I3O THE A B C OF PHOTO - MICROGRAPHY 



which is given in all books on photography, 

 until the desired reduction is reached, when 

 it is to be washed and dried spontaneously. 

 My own practice is to make this reducer by 

 "rule of thumb," as follows: About half an 

 ounce of potass ferricyanide (red prussiate of 

 potash) is dissolved in four ounces of water, 

 and put in a well-stoppered bottle, where it 

 will keep very well in a dark place or if the 

 bottle is covered with opaque paper, the 

 solution spoiling if exposed to light in a 

 short time : this is kept for stock. To make 

 the reducer, I dissolve i ounce of sodium 

 hyposulphite in 4 ounces of water, and add 

 a small quantity of the ferricyanide solution, 

 stirring the whole to mingle the ingredients 

 evenly. Should its action be abnormally tardy, 

 more of the ferricyanide may be added, but 

 a slow, steady reduction by a somewhat weak 

 solution gives more satisfactory results than 

 rapid work with a strong one. This bath 

 will not keep and should be thrown away 

 after using. 



Persulphate of ammonium is also a most 

 excellent reducing agent, and as it seems to 

 attack the denser portions of the negative 

 first is especially valuable in many cases. A 

 2 per cent solution is about the proper 



