PRACTICAL PHOTOMICROGRAPHY. 133 



not only a salt, the nature of which they do not state, but the 

 platinum salt which is not in this case present in the paper at 

 first. Full instructions are given with the paper, and these 

 directions are so complete and accurate that failure is unlikely 

 if the negatives be suitable for the process. The printing is 

 performed in a frame and by daylight, as before, but after the 

 printing, the paper is caused to take up a certain amount of 

 moisture, which it readily does on exposure in a damp apart- 

 ment or box, the damping and the printing being kept in 

 certain relations to each other. Then follows development on 

 the u cold bath," which gives the name to this process. Devel- 

 opment is less rapid than with the hot bath ; in fact, the print 

 having been floated for a moment or two on the cold develop- 

 ing solution is usually thereafter held in the hands till 

 development is seen to be complete. The clearing process in 

 acid and the washing are as in the hot bath process. 



