METACETONIC ACID. 55 



in every proportion, gradually becomes acid when exposed to the 

 air, but does not reduce a solution of a silver-salt ; hence, it is still 

 questionable whether this fluid should be ranked among the alde- 

 hydes. 



Preparation. Metacetonic acid is formed during the sponta- 

 neous decomposition of many vegetable substances, as, for instance^ 

 peas, lentils, and tan ; by the action of hydrated potash on sugar, 

 starch, gum, &c. ; also during the fermentation of tartrate of lime 

 in contact with nitrogenous bodies, in the decomposition of cyanide 

 of ethyl by caustic potash ; and lastly, (and, in a zoo-chemical view, 

 this mode of its formation is the most important) in the oxidation 

 of fats by nitric acid (Redtenbacher),* in the oxidation of albumi- 

 nous bodies by chromic acid, or by sulphuric acid and peroxide of 

 manganese (Guckelberger),t and in the fermentation of glycerin, 

 the well known product of decomposition of the fats, by means of* 

 common yeast (Redtenbacher).{ This acid is obtained most easily 

 and in the purest form either by distillation of the product of the 

 fermentation of yeast and glycerin, or by treating metacetone with 

 chromic acid or hydrated potash ; otherwise, it is ordinarily pre- 

 pared by treating 1 part of sugar with 3 of hydrated potash, in 

 which, however, it has to be separated from the other acids which 

 are simultaneously developed, namely oxalic, formic, arid acetic acids. 



Tests. Metacetonic acid must, in the first place, be separated 

 by distillation from other non-volatile organic substances with 

 which it may have been mixed, and then by oxide of mercury, 

 from any formic acid that may be present. If acetic acid be 

 also present, the best method is to combine both acids with 

 soda, when, on evaporating the saline solution, the acetate crystal- 

 lises sooner than the metacetonate. The salt which metacetonic 

 acid forms with lead is not crystallisable, while, as every one knows, 

 the acetate of lead crystallises very readily. How this acid is to 

 be separated and distinguished from the remaining acids of this 

 group, will be described when we treat of those acids. Since, how- 

 ever, nothing can be concluded regarding the identity of any given 

 substance with metacetonic acid either from the forms of its salts, 

 which have not yet been determined with crystallographic accuracy, 

 or from the boiling point of the fluid, it is only by the elemen- 

 tary analysis of a pure salt that the presence of metacetonic acid 

 can be scientifically determined. 



* Ann. d. Ch. u. Pharm. Bd. 59, S. 41-57. 

 f Ibid. Bd. 64, S. 46 ff. 

 J Ibid. Bd. 57, S. 174-177, 



