148 HOW WE USE LIGHT 



Tray 1. Developer Tray 2. Cold water Tray 3. Hypo 



You will need two squares of glass and two clothespins. Lay the 

 negative dull side up on one piece of glass. Upon this lay a sheet 

 of sensitized paper, smooth or coated side down upon the negative. 

 Cover with the other piece of glass. Hold the two pieces of glass 

 tightly together with the clothespins. Light a 100-watt lamp 

 and hold the glass film side towards the light and 3 feet from 

 it for 10 to 15 seconds. Extinguish the lamp. Remove the paper. 

 Immerse the paper in the developer. If it comes up too black 

 within 30 seconds, it had too much light; if it does not come up 

 dark enough in 30 seconds, it needs longer exposure. A little 

 experience will help you judge the time of exposure. After the 

 picture has developed to the point you wish it, rinse quickly in 

 water and place in the hypo. Move it around occasionally. 

 After, 15 minutes remove from the hypo and wash an hour in run- 

 ning cold water. Lay face down on a piece of cheesecloth stretched 

 over a frame to dry. 



With the directions just given you should soon become an expert 

 amateur photographer. Why not organize a camera club if your 

 school does not have one? You will be surprised how much this 

 photography will help you in your science work, besides giving you 

 and your friends a lot of fun. 



SELF-TESTING EXERCISE 



Select from the following list those words which best fill the blank spaces 

 in the sentences below and arrange the words in proper numerical order 

 A word may be used more than once. 



chemical positive fixed camera 



visible negative focus image 



diaphragm neutral opening black 



shutter hypo closed light 



developer acid dark lens 



results recorded red sensitive 



There are chemicals which are (1) to light. When these 



chemicals are held on the surface of a film or glass plate in a little 



gelatin and an (2) is thrown upon the film, a latent image is 



(3) When the film is developed, a picture with (4) and 



(5) parts reversed from what they were in the original view 



(6) After development, the film is (7) or made perma- 

 nent in the (8) bath. The resulting film is called a (9) ; 



from this a (10) print is made. The (11) excludes (12) 



except when the (13) is open. The size of (14) to control 



the amount of light is regulated by the (15) 



