BUTYRIC ACID. 59 



it has been found in certain processes of fermentation of non- 

 nitrogenous bodies, as starch and sugar, where the nitrogenous 

 admixtures only act as ferments. Lactate of lime, in the presence 

 of nitrogenous matter, becomes converted into butyrate of lime. 

 To obtain pure butyric acid on a large scale, we should have 

 recourse to the last-named method. The most simple mode of 

 procedure is to expose carob (the fruit of Ceratonium siliqua), or 

 sugar, with sour milk and a little cheese, and with some car- 

 bonate of lime, at a temperature of 30 to 35, as long as gas conti- 

 nues to be evolved, namely for five or six weeks; the filtered 

 fluid is then decomposed with carbonate of soda, which causes a 

 precipitation of carbonate of lime ; the solution of butyrate of soda 

 is now strongly concentrated, and, after being decomposed with 

 sulphuric acid, is distilled ; finally, the butyric acid is freed from 

 water and acetic acid by fused chloride of calcium. 



Tests. This acid must first be separated by distillation from 

 the non-volatile substances, as, for instance, lactic acid, with which 

 it is not unfrequently associated; in the distillate we can then only 

 have the acids of this group. We shall here refer to the means of 

 distinguishing it from the acids which have been already described, 

 namely, formic acid, acetic acid, and metacetonic acid. The first 

 may be very easily removed by means of its property (to which 

 we have frequently referred) of reducing the oxides of the noble 

 metals. The acids must then be combined with soda, when the 

 greater part of the acetate of soda may be removed by crystallisa- 

 tion. The soda-salts of the mother-liquid are afterwards to be 

 decomposed by tolerably concentrated sulphuric acid, yielding in 

 the receiver metacetonic and butyric acids, with a little acetic acid; 

 from these the butyric acid may be pretty well separated by frac- 

 tional distillation, since that which passes over at 140 is only 

 metacetonic acid, with traces of acetic acid, and it is not till the 

 temperature is raised to 160 or 165, that tolerably pure butyric 

 acid enters the receiver. If other analogous acids be also present, 

 we must not be contented with this mode of procedure ; specific 

 as it may appear to be, we must not rely on the peculiar odour of 

 butyric acid, but we must convert the butyric acid into one of the 

 above-described butyrates, and after comparing the salt thus 

 obtained with the corresponding salt of pure butyric acid, we must 

 institute an elementary analysis, or at the least we must determine 

 the atomic weight or the saturating capacity. 



The atomic weight of the hypothetical anhydrous butyric acid 

 is 987*5 (for 8 at. carbon =600*0, 7 at. hydrogen = 8 7'5, and 3 at. 



