FATTY ACIDS. 51 



It is very difficult to prepare tte anhydrous acid by distillation 

 alone, the last traces of water being retained with great obstinacy ; 

 dehydrating agents remove this water, and the acid is somewhat 

 hygroscopic. It is soluble in all proportions in water, but is 

 separated as an oily layer on saturating the solution with 

 ■calcium chloride. It is extracted from aqueous solution by 

 ether. 



From dilute solutions it distils 2-1 times as fast as water — i.e., 

 the vapour arising from a dilute solution contains 2-1 times the 

 proportion of butyric acid contained in the solution. Its solu- 

 bility in the mixture of higher fatty acids of milk fat is very 

 small. 



By the action of strong chromic acid at the boiling point it is 

 •oxidised to a mixture of carbon dioxide and water, but dilute 

 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. \Vhen 

 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 0° C. dissolve 19-4 parts. 

 ,; „ 20° „ 17-6 ,, 



,, 60°-85° ,, 150 ,, 



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 245 parts at 14° according to Luck, who has used this method 

 of separating it from barium formate, acetate, etc. 



Silver butyrate crystalUses 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 Heracleum giganteum and H. spondi/lium, 

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

 seeds of the parsnip {Pastinaca sativa) consists chiefly of octyl 



