426 Prof. H. E. Roscoe on the Specific Gravity of [May 23, 



first used for the preparation of chlor-iodide of ethylidene. The iodide 

 was agitated in the cold for some time with a weak solution of 

 bromide of iodine,* the excess of bromide was separated, and the pro- 

 duct was washed with dilute potash. On subjecting this to distilla- 

 tion almost the entire quantity passed over between 130 and 165° C. 

 On fractioning I obtained a large quantity of fluid distilling between 

 140 and 148°, most between 142 and 144°. The following equation 

 explains the formation of this compound : 



CH 3 CH 3 



| +BrI= | +11. 



CHT 2 CHBrI 



On analysing this body I obtained the following results : 



Theory C 2 H 4 BrI. Experiment. 



Carbon , 10 *21 10 "24 



Hydrogen 1 70 1 '82 



Brom-iodide of ethylidene is nearly colourless when freshly prepared. 

 It has a sweet taste, and distils without decomposition between 142 

 and 144° C. This is about 20 degrees lower than the boiling point of 

 its isomer, the brom-iodide of ethylene (163° C). It refuses to become 

 solid even when surrounded with a mixture of ice and salt, differing 

 in this respect also from its isomer. Heated with alcoholic potash 

 it yielded a volatile vapour containing bromine, probably bromide of 

 vinyl, and iodide of potassium. 



This body is probably identical with those obtained by Pfaundlerf 

 and by BeboulJ by exposing bromide of vinyl to the action of hydri- 

 odic acid. The boiling points of their compounds agree pretty well 

 with each other and also with mine. 



I am at present engaged in studyiug the behaviour of these com- 

 pounds towards several reagents. 



I have to thank my young pupil, Mr. Harrington, for his valuable 

 assistance during the progress of this research. 



VII. " Note on the Specific Gravity of the Vapours of the Chlo- 

 rides of Thallium and Lead." By Henry E. Roscoe, F.R.S., 

 Professor of Chemistry in Owens College, Manchester. 

 Keceived May 8, 1878. 



Experimental difficulties of so serious a nature surround the attempt 



* Eor the preparation of the bromide of iodine, see Proc. Roy. Soc., No. 149, 

 1874. It was made a little weaker for this process, 

 f " Jahresbericht," 1865, p. 483. 

 X Ibid., 1870, p. 439. 



