INCUBATORS OR THERMOSTATS 159 



1. Immerse the thermoregulator up to the lower lateral branch, 

 which carries the regulating screw in an almost completely rilled 

 flask. With the thermoregulator immerse a thermometer. Heat the 

 water in the flask to 40 C., over a small flame which does not burn 

 directly under either the thermometer or thermoregulator. Now 

 regulate the screw on the lower lateral branch so that the mercury 

 just closes the lower opening of the T-tube. 



2. Pour water heated to about 40 C. into the compartment 

 between the double walls of the incubator. This is done through an 

 opening on top of the incubator, and it can be facilitated by using a 

 funnel. When the compartment is completely filled, remove the 

 funnel and close the opening with a cork having a small hole in the 

 centre. Provide a perforated cork or rubber stopper for the thermo- 

 regulator and place it in a second opening near the margin of the 

 incubator. The thermoregulator now dips into the water between 

 the walls of the incubator. 



FIG. 82 



Koch's safety burner. Micro-bunsen burner. 



3. Connect the T-tube with the gas pipe and the median lateral 

 tube with the micro-gas lamp by a rubber hose. Open the stopcock 

 of the gas pipe and light the micro-gas lamp under the incubator. 

 The latter will now burn with a small flame, because the thermo- 

 regulator dips into water about 40 C. and the mercury shuts up 

 the larger opening of the T-tube. As soon as the water in the 

 incubator is cooled off, the mercury recedes and the lower opening 

 of the T-tube being now free, more gas goes to the lamp. If the 

 thermoregulator has been set to 40 C., the temperature in the 

 chamber of the incubator, indicated by the thermometer which pro- 

 jects into it, is generally about 37 C. 



Difficulties in Regulating Incubators. The student must not suppose 

 that it is a very easy matter to regulate a thermostat so that it main- 

 tains a fairly stationary temperature. Among other things it is 

 necessary to regulate the stopcock of the gas pipe so that the gas 

 pressure in the thermoregulator is not too high. This pressure in 

 most places, as well known, varies very much, and where this is 



