74 ELEMENTARY PHOTO-MICROGRAPHY. 



Mercury bichloride i oz. at 4<1. oz. 

 Nitric acid . . . . 2 ozs. ,, id. oz. 

 Oxalic acid . . . . 2 ozs. 6d. Ib. 

 Pyrogallic acid i oz. ,, nd. oz. 



Potassium oxalate 



(neutral) . . . . 2 ozs. id. oz. 



Potassium bromide i oz. ,, 2d. oz. 



,, ferricyanide i oz. ,, 3d. oz. 



carbonate . . 4 ozs. ,, 6d. Ib. 



,, metabisulphite 2 ozs. ,, 3d. oz. 



Sodium carbonate, 



washing soda will do i Ib. 4d. Ib. 

 Sodium hyposulphite i Ib. ,, 2d. Ib. 

 sulphite . . i Ib. ,, 6d. Ib. 

 hydrate . . i oz. ,, 2d. oz. 

 Some brands of plates, particularly in warm 

 weather, have a tendency to frill and pucker at the 

 edges, which, if not stopped in time, will result 

 in the film separating from the plate. Soft gelatine 

 or prolonged development or washing may cause it. 

 The best way, of course, is to reject any kind 

 of plate that constantly gives this trouble, but it 

 may be prevented by first rubbing the edges of 

 the plate with a wax candle before the developer 

 is poured on. This will keep the liquid from 

 penetrating between the film and the glass. 



The following kinds of plates will be found 

 satisfactory : 



For low powers (slow), Imperial " Ordinary." 



