398 PROCESSOR W. C. ROBERTS-AUSTEN ON THE DIFFUSION OF METALS. 
values of the factor —, between which the experimental values are found to fall 
in most of the sections. They are plotted in the same manner as the thick continuous 
Jl 
lines, and the value of k corresponding to each value of 9 is calculated and placed 
opposite the dotted line to which it belongs. 
. In fig. 4 it was necessary to plot these dotted lines for more widely divergent 
values of k than was the case in fig. 3. 
Fig. 3, representing the diffusion of gold in lead, is seen to agree very well with 
theory, while fig. 4, representing the diffusion of platinum in lead, shows considerable 
irregularities, which are probably due to errors in the platinum assay. The mean of 
the figures in column 7 is taken as the correct value for 0 , and from this, knowing 
the values of h and t, that of k may be obtained. 
Fig. 2. 
It will be remembered that the length of each section (Table A) was 1'054 centims., 
which is equal to half the length of the part of the tube occupied by the rich gold alloy. 
As, however, this measurement was made on cold solidified metal, it must be corrected 
to the temperature at which the experiment was actually conducted. This correction 
is based on experimental determinations of the linear expansion by heat of the molten 
metals contained in the iron tubes. The corrected value of In, l’082 centims., and the 
value of t, 6’96 days, are substituted in the equation = 0'1184, giving 3‘00 as 
the value of k, the units being the centimetre and day. The experiments, the results 
of which are embodied in Tables B, C, and D, were conducted simultaneously with 
those in Table A, which have just been described. All the experiments in this series 
were, therefore, subjected to exactly the same conditions as regards time and tempera¬ 
ture. 
Experiments A and B were diffusions of gold, and C and D of platinum, in lead. 
The results of these gave k for gold in lead as 3'00 arid 3'07, and for platinum in lead 
as U69 and 1’69 respectively, the temperature in each case being 492° C. It may 
