to the
instructor, puts all the materials back in the box, replaces the box in
its proper place in the closet and proceeds with the next experiment.
With this indicator there is no difficulty in managing fifty students or
more.

Comparatively little apparatus need be duplicated. Where apparatus is
fixed against a wall a number may be tacked upon the wall and a card
containing the information desired. The procedure is then the same as
with the boxes. The cards on the board being removable, other ones may
be inserted containing information in reference to other boxes having
the same number but containing different materials. There can be no
successful tampering with the board, for the record of experiments
performed is upon the blanks which the students turn in and also in the
individual note books which are written up and given to the instructor
for daily examination.

Lafayette College. J.W. MOORE.

* * * * *

NEW METHOD OF EXTINGUISHING FIRES

This is by George Dickson, of Toronto, Canada, and David Alanson Jones.

A mixture of water and liquefied carbon dioxide upon being discharged
through pipes at high pressure causes the rapid expansion of the gas and
converts the mixture into spray more or less frozen, and portions of the
liquid carbon dioxide are frozen, owing to its rapid expansion, and are
thus thrown upon the fire in a solid state, where said frozen carbon
dioxide in its further expansion not only acts to put out the fire, but
cools the surface upon which it falls, and thus tends to prevent
reignition.

A represents a receptacle sufficiently strong to stand a pressure of not
less than a thousand pounds to the square inch.

B B water receptacles.

[Illustration: Fig. 1]

In the drawings we have shown two receptacles B and only one receptacle
A; but we do not wish to confine ourselves to any particular number, nor
do we wish to confine ourselves to the horizontal position in which the
receptacles are shown.

C is a pipe leading from the receptacle A to a point at or near the
bottom of the receptacle B.

F is a pipe through which the mixture of water and liquefied gas from
the receptacle B is forced by the expansion of said liquefied gas, the
said pipe taking the mixture of water and liquefied gas from the bottom
of the receptacle.

[Illustration: Fig. 2]

To use the apparatus, open the stop cock D in the pipe C, leading to one
of the receptacles B, wher