MILK 



47 



Indices of Refraction Corresponding to the Divisions on the 

 Refractometer Scale. 1 



Small differences in the composition of the caustic potash 

 solution can have a very considerable effect upon the results 

 got by the refractometer method. It is therefore advisable 

 after making up a new supply of this solution to make several 

 parallel tests with other reliable methods, e.g. Rose-Gottlieb's 

 (see below), and to correct the refractometer determinations if 

 differences are found. 



If the test is carried out exactly as described above, the 

 refractometer gives very accurate results, but the method is so 

 sensitive that the least departure from these rules influences 

 the results. One great advantage, however, of this method is 

 that where a large number of tests have to be made, it is 

 possible, with the refractometer, to do 150 in an hour without 

 effort. 



With separated milk very good results are also obtained, as 

 the author has shown, 2 and he is also of the opinion that slight 

 errors of manipulation do not have such a powerful influence 

 as with whole milk. 



3. Extraction Methods. 



These methods are based upon the drying of a certain quantity 

 of milk on some porous material, and then extracting the fat 

 by means of ether or petroleum ether. On evaporation of the 



1 The columns A, ? give the changes in the refractive index expressed as 

 units of the fourth decimal for each division on the scale. 

 a Revue Gen. du Lait, II, p. 145. 



