€ 330 ) 
a. Determination of q by extrapolation. 
The change undergone by Zn SO,. 7H, O at 39° may be repre- 
sented by equation (3) on p. 335. 
According to the solubility determinations in table II, the value 
to at 39% is 12.19. 
Equation (3) therefore becomes: 
1.1 Zn SO4. 7 Hy O=0.941 Zn SO, 6 Hy O + 0.162 Zn SO, 12.79 Hy O. 
According to THomsEN !): 
The heat of solution Zn SO, 7 H,0 — Zn SO, 400 H,O = — 4260 cal. 
The heat of solution Zn SO, 6 H,0 — Zn SO,.400 H,0 = — 843 cal. 
Heat of dilution Zn SO,.20 H,0 — Zn SO,. 200 1,0 = + 390 cal. 
(THOMSEN Ì.e. p. 37). 
Heat of dilution Zn SO,. 20 1,0 — Zn SO,. 50 H,0 = + 318 cal. 
From the last figures we find by extrapolation : 
Heat of dilution Zn S0,. 12.79 H,0 — Zn SO,. 20 H,O = 
518 
30 
(20 — 12.79) = + 16.3 cal. 
Therefore heat of dilution 
Zn SO, 12.79 HzO — Zn SO,. 200 H, O = 390 + 76.3 = + 466.3 cal. 
Since further, the heat of dilution 
Zn S04. 200 HO — Zn SO,. 400 HO = + 10 cal. 
(THomsen, l.c. p. 91). 
we find: 
Heat of dilution Zn SO, 12.79 H,O0 — Zn SO,. 400 H,0 = + 476 cal. 
The heat evolved by the change represented by equation (3) is 
therefore: 
—1.1 X 4260 + 0.941 X 843 — 0.162 X 476 = — 3970 cal. 
1) Thermochemische Untersuchungen, IIT, 138, 
