BULLETIN OF THE BUSSEY INSTITUTION. 219 
course, that all the carbonic acid (and other compounds of carbon) in 
the soil, came originally from the air; but there is every reason to 
believe that the amount brought down directly by rain and dew is 
insignificant by comparison with that conveyed to the soil by way of 
vegetable growth and decay. It may even be true, as the experiments 
of Reichardt and Blumtritt * suggest, that the absorptive power of dry 
earths for the gas is a more efficient means than rain of bringing car- 
bonic acid to the soil from the air.t This attraction of the gas by 
dry solids would seem to be of special importance, moreover, as a 
means of retaining in the soil the carbonic acid which is formed there 
by the oxidation of organic matters; 7.e. of hindering the too rapid 
escape of the gas into the air. 
Still another possible reaction deserves to be considered. As is 
well known, comparatively little supercarbonate of lime finds its way, 
as such, into the waters of brooks, rivers, and wells, in countries devoid 
of limestone, —such, for example, as the region in the vicinity of 
Boston. But, on the other hand, the well-waters hereabouts often contain 
much sulphate of lime, and the question presents itself, whether a part 
of this sulphate may not perhaps be derived in some cases from the 
reaction of supercarbonate of lime that has been formed, at the sur- 
face, upon sulphates of iron and alumina that have resulted from the 
oxidation, in the gravelly subsoil, of the iron pyrites which is no uncom- 
mon constituent of our rocks. So far as the mere formation of gyp- 
sum goes, it is, of course, easy to suppose that the whole of it might be 
formed, in the given case, from the reaction of the sulphates of iron 
and alumina upon silicates of lime in the earth; but it is none the less 
true that these sulphates would decompose supercarbonate of lime, in 
case it should come in contact with them, and that they must conse- 
quently tend to prevent the supercarbonate from flowing to the ocean 
as such. Indeed, W. Stein ¢ long ago insisted at some length that the 
occurrence of large quantities of carbonic acid in the waters of min- 
eral springs may often be attributed to the reaction of carbonate of 
lime upon sulphates of iron and alumina formed through oxidation of 
pyrites in the earth. 
* “ Journal fiir praktische Chemie,” 1866, 98. 418, 476. 
t+ Compare Mulder “ Die Chemie der Ackerkrume,” 1, 182, for an excellent 
statement of the influence of condensation of gases by solid bodies upon the 
formation of soils. 
¢ Leonhard & Bronn’s “ Neues Jahrbuch fiir Mineralogie,” 1845, p. 804. 
