ON THE NATURE OF ALLOYS. 175 



The Nature of Alloys. — Report of the Committee consistinriqfMr. F. H. 

 Neville (Chairman and Secretary), Mr. C. T. Heycock, and 

 Mr. E. H.. Griffiths. 



The research for which this Committee was formed is completed, and a 

 summary of the results has been published in the ' Proceedings of the 

 Royal Society/ vol. Ixix., p. 320. A copy of this paper has been sent to 

 the Secretary of the British Association. 



The work consists in a study of the chemical compounds and solid 

 solutions to be found in alloys composed of copper and tin. 



At least three series of solid solutions are formed during the solidifica- 

 tion of these alloys. 



The first series, which may be called Alpha, consists of crystals, 

 isomorphous with pure copper, and varying in composition from pure 

 copper to an alloy containing about 9 per cent, by weight of tin. These 

 alloys solidify to a uniform mass, and apparently remain unchanged at all 

 lower temperatures. 



The second series, which may be called Beta, contains percentages 

 of tin varying from 22*5 per cent, to 32 per cent. Alloys between 9 per 

 cent, and 22 '5 per cent, of tin solidify as a complex of crystals of Alpha 

 and of Beta. But all the alloys from 9 per cent, to 32 per cent, of tin 

 undergo important re-crystallisations after they have wholly solidified, 

 and their final condition below 500° C is that of a complex of Alpha and 

 a crystalline body which is probably Cu4Sn. 



Alloys from 32 per cent, of tin to 57 per cent, begin to solidify by the 

 formation of a third type of crystalline solid solutions, which may be called 

 Gamma. But the Gamma crystals break up at lower temperatures into a 

 complex of crystals of the body CujSn and another substance. The alloy 

 of the formula Cu3Sn is apparently a solid solution when first solidified, 

 and is not converted into the compound until a lower temperature is 

 reached. 



Gamma crystals containing more than 41 per cent, of tin have the 

 peculiarity that, in cooling, they break up into solid CujSn and a liquid. 

 Between 57 per cent, of tin and 93 per cent., the first solid that forms 

 when the liquid alloy begins to solidify consists of crystals of CuySn ; but 

 when the temperatui'e falls to 400° 0. these crystals become unstable, and 

 a reaction takes place between them and the liquid, which results in their 

 partial transformation into a body that is nearly, or quite, pure CuSn. 

 Between 93 per cent, and 99 per cent, of tin the substance CuSn is the 

 first body formed during solidification. Between 99 per cent, and 

 100 per cent, tin appears to crystallise first. 



Assuming the alloys to have been cooled with sufficient slowness, we 

 may summarise their condition at ordinary temperatures as follows : — 



to 9 per cent, of tin. 



A uniform solid solution (Alpha) of copper containing tin, or, more 

 probably, containing a compound, in solution. 



9 to 25*5 per cent, of tin. 



A complex of large cystals of Alpha in. a minute eutectic of Alpha 

 and Cu^Sn. 



