64 



INCUBATORS 



size^of the flames is somewhat diminished. If now the opening, 5, be hermetically 

 plugged, any further increase of temperature causes the water to expand within 

 the double wall, and so to force the lamina downwards, with the result that the 

 gas is cut off. In practice, instead of completely sealing the opening a plug 

 carrying a piece of glass tubing is inserted, and as the water expands it rises in 

 this tube and at the same time the pressure on the bottom of the wall of the 

 incubator increases, and the lamina is pressed down. 



Note. Recently-boiled water should be used for re-filling the incubator : if tap water 

 be used the bubbles of air which are driven off when the water is heated will alter the 

 water level, and the mechanism will be disturbed. 



FIG. 53. Roux's incubator. 



In another form the regulator is placed in the side of the incubator, and a rubber 

 membrane which is more sensitive is substituted for the steel lamina. 

 D' Arson val's incubator has several disadvantages. 



1. By reason of its shape only a small part of its total capacity is available 

 for use. 



2. The regulation of the temperature being a function of the level of the water 

 in the tube, 8, it follows that the temperature within the incubator rises as the 

 height of the water falls. Since this may happen as a result of evaporation, leaking 



