236 PHOTOGRAPHIC FACTS AND FORMULAS 
20° C. (65° to 68° F.) for 20 to 35 minutes, and apparently 
no change takes place; but, if washed for 1¥4 hours, the sepia 
tone makes its appearance. 
Liver of sulphur or polysulphide process (Woodman) .— 
Wash the prints free from hypo, harden by immersion in 
formaldehyde solution, and place at once in a solution of 
liver of sulphur (sulphurated potash) made by dissolving 
a piece about the size of a pea in 200 ccm (7 oz.) water. 
Ammoniacal liver of sulphur (Vero).—The prints must be 
free from hypo and must not have been dried. Harden by 
10 minutes’ immersion in a 10 per cent solution of formalde- 
hyde, wash, and immerse in: 
Liver of sulphur 7g 54 gr. 
Water 1000 ccm 16 oz. 
Ammonia a few drops 
Toning is very rapid and purplish-brown tones are obtained. 
Ammonium sulphide (Kropf )— 
A. Ammonium sulphide 25 ccm 192 min. 
Water 1000 ccm 16 oz. 
B. Ammonium carbonate 3.75 g 29 gr. 
Water 125 ccm 2 oz. 
C. Ammonium persulphate 1252 10 gr. 
Water 125 ccm 2-02; 
Mix in the above order. The colour of the mixture should 
be greenish-yellow, and, in about half an hour, turn to 
golden yellow, when it is ready for use. Prints should be 
washed for a short time after fixing, and then immersed in 
the bath at normal temperature; toning takes about 15 min- 
utes. If heated to 30° C. (86° F.), toning is complete in 10 
minutes. 
Sodium sulphide-ferricyamde (Brown).— 
Sodium sulphide, 20% sol. 400 ccm 8 oz. 
