CHEMICAL COMPOSITION AND ANALYSIS OF CHEESES. 273 



although it be correctly carried out, because ripe cheeses contain, in 

 addition to unaltered nitrogenous matter, quite a number of pro- 

 ducts of the decomposition of nitrogenous bodies, which do not 

 belong to the group of albuminoids. 



The investigation of fresh cheese is much simpler, since, in its 

 case, the individual constituents of the milk, although they have 

 partly undergone change, are yet in a condition which does not 

 offer especial difficulty in their separation and determination. 



In the investigation of fresh cheese the following method may be pur- 

 sued : 



(1) Determination of Water and Fat. The sample of cheese to be 

 investigated is cut into small square pieces, of which 2*5 to 5 grams 

 exactly are weighed out, and carefully warmed to 40 C. They are then 

 brought, in an open glass capsule, under the receiver of a hand air-pump, the 

 air from which is pumped out. It is left for some time standing, again 

 warmed, and this is again repeated, until no further loss in weight is 

 observed. It is then digested several times with cold ether, removed 

 from the capsule, and pressed in a dish. It is then brought on to a 

 weighed filter; the capsule and the dish being rinsed with ether. The 

 cheese is then extracted on the filter with warm ether, the different 

 washings being all brought together. The cheese, from which the fat has 

 thus been extracted, is dried at from 100 to 110 C., cooled, and is 

 weighed on the filter, the weight of which is deducted. After the ether 

 has been distilled off from the ether extract, the fat remaining behind is 

 dried carefully at from 100 to 105 C., cooled, weighed, and the percentage 

 of fat of the cheese thus estimated. By subtracting the sum of the weight 

 of the cheese from which the fat has been extracted, and which has been 

 dried, and of the fat, from the weight of the cheese originally taken, the 

 percentage of water in the cheese is obtained. If the largest part of the 

 water has not been removed before its treatment with ether, it may 

 happen that in the extraction process small quantities of mineral salts, 

 which are soluble in water, and perhaps also small quantities of milk- 

 sugar, may go into the extract, and render the determination inexact. In 

 the investigation of sour-milk cheeses, it must be remembered that the 

 lactic acid present is soluble in ether. On this account the determination 

 of fat must be carried out in a specially prepared sample, which has been 

 rendered weakly alkaline with soda, and then carefully dried. 



(2) Determination of Nitrogenous Matter. This is determined in another 

 quantity of the cheese, or in that portion from which the fat and the 

 water have been separated, either volumetrically, by Dumas' method, or 

 by the Kjeldahl process, the nitrogen obtained being multiplied by the 



(M175) S 



