DIFFUSION OF HYDROCYANIC ACID VAPOR 195 



"It is clear from the results that the acid vapor 

 rises from the generator vertically, follows the ceiling, 

 descends on the opposite side of the room and com- 

 pletes the circuit by returning to the generator. Thus 

 the point immediately at the side of the generator is 

 the last to receive any vapor, while the opposite point 

 on the floor quickly receives almost its normal amount. 

 This is what might be expected from the shape of the 

 generator, an open jar, 15 inches high and 8 inches 

 in diameter, which has the effect of projecting the 

 charge of vapor directly upward; and, furthermore, 

 while the density of hydrocyanic acid vapor, a very 

 little less than that of air, is not small enough to cause 

 it to rise rapidly, yet its expansion by the heat of the 

 reaction is considerable. Hence the tendency of the 

 acid vapor to ascend is, for several reasons, the natural 

 thing to expect, and to secure rapid diffusion a counter- 

 acting cause must be set to work. At the moment of 

 generation the vapor, or, rather, the accompanying con- 

 densed steam, may be actually seen to take the course 

 that has been described, though naturally but for a 

 minute or two. 



' ' When the generator is moved to the center of the 

 floor, the intake remaining in the same place, after ten 

 minutes there is found 75 and 88 per cent, in the two 

 corners and 123 per cent, in the center of the ceiling. 

 This is in general agreement with what has already 

 been noted, as in this case the two corners are arranged 

 alike in reference to the generator, and, as before, the 

 greater part of the acid vapor is at the ceiling. 



' ' Where the generator is in the corner of the room 

 and the three intakes are in a vertical line in the 



