510 EXPERIMENTAL PHARMACOLOGY 



repeatedly. It will by degrees become alkaline by the grad- 

 ual addition of developer adhering to the prints. It should 

 be discarded entirely when it becomes frothy, and a fresh 

 bath prepared. 



In fixing, the prints should be placed in the bath face 

 downward. They should be kept well separated and in mo- 

 tion for a few seconds until the solution is evenly distributed 

 over them. From 15 to 20 minutes should be a sufficient 

 length of time to insure proper fixing. The prints should 

 then be thoroughly washed in water and dried. This may 

 be done by spreading them out face upward on a large sheet 

 of paper in a quiet place where dust, etc., cannot fall on 

 them. 



After the prints are thoroughly dried they may be 

 trimmed to the desired size and mounted by applying mount- 

 ing paste to the back of the print with a brush, after which 

 the print is placed in position on a card mount and rolled 

 down smoothly with a squeegee roller. 



Blue Prints. One of the simplest of all photographic 

 processes is the making of blue prints, which require only 

 to be printed and then washed thoroughly in water. Blue 

 print paper is sensitized by the application to the paper of 

 a solution of ferric ammoniocitrate and ferricyanide of 

 potassium. The process may be carried out as follows : 



Solution A 



Ferric ammonium citrate 1% oz. 



Water 8 oz. 



Solution B 



Potassium ferricyanide 1% oz. 



Water 8 oz. 



To make the sensitizing bath, take equal parts of each 

 solution in a tray or flat dish a little larger than the paper 

 you wish to sensitize. Float the paper on this bath for two 

 or three minutes, being very careful to avoid any air bubbles 

 that may prevent the solution from reaching the paper. 

 Hang up the paper to dry. This whole process of sensitizing 



