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.
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 gasburner or over the top of the chimney of a kerosene lamp, so as to form 2 right angles, one end extending close to the bottom of the bottle 6 as shown.
Having fitted up the apparatus, about 2 oz. soda hyposulphite are placed in the bottle a, while the bottle b is about 3/4 filled with water - distilled or melted ice water is to be preferred; some sulphuric acid - about 2 oz. - 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 6, and about 2-3 oz. 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 6 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 agitate it thoroughly by turning the bottle upside down. As the sulphurous acid gas accumulated in the air space over the water is absorbed by the water, a partial vacuum is created, and when the stopper is eased an inrush of air may be noted. When, after passing fresh gas through the liquid for some minutes, no further inrush of air is noted on easing the stopper as before described, after agitating the bottle, it may be concluded that the water is thoroughly saturated with sulphurous acid, and is strong enough for immediate use. More gas can be generated by adding more dilute sulphuric acid to the hypo until the latter is decomposed; then it should be thrown aside, and a fresh charge put in the bottle.
On preparing the solution it is well to set the bottles on the outside ledge of the window, or in some other open situation where no inconvenience will result from the escape of the excess of sulphurous gas as it bubbles through the water.
The solution, of sulphurous acid, if preserved at all, ought to be kept in small bottles, completely filled and perfectly closed; but as it is very easy to saturate a considerable quantity of water with sulphurous acid gas in a short time, there is but little inducement to use a solution which may possibly have become weakened by keeping.
Care should be taken not to add too much dilute acid to the hypo at a time, else excessive effervescence will occur, and the solution will froth over the top of the bottle.
Braun, of Angouleme, has presented to the Photo Society of France a new instantaneous shutter. The shutter is formed by a revolving metallic disc out of which a segment has been taken. This disc is placed in the centre of the diaphragms, in order to obtain the greatest rapidity combined with the least possible distance to travel. On the axis to which this circular disc is fixed is a small wheel, to which is attached a piece of string, and when the disc is turned round for the exposure the string is wound round the wheel. If the string be pulled, naturally the disc will revolve back to its former position so much the more quickly the more violently the string is pulled. Braun has replaced the hand by a steel spring attached to the drum of the lens (Fig. 229). By shortening or lengthening the string, more or less rapid exposures may be obtained, a is the lens; 6, aperture of lens; c, metallic disc; d, wheel on the axis; e, cord or string; f, knots in string; g, steel spring; h, catch; i, socket for catch.
It is often annoying, when wishing to use different lenses for instantaneous exposures, to find that each lens or tube requires a different drop-shutter to be fitted to it. By the following sketches and description an arrangement may be made that will answer the purpose. It is very simple, easy to construct, and practical.
Two pieces of soft wood | in. in thickness, shaped as shown in c, Fig. 230, are attached to the back of the main board a, by means of 2 thumbscrews e, which are put in from the front, having square plates at this end, which must be fitted and sunk into the wood to present an even surface all over, against which the drop-board slides up and down (see Fig. 231, c e).