EFFECT OF TEMPERATURE. 11 



sisting of a coil of wire wound on a porcelain tube over which enamel 

 had been baked, with 8 taps taken off at even points along the tube. 

 The small shunted current used in actuating the relay was taken 

 from two adjacent taps. It was thus at a potential difference of 

 about 11 volts when the resistance coil was connected in the 110-volt 

 circuit. 



A rheostat, K, was found useful in regulating the amount of 

 current supplied to the heater. If the amount sent through is but 

 slightly more than sufficient to supply the usual losses of heat from 

 the incubator, the current will be on nearly all of the time and the 

 regulation of the temperature will be very exact. If the room 

 temperature should be considerably lowered, however, sufficient 

 heat would not be supplied. If, on the other hand, much current 

 is used, the heat would be on for but a small fraction of the time, 

 but the temperature would vary within wider limits. It was found 

 well to adjust the rheostat so that the circuit was closed about half 

 the time. The current strength was about 3 amperes. 



Except for the thermostat, which should be made by an expert 

 glass worker, the entire outfit may be selected from electrical sup- 

 plies now on the market. 



COLLECTION AND ESTIMATION OF CARBON DIOXID. 



As stated on page 8, the air was withdrawn from each desiccator 

 and passed through a Reiset absorption apparatus where the carbon 

 dioxid was quantitatively removed. The Reiset tubes were similar 

 to those used by Reiset * and by Brown and Escombe. 2 Each 

 apparatus consisted of a long, wide glass tube fixed vertically in a 

 side-arm flask by a gasket made from a rubber stopper. The tube 

 was 50 cm high and 2 cm in diameter. Platinum disks were fixed 

 at the lower end, 12.5 and 25 cm, respectively, from .the bottom. 

 These disks were pierced with fine holes about 0.5 mm in diameter 

 and their edges sealed into the walls of the tube. 



When in operation, the absorbing liquid rises in the tube, the air 

 which is then drawn through the lowest disk " rises through the 

 column of liquid in a rapid stream of small bubbles which are broken 

 up and reformed at each of the two succeeding plates, thus producing 

 a very effective 'scrubbing' action.'' 3 



Generally 100 cc of normal sodium hydroxid were used as the 

 absorbent, but at times double normal alkali was employed. During 

 the early part of the work two Reiset tubes connected in series were 

 used, but later it was found that one was sufficient unless very large 

 amounts of carbon dioxid were to be collected. 



1 Compt. rend., 1879, 88 : 1007; 1880, 90 : 1144; Hempel, Gas Analysis, 1902, p. 110. 



2 Royal Society, London, Proc. 1905 (B) 76: 29. 



3 Brown and Escombe, loc. cit., p. 33. 



