Popular Science Monthly 



473 



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. 



