EUTECTIC RESEARCH: THE ALLOYS OF LEAD AND TIN. 121 



small testing-machine, pressures up to 35 tons per square inch being put on the metal. 

 The small buttons of solid metal produced in this way were subsequently cut and 

 polished for microscopic examination, and their appearance under a magnification of 

 80 diameters is shown in figs. 40 and 41. Fig. 40 is taken from a part of the 

 specimen which had been subjected to severe flow under the action of the plunger, 

 while No. 41 is taken from a part where the pressure had acted uniformly in all 

 directions. It will be seen at once that this compound mass of metal can scarcely be 

 regarded as a true alloy at all ; the .particles of lead and tin are merely juxtaposed 

 and held together by surface cohesion. It is intended to observe these specimens 

 from time to time, both when kept at the ordinary temperature and when maintained 

 at temperatures just below the melting-point of the eutectic, with a view to detecting 

 the process of diffusion which will probably occur, but so far the time has been too 

 short to allow of definite results being observed. 



For the purpose of furnishing a more delicate test of such a diffusion process, 

 specimens of an alloy containing 1 7 per cent, of tin were prepared in a similar 

 manner ; their micro-structure is shown under a magnification of 80 diameters in 

 fig. 42. Prepared from fusion and very slowly cooledj this alloy would be very nearly 

 homogeneous, so that the difference between the true alloy and the mechanical 

 mixture obtained by the compression process is very marked in this case. 



The author is indebted to Dr. E. T. GLAZEBROOK, F.E.S., the Director of the 

 Laboratory, for his kindly interest in the progress of the present research, and to his 

 colleagues on the staff of the Laboratory for much valuable help in various details 

 of the work. 



VOL. CCIX. A. II 



