Platinotype 
This process is based on the light-sensitiveness of ferric 
oxalate, which is reduced by the action of light to ferrous 
oxalate, which dissolves in the alkaline oxalate used as a 
developer, thus reducing the platinum salt, used in the sensi- 
tiser, in situ; the iron salts form no part of the image. 
It is important that the ferric oxalate should be free from 
ferrous salt, and the most satisfactory way to ensure this is 
to prepare it. The following method should be adopted: 
Ammonia iron alum 520 ¢ . 90z4 S0iee 
Water 500 ccm 8 oz. 
Heat until dissolved, allow to cool slightly, and add: 
Ammonia 200 ccm 31% oz. 
Stir well for about 5 minutes. Then filter the solution, and 
wash the filter with repeated lots of water until the filtrate 
is no longer alkaline to litmus paper. Then dissolve in: 
Oxalic acid, pure 215¢ 1651 gr. 
Hot water 800 ccm 12 oz. 
Pour this solution over the filter repeatedly until all the 
ferric hydroxide is dissolved; wash the filter with sufficient 
water to make the volume of the solution 1000 ccm (16 0z.). 
An alternative method, which obviates the necessity of filter- 
ing, but takes longer, is to powder some iron alum, and 
weigh out the above quantities. Place the powder in a tall 
graduate; the tall metric cylindrical graduates are the most 
convenient. Pour on the powder the above quantity of am- 
monia mixed with an equal volume of water. Stir for a few 
minutes, and allow to stand for 10 minutes. Fill up the 
graduate with water, shake or stir well, allow to stand until 
the precipitate has somewhat subsided, and syphon off the 
274 
ARG 
= = 
eS ee —. > 
