1903.] Constitution of the Copper-Tin Scries of Alloys. 409 



Bakerian Lecture. — " On the Constitution of the Copper-Tin 

 Series of Alloys." By C. T. Heycock, F.E.S., and F. H. 

 Neville, F.E.S. Keceived February 26, — Lecture delivered. 

 February 26, 1903. 



(Abstract.) 



This paper is an attempt to fill a very serious gap in the study of 

 alloys. As a rule, an alloy begins to be interesting when the tempera- 

 ture of the liquid alloy has fallen to its freezing point. This point t 

 which records the moment when solid first appears in the liquid, is 

 easily observed on account of the evolution of latent heat that occurs 

 on the formation of solid, and if the freezing points of all the alloys 

 of a series are determined, we can plot the freezing-point curve. 

 Many such curves have been traced in the last ten years : that of the 

 copper-tin alloys is given by the upper line in our diagram. The 

 curve consists of several branches cutting each other in angular 

 points. The one thing that these curves record without ambiguity is 

 the number of different solids that can crystallise out of the liquid 

 alloys, for each branch corresponds to the crystallisation of a different 

 substance. But this is almost all that such curves tell us with certainty. 

 They do not tell us whether the solids forming are the pure metals, 

 or pure compounds, or crystalline solid solutions of the metals. Other 

 experiments are needed to decide such questions. 



The other great branch of the study of alloys consists in the 

 microscopic examination of the solid alloys after they have cooled to 

 ordinary temperature, that is to say, after they have, in general, ceased 

 to undergo change. Between these two series of experiments there is 

 an enormous gap of temperature, it may be 1000 or 500 degrees, and it 

 is in this range of temperature that the whole life-history of the alloy, 

 regarded as an organism, is to be found. The only fruitful experiments 

 we know of dealing with this intermediate region are the cooling 

 curves of Roberts- Austen and Stansfield. These observers traced auto- 

 matically the whole of the cooling of the bronzes and obtained some 

 remarkable results. They found that the evolution of heat at the 

 freezing point was often succeeded at much lower temperatures by 

 other evolutions of heat, and that many of these must have occurred ~ 

 after the alloy had wholly solidified. These thermal changes point to 

 important chemical or physical changes, though they do not tell us 

 what these changes are. They suggest, however, that the final patterns 

 found by the microscope in the solid alloys are likely to be very 

 complicated, as they may contain several records superposed the one 

 on the other. We found these patterns very beautiful, but hopelessly 

 complicated. 



