196 BULLETIN OF THE BUSSEY INSTITUTION. 
pressure, gave liquids in which precipitates of carbonate of lime were 
formed, on the addition of lime water. He remarks, incidentally, that 
these precipitates were not much larger than those obtained from the 
water of ordinary springs, and that 100 cubic inches of the liquid ex- 
pressed from a loam gave off only about two inches of carbonic acid, 
on being boiled. Verdeil & Risler,* also, on the occasion of their 
experiments upon the soluble matters in soils, remark that carbonate 
of lime is found in the extract or aqueous solution obtained from 
loams, as well as in the ashes which are left on burning the dry resi- 
dues obtained by the evaporation of such solutions. Many other analy- 
ses} of waters that have filtered through earth point more or less 
emphatically toward the conclusion that carbonate of lime is, at the 
least, occasionally present in the waters of surface soils. But, in so far 
as I am aware, it has not been recognized hitherto that long-continued 
dryness of the surface soil (in the case, at least, of soils which are not 
naturally calcareous) is an important condition for the effective solu- 
tion of the lime-carbonate on the addition of water. 
To illustrate the fact of the solubility of the lime-carbonate, a quan- 
tity of loam no larger than will fill a tube 40 em. high and 24 cm. in 
diameter is amply sufficient; and I have no reason to doubt that a much 
smaller quantity of earth than this would serve the same purpose. On 
pouring water upon the top of the column of dry earth until the latter 
has become supersaturated so that drops begin to fall from the bottom 
of the tube, and then testing the filtrate, either with lime water, am- 
monia water, or caustic soda,t a flocculent precipitate of carbonate of 
lime will be produced. It may readily be shown, moreover, in other 
ways, that the filtrate from the earth contains carbonic acid. Not 
only do the precipitates just mentioned effervesce freely on being sep- 
arated from the liquid and treated with an acid, but on taking some 
of the original filtrate, to which no reagent has been added, placing 
* “Journal fiir praktische Chemie,” 1852, 57. 115. 
+ Compare the authorities cited by Professor Johnson in his “ How Crops 
Feed,” pp. 310-314. 
¢ It may here be said that the utmost pains were taken to use perfectly pure 
reagents in this research. The ammonia water was carefully freed from car- 
bonic acid by redistillation from milk of lime, and the soda was prepared 
immediately before using it by exposing metallic sodium to the air. The lime 
water was boiled just before use, and drops of the percolate were allowed to 
fall into the hot liquid. 
