414 PROFESSOR W. C. ROBE RTS-AUSTEN ON THE DIFFUSION OF METALS. 
appear, therefore, that the melting points of the metals have a dominating influence 
on the resistance offered to diffusion. 
Diffusion from a Hot to a Cold Portion of Solid Metal. 
It is well known that, in the liquid diffusion of salt solutions, osmotic pressure will 
drive molecules from the hot to the cold portions. Professor Thorpe suggested that 
an experiment of this nature should be tried with solid alloys. The principle of 
“ reflection,” which would, of course, be involved in such an experiment, has already 
been alluded to under the liquid diffusion of metals (see Part I., p. 394). The 
difficulty is to obtain a solid alloy of uniform composition, but, after many experi¬ 
ments, a rod of bismuth was obtained, in which it was believed that 375 per cent, of 
gold was uniformly distributed. This was arranged, as shown in fig. 7, which repre¬ 
sents, in sectional plan, a double block of brass, enabling half the rod to be heated 
Fig. 7. 
to 170°, which is below the melting point of the bismuth-gold eutectic alloy, while 
the other half can be cooled by a stream of water. The heating was maintained for 
six days. The result proved that there was a distinct concentration of 0'1 per cent, 
gold at the point A, where the bar entered the cooled chamber. Similar results have 
been obtained with gold-lead alloys, and, if the bar be maintained at 240°, which is 
above the melting point of the eutectic alloy, the effect is very marked. I offer 
these statements with some reserve, as they require confirmation. 
The data now published form but a small portion of the investigation which has 
been long in progress. The manipulation it involved was singularly difficult and 
tedious, and it would probably have been far less advanced than it is, if I had not 
had the advantage of the aid of one of my former students at the Royal School of 
Mines, Mr. Alfred Stansfield, B.Sc. He made the calculations which were neces¬ 
sary to extend Stefan’s tables to the range covered by the present experiments, and 
has shown untiring interest in conducting that part of the series which has been 
undertaken during the past two years. 
