No. 1. Sulphite soda crystals, 400 grs.
Dissolve and filter, and add water to make 6 oz.
Hydrochinon, - - 120 grs.
No. 2. Carbonate potassium, 240 grs. Water to make 6 oz.
For use take one ounce each of Nos. 1 and 2, and add two ounces of water; the quantity of water added can be increased or decreased as may seem best. -With this developer, the image begins to make its appearance in about thirty seconds, after which it proceeds rapidly. The development should be carried on until the picture comes out clear and distinct. That part of the plate outside of the image should be carefully watched during the development, as the plate should be removed from the devel oper before these parts lose their white color. lf washed and transferred to the fixer, while this part of the plate is still white, after fixing the white portion becomes clear glass, as it should be in a perfect lantern slide. If, however, the plate is left in the developer until the white of these portions has turned slightly gray, or a little darker in shade, those parts after fixing will be found somewhat clouded, and the image on the glass in conse quence will be too intense.
The fixer, for lantern slide plates developed with hydrochinon, should be a little weaker than is used in ordinary fixing baths. We have found a good proportion for this, is one ounce hypo. dis
solved in ten ounces of water. A weaker solution of hypo. will fix lantern slides; we have used it as weak as one ounce hypo. to twenty-four ounces of water. The exact proportions do not appear to be very important, but we think it should always be much weaker than for ordinary plates. After fixing, the plates should wash in running water for half an hour, then carefully swab under the tap, with a wad of fine cotton wool and place in the rack to dry.
Lantern slides, for use in the lantern, require to be mounted. The usual way is to cover the slide with a plate of thin, clear g] ass , placing between the glasses a mask of thin black paper, cut out the proper shape inside to show the picture, and then the edges of the two plates are bound with a strip of black needle-paper: it be ing understood, of course, that the film side of the slide comes between the two glasses. Another way, which we have found to be practically as good as the above, is to paint the slide with Gihnn's Opaque, applying this to the film, covering all of the plate except the picture, and leaving if desired, a slight margin of clear glass around the image. After this is thoroughly dried, it can be covered with thin glass and the edges bound as above.