PROFESSOR W. C. ROBERTS-AUSTEN ON THE DIFFUSION OF METALS. 403 
the meaning of the final distribution rather uncertain. The results of these and 
some of the very early experiments have been dealt with by the aid of tables of 
theoretical distributions, similar to those of Stefan, but calculated for the case of an 
infinite tube having constant concentration at one end, which nearly corresponded to the 
actual conditions under which my earlier experiments were conducted. The values 
given by these experiments agree very fairly with those obtained later, but the 
inequalities of temperature made the value of k vary from point to point of the tube, 
so that it was impossible to determine it with any degree of precision. 
Diffusions of Amalgams in Mercury .—A number of experiments were made on the 
diffusion, at ordinary temperatures, of gold and other metals in mercury, which will 
he included in a subsequent communication. I may, however, mention, for the sake 
of comparison, that the diffusivity of gold in mercury at 11° C. is 0’72 sq. centim. 
per day, the diffusivity of gold in lead being 3‘0 sq. centims. per day at 500°. As 
already stated, Dr. Guthrie”' published in 1883 particulars of some experiments of 
this kind, the metals he selected being zinc, tin, lead, sodium, and potassium, 
diffusing in mercury. He did not make any calculations with a view to obtain either 
the absolute or the relative diffusivities of these metals in mercury; indeed, after 
giving the percentage of the diffusing metal in successive quantities of mercury, he 
observes : “ It is scarcely worth while dividing these diffusion percentages by the 
so-called atomic weights of the metals.” His experiments were complicated by the 
fact that in some cases he employed solid metals instead of fluid amalgams, as the 
source of the diffusing metal. Approximate results have, however, been obtained 
from his data, and from certain measurements of the original apparatus, now deposited 
in the South Kensington Museum. These show that his inference “ that potassium 
and sodium have a far greater diffusive energy than the heavier metals examined ” is 
not supported by the actual result of his experiments. His results, calculated by the 
method given in the present paper, give the values of k, in square centimetres per day, 
as follows :— 
Tin in mercury at about 15 c 
Lead ,, ,, 
Zinc ,. ,, 
Sodium ,, ., 
Potassium ,, 
1-22 
10 
1-0 
0-45 
0-40, 
* Loc. cit. 
3 F 2 
