204 BULLETIN OF THE BUSSEY INSTITUTION. 
temperature, and with constant stirring, directly upon the floor of a large 
iron muffle; and the new sample was placed in the percolator as soon as 
it had become fairly cold. . 
Both specimens were percolated with pure water, and 25 cc. fractions of 
the percolates were collected for testing. It appeared in each fraction 
that the precipitate produced by ammonia was. more voluminous in the 
case of the recently calcined earth than in that of the earth that had been 
exposed to the air for a long time after the calcining; and that, while the 
fourth fraction of percolate from the latter gave no appreciable precipitate 
with ammonia, this reagent produced a distinct precipitate in the fourth 
fraction from the recently calcined earth, which was as far as the experi- 
ment was carried. 
Contrary to what might, perhaps, have been inferred from the results 
previously obtained with the Beatley earth, it seems plain, from the 
behavior of the calcined Saltonstall earth, that the excess of carbonic acid 
found in the percolates could not have been simply absorbed by the earth 
from the air after the calcination. On the contrary, the inference to be 
drawn from these experiments is, that a part of the carbonic acid result- 
ing from the combustion of the organic matter of the original loam is 
retained with a good deal of force by the calcined product. It is here 
a case of ‘‘occlusion,’’? pure and simple. The following experiments 
were made to test this point: A quantity of the earth that had stood 
two years after calcination was placed in a wrought-iron tube, and ignited 
for an hour as strongly as possible in a combustion furnace, while a cur- 
rent of air free from carbonic acid was forced through the tube, and made 
to pass into lime water as it left the tube. ‘This test liquor indicated 
that an abundance of carbonic acid was expelled from the earth. After 
the ignition, the earth was allowed to cool in the current of air, and it was 
finally percolated with pure water; but no perceptible precipitate was pro- 
duced on adding ammonia to the percolate, not even in the first 25 cc. 
fraction. 
It was noteworthy that both the mechanical and the chemical condition 
of the earth had been greatly altered by the ignition. The original cal- 
cined earth was of a reddish-yellow color before its ignition in the iron 
tube; but after the ignition the earth was gray; and, on heating this gray 
product with nitric acid, the original reddish coloration was restored. To 
see if this reduction of ferric oxide was to be attributed wholly to the iron 
of the tube, another portion of the original calcined earth was heated as 
before, for one hour, in a combustion tube of hard glass; but this portion 
did not become gray, and the percolate from it gave a precipitate with 
ammonia. . 
Still another portion was finally heated as strongly as possible for two 
hours in a glass tube, in a current of pure dry air, and it was noticed that 
the color of the earth became deeper in all parts of the tube, and that at 
length the earth became gray at the middle of the tube where the heat 
was greatest, as it had done in the iron tube. On treating this gray earth 
