12 MILK ANALYSIS 



nitric acid, evaporate to dryness, and burn at a low red heat 

 till the ash is free from carbon. 



Fat. Many methods for fat determination have been de- 

 vised. The following will suffice for all practical work: 



Adams' Method. This consists essentially in spreading the 

 milk over absorbent paper, drying, and extracting the fat in an 

 extraction apparatus; the milk is distributed in an extremely 

 thin layer, and by a selective action of the paper the larger 

 portion of the fat is left on the surface. A paper, manufac- 

 tured especially for this purpose by Schleicher & Schuell, is 

 obtainable in strips of suitable size. Each of these yields to 

 ether only from o.ooi to .0.002 gram of extract. 



Coils made of thick filter-paper, cut into strips 6 by 62 cm., 

 are thoroughly extracted with ether and alcohol, or the weight 

 of the extract corrected by a constant obtained for the paper. 

 From a weighing bottle about 5 grams of the milk are trans- 

 ferred to the coil by means of a pipet, care being taken to 

 keep dry the end of the coil held in the fingers. The coil is 

 placed, dry end down, on a piece of glass and dried for one hour, 

 preferably in an atmosphere of hydrogen; it is then transferred 

 to an extraction apparatus and extracted with absolute ether, 

 petroleum spirit of boiling-point about 45 or, better, carbon 

 tetrachlorid. The extracted fat is dried and weighed. 



The above procedure is very satisfactory, but the drying 

 in hydrogen may usually be omitted. After the coil has re- 

 ceived at least twenty washings, the flask is detached, the ether 

 removed by distillation, and the fat dried by heating in an air- 

 oven at about 105, and occasionally blowing air through the 

 flask. After cooling, the flask is wiped with a piece of silk, 

 allowed to stand ten minutes, and weighed. 



Richmond states that to perform a -rigidly accurate deter- 

 mination attention to the following points is necessary: The 

 ether must be anhydrous (drying over calcium chlorid and 

 distilling is sufficient). Schleicher & Schuell's fat-free papers 



