( 615) 
The ZnSO,.7H,O formed will be deposited from the saturated 
solution contained in the cell and be added to the crystals already 
present. 
The heating effect EZ, in the cell is now equal to the difference 
of the heats of formation of ZnSO, and Hgs SO, plus the heat 
effect W of the change represented by equation (C) which may be 
calculated from thermochemical data. 
The value of 4 may be calculated from the solubility determinat- 
ions made by CALLENDAR and BARNES') and ConeN®). Their 
results, which agree perfectly, lead to the equation: 
L = 41.80 + 0.522 t + 0.00496 ¢2 
where L represents the number of grams of Zn SO, which are 
soluble in 100 grams of water at t° 
From this equation it is found that at 18° C. A=16.81 so that 
at that temperature the equation (C) assumes the following form: 
Zn SO, + 0.713 (Zn SO, . 16.81 H,O) = 1.713 Zn SO, . 7 H,0. … (CY) 
The heat effect accompanying this change may be found by 
supposing the systems on the left and on the right hand side of 
the equation to be dissolved in water so that both shall have the 
final-concentration Zn SO4. 400 H,0. 
We then find: 
Heat of solution Zn SO,— Zn SO, . 400 H,O = + 18430 calories 
THOMSEN, Thermochem. Untersuchungen III, S. 275. 
The heat of dilution of (Zn SOs. 16,81 H,O — Zn SOx. 400 HO) 
is calculated as follows: 
The heat of dilution Zn SOs . 20H,O — ZnSO, . 50 H,0 = 
+ 318 calories THOMSEN |. c. p. 90. 
therefore, heat of dilution ZnSO. . 16,81 H,O — Zn 80,4. 20 H,O 
—— #4 (20 — 16.81) = + 33.8 calories. 
Since now, the heat of dilution Zn SOs. 20 HyO—Zn SO4. 200 HO 
= + 390 calories THOMSEN Ì.e. p. 37 
and the heat of dilution Zn SOs . 200 H,O — Zn 804. 400 H,0 = 
+ 10 calories THomsEN |. c¢. p. 91. 
') Proc, Roy. Soc. 62. 117. 
*) Proc. Roy. Acad. Amsterdam. Vol. [L 1900, p. 337. 
