ANALYTIC PROCESSES 13 



weight is sensibly constant. The percentage 

 of residue can be easily calculated. About three 

 hours may be required to secure constant weight. 



When high accuracy is not essential, it will 

 suffice to measure the milk. Vieth advised a 

 pipet graduated to deliver 5 grams, and found 

 that, working with whole and skimmed milk, 

 under the ordinary variations of temperature, 

 the error will not exceed o.i on the total solids 

 and less on the fat. The pipet should have a 

 rather wide opening so that no cream will be 

 retained. 



The Massachusetts State Board of Health has 

 for many years used the routine method of 

 evaporating 5 grams for two hours in a flat plati- 

 num basin over boiling water. 



The A. O. A. C. method is: Heat at 100° to 

 constant weight, about 3 grams in a tared plati- 

 num, aluminum or tin dish of 5 cm. diameter, 

 with or without the addition of 15 to 30 grams 

 of sand. Cool and weigh. 



Ash. — ^The residue from the determination of 

 total solids is heated cautiously over the Bunsen 

 burner, until a white ash is left. The result 

 obtained in this manner is apt to be slightly low 

 from loss of sodium chlorid. This may be 

 avoided by heating the residue sufficiently to 

 char it, extracting the soluble matter with a few 

 c.c. of water, and filtering (using paper extracted 



