TIME DEVELOPMENT 225 



prints before final washing ; chrome alum and citric or 

 hydrochloric acid are useful for this purpose. Washing 

 after fixation must be complete : an hour in running 

 water is sufficient if the water is continually removed 

 from the bottom of the dish. Otherwise let the plates 

 soak for five minutes in each of twelve changes of water. 



Hypo Eliminators. If it is desired to eliminate the 

 hypo as rapidly as possible, the plates are immersed in 

 several changes of a very dilute solution of potassium 

 permanganate until no change in the pate, pink-coloured 

 solution takes place ; a short rinse in water is then all 

 that is necessary. 



Rapid Drying of Negatives. To dry quickly, drain the 

 plate and then immerse for a few minutes in alcohol ; on 

 withdrawal the plate will rapidly dry if placed in a warm 

 place or in a current of air. Or harden in formalin and 

 dry near a fire. 



Hardening Negatives. Negatives may be hardened if 

 desired by immersion in formalin solution ; they are then 

 much less liable to damage. A varnish may also be 

 carefully poured over the negative as a further protection. 



Control by Exposure and Development. A satis- 

 factory printing density, revealing the details in both 

 light and dark parts of the negative, is as necessary 

 as proper contrast, and depends on exposure. If the 

 latter is reasonably correct, time development will 

 unfailingly produce good negatives, and most plates, 

 especially the slower kinds, allow of considerable lati- 

 tude on exposure. Correct exposure and development 

 have so far been understood to mean such as will give a 

 photomicrograph agreeing as closely as possible with the 

 original, or possibly having a somewhat steeper gradation, 

 as that is more often than not desirable in a photo- 

 micrograph. The degree of contrast shown between the 

 various parts of an object must, however, be materially 

 altered in many cases, either increased or decreased, to 



