70 Notes from the Physiological Laboratory 



shut-off when the columns of mercury in A and 

 B are of the same height. In practice the adjust- 

 ment is effected by placing the instrument in a me- 

 dium of the required temperature, the cock D is 

 opened, and air slowly forced in with a syringe, 

 until the mercurial column in B is nearly at the 

 point of bifurcation ; the precise height varying, of 

 course, with the dimensions of the instrument, and 

 being readily ascertained by practice. 



The pressure of the gas employed must be kept 

 quite low, otherwise, as the mercury rises above the 

 point of bifurcation, a portion will be blown out. 

 One of the simpler gas-pressure regulators may be 

 advantageously inserted between the source of gas- 

 supply and the heat regulator. It is w r ell also 

 that the diameter of the limb C should be some- 

 what greater than that of its fellow, and also that 

 its point of junction with B should be somewhat 

 constricted in order that a smaller variation in tem- 

 perature shall effect either the patency or occlusion 

 of the gas exit. 



When the mercury rises in B a trifle beyond the 

 point of bifurcation, the passage of gas from G to 

 E is arrested, and the flame from the burner I is 

 at once extinguished. Were no further provision 

 made, the vessel and its contents would soon cool 



