33 Common Science 



off all the white unchanged part of the silver salt, in 

 another kind of chemical called the fixing bath. This 

 is called " fixing " the negative. 



The only trouble with the picture now is that wherever 

 there should be a patch of white, there is a patch of dark 

 silver particles ; and wherever there should be a dark 

 place, there is just the clear glass or celluloid, with all 

 the silver salt dissolved off. This kind of picture is 

 called a negative; everything is just the opposite shade 

 from what it should be. A white man dressed in a black 

 suit looks like a negro dressed in a white suit. 



How a photographic print is made. The negative not 

 only has the lights and shadows reversed, but it is on 

 celluloid or glass, and except for moving pictures and 

 stereopticons, we usually want the picture on paper. So 

 a print is made of the negative. The next experiment 

 will show you how this is done. 



Experiment 101. In a dark room or closet, take a sheet 

 of blueprint paper from the package, afterwards closing 

 the package carefully so that no light can get to the papers 

 inside. Hold the piece of blueprint paper under your waist 

 or coat, to keep it dark when you go into the light. Now 

 lay it, greenish side downward, on a negative. Hold the 

 two together, or place them in a printing frame, and turn 

 them over so that the light will shine through the negative 

 tpon the greenish side of the blueprint paper. Be sure 

 that the paper is held firmly against the negative and not 

 moved around. Let the sun shine through the negative 

 upon the paper for i or 2 minutes according to the bright- 

 ness of the sun, or let the gray light of the sky, if it is cloudy, 

 shine on it for 5 or 10 minutes. Now quickly put the blue- 

 print paper (not the negative) into a basin of water, face 



