THE BOOK OF THE LANTERN. 119 



have been so added, set the basin aside for an hour or two, 

 then stir its contents with a glass rod, and test with blue 

 litmus paper, adding crystals of acid until the paper turns 

 slightly red. Add to the liquid 30 grains of potassic 

 bromide, allow to settle, and bottle off for use when clear. 



But those who wish to avoid the trouble of making 

 their own potassic oxalate can buy the crystals at any 

 photographic dealer's, in which case its solution should be 

 made with boiling water, and well stirred until all crystals 

 have disappeared. One pound of oxalate will require 

 just a quart of water to make a saturated solution. If 

 more water be used, the solution will not be a saturated 

 one, and will, when mixed with the iron, throw down a 

 muddy red precipitate, and be useless for developing pur- 

 poses. The iron must be added to the potash, and not vice 

 versa, or the same effect will be produced. I have found 

 that with this developer it is always advisable to soak the 

 exposed plate in water as a preliminary step. The gelatine 

 surface then takes more kindly to the solution, and greater 

 density is attained. 



The development should be carried on until the picture 

 looks overdone, for it must be remembered that it has to 

 be ultimately exhibited by transmitted light, and we view 

 it in the developing dish by reflected light only, but hold- 

 ing it up to the red light and looking through it we can 

 judge well when the developing action ought to be stopped. 

 Now follows a rapid rinse under the tap, a few minutes' 

 immersion in alum and water, and fixing in fresh hypo. 

 If ordinary household water has been used, the film will 

 show a milky veil. This is quickly removed by a ten per 



