ON THE CHEMICAL NATURE OF ALLOYS. 187 



definite composition, such as AuCd, Cu,Sn and others, many 

 of which do not obey the ordinary laws of valency, may be 

 held together rather after the fashion of double salts, may 

 in fact be molecular and not atomic compounds. In this 

 case they may be dissociated when in solution, but like the 

 alums, exist in the solid form. Hence in a dilute solution 

 of copper in tin, the copper may exist, as Heycock and 

 Neville have shown, in the form of monatomic molecules, 

 but yet when the mass solidifies the bodies Cu 4 Sn and 

 Cu 3 Sn may be formed. It is certainly somewhat difficult 

 to imagine that the electropositive and self-saturating atoms 

 of gold and cadmium can be held together, in the molecule 

 AuCd, by forces similar to those which maintain the equi- 

 librium of a molecule of hydrochloric acid. 



Future progress in this subject will probably be the re- 

 ward of those who bring physical as well as chemical and 

 microscopical methods to bear on the same problem. 



F. H. Neville. 



13 



