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Page:Popular Science Monthly Volume 90.djvu/489

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Popular Science Monthly

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��bulk of borax (sodium tetraborate, Na, B4 O7). This mixture is placed in a crucible, fused thoroughly, cooled very gradually, and, when cold, dissolved out of the crucible with water. Great care should be taken to obtain the salt in as perfect a crystalline form as pos- sible, for its fluorescence appears to be very much dependent upon this.

A piece of good grade, smooth, light- weight cardboard, 12 in. long by 9 in. wide, is covered with a layer of glue, made by dissolving gum arable in water. Care should be taken to have the glue in a very even layer. The calcium tungstate is sifted onto this from a sieve in as even a layer as possible, not too thickly, yet covering all parts well. This is called the fluorescent screen,

A light, square frame, as shown in Fig. I, of the same size, 9 in. by 12 in., should be made from soft wood about ^2 in. wide by ^ in. thick. The fluores- cent screen should be tacked or glued to the one side of this frame, with the coated side next to the wood, as shown.

Another frame, as shown in Fig. 2, shaped like the frustum of a pyramid the lower base of which is 9 in. by 12 in. (the same size as the frame supporting the fluorescent screen), the upper base 3 in, by 6 in., and the altitude 12 in., is made from wood }4 in. wide by ^ in. thick. The sides of the frame should be covered with black velvet or other dark colored cloth, so that it will entirely cut ofi^ the outside light. This covering should extend about 2 in. or 3 in, over the small end of the frame, so as to form a curtain about the face when looking into the frame. This frame serves to cut off the outside light when looking at the fluorescerkt screen, and may be pro- vided with a handle to facilitate han- dling. It should be provided with flat springs or hooks, as shown in Fig. 3, on the larger end, so as to hold the smaller frame supporting the screen in place. The coated side of the screen is placed inside.

In case it is desired to experiment further, a number of substances will be found which fluoresce under the action of the X-rays, Most of the phosphides of the alkaline earths and the salts of rnanganese, cadmium, strontium and lithium, are active. Liquids are gener- ally inactive, and it is noted that while

��quinine sulphate give a bluish glow, a solution of this sulphate is only very slightly excited.

Thomas A. Edison experimented with some 1,800 phosphorescent and fluores- cent substances, some of which are here given: Ammonium platinocyanide, am- monium salicylate, barium sulphate, boracic acid, cadmic iodide, calcium fluoride, calcium platinocyanide, cal- cium sulphate, calcium sulphide, corun- dum, curcumin, caturine, glass, mica, mercurous chloride, obsidian, penta- decyltolyl-ketone, potassium acetate, potassium iodide, potassium bromide, potassium platinocyanide, quinine salts, rock salt, strontium platinocyanide, strontium sulphate, strontium sulphide, strontium tungstate, uranium fluoride, and uranium sulphate. A few of these substances are active under the rays of a Geissler tube.

The substances most used on com- mercial fluoroscopes are calcium tung- state and barium platinocyanide. Ura- nium ammonia-fluoride gives good re- sults also. Some experimenters claim better results with barium platinocy- anide than with calcium tungstate, but this depends somewhat upon the crys- talline condition of the salts. How- ever, the high cost of barium platino- cyanide more than offsets this possible advantage with the average amateur experimenter. In mounting barium platinocyanide, uranium ammonio-flu- oride or substances soluble in water on the screen, a solution of celluloid in amyl acetate should be used, so as not to injure the crystalline form of the active material. — Charles E. Miller.

��Cutting Holes in Plaster for Switch-Boxes

CUTTING a hole in plaster for the purpose of locating an electric switch-box is a difficult and untidy task and especially where this is to be done on a completed house. The job can be accomplished quickly and neatly if a box is used for the cutting. A box of the proper size, set with its edges to the plaster and driven on the bottom, will cut a neat square or rectangular hole without much eff"ort. Begin by driving on one corner and follow along one side and then around the box. The edge will cut the plaster through and the particles loosened will fall into the box.

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