THE TRON PROCESSES 265 
The image should become black in from 3 to 5 minutes. The 
print may be completely immersed in the developer or floated 
on its surface. As soon as the image is intense enough, wash 
with repeated changes of water, gently blot off the surface 
water, and hang up to dry in a warm place. It should be 
noted that the ferric sulphate used in this process is the basic 
variety, also known as subsulphate, or Monsell’s salt. 
GREASY OR PRINTER’S INK Process.—In this process the 
solubilisation of a colloid by the action of light on the iron 
salts, and the capacity of the insoluble colloids for taking 
greasy ink is employed; it was suggested by Fisch: 
Gum arabic 320 g 2451 gr. 
Water 1000 ccm 16 oz. 
Dissolve, and add: 
Martanicracid 70g 540 er. 
Water : 250 ccm 4 oz. 
And add, with constant stirring: 
Ferric chloride solution, 
45° Be. 225g 302z., 288 gr. 
Then add: 
Manganese sulphate 10g 77 or, 
Water 25 ccm 192 min. 
Allow to stand in the dark for several hours, and then filter 
through fine muslin. Coat the paper in the usual way, and 
dry at 35° to 45° C. (95° to 113° F.). Or the following 
may be used: 
Gum arabic 325 g 2496 er. 
Water 1000 ccm 16 oz. 
Dissolve, and add: 
Tartaric acid TNS 576 gr. 
or Citric acid 300 g 44/5 oz. 
Then add, with constant stirring: 
Ferric sulphate 26g 200 gr. 
