1816.] On the Physical Analysis of Soils. 218 
by the different soils exposed to the atmosphere. Several years ago 
Mr. Alexander Humboldt drew the attention of naturalists to this 
remarkable quality of soils. Afterwards some philosophers denied 
that it existed. This induced me to make new and exact experi- 
ments on the subject. I chose glass globes of the same size, which 
I could seal hermetically. I put into them equal quantities of the 
different soils, and left them for 30 days in the temperature of 
between 61 and 66°, completely shut out of all contact with the 
atmospheric air. I then examined the air in the globes by means 
of the eudiometer of Volta. The proportion of oxygen absorbed 
differed extremely, according to the degree of the dryness or 
moisture of the soils. When the soils were quite dry no oxygen 
was absorbed, or at least very little. I then exposed these soils in 
the month of. May for several days to the open air, and shat them 
up again after they had absorbed some moisture, ‘The air in which 
they were confined now exhibited evident marks of the absorption 
of oxygen. I made the experiment a third time, employing soils 
soaked with moisture. In this state they absorbed a considerable 
quantity of oxygen, as will appear from the table, while water 
itself, in the same time, had absorbed only a very minute quantity 
of oxygen. ‘The excessive quantity absorbed by magnesia surprised 
me; but reiterated experiments with pure magnesia confirmed it. 
The oxygen thus absorbed does not appear to combine chemically. 
Drying the earths and exposing them to a higher temperature, 
deprived them of the gas absorbed, which they absorbed again 
when exposed to a new experiment. Humus alone presents an 
exception. A portion of its carbon combines with the oxygen. 
Carbonic acid gas is formed and escapes by evaporation. 
To remove altogether the objection that the oxygen is absorbed 
by the water rather than by the earths, I made another series of 
experiments, I poured water upon the earths till each was covered 
by two lines of fluid, and proceeding in the manner described 
above I obtained the same result; humus and clay absorbed a great 
deal of oxygen gas, sand very little. 
Columns 13 and 14 show the ‘different specific heats of the soils. 
In my experiments on this subject I followed different methods, 
First I mixed the soil with water raised to different degrees of heat, 
then I exposed each in‘ Lavoisier’s calorimeter ; finally, 1 heated 
equal quantities of soil to a determinate temperature, and then 
ascertained the time requisite for each to cool down to another 
determinate degree. The general results obtained by these differ- 
ent methods were the same. Sand always exhibited the maximum 
and magnesia the minimum of specific heat, when the volume of 
each was the same; the only mode of comparison which appears 
to me just when we speak of great masses of soil. On this basis, 
fixing the specific heat of the sand of lime at 1000, I found the 
numbers contained in the 18th column, Of the three methods 
above mentioned the last appears to me the best, as being the most 
