On the Results of Chilling Copper- Tin Alloys. 



171 



"On the Kesults of Chilling Copper- Tin Alloys." By C. T. 

 Heycock, F.B.S., and F. H. Neville, F.B.S. Eeceived 

 February 12,— Eead February 28, 1901. 



(Plates 2-3.) 



In the Third Eeport of the Alloys Eesearch Committee, published 

 in 1895, Sir W. Eoberts- Austen gives an appendix, by Dr. Stansfield, 

 containing an extremely interesting series of cooling curves of the 

 copper-tin alloys. These curves made it evident that for many per- 

 centage compositions there were three or even four halts in the cooling 

 due to separate evolutions of heat, and that some of these changes must 

 have occurred when the metal was solid. A freezing-point curve was 

 also deduced from the cooling curves. The report contained interest- 

 ing remarks on the meaning of the curves, but a satisfactory explana- 

 tion was not at that time possible. In June, 1895, Professor H. Le 

 Chatelier also published a freezing-point curve, giving the upper points 

 only. These two curves agree in locating a singular point near the 

 composition Cu 4 Sn, but do not give any singular point nearer to the 

 copper end of the curve. 



In 1897 we also gave, in the ' Philosophical Transactions,' a freez- 

 ing-point curve of these alloys. This curve was inferior to Dr. Stans- 

 field's, inasmuch as it gave no information concerning the changes 

 that go on in the solid metal, but it was a more accurate statement 

 of the upper freezing points than had been given before. In particu- 

 lar, it pointed out a new singular point at 15*5 atomic per cents, of 

 tin, the point marked C in the figure (fig. 1), and a straight branch of the 

 curve joining C to the other singular point marked D in the figure^ 

 Both C and D are the origins of rows of second isothermal freezing 

 points, better called transformation points. Like Dr. Stansfield, we 

 found it impossible to offer a satisfactory explanation to the curve, 

 but we hazarded the surmise that the steepness of the branch ABC 

 might be due to chemical combination, and that in the region CDE 

 solid solutions existed. Both of these surmises have since been con- 

 firmed, but at that time we felt no certainty on the subject. 



In their report on alloys presented to the Congres International de 

 Physique in 1900, Sir W. Eoberts- Austen and Dr. Stansfield give a 

 curve embodying all the above-mentioned details and some others, in 

 particular a most important lower curve of changes that take place in 

 the solid alloys.* 



* Our attention lias been called to the fact that the copper-tin curve given 

 by Eoberts-Austen and Stansfield in the International Report on Physics in 

 1900 had already been published by them in the Fourth Eeport to the Allojs 

 Eesearch Committee in 1897. This correction does not alter the chronological 

 sequence as stated in the text, since our paper was read before the Eoyal Society 

 in June 1896. 



VOL. LXVIII. O 



