TOTAL SOLIDS 183 



loosely stoppered flask and portions of 50 c.c. with- 

 drawn and titrated from time to time, the degrees of 

 acidity being plotted against time since milking. 



180. Determination of the Dry Matter or Total 



Solids. 



The water present in milk is driven off by heating for some 

 time at 100° C, and the substances remaining, consisting of fat, 

 proteins, milk sugar, and salts, are termed the dry matter or total 

 solids. 



Direct evaporation of the milk at 100° C. is not generally 

 employed, as the skin of coagulated albumen found on the surface 

 interferes with the evaporation. If the skin be repeatedly broken, 

 however, accurate results are obtained. 



The most usual method is to employ some absorbent material 

 such as sand or powdered pumice, to which the milk is added 

 before the heating is commenced. 



About 12 grams of sand or powdered pumice are 

 ignited, cooled, and placed, together with a glass rod 

 to act as stirrer, in a platinum or porcelain basin, 

 which is then heated to loo'^ C. in the steam oven 

 for an hour, and weighed. 



About 10 c.c. of the milk is placed in a small beaker, 

 which is weighed with its contents ; the milk is then 

 poured on to the sand or pumice in the basin, the 

 beaker again weighed, and the weight of milk taken 

 obtained by difference. 



The dish is then placed in the steam oven and 

 heated for two or three hours, the mixture being stirred 

 repeatedly. After cooling in the desiccator and weigh- 

 ing, the heating and stirring are again continued for 

 some time, and the basin and contents cooled and 

 weighed as before. The drying is not complete until 

 two successive weighings give the same result. When 

 this is attained the percentage of dry matter left is 

 calculated. 



