1890.] 



Experiments on Vapour-density. 



53 



tube and stopcock next the globe to a much higher temperature, in 

 order to volatilise the iodine ; consequently there was great risk of 

 cracking the stopcock, and this indeed happened several times. The 

 first (trial) series gave results which pointed towards normal 

 density. 



In the next series an attempt was made to find the vapour-density 

 as nearly as possible at the saturation-pressure. The vapour-pressure 

 of iodine at 132 is 164'6 mm., from the results of Professors Ramsay 

 and Young (' Chem. Soc. Journ.,' vol. 49, 1886, p. 455), and several 

 determinations were made at about this temperature and at about 

 150 mm. pressure. Constant results were not obtained, although 

 much time and trouble were expended on the experiments. The 

 numbers obtained were: 247'6, 251'2, 204'5, and 184'9. The iodine 

 was allowed to blow out until none could be seen on the bottom of 

 the globe, but it was extremely difficult to decide whether it had all 

 volatilised or not, and no reliance can be placed on the results, not- 

 withstanding the close agreement of the first two numbers with 

 254 (= 2 X 127). Another plan was then adopted. 



Vapour-density of Iodine from Determinations of the Velocity of Sound 

 ly Kundt's Method (' Poggendorff's Annalen,' vol. 135, 1868, p. 337). 



The apparatus is best understood from the diagram (fig. 4). The 

 glass tube CD, about 2 feet long and f inch in diameter, was sup- 

 ported inside a larger tube, GH, by corks, as shown ; CD was slightly 



FIG. 4. Sectiou of Apparatus. 



inclined one way, and GH the other. The bulb E contained chloro- 

 benzene ; F is a condenser ; AB is a small-sized tube sealed into the 

 tube CD at C ; it was enlarged at B, so as to fit the tube loosely, 

 but not to touch the walls. 



Method of Procedure. Some solid powdered iodine was introduced 



