257 



being 158 and 160; residual measures with the metal coating 2'5 

 measures, or about the ^th of the total charge; with paper coating, in 

 some experiments 80 measures, or about T 8 ^ths of the total charge, so 

 that the residual charges with metal and paper are as 1 : 32. Thermo- 

 electric effect for metal coating 8, for paper coating nothing. It 

 appears from these and similar experiments, that the interposition of 

 imperfect conductors between the coating and the glass of the Leyden 

 jar must necessarily impair its efficiency, and change its electrical 

 indications, especially when of any considerable thickness. Three 

 turns of common linen interposed between the outer coating and the 

 glass reduced the force of discharge from 11 to 6, nearly one-half, 

 whilst the residuary or retention of charge is considerably increased : 

 this question, as bearing in some degree on the retention of charge by 

 the electric cable, may not be undeserving of further investigation. 



IV. " On the Bromide of Carbon." By ARTHUR C. W. LENNOX, 

 Esq. Communicated by Dr. HOFMANN. Received May 24, 

 1861. 



The compounds of carbon with bromine have as yet received but 

 limited attention. The tetrabromide of carbon, CBr 4 , of the methyl- 

 series is altogether unknown. Kolbe failed in obtaining this com- 

 pound by submitting disulphide of carbon at a high temperature to 

 the action of bromine, and I learn from Dr. Hofmann that the action 

 of pentabromide of antimony on the disulphide gives no better result. 



The bromide of carbon, C 2 Br 4 , has been obtained by Lowig*, who 

 procured this substance by the action of bromine on alcohol or on 

 ether, when it is formed according to the equations 



C 2 H 6 O + 4Br 2 = C 2 Br 4 + 4HBr+H 2 O. 

 C 4 H 10 O + 8Br 2 =2C 2 Br 4 + 8HBr + H 2 O. 



These processes appear, however, to be attended with difficulties ; 

 at all events, Volckelf, who repeated Lowig' s experiments, failed in 

 obtaining the substance described by that chemist. 



A simpler method for obtaining this bromide of carbon appeared to 

 present itself in the perfect substitution of bromine for the hydrogen 

 in olefiant gas. 



* Annalen der Chemie und Pharmacie, iii. 292. f Ibid. xli. 119. 



