��POTENTIAL DIFFERENCE.
��CHAP.
��Solution Pkessure, P, of the Metals in Atmospheres.
��Volts.
Magnesium 10**
Aluminium lO*^
Cadmium 10^
Iron 10»
��Volts.
Lead 10-«
Hydrogen 10^*
Copper 10-«
Mercury 10^**
Silver lO-'-^^
��The elements used in these determinations were (the sum
��of Metal I Zn and Zn volt : see p. 240) —
��MgSO, CdSO^ FeSO^ PbACj CuSO^ AgjSO^ Zn I ZnSO, | H^SO, | H^CPd) = 0760 .-. Hj | H,SO,
��Zn
�ZnSO,
�MgSO,
�Mg
�Zn
�ZnSO^
�CdSO,
�Cd
�Zn
�ZnSO,
�FeSO,
�Fe
�Zn
�ZnSO,
�PbACg
�Pb
�Zn
�ZnSO,
�CuSO,
�Cu
�Zn
�ZnSO,
�Ag,SO,
�Ag
��VoltB.
��/. Mg /.Cd .-.Fe /. Pb .'. Cu /. Ag
��Volta.
��Heat of lonisation. — ^As Ostwald has shown, we can calculate TV, in this case the heat of ionisation, from the formula already given —
o.. n-n^^ - 23,070f - W
- dT T
if we kncTw P, the potential difference between metal and
solution. The value of j^ can easily be determined by
arranging in opposition to each other two surfaces, Metal
I Salt solution kept at different temperatures. Thus we
dP find for Copper | Copper acetate, -^^ = 000774 volt; for
Copper I Copper sulphate, 0000757 volt, or as the mean value 0000766 volt per degree. Therefore, if T = 290°—
23,070 X 0000766 X 290 = 23070 x 0*60 - TV,
from which —
��TV= 13,842 - 5124 = 8718 cal.
�� �
