480 On certain Ternary Alloys. [Mar. 28, 



present, the mass divides itself into two different ternary alloys, lead 

 predominating in the heavier one and zinc in the lighter one. This 

 phenomenon is entirely distinct from the segregation of alloys during 

 solidification, in consequence of formation of eutectic or other differ- 

 ently fusible alloys. 



If there is little or no inequality of temperature at different parts 

 of the mass, separation by gravitation only is complete in a few hours, 

 at any rate when tolerably pure metals are employed; but if the 

 mode of heating is such that convection currents are set up, the 

 separation is greatly interfered with, and in extreme cases almost 

 entirely prevented. 



The heavier alloy is a saturated solution of zinc in lead containing 

 tin, and the lighter one a similar solution of lead in zinc containing 

 tin. No matter what the relative proportions between lead and zinc 

 in the original mass, the two alloys always correspond to two conju- 

 gate points on the solubility curves of zinc in lead-tin and of lead in 

 zinc -tin. 



But little, if any, difference in the way in which a given mass 

 divides itself is noticeable, whether the temperature at which the 

 molten mass is maintained is below 600 C. or above 700 C. 



The tin contained in the mass does not distribute itself equally in 

 the two alloys except when present in one particular proportion, 

 which varies with the ratio of the zinc to the lead in the entire mass. 

 With less tin than this the lighter alloy, and with more the heavier 

 one, takes up the higher percentage of tin. 



Curves drawn representing the tin present in the heavier alloy as 

 abscissae, and the (+ or ) excess of tin in the lighter alloy over 

 that in the heavier one as ordinates, are found to differ with the ratio 

 of zinc to lead in the entire mass. They always possess the same 

 general features, viz., rising from the origin to a maximum elevation, 

 then sinking down again to the base line, and crossing it so as to 

 become negative ; but the position and height of the maximum, the 

 crossing point, and the general dimensions of the curve vary with the 

 ratio of zinc to lead in the mass. 



As a result of this, whilst an indefinite number of different mix- 

 tures may be prepared, each one of which will give the same heavier 

 alloy, the lighter alloy simultaneously formed will be different in each 

 case ; and conversely. 



When no tin is present, lead dissolves zinc to such an extent as to 

 form an alloy containing 1*24 per cent, of zinc, and zinc dissolves lead 

 forming an alloy containing 1*14 per cent, of lead ; the higher values 

 found by previous observers being slightly incorrect through imper- 

 fect separation. 



Before attempting to theorise on the causes leading to the remark- 

 able way in which tin is distributed in these ternary alloys, we desire 



