PROFESSOR GRAHAM ON THE MOTION OF GASES. 
371 
The common multiplier by which the numbers of the oxygen scale have been de- 
rived from the air scale is 0'898. Excluding the last result, we have, on the oxygen 
scale, — 
The mean transpiration time of ammonia 0*51 15 
This time for ammonia corresponds very closely with the results previously obtained 
by the long single capillary M, namely, 0'5119 and 0‘5134. The coincidence in the 
rates of M with those of the compound capillary, for a liquefiable gas like ammonia, 
is a circumstance of considerable importance, as a large proportion of the experiments 
which 1 have to detail on gases of this class were made with the first-named only of 
these capillaries. The number for ammonia certainly approaches to 0‘5076 and 
0*5093, the mean transpiration-times of olefiant gas, but cannot be said to coincide 
with them, and is of course somewhat more distant from 0*5. 
4. Cyanogen. 
This gas was prepared from well-crystallized and perfectly dry cyanide of mercury. 
To secure its purity the gas was besides passed over red oxide of mercury and chlo- 
ride of calcium. The gas was conveyed to the capillary in the same manner as am- 
monia. The capillary employed was the long tube M, of 52*5 inches, the gas under 
the pressure of the atmosphere being drawn into the two-pint aspirator-jar, exhausted 
as usual upon the plate of an air-pump. Thermometer 60°, barometer from 29*910 
to 29*864 inches. 
The experiments were made in the following order: — air, 1113, 1114 seconds; 
cyanogen, 626, 628, 627 and 627 seconds; air, 1117, 1117 seconds. The slight in- 
crease of the air-time in the last-made experiments is undoubtedly owing to the fall 
of the barometer. The ratio of the cyanogen to the first air-time is 0*5631, and to 
the second air-tirne 0*5613; or 0*5068 and 0*5052, with oxygen =1. The mean of 
the two results gives, — 
Transpiration time of cyanogen ......... 0*5060 
The transpiration time of cyanogen may therefore be confounded with that of ole- 
fiant gas, 0*5076, transpired in the same manner, although the densities of these two 
gases differ so widely as 14 to 26 (oxygen =16). 
5. Hydrocyanic Acid. 
A considerable quantity of the absolute acid was prepared by distilling 15 ounces 
of crystallized ferrocyanide of potassium with 9 ounces of oil of vitriol diluted by an 
equal weight of water. The liquid acid was afterwards dried by digesting it over 
pounded chloride of calcium. 
As hydrocyanic acid is liquid at the usual temperature, air or hydrogen saturated 
with the vapour of the acid was transpired instead of the pure substance itself. The 
air or hydrogen was made to stream through the liquid acid contained in a wash- 
bottle to a depth of 2 inches, and surrounded with water to which a slight heat was 
applied, so as to maintain the water and wash-bottle at the fixed temperature of the 
