The Optical Magic Lantern Journal (October 1890)

The Optical Magic Lantern Journal and Photographic Hularger. ae eRe) done by yellow light. When quite dry redissolve the pellicle in 150z. of a mixture of equal parts of absolute alcohol and sulphuric cther, and after | being well shaken up it is filtered and ready for use. After trial, if any fog appears on the image the addition of one or two drops of an alcoholic solution of iodine will prevent its recurrence. After being coated the plates may be quickly | dried by heat. : The developer recommended is :— F 1 rors Acid ... 06 grains * {Absolute Alcohol a T ounce ; Saturate Sol. Ammonium Carbonate — 4 ounces | Potassium bromide 1 drachm * ) Soda acetate 2 drachms Water ... re ae ae 12 ounces For use, mix in theproportion of five to ten drops of No. 1 to three drachms of No. 2, but the precise quantity of No. 2 used must depend upon the intensity of the negative. Before commencing to develop, pour a little methylatcd alcohol on the plate, and after ten or fiftecu seconds wash it off with water. 0: Hand Cameras for Obtaining Slides for the Lantern. No. 6.—“OPTIMUS” MAGAZINE. THIS camera, for which a patent was granted to Mr. Alfred Smith on July 20 of last year, is manufactured by Messrs. Perken, Son, and Rayment, who are the sole agents. The external measurements of this camera are S3in. by sin. by Sin., and it is strongly made in mahogany, with brass bindings, which should enable it to withstand any climate. The internal arrangement and mechanism may be seen from the cut. It will be observed that twelve plates can be carried and exposed without the necessity for opening the camera, which, after being “charged " in the dark room, is locked. The plates (12), placed in sheaths, are inserted in a series of grooves which run from the top to the bottom of the camera. These grooves are divided about mid-way by a box through which the rays of light pass from the lens to the exposing plane, and it is upon the top of this box that the stock of plates rest. The series of grooves move from the front to the back of the camera, and, as each groove travels sufficiently to clear the top of the partition upon which the plates rest, a plate descends to the exposing plane. This, in In order to effect a change of plate a milled head is turned. This, in the outfit sent to us, is situated at the end of the camera, oppositeto the lens, and communicates with a screw, which draws the series of grooves backwards as desired. Inthe camera shown in the cul this motion is imparted by a rack and pinion movement, the knob being situated low down at the side of the camera. But, as regards smoothness of motion and general handiness, we think the screw and knob atthe rear is the better method. As the grooves must necessarily be sufficiently far apart to allow even the thickest plates to pass easily, an arrangement is provided whereby each plate, notwithstanding variation in thickness, is brought to the | exact focus. Thisis done by a slight turn ofthe milled i head in the opposite direction after the plate has descended. If desired, the plates may be used withwithout sheaths, but in this case non-actinic paper must be stuck on the back of the plate. This, however, is sold ready gummed and cut to size. The lens, which is an “ Optimus ” of rapid rectilinear type, needs no comment, thename of the makers being sufficient recommendation. The exposing shutter is actuated by two pins at the side, and always remains “set.” The front of the camera is hinged to enable any desired stop to be inserted in the lens, and as this front carries the exposure shulter, a safety slide is placed immediately behind the lens. Two finders are also provided. As part of the back of camera has a sliding opening, a ground glass may be insertcd in the end groove, focussed on any near object, and a sensitive plate substituted for the ground glass. If for a prolonged exposure the shutter behind the lens may then be found most convenient, the front of the camera being left open. The most minute wants have been fully anticipated in the working out of the details of this camera. Photomicrographic Lantern Transparencies for Histological Teaching and Research. By M. HEvbiey. (Continued from page 30.) Lrvatum.—On p. 30 of last issue, fifth line from botfom of first column, read ‘‘ The sodium-theosulphate” instead of “the sodium. This sulphate.” “ ACCORDING to the length of time the plate is immersed the tone passes from a brown to a red. This method is very useful for some shades, giving a slightly opaque red. The process would appear to be that silver and potassium ferro-cyanides are formed, and the latter is subsequently decomposed, forming uranium ferro-cyanide, the silver salt remaining and giving rise to the opacity mentioned. At this stage the colour can be very much heightened, and rendered more transparent by placing the slide in sodium theosulphate, which dissolves the silver salt, and leaves an image formed solely of uranium ferro-cyanide. The shade thus obtained strongly resembles that of insects ordinarily prepared for microscopic examination, and those who have occasion to photograph these will find turn, recedes, and another takes its place. this method of transparency staining of considerable