772 



Popular Science Mo)ithly 



as an example; even oil, gas or a 

 match, held a foot from the frame, may 

 be used instead. The exposure would 

 then have to be determined by experi- 



. , y . ,,- ment, of course. 



'I "* I " 1^ r When the ex- 

 posure has been 

 made, the plate is 

 taken from the 

 frame and placed 

 Detail of in a tra\- contain- 

 support i,^g ^\^^ developer. 



The writer favors the popular M.Q., 

 sold in tubes and merely dissolved in 

 water. In about thirty seconds the de- 

 tails of the image will come up under the 

 action of the developer, and in possibly a 

 minute and a half, the development will 

 be complete. This is determined when 

 the entire image is plainly visible, though 

 hazy, on the reverse side of the plate. 

 Another test is to look for the details 

 in the highlights; when they are visible, 

 the plate is developed. The tray should 

 be rocked continually- throughout de- 

 velopment. 



The next step is to rinse the plate in 

 clear water and immerse it quickly in a 

 bath of hypo, which may be purchased in 



Safe base sV-' dross feefi'/i/gh-' 



3 Coils each containing 5 ft. of No. 22 re- 

 sistance wire. Wind 48 turns on Jin. rod 



Fig. If). Details of a small rheostat. In the 

 slate base nine brass pillars are mounted 



small packages readx- lo be dissolved in 

 water. When nt) more of the milky white- 

 ness can be <kle(ted on th<' ])late when 



//ofo/fcircu// ^'6- 17- viewed from the back. 



Diagram j^ g,^,,^,,^, |,^. [^.fj -^^ 



of thewir- , , 



from ^he hypo ten mmutes 



nearby longer, and then taken 



lamp-soc- out and washed under 



mg 



ket to the 

 rheostat 



fi/)easM, 



^eoafive 



running water for a 

 half hour. All of these 

 operations must, of 

 course, be performed 

 under the orange light. 

 The trick which is 

 perhaps the most im- 

 portant of all in the 

 making of a slide has 

 been left until the 

 last, where it will be 

 noted and remem- 

 bered. When the slide 

 plate is placed in the printing frame 

 ready for the exposure, a piece of black 

 paper should be placed over the back of 

 it before the cover of the frame is 

 clamped in place. This is to prevent a 

 disagreeable foggy flatness from spread- 

 ing all over the slide-plate, which will 

 happen if the reflected light from the 

 white backing of the printing frame 

 strikes through the glass. The author 

 has made hundreds of slides without the 

 slightest difficulty since he discovered 

 this little stunt. Prior to that time 

 he had foimd it impossible to secure a 

 brilliant slide from any but the snappiest 

 of negatives. 



A concluding word of caution is to 

 avoid touching the emulsion side of the 

 slide plate at any stage of the operations. 

 The emulsion, when wet, is soft and 

 easily injured and, when dry, the oil 

 from the fingers will leave a mark. 

 While the slide is drying, it should be 

 |)rolcrled from dust and dirt, preferably 

 by [)lacing it in a clean, dry i)lace. \ 

 mat or mask and a cover-glass boimd on 

 the slide with passe partout binding 

 complete the work. 



A^ 



A Substitute Blow Torch 

 for Soldering Joints 

 N easily impro\iscil blow torch lor 

 soldering joints in wires is ni.ule as 

 follows: Take a \'i-\n. tube, and till it 

 with cotton waste or with old cloth satu- 

 rated with gasoline. Cut a notch in a 

 piece of ]/\-\n. loom, insert it into one end 

 of the tube, and light the waste. Blowing 

 through the loom makes a hot flame. 



