_(a) Oxyazo Reaction_.--About 5 c.c. of the tannin solution are rendered alkaline with caustic soda; after cooling with ice, about half the volume of alcohol is added. 3-4 drops of diazo solution are then added. Frequently, this results in the solution assuming a blue coloration. If not, the solution is acidified with hydrochloric acid, ether added, and the mixture well shaken. The water is now separated from the mixture, fresh water added, together with some caustic soda solution, when, if Neradol D be present, the salt of the colour acid formed dissolves in the water with a beautiful green or bluish-green colour. At the place of contact of the water and the ether a bluish-green ring appears. The diazo solution is prepared by dissolving _p_-aminophenol or its hydrochloric in a little dilute hydrochloric acid, cooling in ice and carefully diazotising in the cold till a slight excess of nitrous acid is present. It is essential that this solution should be tested before use, and this is carried out by coupling it with an alkaline phenol solution; if a dark blue oxyazo colour is formed, the solution may be used. It must be kept cool by surrounding it with ice. _(b) Indophenol Reaction_.--To 5 c.c. of the solution to be tested, a drop of a solution of dimethyl-_p_-phenylenediamine is added, the solution rendered alkaline with caustic soda and 1-2 drops of a 5 per cent. solution of potassium ferricyanide added. If Neradol D be present, a blue colour appears, either immediately or after some time. The reaction is rendered more sensitive if alcohol is carefully poured on the solution after it has been rendered alkaline, and potassium ferricyanide is then added. At the place of contact a blue layer is formed, which ultimately diffuses into the alcohol. According to Lauffmann [Footnote: _Collegium_, 1917, 233.] the presence of natural tannins as well as that of wood pulp diminishes the sensitiveness of the reactions described above; [Footnote: _Zeits. f. ang. Chem._, 1916, 333.] this investigator recommends a modification of these reactions. 2. Electro-Chemical Behaviour of Neradol D