309 



fractions of a per cent, of iron mixed with pure copper gave a higher 

 conductivity than a nominally pure copper, with which the alloys 

 were prepared. I must mention further, that in two series the alloys, 

 both prepared by Messrs. Matthey and Johnson, and as I have been 

 assured with equal care, gave results presenting considerable discre- 

 pancies ; the conductivity of the pure copper in the first stood high, 

 nearly agreeing with the 100 of my first scale, the pure copper of 

 the second series fell considerably below that limit. On this account 

 it appears that even pure copper, carefully prepared by the electro- 

 type process, does not always give us results which show perfectly in 

 point of conductivity ; but to make such experiments in a satisfactory 

 manner, it would be necessary to have a thorough chemical investi- 

 gation, both synthetical and analytical, of the metals used ; such a 

 thorough investigation I have not been able to carry out, in conse- 

 quence of the large expense which it would entail. I may mention 

 that Mr. Matthiessen has gone through a series of experiments on 

 alloys, of which the chemical composition has been ascertained with 

 all possible accuracy, and has, I believe, arrived at highly important 

 results relative to electrical conductivity. I have been in communi- 

 cation with him, and have supplied him with a specimen of one of 

 my standards. He mentions to me that he has obtained specimens 

 conducting better to a considerable extent than the 100 of my first 

 scale. In that respect he has confirmed what I have myself ascer- 

 tained, having myself found specimens as high as 1 1 1 on that scale. 

 A number of alloys of definite chemical composition, prepared with 

 great care by Mr. Calvert of Manchester, and already tested by him 

 for thermal conductivity and for mechanical properties, have been 

 put into my hands, in order that I may measure their electric con- 

 ductivities. I hope soon to be able to obtain and publish results for 

 this series of alloys. 



III. " On a new Method of Substitution ; and on the formation 

 of lodobenzoic, lodotoluylic, and lodanisic Acids." By 

 P. GRIESS, Esq. Communicated by DR. HOFMANN. Re- 

 ceived January 3, 1860. 



In a previous notice* I have pointed out the existence of a new class 

 * Proceedings of the Royal Society, vol. ix. p. 594. 



