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 



