CHEMICAL TESTS AND ANALYSES 357 



the tube 10 to 11 grams of a 40 per cent solution of the substance 

 add 1^ c.c. of concentrated ammonium hydroxid (2 c.c. if the 

 sample b.e sour) and mix thoroughly with the milk. Add 10 c.c. 

 of 95 per cent alcohol and mix well. Then add 25 c.c. of washed 

 ethyl ether and shake vigorously for half a minute, then add 25 

 c.c. of petroleum ether (redistilled slowly at a temperature below 

 60 degrees C. preferably) and shake again for half a minute. 

 Let stand 20 minutes or until the upper liquid is practically clear 

 and its own lower level constant. Draw off of the ether solution 

 as much as possible usually 0.5 to 0.8 c.c. will be left into a 

 weighed flask through a diminutive quick acting filter, of selected 

 paper. The flask should always be weighed with a similar one 

 as counterpoise. 



"Re-extract the liquid remaining in the tube, this time with 

 only 15 c.c. of each ether, shaking vigorously half a minute with 

 each, and allow to settle. 



"Draw off the clear solution through the small filter into 

 the same flask as before and wash the tip of the spigot, the funnel 

 and the filter with a few c.c. of a mixture of the two ethers in 

 equal parts (previously mixed and free from deposited water). 



"For perfectly exact results the re-extraction must be re- 

 peated. This extraction yields usually not more than about a 

 milligram of fat, if the previous ether-fat-solutions have been 

 drawn off closely an amount averaging about .02 per cent on 

 a 4-gram charge. 



"Evaporate the ether slowly on a steam bath, then dry the 

 fat in a boiling water oven until loss of weight ceases. 



"Prove the purity of the fat by dissolving in a little pe- 

 troleum ether. Should a residue remain, wash the 'fat out com- 

 pletely with petroleum ether, dry the residue, weigh, and deduct 

 the weight. (This should not often be necessary.) 



"Finally deduct the weight obtained by blank determination 

 on the chemicals used. 



"By this method practically absolute results can be ob- 

 tained." 



Sucrose. 



Determine by difference, deducting the milk solids (ash 

 plus proteids plus lactose plus fat) from the total solids, or 



