66 
MESSRS. C. T. HEYCOCK AND F. H. NEVILLE ON 
clianges abruptly at this composition, We get here a maximum for electrical 
conductivity, for density, and for coefficient of dilatation. 
Hence various writers have concluded that the compound SnCug exists ; but there 
has not been the same unanimity with regard to the existence of SnCu^. 
Our results, though they cannot be called final, point we think, to the view that 
wlien alloys poor in tin begin to freeze, copper separates from a liquid containing 
molecules of a compound of tin and copper. That wdien the alloy SnCtiQ is reached, 
copper ceases to separate as such ; and instead, this body, or more probabl}^ an 
isomorphous mixture of SnCug and SnCu^, separates. The double freezing points 
from 18 to 20, however, show that the liquid does not solidify homogeneously, so 
that the isomorphism cannot be of an absolute character. 
At 20 atoms of tin we think that the evidence points to the existence of the body 
SnCiq. Between 20 and 25 atoms, perliaps the most probable explanation is to 
suppose that an isomorphous'"" mixture of SnCu^^ and SnCug solidifies homogeneously. 
At 64 atoms of tin the curve is not incompatible with the existence of the compound 
SnCug, and with still more tin the molecule of any compound that may exist must 
idtimately, for very dilute solutions of copper in tin, contain only one atom of copper 
(J.C.S., Joe. ciL). 
The criticisms of Beheens, however, on the alloy SnCug suggest another explana¬ 
tion of the phenomena which is not without probability. It may be that with 
more tin than SnCui, the licjuid alloy breaks up into tv:o conjugate liquids, and 
that this state exists until more than 25 atoms of tin are present. If this were so, 
we should have expected, as in the copper-lead curve, that this part would have been 
horizontal; but, assuming the two conjugates to differ little in density, the slight, 
but real, slope in this part of the curve might be accounted for by imperfect realiza¬ 
tion of equilibrium at the freezing point. 
The interesting complete cooling curves of copper-tin alloys given by Professor 
Boberts-Austen, in his Pteport on Alloys, wfill, we think, be found to be consistent 
wfith the facts observed by us, although wm should not perhaps altogether agree with 
him in the inferences that can be drawn from these facts. 
The Silver-Antimomj Curve. (Fig. II.) 
In this curve it will be seen that up to 25 atomic per cents, of antimony the 
steepness increases with increase in the amount of antimony. As in the case of the 
similar feature of the tin-copper curve, we can explain this by assuming that the 
antimony combines with the silver to form a compound molecule. 
At 25 atomic per cents, of antimony there is a well-marked angle, and although 
there is only one point determined between 15 and 25 atomic per cents., yet the 
direction of the lines leaves little doubt as to the position of this angle. 4'he angle, 
* Kustur, ‘ Zeits. Pliys. Cliem,,’ 1890, v., p. 601. 
