DIFFUSION OF HYDROCYANIC ACID VAPOR’ 195 
“Tt 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 
