DIFFUSION OF HYDROCYANIC ACID VAPOR 187 



after standing over night it was as little as 0.66 per 

 cent., averaging 4.71 per cent.; the particular amount 

 was determined for each experiment and was deducted 

 to determine the amount of actually liberated or avail- 

 able hydrocyanic acid vapor. 



In the case of the room experiments the average 

 residual hydrocyanic acid was found to be 4.97 per 

 cent, of the whole amount; this was deducted in each 

 case to determine the liberated or available vapor. 

 Thus, at the temperature at which the experiments 

 were made, both with large and small quantities of 

 reagents, the proportion of acid and water used gave 

 about 95 per cent, of available vapor. This liberated 

 or available vapor on an average 0.07623 gramme per 

 cubic foot of space, called by Professor Penny the 

 "HCN," was taken as the basis of calculation to 

 determine the ratio of diffusion; in other words, that 

 amount found in a cubic foot would be called a diffusion 

 of loo per cent. 



Quite as important as the average percentage of 

 diffusion, Professor Penny shows, is the average per- 

 centage of fluctuation. In such work absolute uni- 

 formity of conditions with the facilities available is 

 not attainable; hence repeated trials with conditions 

 apparently the same often give different results, some- 

 times widely different. As perfectly air-tight walls, both 

 of boxes and of the room, are difficult to secure, there 

 are varying conditions that make no two trials exactly 

 alike. Such discrepancies, although they cannot be 

 foreseen, may be explained by variations in the force 

 and direction of the wind, varying amounts of humidity 

 and the host of minor conditions that are never quite 



