212 Mr. J. A.Wanklyn on the Movements of Gases. 



A second experiment with the same tube, and the same length 

 of exposure, gave — 



Air 20-3 



Carbonic acid . . . 79*7 

 1000 

 A third experiment, also with the same tube and same expo- 

 sure, gave — 



Air 26-6 



Carbonic acid . . . 73 - 4 

 1000 

 Three more experiments, where the time of exposure was twenty 

 seconds, other conditions remaining unaltered, gave — 



I. II. III. 



Air 49-67 60-68 51*34 



Carbonic acid .... 50-33 39-32 48-66 

 10000 10000 100-00 

 The differences observed between the quantities of gas which 

 escaped in the same times in the different experiments are no 

 doubt caused by the action of currents of air which are produced 

 by the act of unclosing the tube, which currents are necessarily 

 variable in extent and direction. Though it would be idle to 

 draw any inference as to the precise numerical relation subsist- 

 ing between times of exposure and quantities of gas fallen, yet 

 these oscillations in our different experiments do not at all affect 

 the certainty of the general result. 



In five seconds about one quarter of the carbonic acid escaped ; 

 in twenty seconds about one half. 



Let us translate this into retardation of the fall of the gas. 

 Our tube was 232 millimetres long. Therefore, in five seconds 

 three-fourths of the gas cannot have fallen more than 60 milli- 

 metres in vertical distance. By comparing this with the distance 

 through which carbonic acid, contained in a balloon, would fall 

 in five seconds, we arrive at an estimate of the retardation which 

 we seek to measure. 



At first sight, the cause of this retardation would appear to be 

 friction between the carbonic acid and air which must enter 

 to supply the place of the carbonic acid. But if we carefully 

 consider the conditions under which we find the gases in these 

 experiments, we shall sec that another explanation is possible. 



For, notwithstanding the absence of cohesion in gases, the 

 carbonic acid in our experiment seems to be very much in the 

 condition of water in the two arms of an equal-armed siphon ; 

 the essential difference between the two cases being that, where- 

 as the cohesion between the particles of water hinders all move- 



