PHOTOGBAPHIC PEOCESSES 231 



There are a considerable number of other substances used 

 as reducing agents ; but these, or one or two of them, will be 

 found to perform all that is required. Every maker places 

 in each box of plates sent out some formulae with which the 

 particular plates may be developed, and it is obvious that if 

 these are followed they may be expected to give perfectly good 

 results. On the other hand, nearly all plates now have a certain 

 amount of latitude, and may be expected to give quite as good 

 results with standard solutions, in which there are suitable 

 amounts of developer. 



To reduce the number of solutions required as far as possible, 

 the following four may be made up : 



Solution No. 1. 



Pyrogallic acid ... 8 grammes. 



Soda metabisulphite . . 4 grammes. 



Water . . to make up to 1000 c.c. 

 Solution No. 2. 



Sodium carbonate ... 50 grammes. 



Sodium sulphite ... 50 grammes. 



Water . . to make up to 1000 c.c. 

 Solution No. 3. 



Metol 4 grammes. 



Hydrokinone .... 8 grammes. 



Potash metabisulphite . . 4 grammes. 



Water . . to make up to 1000 c.c. 

 Solution No. 4. 



Potassium bromide . . . 10 grammes.- 



Water . . to make up to 100 c.c. 



The advantage of adopting these solutions is that they may 

 be employed with any plate, with which the writer at least has 

 had any experience. There is the additional advantage that 

 by using them in suitable combination with one another, the 

 same solutions may be used for developing either negatives, 

 lantern-slides, or for printing on bromide paper. The pyrogallic 

 acid and sodium carbonate solution will be found in many 

 respects most suitable for negative-making, and to compound 

 a solution, equal parts may be taken of No. 1 and No. 2. 



Solution No. 4 is a restraining solution only, and in cases 

 where the negative is known to be somewhat over-exposed, or 



