12 NEW HAMPSHIRE EXPERIMENT STATION [Bull. 261 



should be multiplied by 4.825, the caloric value of a liter of oxj'gen when 

 mixed foods are burned, or by 4.7, the caloric value when decidedly fatty 

 food samples are burned. This step gives the calories per gram of air- 

 dry matter. The total energj^ content of the substance is obtained by 

 multiplj'ing by the total air-dry weight. The total protein content is 

 computed from the deteixnined nitrogen percentage and the air-drv 

 weight of the substance, on the assumption that one gram of nitrogen 

 equals 6.25 grams of protein. 



THE SIMPLER FORM OF OXY-CALORIMETER 



The spirometer type of oxy-calorimeter is recommended for general 

 use, but if it is not available, the combustion chamber and the blower 

 can be attached to some of the other forms of respiration apparatus in 

 use in many laboratories and clinics. The principle of the oxy-calorime- 

 ter is, therefore, easily employed for the combustion of foods and ex- 

 creta so frequently desired in hospital and dietetic laboratories. One 

 such adaptation is shown in Figure 2, in which the combustion chamber, 

 A, and the blower, C, have been attached to a modified form of the 

 student respiration apparatus," and a cooling device has been provided 

 so that the temperature is as well controlled with this type of oxy- 

 calorimeter as with the spirometer type. In this apparatus a large mass 

 of soda-lime is contained in the metallic can, B, and in place of the 

 spirometer the expansion or contraction chamber is provided by a light, 

 pure gum bathing-cap, b, fastened to the top of the can, B. The blower, 

 C, and the combustion chamber, A, are the same as those shown in 

 Figure 1. 



Although the can, B, is constructed of copper, it has been found 

 impracticable to cool it by external devices. Hence a simple method of 

 internal cooling is recommended. A coil of soft copper tubing (4 mm. 

 internal diameter, 6 mm. external diameter, and about V/j meters long) 

 is placed in the bottom of the can. Both ends of this coil pass out 

 through the rubber stopper, E, fitted into a thimble soldered into the 

 base of the can a little to one side of the air pipe connecting with the 

 pipe, c. The can is about two-thirds filled with soda-lime, and a ther- 

 mometer is inserted through a side opening, with its bulb just above the 

 top of the soda-lime. To this side opening is attached an upright, H, 

 which supports a clamp and a small plate, d, used as an index of the 

 degree of distention of the bathing-cap, b. 



The weighed, air-dry substance and the ignition wire are placed in 

 the combu.stion chamber, but before beginning the combustion oxygen 

 is supplied through a petcock at the bottom of the can. The apparatus 

 is filled with oxygon until the small button, e, on top of the bathing- 

 cap, b, just comes in contact with the plate, d. The oxygen is then 

 forced through the system by removing the cork in the tee at the top 

 of the lamp chimney and depressing the bathing-cap with the hand. 



^Benedict, F. G., and C. G. Benedict, Boston IMed. and Surg. Journ., 1923, 

 188, p. 567; ibid., Skand. Arch. f. Physiol., 1923, 44, p. 87. 



