1200 Journal of Applied Microscopy 



negatives with much detail ; while others, such as hydrochinone, afford density. 

 Contrast being desirable, it is well to choose a developer containing a reducing 

 agent that will best produce it. In doing this, however, it is often advantageous 

 to combine reducing agents with opposing characters in order to secure a nega- 

 tive well balanced in detail and density. 



If asked to recommend developers of this character I should suggest three 

 that do the work well and, at the same time, differ otherwise so as to make them 

 applicable under different conditions. 



The simplest of these is known by the trade name " Rodinal." To prepare 

 it for use, it is only necessary to dilute it with twenty parts of water. This, with 

 its good keeping qualities, makes it convenient for those who have only an occa- 

 sional negative to develop. Persons unfamiliar with its use will perhaps be 

 startled at the suddeness with which the image flashes into view under its action, 

 and will consider a normally exposed negative overtimed. It is, further, some- 

 what deceptive in the relative amount of density apparent before and after fixing, 

 since the negatives produced by its use lose more under the action of the hypo 

 than do almost any others. As it does not produce chemical fog, even after long 

 action, it is well to let it operate until an apparent excessive density is produced. 

 Among the class of one-solution developers that may be prepared by the 

 operator and kept for some time, I like the metol-hydrochinone mixture prepared 

 after the following formula : 



Water, distilled .... 500 c. c. 



Metol 3 gm. 



Hydrochinone ..... .5 " 



Sodium Sulphite . . . . . 18 " 



Sodium Carbonate . . . . 14 " 



Mix in the order given, and when wanted for use dilute with an equal quantity 

 of water. 



As a type of the two-solution developers, I would recommend the one given 

 by Carbutt for use with his plates. This is prepared as follows : 

 Solution 1 : 



Water, distilled .... 600 c. c. 



Sulphite of soda ..... 120 gm. 



Eikonogen ..... '2'2 " 



Hydrochinone . . . . . 10 " 



Add water to make .... 960 c. c. 



Solution 2 : 



Water, distilled .... 600 c. c. 



Carbonate of potash .... 60 gm. 



Carbonate of soda . . . . . 60 " 

 Add water to make .... 060 c. c. 

 To use, mix one part each of 1 and "2 with four parts of water. 

 Greater contrast can be obtained from any developer by decreasing the 

 amount of alkaline solution or by the addition of a few drops of 10 per cent, 

 potassium bromide solution. 



