( 156 ) 
Temperature. Ratio —- 
9 
5° 1,067 
10° 1,043 
15° 1,017 
20° 1,000 
The ratio is calculated by means of the equation 
nE_ 
Po ‚ ,0.0001983 7 
= > 
5. Below the transition temperature the modification which is 
metastable (the white) should have a greater solution tension than 
the grey (Pv > P). From this it follows that grey tin must be 
precipitated from tin solutions below 20° C. when white tin is 
brought in contact with them, just as copper is precipitated from 
a copper solution into which a zine rod, for example, is dipped. 
The metal with the greater solution tension goes into solution 
whilst that with the smaller is precipitated. 
6. In our researches on the Enantiotropy of tin!) it was found 
that the conversion of white tin into the grey modification is highly 
favoured by the presence of traces of grey tin. 
What has just been said about the solution tension of the two 
modifications explains the fact that the presence of a solution of a 
tin salt is also very favorable to the conversion of white tin into 
grey tin. 
Below 20° C. grey tin is always precipitated from the solution 
of a tin salt by white tin; this process takes place, by analogy 
with what we know of other metals, very fast. In contrast to what 
so often happens with salt solutions, supersaturation does not occur. 
If traces of grey tin are once present, they have a further acce- 
lerating action on the process. (According to experiment.) 
7. We may now deduce another relationship which must exist 
between the displacement of the transition point of the reaction 
grey tin 2 white tin 
with the external pressure exerted on the system and the tempera- 
ture coefficients of our transition element. 
For the grey tin electrode we have 
1) See note on pag. 149. 
