1 88 FUMIGATION METHODS 



the same, but yet influence the result. Hence, in 

 addition to the average diffusion, the fluctuation in 

 percentage between repeated trials is given. This 

 indicates the degree of constancy in the work. 



It might be supposed, says the author, as pure 

 hydrocyanic acid is a liquid that boils at 80 F. , and 

 inasmuch as most practical applications of the acid 

 are made below that temperature, that ordinarily 

 but a small portion of the acid would vaporize, and 

 that this portion would diminish rapidly with a falling 

 temperature. Such, however, is not the case. The 

 proportion of the acid used in Professor Penny's experi- 

 ments, if it were all liberated, would amount in weight 

 and also in volume to only one five-hundredth part of 

 the air. As the vapor pressure of the acid is half 

 an atmosphere at 40 F. , it is clear that even in this 

 low temperature many times as much acid as could 

 ever be used (in fact, over two hundred times as much) 

 would still remain in the state of vapor. Hence the 

 condensation of the minute trace of hydrocyanic acid 

 that is ever used in practice would be impossible at any 

 natural temperature whatever. The " surf ace con- 

 densation," referred to later by Professor Penny, is the 

 solution of the acid in the film of condensed moisture 

 adherent to walls and other surfaces. 



The results. The results summed up below were 

 obtained by Professor Penny with a box of sixty cubic 

 feet capacity, of which the horizontal dimensions were 

 8 feet by 3 feet and the vertical depth 2^ feet. The 

 box had double wooden walls, with paper between 

 them, and made as nearly air-tight as possible. The 

 generator and the point at which the sample was 



