300 



THE ALLOTROPISM OF CHLORINE. [MEMOIR XX. 



so as to confine the hydrogen, and they were released 

 from the cork h of the drying-tube K, Fig. 50, the lower 

 extremity of each was dipped beneath the surface of 

 some water contained in a saucer, P, Fig. 51 ; the two 



sets of tubes being held 

 steadily in a proper posi- 

 tion by the aid of a wooden 

 frame, Q R. The tubes now 

 differed from one another 

 in nothing but the circum- 

 stance that the chlorine of 

 one had been exposed to 

 the sun, and that of the 

 Fi s- 51 - other had not. 



The gases were now brought in contact. This was 

 easily done by sliding each pair of ground glasses until 

 their apertures coincided, as shown at p in Fig. 51. The 

 hydrogen now rose through the hole into the upper ves- 

 sel, the chlorine descending through it, mutual and per- 

 fect diffusion of the two gases rapidly taking place. 

 This was done by lamplight in the dark room. And 

 now it could be ascertained that the gases were at the 

 same temperature in the different tubes, and that the 

 experiment had thus far been carried on successfully, by 

 the water retaining its level at the same point in the 

 tubes c of both sets. If that which had been in the 

 sunshine was warmer than the other, as soon as the 

 apertures coincided a bubble of gas would have escaped 

 through the water, or at all events the level would have 

 changed. 



It remained now to open the shutter of the dark room, 

 the tubes having been previously set in such a position 

 that the light would fall equally on both. As soon as 

 this was done, the chlorine which had been exposed to 

 the sun united at once with its hydrogen, and the water 



