COMPLETE FREEZING-POINT CURVES OF BINARY ALLOYS. 
29 
freezing point caused by the presence of B to be less than the normal. It is not quite 
certain that the experiments described in the present paper contain any examples 
supporting Van’t Hoff’s theory of solid solutions. 
On the other hand, the fact proved experimentally by Kuster and by Le Chatelier, 
that when the solid separating is an isomorphous mixture of A and B, all the freezing- 
points lie on a straight line joining A to B, is probably illustrated by part of the 
copper-tin curve. 
When the liquid AB separates into two conjugate liquids before the formation of 
solid, this process, which, since it generally occurs with falling temperature, may be 
expected to be exothermic, might evolve enough heat to affect the thermometer and 
give a false freezing pointc The freezing point curve of a pair of conjugate liquids 
in contact with each other is perfectly illustrated by our copper-lead curve. 
Section II. 
The Experimental Method. 
The experimental details of our work, including the method of employing and 
standardising the pyrometers, has been fully described in a paper already published 
by us ;* we shall, therefore, treat these matters with great brevity. 
The composition of each alloy was determined synthetically : a weighed amount of 
one metal being melted, and successive weighed quantities of the second metal added 
to it. Each freezing point was in general determined twice, the alloy being com¬ 
pletely re-melted before the second reading. When the two differed, the second was 
generally a little higher than the first, and was accepted as the most trustworthy. 
The alloys were fused in cylindrical salamander (plumbago) crucibles, 42 millims. 
wide and 105 millims. high; these were in most cases surrounded by an outer 
crucible, to secure a slow rate of cooling. The crucibles were heated in a small 
Fletcher blast furnace, so arranged that the products of combustion escaped at the 
side. The oblique hole, usually seen in the cover of these furnaces, was replaced by 
an axial circular hole that exactly fitted the crucible. The mouth of the crucible 
passed through this hole, and the joint was made approximately gas-tight by a packing 
of asbestos paper. The surface of the alloy was in this way protected against the 
furnace gases. As there was thus no draught across the mouth of the crucible, we 
were able to keep a small flame of coal-gas, or hydrogen, constantly burning over the 
surface of the metal. This was introduced into the crucible through a pipe-stem, and 
effectually prevented the oxidation of the metals or the absorption of oxygen by the 
silver. The hydrogen was made by the action of sulphuric acid on zinc free from 
arsenic, but we did not find that the substitution of coal-gas altered the freezing- 
point. For all temperatures above the melting point of silver, the coal-gas, burning 
* ‘ Chem Soc. Jour.,’ 1895, p. I6U. 
