xcv. 2i. 1915 hnpyoxed Respiration Calorimeter 335 



which is such a good heat insulator that appreciable changes in the tem- 

 perature of the air in the laboratory affect the temperature of the air 

 confined in the spaces between the cork board and the zinc wall very 

 slowly. The temperature of the air in this space adjacent to the zinc 

 wall is raised by converting electrical energy into heat in a resistance 

 wire that is strung on porcelain insulators attached to the wall; and it 

 is lowered by passing cold water through small-bore brass pipes supported 

 by small iron hooks screwed to the framework to which the wall is 

 attached. Short sections of both pipes and wires and the method of 

 attaching them to the wall are shown in Plate XXXIV, figure 2. 



By wooden strips extending from the metal wall to the cork board, 

 the air space surrounding the zinc wall is divided into sections corre- 

 sponding with the top, the upper and lower zones of the sides, and the 

 bottom of the chamber, as already described in the case of the thermo- 

 elements in the walls. A portion of one strip is shown in Plate XXXIV, 

 figure 2. Each section has its own heating device and cooling device, 

 so that the temperature of the corresponding portion of the zinc wall 

 may be controlled independently of the conditions in any other space, 

 and the possibility of heat entering the chamber in one part of the wall 

 and leaving it in another is prevented. 



The current of water for cooling the zinc wall flows through brass pipe 

 of about 7 mm. bore (so-called ,V^-inch pipe). In the top and bottom 

 sections the pipe extends forward and back from end to end for the 

 whole width of the space, the successive lengths of pipe being about 15 

 to 20 cm. apart. In the upper and lower zones the pipe extends con- 

 tinuously around the four sides of the walls, the succeeding turns of 

 the coil being about as far apart as those in the other sections. This 

 furnishes ample cooling effect, which can be regulated by varying 

 the temperature of the water flowing in the pipe, or the rate of flow, or 

 both. The inlet ends of the four pipes are connected with the feed- 

 water pipe, with the small brass needle valves used for regulating the 

 flow in the cooling coils close together and convenient to the operator 

 at the obser\-er's table (PI. XXXVI, fig. 2). The outlet ends of the 

 coils are also brought together in a funnel below the regulating valves, 

 so that the effect of the valves on the rate of flow may easily be seen. 



The electric current for heating the zinc wall is conducted by a non- 

 corrosive wire of a high carrying capacity, the resistance of which is 

 about 3.5 ohms per meter. In each space the wire is distributed, as 

 the cooling coils are, over practically the whole surface of the zinc, the 

 successive lengths of wire extending from one end of the space to the 

 other, about 15 cm. apart. The amount of wire in each space is such 

 that without regulation of the current in it the heating effect w^ould be 

 greater than necessary. With the proper ballast resistance in series 

 with each heater the heating effect in each section may, if desired, be 

 made proportional to the area of zinc to be heated. In the upper zone 



