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INSTANTANEOUS PHOTO SHUTTER.

M. Audra, in the name of M. Braun, of Angouleme, has presented to the Photo Society of France a new instantaneous shutter.  The shutter is formed by a revolving metallic disk out of which a segment has been taken.  This disk is placed in the center 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 disk is fixed is a small wheel, to which is attached a piece of string, and when the disk is turned round for the exposure the string is wound round the wheel.  If the string be pulled, naturally the disk will revolve back to its former position so much the more quickly the more violently the string is pulled.  M. Braun has replaced the hand by a steel spring attached to the drum of the lens (Fig. 2) By shortening or lengthening the string, more or less rapid exposures may be obtained.

[Illustration:  AAA, lens; B, aperture of lens; C, metallic disk; D, wheel on the axis; E, cord or string; EEEE, knots in string; G, steel spring; H, catch; K, socket for catch.]

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SULPHUROUS ACID.—­EASY METHOD 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.