THE INCUBATOR 



149 



Fig. 30 



tance above this point with a capillary opening, g, in one 

 of its sides. 



When ready for use the cylinder e is filled with mercury 

 up to about the level shown in the figure. It is then allowed 

 to stand, or is suspended, in the 

 bath the temperature of which it 

 is to regulate. The rubber tubing 

 coming from the gas-supply is at- 

 tached to the outer end of the 

 glass tube a, and the tube going to 

 the burner is slipped over the 

 branch tube b. The gas is turned 

 on and the burner lighted and 

 placed under the bath. The gas 

 now streams through the tube a 

 into the cylinder e and out at b 

 to the burner; but as the tem- 

 perature of the bath rises the 

 mercury contained in the cylinder 

 e, under the influence of the ele- 

 vated temperature, begins to ex- 

 pand, and, as a continuous rise 

 in temperature proceeds, the expan- 

 sion of the mercury accompanies 

 it and gradually closes the slanting 

 opening h of tube a. In this way 

 the supply of gas becomes dimin- 

 ished and the rise in temperature of the bath will be less 

 rapid, until finally the opening at h will be closed entirely, 

 when the supply of gas to the burner will now be limited 

 to that passing through the capillary opening g. This is 

 not sufficient to maintain the highest temperature reached, 



Mercurial thermo-regulator. 



