330 AGRICULTURAL CHEMISTRY 



means of a press. The object of making the material 

 into a pellet is that it may form a compact mass and 

 burn evenly and not be scattered about in the calorim- 

 eter cylinder and be only partially burned. The pellet 

 is placed in the small platinum crucible O (Fig. 95). 

 This crucible is supported by platinum wires attached 

 to the cover of the calorimeter. Above the crucible a 

 small coil of fine iron wire is stretched from the 

 platinum wires. The cover is screwed tightly upon the 

 cylinder of the bomb and oxygen is admitted from 

 an oxygen tank under pressure through valve G of 

 the cover until a pressure of twenty atmospheres is 

 secured, when the valve is securely closed. The bomb 

 with the substance to be burned, and charged with 

 oxygen is placed in the metal cylinder Q, which con- 

 tains a definite amount of water, the temperature of 

 which is carefully determined by means of a thermom- 

 eter that reads to 0.005 C. The water is kept at an 

 even temperature by means of the metal stirrer SS, 

 operated by a water motor. A connection is made, 

 with a storage battery which ignites the small iron wire 

 that is suspended above the substance. The burning 

 wire falls upon and ignites the material in the platinum 

 crucible O. The heat from the combustion of the mate- 

 rial raises the temperature of the water in the calorim- 

 eter cylinder. A number of readings are taken so as 

 to secure the actual rise in temperature, caused by the 

 combustion of the substance. Due allowances are 

 made for the heat contributed by the combustion 

 of the iron wire, the heat absorbed by the steel bomb 



