CHAPTER XVI. 

 THE ANALYSIS OF MILK AND MILK PRODUCTS. 



FOR a detailed account of the methods employed in making a 

 complete analysis of these substances the reader must consult a 

 manual on analysis. Only a few of the more important determina- 

 tions in the analysis of milk, butter and cheese will be described here. 



MILK. For many purposes an examination of milk directed to 

 the estimation of the percentages of total solids and fat and the 

 absence or presence of preservatives is sufficient. 



The Amount of Fat, as already stated, is subject to greater 

 variation than that of the other constituents, and, from a practical 

 standpoint, is usually considered the most important criterion of the 

 value of a sample. 



Of many methods which have been described, the following are, 

 among the most reliable and best known : 



1. Adams's yaper-coil method. In this process, 5 c.c. of the milk 

 are allowed to run from a pipette upon a strip of filter paper (from 

 which all matter soluble in ether has previously been removed) about 

 22 in. long by 2 in. wide. The paper is then dried by holding 

 it near a fire, care being taken not to scorch it. It is then rolled 

 into a coil round a short piece of wide glass tubing sealed up at each 

 end (containing a little mercury so that it may not float in ether) l 

 and introduced into a Soxhlet extractor, in which it is repeatedly 

 treated with ether, the ether with the dissolved fat being received in a 

 wide-mouthed small flask, previously weighed (Fig. 14). After eight 

 or ten siphonings the flask is removed from the extractor, the ether 

 distilled off into another condenser, the flask heated in the steam bath 

 for an hour or so, cooled, and weighed. The increase in weight of 

 the flask is taken as fat. The percentage is then calculated, knowing 

 that the weight in grammes of milk taken = 5 x specific gravity. 



In this, as in all operations in which ether is employed, great care 

 should be taken to avoid ignition of the heavy ether vapour. The 

 most convenient condenser to use with the Soxhlet extractor is the 

 form consisting of two concentric metal spheres, the inner one kept 

 cool by a stream of cold water and the vapour passed into the narrow 

 space between the spheres. This method of estimating fat is one of 

 the most accurate, especially if dry ether be used. 



1 This device greatly hastens the extraction, by diminishing the amount of 

 ether required to fill the apparatus. 



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