DEVELOPERS 221 



disadvantage that the pyro does not keep well in solution 

 and that the solution stains the hands. A good plan is 

 to prepare the No. 2 solution as stock, and to add weighed 

 quantities of dry pyrogallol when required, but, if sub- 

 limed pyro in powder is used, it is almost equally accurate 

 to measure it. For this purpose a teaspoon may be 

 used, the weight of the contents of which is known. 

 This developer is not suitable for papers on account 

 of its staining property. A yellow-stained negative is 

 often, on the other hand, better than a clear black 

 one. The very non-actinic image gives a more contrasty 

 print. 



Metol-Quinol is an exceedingly fine developer, acting 

 more quickly than pyro soda, and useful for papers as 

 well as plates. It has, however, the great drawback 

 that metol may cause a painful skin affection, and for 

 that reason the fingers should be dipped into it as little 

 as possible, papers being manipulated by means of forceps. 

 A rinse in a very dilute hydrochloric or acetic acid 

 solution is a preventive of the poisoning. The formula 

 given .is the concentrated solution of Mr. R. L. Boyd, and 

 keeps good for a long time in a tightly corked bottle ; it is 

 diluted as required for use. 



Hydroquinone or Quinol tends to give very harsh 

 contrasts, and is selected when that is required, but the 

 mixture with metol is generally preferable. The metol 

 supplies detail and rapidity. 



Potassium Bromide in Developers. There is a growing 

 tendency to the omission of potassium bromide in 

 developers, but as it generally helps to give crispness to 

 a negative and prevent fog it is well to include it for 

 photomicrography, as bright contrasty negatives are 

 required. One or two drops of a 10% solution is usually 

 sufficient per oz. of developer. 



Development of the Plate. The aim of development is 

 to produce a negative having sufficient contrast to show 



