BULLETIN OF THE BUSSEY INSTITUTION. 209 
to saturate the earth, the water was followed by carbonic-acid water, 
and no direct reaction for carbonic acid with lime water was obtained 
until 550 cc. of percolate had passed through the earth In another 
similar instance, where the earth had been dried a week, then percolated 
with pure water (of which 850 cc. were required to saturate it) until 
the percolate no longer gave a precipitate with ammonia, and then 
treated with carbonic-acid water, 1,000 cc. of percolate came through 
before carbonic acid could be detected by direct tests with lime water ; 
and some 200 cc. more came through before the reaction for carbonic 
acid was as strong as in the original carbonic-acid water. This point 
was finally tested with the utmost care as follows: A quantity of 
earth taken directly from the Plain-field was dried as rapidly as possi- 
ble upon a water bath, and 1,000 grms. of the dry earth were perco- 
lated, first with pure water, and then with carbonic-acid water. 475 ce. 
of water were required to saturate the earth. ‘The pure water perco- 
late gave a slight indication of carbonic acid when boiled with lime 
water; but no reaction occurred when drops of the percolate were 
allowed to fall into hot lime water. Carbonic-acid water was then 
poured upon the column of moist earth and the percolate was tested 
methodically, by allowing two or three drops of it to fall into 10 ce. por- 
tions of hot lime water contained in a test tube. After beginning to 
use the carbonic-acid water, nearly 600 cc. of percolate came through 
before a drop of it falling into lime water produced any perceptible 
cloudiness. After 600 cc. of liquid had passed, the cloudiness in- 
creased gradually, as the drops fell into lime water; but the reaction 
was not as strong as that given by the original carbonic-acid water 
until about 700 cc. of percolate had been collected. 
Another 1,000 grm. portion of the dried earth was percolated with 
carbonic-acid water directly, without the previous addition of any 
water. 475 cc. of the liquid were absorbed by the earth, and 150 ce. 
of percolate came through the earth before any cloudiness could be 
detected on dropping the percolate into hot lime water. This cloudi- 
ness became more decided in the later portions of the percolate; but 
at 300 cc., when the experiment was brought to a close, it was not 
equal to the reaction obtained with the original carbonic-acid water. 
When, instead of carbonic-acid water, dry carbonic-acid gas was 
passed through the earths, as contained in the cylinders, and the earths 
thus charged with the gas were percolated with pure water, precipitates 
VOL. II. 14 
