
. ~ pal em - - 
oe. - . =~, a ae rig 
‘Parr IL Sect. ii. §2.] CHEMISTRY OF SPRINGS. 347 
Theat of the earth. hese are termed Thermal Springs. The 
hottest springs are found in volcanic districts. But even at a 
great distance from any active volcano, springs rise with a temperature 
of 120° Fahr. (which is that of the Bath springs) or even more. 
These have probably ascended from a great depth. If we could 
assume a progressive increase of 1° Fahr. of subterranean heat for 
every 60 feet of descent, the water at 120°, issuing at a locality whose 
ordinary temperature is 50°, should have been down at least 4200 
feet below the surface. But from what has been already stated 
(p. 47) regarding the irregular stratification of temperature within 
the earth’s crust, such estimates of the probable depth of the sources 
of springs are not quite reliable. The source of heat in these eases 
may be some crushing of the crust or ascent of heated matter from 
underneath, which does not however produce volcanic phenomena. 
I. Chemical Action.—Every spring, even the clearest and most 
sparkling, contains dissolved gases, also solid matter abstracted from 
the soils and rocks which it has traversed. The gases include those 
absorbed by rain from the atmosphere (p. 330), also carbon dioxide 
supplied by decomposing organic matter in the soil, sulphuretted 
hydrogen, and marsh gas or other hydrocarbon derived from decom- 
positions within the crust. 7 
The solid constituents consist partly of organic, but chiefly of 
mineral matter. Where spring water has been derived from an 
area covered with ordinary humus, organic matter is always present 
in it. Organic acids are abstracted from the soil by descending 
water, and these, before they are oxidized into carbonic acid, appear 
to be effective in decomposing minerals and forming soluble salts 
(p. 433). The mineral matter of spring water consists principally of 
carbonates of calcium, magnesium, and sodium, sulphates of calcium 
and sodium, and chloride of sodium, with minute traces of silica, 
phosphates, nitrates, kc. The nature and amount of mineral impregna- 
tion depend on the one hand upon the chemical energy of the water, 
and on the other upon the composition of the rocks. Various sources 
of augmentation of its chemical energy are available for subterranean 
water. (1.) The abundant organic matter in the soil partially 
abstracts oxygen from the water, but supplies organic acids, especially 
carbonic acid. In so far as the water carries down from the soil any 
oxidizable organic substance its action must be to reduce oxides. 
Ordinary vegetable soil possesses the power of removing from 
permeating water potash, silica, phosphoric acid, ammonia, and 
organic matter, elements which had been already in great measure 
abstracted from it by living vegetation, and which are again ready to 
be taken up by the same organic agents. (2.) Carbon dioxide is here 
' Studer points out that some springs which are thermal in high latitudes or at 
great elevations, would be termed cold springs near the equator, and, consequently, that 
springs having a lower temperature than that of the inter-tropical zone, that is from 
C. 0° to 30° (Fahr. 32°-84°), should be called “relative,” those which surpass that limit 
(C. 30°-100°) “absolute,” and he gives a series illustrative of each group—* Phy- 
sikalische Geographie,” ii. (1847), p. 49. For volcanic thermal springs see ante, p. 236. 
