THE BOOK OF THE LANTERN. 135 



C Neutral potassic oxalate ... ... 2 ounces. 



A 3 Sal ammoniac ... ... ... 40 grains. 



( Water (distilled) 1 pint. 



f Iron sulphate ... ... ... 4 drachms. 



p. \ Citric acid ... ... ... ... 2 



B 1 Alum 2 



(. Water (distilled) 1 pint. 



For use, pour a portion of B into an equal quantity of A. 



If the operator is accustomed to the ferrous oxalate 

 developer pure and simple, he will find that it will develop 

 this description of plate, but it is better for being restrained 

 with a few drops of 10 per cent, solution of sodic citrate. 

 Whether he use one or the other, let him be particularly 

 careful in the matter of cleanliness of fingers. A hypo- 

 defiled finger will spoil the developer instantly. To avoid 

 this disaster, the potency of which I have learned by 

 sad experience, I have adopted the following method of 

 working : 



I use a brilliant yellow light, so that I can work comf ort- 

 . ably, for chloride plates are, as already stated, insensitive to 

 yellow rays ; the developing tray stands in front of it, and at 

 one side is placed a large tray filled with water, to which a 

 little alum solution has been added. Hypo is, for the pre- 

 sent banished from the scene altogether. I expose my plate, 

 and put it into the developing solution. In a few seconds 

 the picture flashes out in the unceremonious manner com- 

 mon to chloride plates. I hold it up to the light, look 

 through it, and find that it is but a ghostly image after all. 

 I expose another plate in an adjoining room, and put it by 

 the one which is in course of development, and which by 

 this time has most likely gained sufficient density. If it 

 has, I wash it for a few seconds under the tap, and drop it 



