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PROFESSOR GRAHAM ON THE MOTION OF GASES. 
mercury. This circumstance prevents the times being observed with the same pre- 
cision as in other gases. 
With the thermometer from 72° to 74°, and barometer from 30-076 to 30*028 
inches, the times of descent of the gauge barometer from 28*5 to 23*5 inches were, 
with air, 865 and 863 seconds ; with air saturated with sulphuric acid vapour at 
73° Fahr., 960, 961, and 958 seconds. The ratio of the last times to air is T1106; 
and multiplying by 0*9, we obtain, — 
Transpiration time of air saturated with vapour of SO 3 at 73° . . 0*9993 
The tension of the vapour of anhydrous sulphuric acid at 73° was observed to be 
1 1*50 inches. 
The experiments on sulphuric acid vapour were repeated: thermometer 67°'5, 
barometer 29*914 to 29*908 inches ; the range of the gauge barometer now observed, 
however, being only from 28*5 to 24*5 inches. 
The time for air was 695 and 694 seconds ; for oxygen saturated with the vapour 
of sulphuric acid at 67°*5, 786 and 782 seconds ; for oxygen alone at 68 °, 774 
seconds ; and for air alone again 692 seconds. The result to be deduced is, — 
Transpiration time of oxygen saturated with vapour of SO 3 at 67°'5 . . 1*0130 
The sensible equality of the times of air observed at the beginning and end of the 
experiments proves that the working of the apparatus was not deranged by the sul- 
phuric acid vapour. It is evident that the time of pure sulphuric acid vapour itself 
cannot deviate far from that of oxygen gas. Sulphuric acid appears to be one of the 
very few gases, the transpirability of which, if not really coincident with, is slightly 
inferior to, or slower than, that of oxygen. 
10 . Chlorine. 
The transpiration time of chlorine has a peculiar interest as that of an elementary 
substance. The same arrangements were had recourse to with this corrosive gas as 
with sulphuric acid. It was found necessary, in addition, to preserve a small column 
of water above the mercury in the gauge barometer, to defend the metal from the 
action of the chlorine, or at least to prevent the surface of the metal from becoming 
foul and adhesive. This gas immediately reached the capillary, like ammonia, from 
a bottle with a relief tube, to permit the escape of the redundant supply. It was 
dried by means of chloride of calcium. 
( 1 .) The transpiration was made by capillary K, 8*75 inches in length, into the six- 
pint globular receiver as aspirator, from 28*5 to 23*5 inches by the gauge barometer 
attached to the latter: thermometer 70° to 71°, barometer 30*222 to 30*208 inches. 
The times of air in two experiments were 865 and 866 seconds ; the times of chlo- 
rine 670 and 672 seconds ; giving the ratio to air of 0*7753. Multiplying the latter 
number by 0*9, we have — 
Transpiration time of chlorine 0*6978 
( 2 .) In a second series of experiments with the same capillary, the following 
