110 ELEMENTARY PHOTO -MICROGRAPHY. 



a dirty deposit will be found at the bottom of the 

 trough. The liquid should be examined in full 

 light after all the holders are removed, and if it is 

 muddy at the bottom it should be thrown away 

 and fresh made. With this precaution the holders 

 and fixing solution may be left in the vessel after 

 use, so that they are always ready ; but hypo 

 is very cheap, and it is false economy to use the 

 same solution too often. 



Negatives improperly exposed or developed may 

 appear quite black and opaque when examined 

 only on the surface of the plate before fixing, yet 

 after fixing will be quite thin. 



Opacity should be judged by holding the nega- 

 tive up to the light. When washed and dried the 

 negative may be varnished if it is likely that it will 

 be much used, otherwise varnishing is not necessary. 



A good method of preserving negatives, and at 

 the same time of providing a ready method of 

 selection, is to put each one in an envelope with a 

 consecutive number outside. These may be stored 

 in disused dry plate boxes, outside of which should 

 be boldly printed the numbers of the slides therein. 

 For example, the first box will be i to 12, the 

 second 13 to 24, and so on. 



A book index will facilitate reference. Each 

 envelope may have also written upon it the full 

 particulars of exposure, though this may be ob- 



