74 THE MICROSCOPE. [May, 



ON THE DARK ROOM AND ITS FITTINGS. 

 By F. W. Mills, 



HUUDERSFIELD, ENGLAND, 



Author of An Introduction to the Study of the Diatomaceae 

 [From " Photography applied to the Microscope," pp. 38-40.] 



Although development may be carried out in the bed-room at 

 night, or in a cupboard, under stairs, or in the wine-cellar, and 

 such places, these are obviously inconvenient and quite unsuitable 

 to any systematic scientific work being done. A room should be 

 fitted up especially for the purpose, and the most convenient is to 

 convert at will the room in which the apparatus stands into the 

 dark room — in other words, make the dark room of such size 

 that the apparatus can be kept in it. 



The room should be well ventilated, this being a very impor- 

 tant item, as when artificial light is used the air gets foul, espe- 

 cially when ammonia is being used. It should also have a good 

 water supply, and a sink, over which development can be done. 



Illumination. — Gas is the most convenient when it can be 

 obtained, one jet being provided with a by-pass, the pilot flame 

 of which burns behind a collar, thus showing no light when 

 turned down. This does to illuminate the room on ordinary oc- 

 casions, and for exposing bromide prints, etc. Another jet is 

 placed inside a lantern glazed with ruby glass ; the screen-hold- 

 ing glass being removable and replacaeble with one of yellow, for 

 use during printing or the development of plates other than 

 orthochromatic. If gas is not available, paraffin lamp or candles 

 must be made to suffice ; but these are not so generally useful as 

 the gas, the heat from it being easily used as a means of vetilating 

 the room. The flue from the lantern should be led out of the 

 room. A set of half a dozen dishes of porcelain will be found 

 sufficient. Two or three shelves ought to be fitted up to hold 

 the bottles of reagents. The reagents required and the strengths 

 convenient for photographic use are as follows : 



Pyrogallic acid, 10 percent. ; bromide potassium, 10 per cent. ; 

 ammonia, 10 per cent. ; potass, ferrocyanide, 10 per cent. ; 

 quinol. crystalline: potass, hydrate, in sticks; potass, meta- 

 bisulphite ; sulphite of soda, crystalline ; citric acid, crystalline ; 

 ferrous sulphate, sat. sol. ; neut. oxalate potass., sat. sol. ; mer- 

 cury perchloride. sat. sol. ; thiosulphate soda (hypo), sat. sol. ; 

 powdered alum, sat. sol. 



The first three substances on the list are most conveniently 

 kept in dropping-bottles of about two to four ounce capacity, 

 the alum and hypo being kept in stone jars. Two measuring 

 glasses should be obtained, one of ten-ounce capacity and another 

 of one drachm. A pair of small balances with glass pans are 

 also required. The fixing bath should have a wooden lid to pre- 

 vent dust falling in ; it also prevents evaporation when not in use. 



