

 solution it distils 3-9 times as fast as water. 



The calcium salt differs from calcium butyrate by increasing 

 in solubility on heating ; 100 parts of water dissolve at 11 to 

 12 2-36 parts, at 17-5 2-58 parts, and at 18-5 2-71 parts of 

 calcium caproate. It crystallises in needles. The barium salt 



