372 
PROFESSOR GRAHAM ON THE MOTION OF GASES. 
experiment, and to compensate for the cold of evaporation. The tension of the 
hydrocyanic acid vapour at 59°, the temperature of the experiments, was found to be 
1 8'8 inches. The composition of the mixed vapour operated upon was — 
Volumes. 
Air or hydrogen 10‘8 or 36*48 
Hydrocyanic acid . . . . 18*8 or 63*52 
29*6 100*00 
The vapour was transpired under the pressure of the atmosphere by the capillary 
M, 52*5 inches in length, into the two-pint aspirator-jar, through the usual range 
(28*5 to 23*5 inches) of the attached barometer. Thermometer 59°, barometer 29*5 18 
to 29*644 inches. 
The transpiration time of air was 1138 and 1138 seconds in two experiments. The 
time of air impregnated with hydrocyanic acid was 80/, 809, 808, 808 seconds, in 
four experiments ; which gives to the latter the ratio of 0 * 7100 . Multiplying by 0*9, 
we obtain — 
Transpiration time of air saturated with hydrocyanic acid vapour at 59° 0*6390. 
It is obvious therefore that hydrocyanic acid vapour is greatly more transpirable 
than air. The theoretical density of hydrocyanic acid vapour is 13*5, the density of 
oxygen being 16. 
Hydrogen gas equally impregnated with hydrocyanic acid vapour was transpired 
in the times 579 and 579 seconds, which gives the ratio to air of 0*5088. Multi- 
plying by 0*9, we obtain — 
Transpiration time of hydrogen saturated with hydrocyanic acid vapour at 59°, 
0*4579. 
Judging from our former results on mixtures of hydrogen with denser gases, in 
which it appeared that the rate of the mixture never deviated far from that of the dense 
gas in a state of purity, unless the proportion of hydrogen exceeded 50 per cent, it 
may be inferred that the transpiration time of pure hydrocyanic acid vapour is be- 
tween 0*4375, the time of hydrogen, and 0*4579, the observed time, but much nearer 
to the latter than to the former. For the transpiration of gaseous mixtures of more 
nearly equal density, it is known, on the contrary, that the transpiration time does 
not deviate far from the mean time of the constituents when transpired separately. 
Taking the transpiration time of air as 0*9, and that of hydrocyanic acid vapour as 
0*46, then 36*48 volumes of the first and 63*52 volumes of the second would give a 
mean time of 0*6205. 
The time observed of a mixture in these proportions was 0*6390. 
Hydrocyanic acid is composed of equal volumes of cyanogen and hydrogen united 
without condensation. The transpiration time of the compound gas is intermediate 
between the times of its constituents. 
