_Cyanuret of Potassium._--I have been using lately 12 grs. of cyanuret of
potassium in 1 oz. of water for clearing the collodion plates, instead
of hypo. There is one advantage, that there are no crystals formed if
imperfectly washed, which is too common with hypo. You must take care to
well wash off the developing fluid, whether pyrogallic, protonitrate,
or protosulphite: if you use the latter 40-grains strong, the _whitest_
pictures can be obtained, nearly as white as after bichloride of mercury.
A good formula to make it is--
Distilled water 11 drachms.
Alcohol 1 drachm.
Nitric acid 20 minims.
Protosulphate of iron 60 grains.
This I know to act well with care, and it will keep a long time.