188 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 fa¢t, 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 ‘‘surface 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 
