lO ROYAL SOCIETY OF CANADA 



The factors heretofore used for this purpose by différent analysts vary 

 from 6.25 to 6.45, according to the percentage of nitrogen which they 

 believed to be present in pure casein. These two figures correspond re- 

 spectively to 16.0 and 15.5 per cent. The average of the factors (6.35) 

 corresponds to a nitrogen percentage of 15.75, which is quite close to the 

 average of the analyses of Hammarsten and Chittenden (15.78), who 

 followed the same method of preparing pure casein. 



Table II. explains itself. Interest attaches chiefly to the percent- 

 age of nitrogen contained in the organic ir.atter of the alcoholic and 

 aqueous extracts. In the former this varies from 3.71 to 8.21 joer cent, 

 while the aqueous extract contains a much larger proportion varying 

 from 11.33 to 15.19 per cent. No doubt these extracts contain different 

 bodies, and in the case of the alcohol extract more or less lactose, lactic 

 acid or lactates may be present. At the same time it is to be remem- 

 bered that they are mostly products of the alteration of casein and con- 

 tain less nitrogen than that substance. It is therefore reasonable to con- 

 clude that the process of ripening is accompanied by an elimination of a 

 certain quantity of nitrogen. Some of this in the form of ammonia is 

 contained in the alcohol extract probably combined with lactic acid and 

 may be liberated by heating with magnesia. But its quantity is small 

 compared with the total nitrogen of the alcohol extract, and therefore 

 other nitrogenous bodies must be present. To ascertain the relative 

 quantities of these and ammonia in the alcohol extract, as well as the 

 quantity of free lactic acid, another series of examinations was under- 

 taken, the results of which are given in Table III. In the manipulation 

 necessary to obtain the figures contained in Tables II and III, I obtained 

 very substantial assistance from my son, Mr. A. C. Macfarlane. In the 

 Table. III. .series the volatile acids were also determined by distillation 

 and titration, their quantity being calculated as butyric acid and deduct- 

 ed from the loss on drying. In estimating the free lactic acid in the 

 dried cheese an extraction by ethylether was allowed to precede that by 

 alcohol, and the acidity of the extract is stated as lactic acid. 



