Messrs. A. Boake & Co., of Stratford, London, England, have devised
a convenient apparatus for charging water with sulphurous acid which
is useful in the making of photographic developers. The following
description has been furnished by the firm:
The figure shows one of the siphons connected with a very convenient
form of apparatus for preparing a solution of sulphurous acid in water,
or of sulphites, as may be required.
The siphons are easy to manage, the flow of gaseous acid being
regulated with the greatest nicety by simply turning the milled head
shown in the engraving, the liquid acid being gradually converted
into gas as the pressure is relieved. There is, moreover, no danger
attending the use of this simple apparatus; sulphurous acid exerting at
ordinary temperatures a pressure of about 30 pounds on the square inch,
while each siphon is carefully tested under a pressure of 200 pounds on
the square inch before being sent out.
[Illustration: APPARATUS FOR SATURATING WATER WITH SULPHUROUS ACID.]
In preparing a solution, say, of sulphurous acid in water, the ground
stopper carrying the tubes for passing the gas should be removed from
the glass jar in immediate connection with the siphon, and two-thirds
filled with distilled water; the stopper is then to be replaced, and
the second glass jar half filled with caustic soda solution. The soda
solution is used to absorb any sulphurous acid not dissolved by the
distilled water, and so prevent the escape of this irritating gas into
the air. Solution of sulphite of soda, and also of bisulphite, can be
prepared in a similar way, substituting only pure caustic soda solution
for the distilled water employed in the case of preparing the solution
of sulphurous acid; but we must rather devise the purchase of the pure
solid forms of these salts specially prepared, and put up by us in
one-pound stoppered bottles for use in photography; these preparations
can be obtained either direct from the manufacturers or from any
wholesale chemical firm. The siphons may be obtained either separately
or already connected with the absorbing jars. It may be mentioned
that these siphons contain about two and a half pounds of liquefied
sulphurous acid, and can be refilled when required; but those requiring
larger quantities can obtain the acid compound in copper drums.
_The Photographic News_ says: It will be noticed that Messrs. Boake
say there is no danger attending the use of the siphons, as the glass
vessels are tested at a much greater pressure than that ordinarily
exerted by the condensed sulphurous acid; but our readers must remember
that a blow against a hard substance may cause the glass to become
fractured, and that under these circumstances the bursting of a siphon
might cause a serious injury. Still, if proper care is exercised, there
need be no accident; but we would suggest that the condensed acid
should always be kept in the coolest place available, as the pressure
it exerts becomes much greater when the temperature is raised.
The above caution is necessary, as a bare statement that there is no
danger may cause persons to handle the siphons without reasonable care.
The risk is precisely analogous to that attending the use and handling
of bottles containing ordinary aerated waters, only the irritating
nature of the sulphurous acid must be taken into account. Instances
have occurred in which serious injury has resulted from the bursting of
a bottle of soda water; but few, if any, are deterred from the use of
soda water or lemonade on this account.