METHODS OF EXAMINING MILK 241 



water oven for a half hour, removed to the desiccator 

 until cool and then weighed. After they are placed in 

 the oven they should be handled with tongs or forceps 

 and should not be touched with the fingers. As each 

 dish is weighed the weight is recorded. The milk sample 

 is mixed thoroughly and some of the milk (3 to 5 c.c.) is 

 transferred to the dish, which is again weighed, the 

 weight being recorded. The dish is placed on a water 

 bath where it remains until the milk is evaporated to 

 dryness. It is then removed to the desiccator and when 

 cool it is weighed. Following this it is placed in the 

 hot-water oven for 30 minutes, after which it is again 

 cooled in the desiccator and weighed. If the two weigh- 

 ings agree, or are within 0.2 milligramme of each other, 

 the water has all been driven off . If the weighings do 

 not agree to this extent, the dish must be returned to 

 the hot-water oven for another period, then placed in the 

 desiccator until cool and again weighed, and this must 

 be continued until the weight is constant, or within 0.2 

 milligramme of being the same. The last weight minus 

 the weight of the dish represents the weight of the dry 

 matter or total solids in the charge of milk. Multiplying 

 the weight of the dry matter by 100 and dividing by the 

 weight of the charge will give the per cent, of dry matter 

 in milk. The per cent, of ash may be determined by 

 heating the dry matter until the ash is free from carbon, 

 placing the dish in the desiccator until cool, weighing, 

 subtracting the weight of the dish, multiplying the re- 

 mainder by 100 and dividing by the weight of the charge. 

 By Calculation. There are several formulas for 

 calculating the total solids and solids not fat from the 

 specific gravity and per cent, of fat. Of these Babcock's 



16 



