114 ANALYSIS OF MILK. 



later with Miller, that the results of estimation of fat by the 

 maceration method agree with those obtained by other methods 

 which are admitted to give substantially accurate results, and 

 Simmonds has also obtained results which show that accurate 

 determinations can be made on samples of homogenised milk. 



Estimation of Fat in Sour Milk.— At the Government Labora- 

 tory it has been shown that the fat in the sour milk varies from 

 O-O'e per cent, more to 0-15 per cent, less than in the fresh milk, 

 and averages 0'05 per cent. less. 



The author and Miller find that the results on eighteen samples 

 of sour milk are in very fair agreement with those obtained when 

 fresh by Gottlieb's method ; the results varying from O'lO per 

 cent, above to 018 per cent, below, and averaging 0'03 per cent, 

 below. 



The difierence between the results obtained on the fresh milk 

 and those on the sour milk is partly due to the difficulty of com- 

 pletely redistributing the fat in the curdled milk. Examination 

 of an apparently well-mixed sample of sour milk with a low- 

 power lens shows the presence of quite large particles of cream, 

 and no amount of whisking with a wire brush appears to reduce 

 the milk to the same homogeneous condition easily obtained 

 with fresh milk. 



Estimation of Solids not Fat in Fresh Milk. — The author and 

 Miller have made a number of comparisons of the solids not fat 

 by the maceration method with those obtained by the Society 

 of Public Analysts' method, and find that invariably the former 

 are higher than the latter. The average difference was 0'20 per 

 cent." 



It appears from experiments by Miller and the author that the 

 solids not fat obtained by the maceration method contain a 

 portion of the sugar as hydrated sugar, but the amount of water 

 of hydration, which averages about O'l per cent., is not sufficient 

 to explain the difference between the results. 



Another source of error in the maceration method is due to 

 the presence of aldehydes in the ether ; milk solids remove the 

 aldehyde completely from ether, and this appears to be due to 

 a condensation of the — COH group with the free amino groups 

 of the protein. The solids not fat obtained by the maceration 

 method are always more acid than the milk, and the aldehyde 

 figure is less, the increase of acid and the decrease in the aldehyde 

 figure being within the limits of experimental error identical. 

 These figures afford data for the estimation of the increase of 

 weight due to the condensation of the aldehyde, and assuming 

 that it is acetaldehyde, the error is almost constantly 0'03 per 

 csnt. unless freshly-distilled aldehyde-free ether be used. 



Even this addition does not explain the whole of the difference 



