303 



On the other hand, I have found by experimenting on artificial 

 alloys, that comparatively large admixtures of lead, iron, silver, and 

 zinc seem to produce sometimes improvement, sometimes little or no 

 sensible influence, and sometimes (as in the case of zinc) an injurious 

 effect on the conductivity of specimens of pure electrotype copper 

 from which the alloys were made. The largeness of the proportion 

 of other metal required to produce any considerable deterioration in 

 comparison with that of the whole amount of impurities which Pro- 

 fessor Hofmann's investigation demonstrates in specimens of low 

 quality as to conductivity, is worthy of remark, and seems to 

 indicate that this low quality must be due to other than metallic 

 impurities. 



The great difference between the conducting qualities of two spe- 

 cimens of electrotype copper, from which two series of alloys were 

 separately prepared, seems also to indicate some as yet undiscovered 

 cause, as operative in general. I am assured by Messrs. Matthey 

 and Johnson, by whom all the alloys were prepared, that similar 

 methods were followed and equal care bestowed to ensure purity in 

 the two cases. 



The results of my measurements of conductivity are shown in the 

 following Tables : 



TABLE I. Two Series, Nos. 1-10 and Nos. 1-32, of Specimens 

 prepared by Messrs. Matthey and Johnson from pure electro- 

 type copper, and the same alloyed with other metals, as spe- 

 cified. 



