SCIOPTICON MANUAL. 89 ^ 



The crystallization of many other substances, such as 

 bichromate of potash, alum, &c., and the precipitation 

 of iodides of silver, mercury, and other salts, all form 

 beautiful objects on the screen. 



THE DEVELOPMENT OP A PHOTOGRAPH ON THE SCREEN. 

 For this we require a tank with one of its faces of 

 yellow glass, which side should be next the condenser. 

 Place a small statuette in the rays of the lantern, and 

 having prepared a small plate with collodion and sensi- 

 tized it, expose in the camera for about a minute; then, 

 having filled the trough with developing solution, place 

 in it the slide, and as tbe development proceeds the 

 image will gradually appear on the screen. A trans- 

 parency might then be made from this, and, after drying, 

 shown on the screen, thus illustrating the formation of a 

 photographic lantern slide. 



CHANGING COLORS. A glass coated with a mixture 

 of gelatine and chloride of cobalt, when placed in front 

 of a slide, will give a rosy effect to the picture, which, 

 however, from the effect of the warmth of the lantern, 

 will gradually change to purple and then to blue. On 

 becoming damp again it will resume its red color, and 

 can be used over and over again. 



COMPLEMENTARY COLORS. A number of beautiful ef- 

 fects, showing complementary colors, may be obtained 

 with the Sciopticon. If we insert a piece of green glass, 

 having any design cut out of black paper and pasted on 

 it, we shall see on the screen a black design on a green 

 ground ; but by bringing another light into the room or 

 turning up the gas, the black design will at once appear 

 to the eye as a brilliant pink. 



By making apertures in a card slide, as circles, squares, 



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