EFFICIENCY OF PLUG-COCK FOG CHAMBER. 



FIG. i. Pressures in plug-cock fog and vacuum chambers, for different initial pressures 

 of latter, the former being initially at atmospheric pressure. (See table i.) The 

 notched curve shows the march of successive pressures for p' = ^ cm. and = 67 

 cm. in a single exhaustion. The upper curves show corresponding temperatures in 

 the fog and vacuum chambers under like conditions. The adiabatic temperature 

 ratio T/T, is here an approximation. 



A few incidental results deserve brief mention. The first of these is 

 the nearly constant difference of about 8p 2 = 2 cm. between the observed 

 value p 2 (nominal) and p 3 . Since for dry air or not 



is constant for a given exhaustion, op' 2 = v/V dp 2 . Hence if 

 dp 2 = 2 cm., since v/V = 0.064, dp' 2 = 0.064X2 =0.13 cm., nearly. 

 This case is illustrated graphically for ' = 45 cm. in the notched curves 

 of the figure in a way easily understood. It seems probable that whereas 

 the smaller fog chamber has lost too much air to even approach the 

 isothermal pressures p 2 , the large vacuum chamber is only a millimeter 

 short of them when the cock is again closed. The constancy of the 

 observed difference p 2 p 3 seemed at first to be referable to the system- 



