18 ANALYTICAL PROCESSES. 



about three hours. When the ash is not to be deter- 

 mined, it is more convenient to follow the method sug- 

 gested by Richmond, using I to 2 grams, accurately 

 weighed. The drying can be completed in about one 

 and a half hours. 



Richmond has pointed out that if the evaporation 

 be slow, some decomposition occurs, and the residue 

 will be brown, but that if the larger portion of the 

 water be evaporated quickly, a white residue is ob- 

 tained. He suggests the following method for use 

 when a higher degree of accuracy is desired : 



About 3 grams of abestos of the best quality are 

 placed in a platinum dish, ignited in a muffle and 

 weighed. By simple ignition over the Bunsen burner 

 the combined water is not always lost. 5 grams of 

 milk are added and dried on the water-bath for about 

 two hours. The residue is then left in the air or water- 

 oven at about 208 F. for twelve hours or more (usually 

 over night). At the end of this time an absolutely 

 constant weight is obtained. 



The residue serves well for the determination of the 

 ash. 



Where rigid accuracy is not essential, it will suffice 

 to measure the portion of milk taken for this and other 

 determinations. Vieth uses a pipette graduated to de- 

 liver 5 grams and finds that, working with whole and 

 skimmed milk, under the ordinary variations of temper- 

 ture, the error will not exceed O.I on the total solids 

 and is less on the fat. 



