BULLETIN OF THE BUSSEY INSTITUTION. 215 
and 7 em. thick, and observed that the filtrate remained perfectly clear 
when lime water was added to it. He noticed, furthermore, that this 
filtrate contained a considerable quantity of sulphate of lime. Finally, 
he percolated a similar column of earth with water that had been 
charged with carbonic acid at the ordinary temperature and pressure, 
and still found that no cloudiness appeared in the filtrate when it was 
mixed with an abundance of lime water; or, rather, no cloudiness 
appeared until after the first portions of liquid which had gone through 
the earth were removed, anda limit was reached, after which, the new 
portions of filtrate became cloudy when lime water was added to them. 
It will be noticed that Van den Broeck’s method of testing for car- 
bonice acid with simple lime water was less delicate than mine, where 
hot lime water was used. Like Van den Broeck, I find, on percolating 
moist garden earth with carbonic-acid water, that a certain not very 
large proportion of the carbonic-acid water fails to pass through the 
earth at first; but I think it probable, as has been said, that this be- 
havior is due to phenomena of adhesion. I find neither any “ power- 
ful retention” of carbonic acid by garden earth, nor any evidence that 
mere loam, as such, can prevent carbonic acid from passing into wells 
and springs. The carbonic acid in the waters of the sand-bed at 
Utrecht is evidently held there by the lime-carbonate whose presence 
has been insisted upon by Van den Broeck, and it is a question to be 
studied at that particular locality, how it happens that the water of the 
upper or garden soil is charged with gypsum rather than with carbo- 
nate of lime. 
It is to be remarked, however, that considerations such as these are 
of subordinate interest in the present connection. The chief points 
thus far arrived at are, that while the percolates obtained by leaching 
moist loams with pure water generally contain very little if any super- 
carbonate of lime, appreciable quantities of this compound are contained 
in the percolates from most loams that have been thoroughly air-dry 
for some little time. Owing to the lack of dry weather in this imme- 
diate vicinity during the past summer, I have had no opportunity to 
test the question, whether field-dried earth will exhibit the same reac- 
tions as that stored in barrels or dried upon plates, though there would 
seem to be no special reason why it should not. ‘The question could 
best be studied in some locality like California, where droughts are 
periodical ; and it is in such countries, doubtless, that the good effects of 
