baad 
spor 
Joseph LeConte—Genesis of Metalliferous Veins. 3 
ti 
combined volumes of constituents—pressure by assisting con- 
traction increases solubility, while only in very exceptional ’ 
cases, as for example sal ammoniac, in which expansion takes 
place in solution, pressure by resisting expansion diminishes 
solubility. These latter cases, however, are so extremely ex- 
ceptional, that we may assume as a law, the increased solvent 
power of water in proportion to pressure. It is even possible 
by experiment thus to determine the mechanical equivalent of 
the chemical force of solution of any given substance, and in 
nase this has been so determined for several substances by Mr. 
There can be no doubt, then, that the solvent power of water 
_ Other solvents.—But the solvent power of subterranean waters 
1s still further and very greatly increased for most vein-matters 
y the presence of alkali in the form of alkaline carbonates, or 
alkaline sulphides or both. This is especially true of the com- 
monest of vein stuffs, viz: quartz and lime carbonate and the 
commonest form of metallic ore, viz: metallic sulphides. The 
solubility of silica in alkaline carbonate waters is well known, 
and with excess of carbonic acid in the waters all the earthy and 
metallic carbonates are also soluble. The solubility of many 
and probably all metallic sulphides in alkaline sulphides, espe- 
cially with excess of hydrogen sulphide,* under pressure and 
Super-heat can no longer be doubted; for iron sulphide and 
mercuric sulphide are now being deposited from such waters 
th at Sulphur Bank and at Steamboat Springs. Mr. Christy+ — 
and others have proved the solubility of mercuric sulphide 
* The affinity of these two feeble acids for bases are so nearly balanced, that 
tite of one involves the excess of the other, and as a matter of fact both 
2 and HS are found in excess in all solfataras. ory err 
t This Journal, xvii, 453, 1879. 
