and earths behave, from this point of view, in a very unequal manner.
For example, an earthen vessel from the Pillivayt establishment
supports some decimeters of water, while the porcelain of Boulanger,
at Choisy-le-Roi, allows of the passage of the gas only at pressures
greater than one atmosphere, which is much more than is necessary.
Wire gauze, canvas, and asbestos cloth resist a few centimeters of
water. It might be feared, however, that the gases, violently
projected against these partitions, would not pass, owing to the
velocity acquired. Upon this point experiment is very reassuring.
After filling with water a canvas bag fixed to the extremity of a
rubber tube, it is possible to produce in the interior a tumultuous
disengagement of gas without any bubbles passing through.

[Illustration: FIG. 2.--ARRANGEMENT FOR THE STUDY OF CAPILLARY
REACTION IN POROUS VESSELS.]

From an electrical point of view, partitions are of very unequal
quality. Various partitions having been placed between electrodes
spaced three centimeters apart, currents were obtained which indicated
that, with the best of porcelains, the rendering of the apparatus is
diminished by one-half. Asbestos cloth introduces but an insignificant
resistance.

To this inconvenience of porous vessels is added their fragility,
their high price, and the impossibility of obtaining them of the
dimensions that large apparatus would call for. The selection of
asbestos cloth is therefore clearly indicated; but, as it does not
entirely separate the gases, except at a pressure that does not exceed
a few centimeters of water, it was always necessary to bring back the
variation of the level to these narrow limits by a special