(157) 
hd 
E, — mid. 
ne, ar 
(1) 
Here Z, is the difference of potential, at the absolute temperature 
T, between the grey tin and the tin solution in which it is im- 
mersed, 7, is the heat of ionisation of the grey tin, n the valency, 
and ¢ = 96540 Coulombs. 
For the white modification we have: 
tie er lle ph ae HE) 
in which # represents the heat of transition. 
From (1) and (2) we obtain, since £, = £, at the transition 
temperature, 
ù Ne ae, pels 
DEN 5 ed aE dT 
of 
eN (: € en AT ( ) 
Now we know that 
dD Tj 
nes je En 
CE en 
where T is the absolute transition temperature, D the external 
pressure, 7} the quantity of heat which is evolved when 1 kg. of 
white tin is converted into the grey modification, that is the heat 
of transition for 1 kg. and V, and V, are the volumes of 1 kg. 
of each modification in cubic metres. Since 7 in equation (3) relates 
to one gram atomic weight and 7 in (4) to 1 kilogram, we have 
1000 r 3 3 , 
r= ———-, where 4 is the atomic weight of the metal forming 
the electrode. 
From (3) and (4) 
AD 1000 (pn ú 
RSB ee) a Ty alt oars cite phitersiar (0) 
pene Voges ya 
dE, aa) 
The quantity to the right of the sign of equality is now expressed 
in Volt-Coulombs, or ergs X 107. If we wish to ascertain the change 
of the transition point produced by a change of pressure of 1 atmo- 
sphere, we may write (5) as follows: 
