122 THE ESTIMATION OF FAT. 



cut off to remove any particles of solids, and the filter containing 

 the pieces cut off is placed in a weighing bottle and dried in the 

 water-oven to constant weight. The ether is distilled, and the 

 residue of fat weighed ; the fat is extracted with petroleum 

 ether, and the small residue insoluble in this solvent subtracted 

 from the weight ; this usually consists of phenol-phthalein, and 

 its weight may be neglected without appreciable error. 



Estimation of Pat in Fresh Milk. It has been shown by 

 Thorpe, and by the author, in conjunction with Hehner and Bevan, 

 and 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 

 Laboratory it has been shown that the fat in the sour milk varies 

 from 0'06 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 (HO per 

 cent, above to 0-18 per cent, below, and averaging 0-03 per cent, 

 below. 



The difference between the results obtained on the fresh milk 

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

 distributing the fat in the curdled milk completely. 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 were 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 Ol 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 



