28 METHODS OF QUANTITATIVE ANALYSIS. 



shows after that time an increased acidity, it was not 

 fresh and should not be used as food for children. 



One may confirm his opinion as to the age of the milk 

 in question by the use of a eudiometer tube. The tube is 

 filled with milk, and the open end placed under mercury 

 to exclude the air. If the milk be old, bubbles of gas 

 will collect in the upper end of the tube. Pure fresh 

 milk after standing 12 hours will develop no perceptible 

 amount of gas. (Schafler.) 



III. DETERMINATION OF TOTAL SOLIDS. 



A platinum crucible with the cover (or in the absenci 

 of this, a porcelain dish with cover) is accurately weighed 

 and into it is measured five or ten c.c. of the sample which 

 has been thoroughly shaken to render it homogenous. 

 The dish and contents are then placed in a water oven and 

 dried at 100 degrees C. The cover is placed on the dish 

 in such a manner as to allow the escape of steam without 

 permitting dust to enter. After 15 to 20 hours the dish 

 is removed from the oven and allowed to cooLover sul- 

 phuric acid in a desiccator, and weighed. It is then 

 placed in the drying oven again for half an hour and once 

 more cooled and weighed. If there be no difference be- 

 tween the first and second weighing, the determination 

 may be considered completed. Otherwise the heating 

 must be continued until the weight becomes constant. 

 By deducting the weight of the empty dish from this 

 last weight obtained, the weight of the residue or dry 

 matter is determined. If it be desired to weigh the milk 

 instead of measuring it, the sample is placed in a tared 

 crucible, and weighed quickly. The cover should be 

 kept in place to avoid evaporation. The desiccation of 

 milk by mixing with some porous substance such as gyp- 

 sum or pumice, or with sand, or by absorbing it with 

 paper, is not to be recommended. Such treatment inter- 



