110 ANALYSIS OF MILK. 



As the result of Soxhlet's researches, Schleicher and SchuII 

 placed a " fat-free " paper on the market, and this is very gene- 

 rally employed. Schleicher and SchuU's " fat-free " paper gives 

 a small ether extract consisting chiefly of loose fibres ; this paper 

 was at first remarkably free from extract, but later batches were 

 found to contain quite an appreciable amount of extract. It 

 is preferable for the analyst to extract his own papers for 

 one to two hours with " acid alcohol." 



Waller and Liebermann objected to the use of ether as a 

 solvent for fat, on the ground that other substances contained in 

 milk were soluble in this menstruum. The author has found, 

 however, that, provided the coil is well dried previous to extrac- 

 tion, chloroform, benzene, and petroleum ether give the same 

 results as anhydrous ether ; ordinary ether, which contains 

 small amounts of water and alcohol, gives, however, slightly 

 higher results, especially if the coils are allowed merely to air- 

 dry. The error introduced by the use of ordinary ether is small, 

 and is very frequently neglected. 



Attempts have been made to substitute other substances for 

 the blotting-paper ; Abraham, indeed, before Adams published 

 his method, had used " Parker's fibre lint." Wiley, and also 

 Johnstone, tried asbestos paper, but the results were not satis- 

 factory. 



The action of the blotting-paper appears to be slightly different 

 from that supposed by Adams. Undoubtedly he was correct in 

 supposing that the milk was spread out over a large surface ; 

 the author's experiments showed that when milk was filtered 

 through blotting-paper the filtrate contained the solids not fat, 

 but only a small amount of fat. This view was found by Vieth 

 not to be entirely correct ; he found that a portion of the casein 

 was also removed from the milk by blotting-paper. When milk 

 is spread on blotting-paper the portion which soaks in consists 

 of the whole of the water, milk-sugar, and salts, and a consider- 

 able proportion of the proteins, together with a small amount 

 •of fat ; the bulk of the fat, together with a proportion of the casein, 

 is left on the surface, and is very easily extracted by the ether. 

 If the fat globules have been broken up by a " homogeniser," 

 the extraction is not complete. 



The following mode of procedure is considered most correct by 

 the author : — 



Hang up a convenient number of strips of " fat-free " paper 

 from clamps (letter-clips are very serviceable). Run on, from 

 a pipette, 5 c.c. of each of the samples to be tested in a slow 

 stream, spreading the milk well over the paper ; the strip should 

 be held by its free end, to be nearly horizontal The weight 

 •of the milk delivered by the pipette should be noted, care being 



