20
Sci ent i fi c Memoi rs by
process of disintegration, the mass gradually crumbling down and ultimately
forming a loose sediment at the bottom of the now turbid water. The mass
of air displaced during the process is evidently very considerable, and the
phenomenon at once does away with any belief in the impermeability of
the material. Numerous experiments were carried out with a view of more
accurately determining the air content of air-dried specimens of the material.
The method employed was one of displacement. The portion of soil experi-
mented with in any case was allowed to subside gently into a glass vessel
which had been previously carefully filled with water just to the point of
overflow. The entrance of the mass of soil of course displaced a mass of
water corresponding to its bulk. The water was caught in a glass saucer in which
the recipient vessel stood, and on being measured gave the necessary datum
of the bulk of the material in the dry. state. As evolution of air bubbles and
disintegration advanced, the water in the recipient vessel gradually subsided, and
when the process had been completed, in place of standing at the overflow point,
was at some lower level. Water was now added from a finely graduated mea-
sure until the overflow point was again attained and the amount necessary to do
this taken as the index to the amount of air space originally present in the mass.
Numerous experiments were carried out in order to test how far this method of
determination was trustworthy. In these the amount of displacement caused
by the introduction of impermeable bodies of ascertained bulk, such as accurately
measured cubes of loaded wax, was determined, as well as the amount of addi-
tion of water necessary to regain the overflow point on the removal of the dis-
placing body, and it was found that with a little care the amount of error was
trifling, amounting only to from 1 to 1·5 c.c. when a cube of wax of 27 c.c. was
employed. Allowing for errors of like amount in the case of experiments with
masses of soil, the specimens were found, as a rule, to contain from 22 to 32 per
cent. of air space. A material of this character can certainly have no pretension
to be regarded as impermeable, and this was further proved by direct experiment.
A mass of the material was taken, and a block, measuring 14·6 c. in length,
13·o c. in breadth, and 9 . 5 c. in thickness, carefully sawed out of it. This was
easily done, as the mass had been kept in its original moist condition by means
of keeping it constantly covered with a wet cloth. A cylindrical hollow was
next excavated in one face of the block as nearly as possible 5 c. in diameter
and 3·9 c. deep, which was the capacity of a glass vessel required to complete
the observations; 75 c.c. of water were then introduced into the hollow and a
like amount into the vessel, and the latter and the mass of soil set side by side
on a table in the laboratory, the mouths of both vessel and hollow being covered
by pieces of fine wire gauze. After the lapse of a period of 40 minutes the cavity
in the soil was found to be empty and 50 c.c. of water were introduced. By the
close of another hour this also had disappeared and 50 c.c. more were added.
An hour later the cavity was almost empty and 50 c.c. were once more intro-