206 BULLETIN OF THE BUSSEY INSTITUTION. 
carbonic acid that it may yield a solution of supercarbonate of lime 
when treated with water. It would seem, at all events, from these 
experiments, that there is no essential necessity for supposing that the 
carbonic acid has been derived from the oxidation of the organic por- 
tion of the loam, in the case of the earths that have long been dry. 
For the present, I wish merely to insist upon the fact, that much 
more carbonic acid will usually be found in loams that have been kept 
for a long time in a thoroughly dry condition, than in fresh earth or 
in that which has only recently been dried. ‘The experiments which 
have forced this conviction upon me are here given in detail. 
Fifteen separate samples of fresh loam were dug up from the Plain- 
field on different days between May and October, 1877; and these 
fresh earths were percolated and tested for carbonic acid, and particu- 
larly for the precipitate of carbonate of lime that is produced by 
ammonia water. The different samples differed widely among them- 
selves as to their condition of dryness, accordingly as the weather had 
been rainy or dry before the times of collecting them; but the results 
of the tests were constant and unvarying. No appreciable precipitate 
was produced by ammonia in the percolates from any of the samples ; 
and only faint traces of carbonic acid were detected on boiling the 
acidulated liquids in a flask, and conducting the vapor into lime water. 
In the case of several of these specimens, a portion of the earth 
was dried rapidly, either completely upon a water-bath, or by spreading 
the earth upon plates, and leaving it to become air-dried in a dry glass 
house in which no plants were growing. But, like the fresh earth, 
these recently dried earths gave no precipitate when percolated and 
tested with ammonia. On leaving the dried earths, however, for six or 
eight days, exposed to the pure dry air of the glass house, and then 
percolating them, precipitates were obtained on the addition of am- 
monia water. In one instance, a quantity of earth collected June 11 
was left exposed to the air in the glass house, until June 18, when a por- 
tion of it being percolated, and tested with ammonia, gave a slight 
precipitate of carbonate of lime. The remainder of the dry earth 
was then divided into two equal portions, one of which was placed 
in a tightly stoppered bottle, while the other was again spread out and 
exposed to the air in the glass house for a month. The two portions 
were then percolated, and tested with ammonia under precisely similar 
conditions; and it was found that the precipitates obtained from the 
