480 



PHYSIOLOGICAL PHYSICS. [Chap, xxxvm. 



substance in M preventing heat passing outwards, 

 while the layer of water in N intercepts heat passing 

 inwards, and ensures the elevation of the tem- 

 perature of the water in 

 L being due to the com- 

 bustion in K. A tube o 

 passes from outside to con- 

 duct oxygenated air to the 

 bottom of the chamber for 

 combustion purposes. The 

 tube eeg permits the es- 

 cape of the gases that are 

 produced by the combus- 

 tion. It takes a winding 

 course through the water 

 of L so that all the avail- 



able heat of the gases is 

 given off to the water before 

 they escape to the outside. 

 The tube b, usually closed 

 by a cock, is for the pur- 

 pose of passing inflammable gases into K if desired. 

 The prolongation a of the chamber is closed by a 

 thick glass plate, and provided outside with a mirror 

 s, set at an angle, to permit an observer to watch the 

 process of combustion. Modifications can be made in 

 such an arrangement as this to suit particular pur- 

 poses. To measure the specific heat of a substance, 

 one may substitute for K a receiver into which the 

 substance, which has been previously heated to a 

 known temperature, is dropped. Or one may sub- 

 stitute a chamber (c in Fig. 197) in which some small 

 animal may be lodged, respirable air reaching it by 

 one tube, and the products of respiration being con- 

 veyed outwards through the water, so that the heat 

 given off by the animal in a given time may be esti- 

 mated. In all cases the temperature of the water in 



Fig. 196. Water Calorimeter. 



