Freezing Point Curves of Binary Alloys. 163 



molecules, a process which, in the case of the silver-lead, might almost 

 -amount to the separation of the alloy into conjugate liquids near 

 50 atomic percentages of lead. 



The lead-copper affords an excellent example of a phenomenon 

 which has been predicted, we believe, by Ostwald, but, so far as we 

 know, has not hitherto been examined experimentally. It is that of 

 the solidification of a system consisting of two conjugate liquids, a 

 saturated solution of lead in copper, and a saturated solution of 

 copper in lead. For dilute solutions of lead in copper, as far as 

 7 atoms of lead, the curve is in harmony with equation (2) ; but as 

 more lead is added its effect rapidly decreases, and from 17 to 65 

 atoms of lead the freezing point remains constant at 954 C. With 

 more lead the freezing point again falls, until it reaches the eutectic 

 point. An examination of the solid alloys shows that the flat part of 

 the curve corresponds to alloys which have separated into two layers, 

 while still liquid. 



The copper- tin curve embraces all the remarkable bronzes, gun 

 metal, bell metal, speculum metal, and it is not surprising to find 

 that it presents singularities. The rapid increase in the steepness of 

 i)he curve as tin is added suggests that the tin is combining with the 

 copper to form complex molecules, perhaps of SnCu 3 or SnCu 4 , which 

 exist in solution. An abrupt change, not only in the direction of the 

 curve, but pJso in the character of the freezing point, and the nature 

 of the precipitate at 15*2 atoms of tin is in accordance with the great 

 changes in the physical and microscopical character of the alloy noted 

 by Behrens as occurring here. The remarkably straight line of 

 freezing points from here up to 20 atoms of tin is best explained on 

 the assumption that an isomorphous mixture of SnCu 4 and another 

 body are separating. The very flat part of the curve between 20 and 

 25 atoms of tin, along which each freezing point is an extremely 

 constant temperature may be due to another case of isomorphism, or 

 may be due to the separation of conjugate liquids. The existence of 

 & body SnCu 3 is not clearly indicated by our curve, although not in- 

 consistent with it. Double freezing points occur on the horizontal 

 lines stretching to the left from 15'2 and 20 atoms of tin. 



The silver-antimony curve shows an angle at Ag 3 Sb, but the 

 eutectic point, though near Ag 3 Sb 2 , is not at this formula. 



It is worthy of note that in three cases in our curves an angular 

 depression, and not a summit, occurs at a formula point. 



We have made a few experiments on alloys of gold, nickel, and 

 iron, in copper. The two latter cause a rise, but gold produces a fall 

 in the freezing point. 



Prom what we have hitherto done, silver bismuth promises to 

 resemble silver-antimony, copper-bismuth to resemble copper-lead. 

 The silver-gold curve, as is already known, rises above the freezing 



