40 APPLIED BACTERIOLOGY 



the left-hand back top corner of the apparatus, is a small 

 metallic hermetically-sealed capsule, which contains a few 

 drops of a liquid having a boiling-point at or near the 

 temperature which we wish to maintain the heated 

 chamber. 



The capsule lies in a little holder suspended below the 

 tube, through which the needle under the screw P (Pig. 7 

 and Pig. 8) passes. 



Soldered to the upper side of the capsule is a thick piece 

 of metal, having a central depression. In this depression 

 the lower end of the needle seen in Pig. 8 rests, and the 

 upper end of the needle enters a short distance into the 



Fig. 7. — Excelsior Gas-valvb. 



socket end of the screw P. Communication is thus estab- 

 lished between the capsule inside and the Excelsior gas- 

 valve outside. 



Above is shown an enlarged view of the gas-valve seen in 

 Pig. 7. 



A is the inlet for gas. C, the outlet to burner. BD, a 

 lever pivoted to standards at G, and acted upon by the 

 capsule through the needle which enters the socket below 

 the screw P. 



The construction of the acting portion of this valve is 

 such that, whenever the end B of the lever BD presses on 

 the disc below the end B, the main supply of gas is entirely 

 cut off. At such times, however, a very small portion of 



