570 JOHN R. MURLIN 



wooden box lined with a heavy layer of compressed cork board. Inside this 

 is a Weinholdt vacuum cup which serves as the receptacle for water. The 

 bomb is lowered into the water by a carriage attached to the top of the 

 box which slides upon two metal supports at the sides. The top also car- 

 ries a motor for operating a stirrer in the water and a Beckman ther- 

 mometer. The substance to be burned is placed in a nickel vessel supported 

 upon platinum wires inside the bomb. The bomb is then charged with 

 oxygen and immersed in the water. When the temperature of the water 

 has become constant (at about 20 C.) the combustion is started by throw- 

 ing a switch which connects the house circuit with a platinum or nichrome 

 wire inside. A standard amount of current is secured by means of a fuse 

 wire, which burns off with just enough current to "fire" the combustible 

 material. The reading at ignition is taken as the initial reading. This sub- 

 tracted from the final reading gives the total rise. The increase in tem- 

 perature multiplied by the weight of water contained in the vacuum cup 

 (plus the hydrothermal equivalent of the apparatus) gives the total heat 

 liberated. Certain corrections have to be applied for the heat caused by 

 the current in firing, and for any nitric acid formed from oxidation of 

 nitrogen. For example in burning a sample of standard cane sugar the 

 weight of substance taken was 1.1466 grams. Weight of water in the 

 cup was 2530 gm. 



Hydrothermal equivalent 470 gm. 



Water equivalent of apparatus 3000 gm. 



Rise in temp, was 1.530C. Ignition heat - 60 cal. 



1.530 X 3000 gm. = 4590 cal. Nitric acid 4.6 cal. 



4590 64.6 = 4525 cal. 64.6 



4525 -T- 1.1466 gm. = 3947 cal. per gm. 



The table on page 571 compiled from various sources gives the heat value 

 of the most important organic substances concerned in metabolism of the 

 higher animals. 



II. Animal Calorimetry 



1. Forms of Calorimeters. The various types of apparatus devised 

 for measuring the heat eliminated by an animal body are classified by 

 Lefevre(g) into four groups : (1) those which make use of latent heats; for 

 example, the ice calorimeter of Lavoisier and the distillation calorimeter 

 of D'Arsonval ; (2) those which depend upon the warming of a fixed quan- 

 tity of water such as the calorimeters of Dulong and Laulanie for animals 

 and the bath calorimeter of Lefevre for man; (3) those which employ 

 circulating mediums (air or water) to carry away the heat just as rapidly 

 as it is produced (compensation method) ; such as the respiration calorim- 



