40 APPLIED BACTERIOLOGY 



the left-hand l)ack 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 (Fig. 7 

 and Fig. 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 Fig. 8 rests, and the 

 upper end of the needle enters a short distance into the 



Fig. 8. — Excelsior Gas-valve. 



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

 lished between the capsule inside and the Excelsior gas- 

 valve outside. 



iew of the gas-valve seen in 



he outlet to burner. BD, a 

 Gr, and acted upon by the 

 ich 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 



