92 PRACTICAL PHOTO-MICROGRAPHY. 



To make the Normal Pyro-Carbonate Developer No. 3 : 



Stock Pyro Solution 30 minims 



Sodic and Potassic Carbonate Solution 120 minims 



(=2 drams). 

 Bromide None. 



Make up with water to one ounce. (No account is taken of 

 the chemicals used merely to preserve the pyro.) 



Normal Developer C. Ferrous Oxalate. 

 Take of the saturated solution of 



Potasssic oxalate 4 parts 



Ferrous sulphate 1 part 



Be careful to pour the Ferrous Sulphate Solution into the Pot- 

 assic Oxalate and not vice versa. 



(Note. The writer does not recommend the Ferrous Oxalate 

 Developer for ordinary photo-micrographic work. This is not 

 denying that it is excellent in some hands and for some kinds of 

 subject. The reader is advised to try the effect for himself ; 

 as a general developer it has some recommendations.) 



The plate after exposure is, in non-actinic light, (see pp. 55 

 and 56,) placed film upwards in a black developing tray, and 

 the developing solution is deftly swept over it ; the developer 

 must not be poured upon one spot but " swished " with a side 

 motion all over the plate, so that as far as possible the plate 

 may be all wetted at once. Some workers prefer to soak the 

 plate, till the gelatine is all wet, in plain water before applying 

 the developer ; this procedure does no harm if air bubbles that 

 may form are removed with a clean brush or finger. In all 

 cases the inexpert must be prepared for air bubbles and remove 

 them if they occur. 



In a certain number of seconds the image ought to begin to 

 appear. The first thing that regulates the time required for 

 this first appearance is the quality or treatment of the gelatine 

 used in the emulsion ; this factor need not be taken into much 

 account. But the important matter is to observe the quality 

 of the image at the time of its first appearance, and still more 

 is it important to note most carefully the pace at which the 

 details follow each other. As a rule an overexposed plate 

 will show some of the details before an underexposed 



