342 



BEPORT — If 



Sii Cuj stand quite apart from the rest of the copper-tin series both in colour, lustre, 

 and electrical resistance. 



It will be specially important to ascertain whether the passage of a strong cur- 

 rent will enable the constituents of the copper-tin series of alloys to be separated, 

 b'ut unfortunately the alloys of these metals have high melting-points, and as the 

 alloyshave to be kept molten by the external application of heat during the pas- 

 sage of the current, the difficulties of manipulation ai'e greatly increased. I con- 

 sidered, therefore, that it would be better to begin with the lead-silver and lead- 

 gold series which have comparatively low melting points, and of which, as I have 

 already stated, much is known concerning their behaviour as solutions. One addi- 

 tional advantage iu the employment of these alloys is presented by the readiness 

 with which variations in their composition may be determined. This is a point of 

 some importance, for if, as Dr. Gladstone has already suggested, the results of 

 passing the current through the molten alloys were only very slight changes in 

 composition, the errors of analysis might overshadow the change. In the case, 

 however, of the lead-gold and the lead-silver alloys, the method of assay by cupel- 

 lation enables very minute changes in composition to be detected, and the amount 

 of change can be determined with great readiness and accuracy. 



Scale one-half. 



P P, Cables from battery. 



H H, Copper holders. 



M M, Cavity for withdrawal of sample, 



I I, Wrought iron rods. 



FFF, Soft fire brick. 



L L, Silver-lead or gold-lead alloy. 



The preliminary experiments need not be described at length : it is only neces- 

 sary to state that fire-brick U tubes, about five millimetres in section, weie em- 

 ployed, and that in them the fluid alloy was kept molten by the external application 

 of heat. The electrodes first used were stout iron-wire terminals of a forty-pint ceil 

 Grove battery ; the passage of the current was maintained for thirty minutes and 



