Permeability 
143 
Table V 
Influence of Concentration on the Diffusivity at 18 0 C. 
(Data from Oholm) 
Coefficient of Diffusion in 
cm. 2 . 
Concentration in 
gram-equivalents 
per litre 
sec. 
X IO- 5 
A 
NaCl 
KC1 
HC1 
KOH 
o-oi 
i*35 
1-69 
2-69 
2-20 
0-02 
i-33 
i-66 
2-64 
2-19 
0-05 
1-32 
1-63 
2-61 
2-17 
o-io 
1-29 
i*6i 
2-58 
2-15 
0-20 
I-27 
1*58 
2*55 
2-13 
1-00 
1-24 
i'54 
2*57 
215 
2-00 
— 
i*53 
— 
2-19 
2-8 
1-23 
■ 5 — 
— . 
1 
3-6 
■ — ■ 
i-55 
— 
5*5 
1-23 
■ Hr I 
- 1 — ' 
— 
That the rate of diffusion of substances increases with rise of 
temperature was observed by Graham. Since these early observa¬ 
tions quantitative determinations on the effect of temperature on the 
diffusivity have been made for a number of substances. Weber (1879) 
found that for every rise in temperature of i° C. the coefficient of 
diffusion of zinc sulphate in water increased by about 0*026 of its 
value at 18 0 C. Later Seitz (1898) confirmed this value and obtained 
a similar one (0*024) f° r zinc acetate. A number of substances were 
examined by de Heen (1884) at temperatures varying from 15 0 to 
6o° C. In Table VI are shown the values he obtained for the co¬ 
efficient of diffusion at any temperature 9 , this being measured in 
centigrade degrees distant from 6o° C. taken as zero, and reckoned 
as positive downwards from 6o° C. 
Table VI 
Influence of Temperature on the Coefficient of Diffusion 
(Data from de Heen) 
Coefficient of Diffusion in 
cm. 2 _ 5 
Substance sec. 
IV^gS0 4 0*85 (1 - 0-01190) 
KN0 3 3-07 (1 - 0-0x270) 
NaCl 2-72 (1 - o-oi210) 
Na 2 HP0 4 2*06 (x - 0-01280) 
K 2 C0 3 1-63 (1 - 0-01270) 
It will be noticed that the relative increase in diffusion for the 
same rise in temperature is almost independent of the substance 
