118 THE ESTIMATION OF FAT. 



extraction (1J hours) was not sufficient to remove the whole of 

 the soluble matter from the blotting-paper as much as ten 

 hours being necessary it followed that the matter extracted by 

 ether from the coil was greater when a milk (containing small 

 amounts of acid) was placed on a coil than when the coil was 

 extracted alone. The difference was represented by the amount 

 of resinous acids equivalent to the acidity of the milk, and was 

 naturally not constant. 



He found that alcohol extracted the coils completely a fact 

 also noted almost simultaneously by Soxhlet but preferred the 

 use of alcohol containing 10 per cent, of acetic acid. Ether 

 containing acetic acid was also efficacious. 



A " fat-free " paper is on the market, and this is very generally 

 employed. This " fat-free " paper gives a small ether extract 

 consisting chiefly of loose fibres ; such paper was at first remark- 

 ably free from extract, but later batches were found to contain 

 quite an appreciable amount. It is preferable for the analyst to 

 extract his own papers for one or 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 gave 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 



