216 BULLETIN OF THE BUSSEY INSTITUTION. 
the disintegration and other reactions in the soil due to dissolved 
supercarbonate of lime will be most conspicuous. 
Several questions of interest naturally suggest themselves, on pro- 
ceeding to inquire what consequences may result from the absorption 
or formation of carbonic acid in dry soils, and what reactions may 
occur when the various constituents of soils are brought into intimate 
contact with a solution of supercarbonate of lime, as when rain water 
falls upon a dry field. For example, does the carbonic acid generated 
and absorbed by dry soils decompose the silicates or other compounds 
of lime in the soils with special facility under these conditions of dry- 
ness? In this connection, the ready conversion of sulphate of lime 
(gypsum) into carbonate of lime, at or near the surface of the soil, 
should be remembered. The fact of such conversion has often been 
noticed, and has been explained as follows: When a soil is warm, 
and highly charged with moisture, some of the gypsum contained in 
it is apt to be reduced to the condition of sulphide of calcium by the 
deoxidizing action of the organic matters in the soil; and the sulphide 
of calcium thus formed is decomposed in its turn on coming in contact 
with carbonic acid. But I find, by direct experiment, that sulphide of 
calcium is readily decomposed by a solution of supercarbonate of lime. 
Even sulphide of calcium that has been prepared in the dry way by 
passing a current of hydrogen gas over sulphate of lime heated to 
redness in a glass tube was readily decomposed with evolution of 
sulphuretted hydrogen, when placed in a solution of acid carbonate of 
lime, prepared by digesting whiting in a solution of carbonic acid in 
water, at the ordinary temperature and pressure of the air. 
A double quantity of simple carbonate of lime will, of course, result 
from this reaction; viz., that formed from the sulphide, and that which 
was previously held in solution by the excess of carbonic acid. 
There are numerous experiments which illustrate this point. De 
Saussure & Pictet * noticed that, after rain, the odor of sulphuretted 
hydrogen is perceptible upon fields that have been plastered. Schiib- 
ler f found that some pure powdered mineral gypsum that was left 
exposed to air, rain, sun, and snow, during six months, was changed to 
such an extent, that 75 grains of the gypsum contained, after exposure, 
* “ Gasparin’s, “ Cours d’ Agriculture,” 8me Edit. 1. 87. 
t “ Schweigger’s “ Journal fiir Chemie und Physik,” 1817, 21. 213. 
