PHOTOGRAPHIC PROCESSES. 77 



When required, it is filtered, and a few crystals 

 added until it regains its proper strength. An 

 argentometer is very useful for ascertaining the 

 amount of silver in solution. 



We now proceed to the manipulations necessai-y 

 for the preparation of the sensitive surface, before 

 exposure in the camera. 



A plate being removed from the dish, we clean it 

 as described, taking care to avoid touching the sur- 

 face with the fingers, then either grasping the right 

 hand upper corner with the thumb and finger of the 

 right hand, or supporting the plate with a plate 

 holder, we pour the collodion on it, forming a pool 

 at the same corner, then flowing it to the opposite, 

 then to the left hand bottom corner, and finally after 

 completely covering the plate, off at the right hand 

 bottom corner. It being now held in a nearly ver- 

 tical position over the mouth of the collodion bottle, 

 a gentle rocking motion is imparted to it to prevent 

 its setting in ridges. When no longer tacky, which 

 is known by barely touching one of the bottom cor- 

 ners with the finger, it is placed in the nitrate of silver 

 bath, by a steady downward motion of the dipper, 

 moved about for a few seconds, and finally left for a 

 period varying from one to five seconds, according 

 to the temperature and condition of the solutions. 



It is then removed, and (after all superfluous fluid 

 has been drained off) placed in the dark slide, ready 

 for exposure in the camera. This should take place 

 as soon as possible, as all delay tends to injure the 

 plate. 



