ETHOD OF PREPARATION FOR PHOTOGRAPHIC PURPOSES.

Within a short period sulphurous acid has become an important element in
the preparation of an excellent pyro developer for gelatine plates; and as
it is more or less unstable in its keeping qualities, some easy method of
preparing a small quantity which shall have a uniform strength is
desirable. A method recently described in the _Photographic News_ will
afford the amateur photographer a ready way of preparing a small quantity
of the acid.

[Illustration]

In the illustration given above, A and B are two bottles, both of which can
be closed tightly with corks. A hole is made in the cork in the bottle, A,
a little smaller than the glass tube which connects A and B. It is filed
out with a rat-tail file until it is large enough to admit the tube very
tightly. The tube may be bent easily, by being heated over a common
fish-tail gas burner or over the top of the chimney of a kerosene lamp, so
as to form two right angles, one end extending close to the bottom of the
bottle B as shown.

Having fitted up the apparatus, about two ounces of hyposulphite of soda
are placed in the bottle A, while the bottle B is about three-fourths
filled with water--distilled or melted ice water is to be preferred; some
sulphuric acid--about two ounces--is now diluted with about twice its bulk
of water, by first putting the water into a dish and pouring in the acid in
a steady stream, stirring meanwhile. It is well to set the dish in a sink,
to avoid any damage which might occur through the breaking of the dish by
the heat produced; when cool, the solution is ready for use and may be kept
in a bottle.

The cork which serves to adapt the bent tube to the bottle A is now just
removed for an instant, the other end remaining in the water in bottle B,
and about two or three ounces of the dilute acid are poured in upon the
hyposulphite, after which the cork is immediately replaced.

Sulphurous acid is now evolved by the action of the acid on the hypo, and
as the gas is generated it is led as a series of bubbles through the water
in the bottle B as shown. The air space above the water in bottle B soon
becomes filled by displacement with sulphurous acid gas, which is a little
over twice as heavy as air; so in order to expedite the complete saturation
of the water, it is convenient to remove the bottle A with its tube from
bottle B, and after having closed the latter by its cork or stopper, to
agit