Dr. Wallace on the Equivalent of Bromine. 279 



hydrogen was mixed, that it \Yas obtained colourless j but it then 

 contained some metallic iron. Taking this into account, the re- 

 sult, Fe = 27*99, was obtained experimentally. 



Any one acquainted with the determination of equivalents 

 will feel how far inferior this method is to those employed before, 

 and how little it is calculated for a check upon them. Indeed we 

 must feel surprise that Dumas, from the result of such determi- 

 nations, did not feel some misgiving as to the unconditional ex- 

 cellence of the method employed with such generality by him. 



These examples may suffice to show that the doubts above 

 expressed are not without foundation. I repeat. The determi- 

 nation of equivalents from the one point of vieiv of the analysis of 

 chlorides appears not to bear critical examination. It is a matter 

 of course that the analogous compounds, differing as much as 

 they do in their behaxdour, cannot be employed with equally good 

 effect for the determination of equivalents. This is as much 

 the case with oxides as with sulphides and chlorides. It is the 

 first and most essential problem in every equivalent determina- 

 tion, to choose as a starting-point a compound as free as pos- 

 sible from sources of error. Now whether such chlorides as are 

 strongly hygroscopic — which at the same time, at least at high 

 temperatures, decompose water with energy, and are thereby 

 liable to take up oxygen — whether these compounds may be 

 regarded as appropriate ones, is a question which I think must 

 be answered in the negative, however exact chlorine detei'mina- 

 tions may be valued as such. 



M. Dumas* once loudly complained of the unconditional 

 trust reposed, according to his opinion, by chemists in the equi- 

 valent determinations of Berzelius, without critical discussion 

 and further examination. He will certainly think it reasonable 

 if chemists now are cautious not to fall into similar errors in 

 relation to his own investigations in the same field. 

 Berlin, June 1859. 



XLIII. On the Equivalent of Bromine. 

 B?/ William Wallace, Ph.D., F.C.S. Glasgow^. 



THE combining proportion or atomic weight of the element 

 bromine has been determined by several chemists, and 

 with remarkably varied results. Balard's estimations varied from 

 74i-608 to 75-432; Licbig obtained the number 75-288; Lowig 

 75-76 ; and Berzelius 78-4. These discrepant results appear to 

 have been owing to the extraordinary difficulty of obtaining com- 

 pounds of bromine free from traces of chlorine. In a recent 



* Comples Rendits, vol. xiv. \t. 5;J8. 



t Communicated by the Author, havinfi; been read at the Meeting of the 

 British Association at Aberdeen, September 20, 1859. 



