10 NEW HAMPSHIRE EXPERIMENT STATION [Bull. 261 



and considerable heat is developed in the can. B. Local cooling of the 

 heat-resisting, Pyrex glass chimnej- is obtained by appljnng directly to it 

 a cloth wet with ice water, and not infrequently a piece of wet cheese- 

 cloth is likewise wrapped around the tube to dissipate some of the heat. 

 When the thermometer indicates that the temperature of the system at 

 the end of the combustion is the same as at the beginning, the cooling 

 bath is lowered and the apparatus may be stated to be in temperature 

 equilibrium. Theoretically, all portions of the closed circuit should have 

 precisely the same temperature at the end as at the beginning of the 

 combustion. One thermometer alone is used, however, and except for 

 the soda-lime container, the other parts of the apparatus are cooled only 

 tmtil they appear to the hand to have the initial temperature. The 

 largest volume of air is that in the soda-lime can and in the spirometer. 

 The spirometer undergoes practically no changes in temperature. Any 

 changes in temperature of the soda-lime are indicated by the ther- 

 mometer. 



Method oj co7nbudion. The substance to be studied is brought to 

 an air-diy condition, and a sample of it is carefully weighed and placed 

 in a small nickel capsule supported in the base of the combustion cham- 

 ber. A fine iron wire is looped across two rods sticking up through the 

 base of the chamber, at the bottom ends of which are two binding posts 

 connecting with the electric current. The central part of this wire loop 

 rests upon the food sample. The spirometer bell is pushed to its lowest 

 level, the lamp chimney is closed at the top, a cork is inserted with a 

 one-hole stopper through which the tube, f, passes, and a cork is in- 

 serted in the brass tee above it. Oxygen from a cylinder is first bubbled 

 through water to saturate it and then admitted into the sj'stem through 

 the petcock, K. and the spirometer bell rises. One should then remove 

 the cork just above the tube, f, pinch together the rubber tube between 

 the blower and the top of the lamp chimney, and press down on the 

 spirometer bell with the hand in order to displace the air in the system 

 with nearly ]»ure oxygen. Finally, the cork is put in place in the brass 

 tee, and the spirometer is filled to a level that will permit the contrac- 

 tion of at least 3 liters. After the blower has been running for a moment, 

 it is stopped and the temperature and the level of the spirometer are 

 recorded, as well as the barometric pressure. The blower is again started, 

 and the substance in the capsule is burned by electric ignition of the 

 iron wire. A piece of fine mesh, brass wire gauze, about 15 cm. square, 

 rolled in cylindrical form but open on one side, may be snapped around 

 the glass lamp chimney, if desired. This will reduce the brilliancy of 

 the combustion so that the operator need not wear colored glasses. 

 The combustion usually proceeds at a fairly regular rate, but if it is too 

 vigorous, one can reduce it by compressing slightly the nibber tube con- 

 ducting the air to the lamp chimney from the tee-tube connection to the 

 spirometer. One should not obstnict the jiassage of air between the 

 base of the combustion chamber and the spirometer, because otherwise 

 air may be sucked in or blown out of the water seal during a poorly 

 regulated combustion. Although the flame of the combustion may ira- 



