400 PROFESSOR W. C. ROBERTS-AUSTEN ON THE DIFFUSION OF METALS. 
Table E contains the results of the more recent experiments which have been 
made ; Jc is given in sq. centims. per diem, and also in sq. centims. per second. The 
result for the diffusion of lead in tin is, however, less trustworthy than the other 
data. 
Table E. 
Diffusing metal. 
Solvent. 
Temperature. 
k in square centims. 
Per diem. 
Per second. 
Gold .... 
Lead . . 
o 
492 
3-00 
1 
3-47 x 10* 5 
5? .... 
15 ... 
492 
3-07 
3*55 
Platinum 
492 
1-69 
1-96 .. 
55 ... 
492 
1-69 
1-96 „ 
Gold .... 
555 
3-19 
3-69 
51 .... 
Bismuth 
555 
4-52 
5-23 
n .... 
Tin ... . 
555 
4-65 
5-38 
Silver 
n .... 
555 
4-14 
4-79 
Lead 
55 .... 
555 
STS 
3-68 „ 
Gold .... 
Lead . . 
550 
3T85 
3-69 
Rhodium 
55 ... 
550 
3-035 
3-51 „ 
These results are presented graphically in Plate 8, which represents the theoretical 
distribution of the several metals after diffusion has proceeded for seven days, the 
temperature being close to 500° C. 
The horizontal ordinate represents distance in the direction in which diffusion takes 
place, the actual length of the plate being the same as that of the tube. The vertical 
ordinate represents concentration. It will be evident that if the plate be turned so 
as to make the horizontal line vertical, the actual distance the metals diffused upwards 
will at once be apparent. Each of the diffusing metals occupied at the beginning of 
the experiment the length a, b of the tube, and they all had the same initial con¬ 
centration. 
If the time had been infinitely extended, the final condition of each experiment 
would be represented by the horizontal line d, e, and the relative diffusivity of each 
pair of metals is shown by the degree of approximation which the distribution in that 
experiment has made to the final condition of things. 
What this final condition would be may be made clear by the aid of fig. 5. The 
length c, cZ represents that part of the tube which is occupied by the gold alloy from 
which diffusion takes place, the alloy having an original concentration denoted by 
c a, so that the area a b d c, represents the whole quantity of gold in the experi¬ 
ment ; all the gold being initially to the left of the line d, b. The final state of com¬ 
plete diffusion is represented by the area c e f g, which is the same as a b d c, since 
the quantity of gold remains unaltered. 
