PRINCIPLES UNDERLYING METAMORPHIC PROCESSES — 505 
above 32.4 to use the (positive) heat of solution of Na.SO, (anhy- 
drous), at lower temperatures the (negative) heat of solution of 
Na.SO,10H.O which is then the stable solid phase in solution. 
The effect of uniform pressure on the solubility of solids can be 
calculated from an equation analogous to equation I whenever the 
heat effect and volume change appropriate to the particular condi- 
tions are known. Hitherto trustworthy direct determinations have 
been made for only four substances,’ of which but one is even of 
indirect geological significance; the mean values obtained are given 
in the subjoined table. . 
TABLE II 
CHANGE OF SOLUBILITY PRODUCED BY UNIFORM PRESSURE (COHEN AND 
COLLABORATORS) 
CdSO,8/3H2O at 25° | ZnSO, + 7H20 aT 25° | MANNITE AT 24.05° NaCl aT 24.05° 
PRESSURE 
IN Cone. of Conc. of Conc. of Conc. of 
ATMOS- Satd. Solu. | Percent- | Satd. Solu. | Percent- | Satd. Solu.| Percent- | Satd. Solu.| Percent- 
PHERES g. CdSO, age g. ZnSO; age |g. Mannite age g. NaCl age 
per 100 g. | Change | per 100 g. | Change | per 100 g.| Change | per 100 g.} Change 
H.0 H.O H.0 2 
Peele OOO! Nil gia. es TO Se wit creer AVN) || sooge BS (Oyo) |) ooone 
SOOM 7OnOLe ol ieh 7 SOT ie Ona 210A) |\-1-2.32 360.55 |+1.81 
THOOON =|) 7O.54, |—-2.08 OSM ar O52 21.40 |-- 3-57 27 RO2N | 312 
RRCOOMPr Erte Wises | Seepseue | ie sien 25.04 |\--472 | 37/30%\4-4-07 
From this we see that it would be likely to require a very con- 
siderable change of (uniform) pressure to change the solubility by 
50 per cent, a change which may easily be produced by a compara- 
tively small change of temperature. Hence the influence of pres- 
sure on the solubility of solids is altogether negligible in compari- 
son with the influence of temperatures. 
Uniform pressure may cause marked increase in the apparent 
solubility in certain cases; namely, wherever we are really dealing 
with an equilibrium, the state of which is displaced by pressure. 
An example of this is afforded by calcium carbonate in presence of 
water and carbon dioxide; increased pressure increases the concen- 
tration of CO, in the water (and hence really changes the character 
1 E. Cohen and L. R. Sinnige, Z. physik. Chem., LX VII (1909), 432; LXIX (1909), 
102; E. Cohen, K. Inouye, and C. Euwen, ibid., LXXV (1011), 257. These authors 
give a critical résumé of earlier work along this line. 
