60 FOODS AND FOOD ADULTERANTS. 



dissolved in 100 to I50cc. of water. To. the clear liquid hydrochloric 

 or sulphuric acid is added to a strongly acid reaction, in order to de- 

 compose the soap. The insoluble fat acids are now separated out as a 

 cheesy mass, which for the most part quickly rise to the surface. The 

 heating is continued for a half hour until the fat acids are melted to a 

 clear oil and the acid aqueous liquid is almost completely clear. Mean- 

 while a thick Swedish filter paper of 4 or 5 inches in diameter has been 

 dried in a water bath. The filter paper must be of the best quality and 

 so thick that even hot water will only pass through it drop by drop. A 

 small beaker glass is now weighed, afterwards a filter tube, and then 

 the filter tube and the filter; in this way is obtained the weight of the 

 filter and the beaker glass. 



The weighed filter is now fitted to a funnel moistened and half filled 

 with water. The aqueous liquid and the melted fat are then poured out 

 of the evaporating-dish into the filter, and the dish and glass rod arc 

 washed with boiling water. There is no difficulty in bringing all of the 

 fat on the filter, so that the evaporating dish does not appear in (he 

 least greasy. To make sure, however, the dish can be washed with 

 ether and the liquid obtained added to the fatty acids. 



The fatty acids are washed upon the filter with boiling water. The 

 filter should be never more than two-thirds full. If the filtrate tested 

 with sensitive litmus tincture does not appear acid, the rest of the 

 water is allowed to run through, and the funnel is dipped into a beaker- 

 glass filled with cold water, so that the surface of the liquids within 

 and without the funnel are at the same level. As soon as the fatty acids 

 have solidified the filter is taken out of the funnel, placed in the weighed 

 beaker-glass, and dried in a -water-bath to constant weight. The dry- 

 ing is continued for two hours and the filter paper is then weighed. It 

 is again dried for two and a half hours and weighed a second time. 

 It must be remembered that it is not a mineral substance which is under 

 treatment, but an easily-oxidizable fat, so that an exact constant weight 

 cannot be expected. 



Butter fat gives between 8G and 87 per cent, of insoluble fatty acids, 

 though in some cases the number may rise to 88 per cent. On the other 

 hand, the animal fats give about 95J percent, of insoluble fats. 



It must be expected that the kind of food which cows receive in. 

 fluenco considerably these numbers. In order to determine this im- 

 portant point, Dr. Turner had a cow fed for a long time exclusively on oil 

 cake, with the object of raising the percentage of insoluble fat acids to 

 the highest point. It is worthy of remark, however, that the butter so 

 produced gave the unusually low percentage of 86.3. 



Method of Muter. 1 The total fatty acids. About 10 grams (or 150 

 grains) of the butter fat at 100 F. are weighed by difference from a sus- 

 pended tube into a clean, dry 15-ouuce ilask, and 5 grams of potassium 

 hydrate with 2 fluid ounces of rectified spirit are added. The flask is 



Analyst, 1877, pp. 10, 11. 



