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MESSES. WALTER ROSENHAIN AND P. A. TUCKER. 



discrepancies from these views were found when the attempt was made to verify 

 them, that it became evident that the investigation of this point had not been pushed 

 far enough. It has accordingly been thought desirable to undertake a complete 

 redetermination of the equilibria of the lead- tin system with a view to placing our 

 knowledge of the constitution of the eutectic on a surer footing. This task was 

 rendered more difficult, as well as more interesting, by the discovery of a trans- 

 formation which occurs in the alloys rich in lead at temperatures below that of 

 complete solidification. 



In the present paper the investigation of the equilibria of the lead-tin system will 

 first be described, some observations on the structure and properties of the eutectic 

 alloy tft' this series being subsequently given. 



Constitution of the Alloy,* of Lead and Tin. 



Preparation, of lie Alloys. Chemically pure lead and tin were obtained from 

 Messrs. Kahlbaum's London agents and on analysis proved to contain only slight 

 traces of impurities. The alloys were prepared by weighing out, on an analytical 

 balance, the requisite quantities of the two metals and melting them together in a 

 suitable manner, the tin being usually melted first and the lead added to the molten 

 tin. In all cases the temperature was kept as low as possible, except in some special 

 experiments where the effect of exposure to high temperatures was studied with, 

 however, only negative results. As a rule the alloys were melted in small fire-clay 

 crucibles heated over gas burners, the metal being protected from oxidation by 

 various means. In some cases a flux of borax and powdered charcoal was employed, 

 while in other cases the metal was melted under oil, glass vessels being employed for 

 the latter purpose. In some cases a very small amount of oxidation was found to 

 occur in spite of these precautions, but the composition of the alloys has been found 

 by analysis not to be materially affected thereby. This is shown in the tabulated 

 results of analyses given in Table I. 



TABLE I. Calculated and Analytically Determined Composition of Alloys. 



