DEVELOPERS oF, 
The iron salt should preferably be pure, and, if covered at all 
with whitish or yellowish powder, a little excess should be 
allowed in weighing out. The crystals are to be placed in a 
flask, covered with water, well stirred, and the water poured 
off. Then the acid should be added to about three-fourths of 
the water, the salt dissolved, and the bulk made up with the 
remainder of the water. As this solution readily oxidises on 
exposure to the air, it is better to keep it in small bottles, and 
fill them right up to the cork: 
B. Potassium oxalate SIO 4. OZ. 
Hot water 1000 ccm 16 oz. 
For use add 1 part of A to 4 parts of B. The usual strength 
is 1:3, but this is apt to deposit the insoluble ferrous oxalate. 
If the order of mixing is reversed, the insoluble iron salt is 
at once precipitated, as there is no excess of oxalate to 
dissolve it. With this developer the image appears in from 
10 to 30 seconds and is complete in 2 to 5 minutes. Potassium 
bromide, may, of course, be added as restrainer. As an 
accelerator a few drops of weak hypo solution may be used, 
about 10 drops of a 1: 200 solution to 100 ccm or 4 drops to 
the ounce; but this is apt to give fog. 
Modifications have been suggested mainly for use with 
gelatino-chloride lantern plates, and, by suitably prolonging 
the exposure and modifying the developer, any tone can be 
obtained from black to red. For black or purple tones the 
following may be used: 
A. Potassium citrate, neutral 450 g LAL Oz: 
Potassium oxalate, neutral ize 784 gr. 
Water 1000 ccm 16 oz. 
B. Ferrous sulphate 200 g o/ aoz. 
Water 1000 ccm 16 oz. 
Mix in equal parts. 
