The methods of Lenssen, or ferricyanide of potassium method, yields very widely differing results.
The first of these is the bleach, or oxidizing mixture of bromide and ferricyanide.
In the case of many formulae, it will be noticed that equal quantities of bromide and ferricyanide are recommended.
The ferricyanide-bromide mixture, however, keeps very much better than a plain solution of ferricyanide alone.
By adding more of the ferricyanide solution the reducing action is quicker, but there is a greater liability to stain the film.
Oxidation of an aniline salt by means of a solution of ferricyanide of potassium.
ferricyanide of potassium produces a rich deep-blue precipitate, insoluble in hydrochloric acid.
The ferricyanide had a small influence and, as might be expected, hyposulphite is fatal to the assay.
ferricyanide of potassium gives a blue precipitate or green coloration; with ferric salts a brown colour only is produced.
To determine the finishing point, place a series of drops of the ferricyanide solution on a dry white glazed plate.