344 GASOMETRIC-MANOMETRIC METHODS 



Since the precision of the jjressure measurement is about 1 nun. 

 water, which corresponds to 0.0001 of the total pressure of 1 atmos- 

 phere, and the total volume of the type of diver commonly used is 

 about 10 /xl., the accuracy of the measurement of the gas volume in 

 the diver is about 0.001 fx\. Holter has pointed out that for profitable 

 work with these divers, the volume changes to be measured should 

 be of the order of 0.01 ix\. per hour. 



(1) TEMPERATURE CONTROL 



It is advantageous to carry out work with divers in a room the 

 temperature of which is not very different from that of the thermo- 

 stat used with the diver apparatus. While not absolutely necessary, 

 additional advantages are obtained if the room has an approxi- 

 mately constant temperature, since only the flotation vessels and the 

 air bottle, which is connected to one end of the manometer, can be 

 conveniently submerged in the thermostat. The manometer itself 

 and the connecting tubing are subject to variations in the room 

 temperature. Rocher (1942,1943) employed the arrangement shown 

 in Figure 112. The manometers are submerged in the thermostat, and 

 a cathetometer is used to take their readings. 



The thermostat used for the apparatus in the Carlsberg Labora- 

 tory is maintained at a temperature 2° above that of the room, 

 which is kept at 21°, and the thermostat is regulated with a precision 

 of 0.01°. The stirrer for the thermostat water must run very quietly 

 and it should not be attached to the thermostat itself in order to 

 prevent its vibrations from being transmitted to the diver. A 40 watt 

 lamp may be used as the heating element for a thermostat of the 

 size used at the Carlsberg Laboratory (58 X 30 X 30 cm.). The 

 light from the lamp should be shaded from the eyes of the operator. 

 High-capacity heaters are to be avoided, since they continue to 

 supply heat for a time after the current is cut off. Lamps are by far 

 the best heaters. 



Since the diver must be observed during the experiment, it is 

 necessary that the front wall of the thermostat be made of glass, 

 and the lighting must also be considered. A ground-glass plate, 

 sufficiently large to form a background for all the flotation vessels 

 may be placed immediately behind the thermostat, where it can be 



