186
SCIOPTICON MANUAL.
water on top is run off by means of an india-rubber tube,
acting as a siphon, the weights replaced on the pan, and
the holder is ready for refilling.
“Where the oxy-hydrogen light is much used, holders are
almost indispensable, and in all cases effect a large saving of
time and material in the preparation and use of the gases.”
The above illustrated article has been préparée! for the
purpose of affording a practical guide in constructing similar
gas-holders, wherever the plan is approved. If the tubs
are made at any distance away, they can be brought in parts
to the place they are to occupy and there set up. The joints
of the galvanized iron holders are made gas-tight with solder.
Wherever illuminating gas is in use, the hydrogen gas
holder can be filled with it, as is done at the Franklin
Institute. If either the alcohol burner, or the concentric
jet with house gas direct from the main is used, only an
oxygen gas holder is required.
So far as we now know, it seems best to generate the gases
by repeated use of the apparatus described on pages 165
and 167. With two retorts, one accustomed to the operation
can roast a double oxygen charge in each alternately till
eight pounds are used, which about fills a gas holder of the
dimensions described.
The use of gas holders renders projecting apparatus much
more available in educational institutions, because the gases
can be made in large quantities at once, stored for an in¬
definite time without deterioration, and used whenever
occasion requires, without delay, with only such darkening
as can be readily effected, either at evening or in the daytime. •
OTHER GAS CONTRIVANCES.
A desire to render the lime-light apparatus more conven¬
ient, inexpensive, safe and portable, gives rise to various