I5 6 AGRICULTURAL CHEMISTRY 



amount thus held depends upon the extent of the pre- 

 vious drying of the material and the hydroscopic condi- 

 tion of the air. Inasmuch as air always contains some 



Fig. 63. Analytical balance. 



water, it necessarily follows that all substances exposed 

 to the air must likewise contain some water. 



In order to remove the last traces of water from a sub- 

 stance, it is dried in either a water- or a hot-air oven at a 



