328 Messrs. C. T. Heycock and F. H. Neville. 



Cooling curves show that this change is exothermic and abrupt, 

 much heat being evolved by the alloys near /, but little by alloys 

 near G. Herein the transformation at G is the reverse of the trans- 

 formation at C. The change from the rounded y crystals to the plates 

 of E' with liberation of liquid is perfectly shown by our photographs 

 of alloys chilled near the G temperature. 



When an FG alloy has cooled below G the phase E' crystallises out 

 of a liquid which is becoming richer and richer in tin. This process 

 goes on between the G temperature of 633 and the H temperature of 

 400. Below 400 the FG alloys follow the same course as the next 

 group. 



8. The GH Alloys, containing from 42 to about 87'5 atomic per cents, of 

 Tin. When these alloys begin to crystallise they deposit plates of E', 

 and this process goes on until the liquid has the composition H and 

 the temperature is 400. At this temperature the body E' becomes 

 less stable than the body H, and the reaction E' + liquid = H, com- 

 mences. This reaction ought to complete itself isothermally until 

 either all the E' or all the liquid is transformed ; but in our experi- 

 ments we find that the reaction is soon arrested through the plates of 

 E' becoming completely coated with H, and thus protected against 

 further action by the liquid. When this has occurred, the temperature 

 begins to fall again, and H crystallises out of the liquid until the 

 eutectic point I is reached. 



The result of this imperfect reaction is that we have four compart- 

 ments in the space E 3 SUH, in each of which one of the three phases 

 that exist would be absent if the equilibrium transformations had been 

 completed. This part of the figure assumes that the formula of the 

 H-body is CuSn. If this should prove erroneous the line H'T would 

 have to be shifted, but otherwise the diagram would be unchanged. 

 In the four compartments of the area EsSUH, Professor Roozeboom 

 has suggested the excellent plan of placing a bracket round the symbol 

 of the phase that has no right to be present 



9. The HI Alloys, containing from 87 '5 to 98'3 atomic per cents, of Tin. 

 In these alloys the solid first forming is H, and the diagram suffi- 

 ciently explains itself. 



10. The IK Alloys, with more than 98 - 3 atomic per cents, of Tin. These 

 alloys contain combs of pure tin in a eutectic of H + Sn. 



Some Observations and Qualifications. 



The Solidas. We have drawn this everywhere as a definite line, but 

 our method of determining it, by the inspection of chilled alloys, is 

 probably not so exact as the method by which the liquidus has been 

 determined, and therefore further work on the solidus is desirable. 

 We think that a determination of the melting point as distinguished 

 from the freezing point would be a promising plan. 



