( 614 ) 
5. If we now calculate this heating effect, by means of the 
incorrect equation A on pag. 611 we find: 
FE, = Heat of formation Zn SO, — Heat of formation Hg, SO,. 
The heat of formation of ZnSO, has been determined by THOMSEN !) 
as 230090 calories, that of Hg, SO, determined by VARET*®) some 
years ago in two totally different ways as 175000 calories. 
By the calorimetric way we therefore find: 
KE = 230090 — 175000 = 55090 calories 
a value differing no less than 26000 calories from that obtained 
by the electrical method. 
If with Mac-Inrosu, we take into consideration the fact that 
Zn SO4. 7 He O is formed, and allow, according to THOMSEN, 22690 
calories for the heat of hydration of Zn SO, to Zn SO,.7 H,O we 
find: 
i, = 252780 — 175000 = 77780 calories 
a figure which still differs considerably from that caiculated (81490 cal). 
6. Having now demonstrated that the prevailing ideas as to 
the reactions taking place in the CLARK-cell lead to great differences, 
we may investigate what really occurs in the cel] when the current 
is closed. 
Suppose 2 X 96540 Coulombs have passed; 1 gram-atom of zine 
will have dissolved and this will have combined with an equivalent 
quantity of SO, from the Hg, SO4 to form Zn SOx. 
This ZnSO, will now immediately abstract water from the satur- 
ated solution of ZnSOs.7 H‚O contained in the cell in order to 
form ZnSOs.7H,0. This abstraction of water will take place 
according to the equation: 
7 
Zn SO, + ge (Zn SO, A H,V) = ; 
Dn 
A 
ze SO,. 7 1,0 = ee (C) 
where A represents the number of mols. of water which are present 
in the saturated solution along with 1 mol. of ZnSO, at the 
temperature 7' of the cell. 
*) Thermochem. Untersuchungen III, 8. 275 en II S, 245. 
*). Ann. de chimie et physique, VIIT (7) (1896). See also Berturtor, Thermochimie 
II p. 860 (1897). 
