This comparison shows that extracts of natural tannins firstly contain certain amounts of "insolubles," whereas Neradol is completely soluble in water, forming a clear solution; secondly, natural tanning extracts contain smaller quantities of soluble non-tannins, consisting of colouring matter and sugars, in addition to small quantities of mineral matters (ash). Neradol D contains considerable amounts of soluble non-tannins, derived from salts of sulphonic and sulphuric acids, again offering a satisfactory explanation of the high ash. If, therefore, a mixture of Neradol D and a natural tanning extract was submitted to a quantitative analysis, the higher non-tannins and the high ash would indicate the presence of Neradol D, provided that wood pulp or a highly sulphited extract were not components of the mixture. The chemical reactions taking place in the preparation of Neradol D may be expressed thus:- OH OH OH OH H ^ H___O_____H ^ H H ^ H__CH_2__H ^ H | | || | | = | | | | + H_2O | | CH_2 | | | | | | H v CH_3 CH_3 v H v CH_3 CH_3 v H HSO_3 HSO_3 HSO_3 HSO_3 1. Neradol D Reactions 1. The quantitative determination of phenols introduced by Bader, [Footnote: _Bull. soc. scient., Bucarexi_, 1899, 8, 51.] which consists in precipitating them as oxyazo compounds, has been modified by Appelius and Schmidt [FootNote: _Collegium_, 1914, 597.] for the purpose of detecting Neradol D:--To 50 c.c. of the tannin solution (analytical strength) 15 c.c. of diazo solution are added, the mixture filtered, if necessary, and the filtrate made alkaline with caustic soda; in the presence of Neradol D in sufficient quantity, a blood-red coloration results. If but little Neradol D be present, the procedure is altered as follows:--The tannin solution, to which the diazo solution has been added, is filtered, and the filtrate poured on a piece of filter paper which is then dried; a solution of caustic soda is spotted on the paper, when, if Neradol D be present, a red-edged spot will appear. According to Tschirch and Edner, [Footnote: _Archiv. d. Pharm_., 1907, 150.] the diazo solution is prepared as follows:--5 gm._p_-nitraniline are introduced into a 500 c.c. measuring flask, 25 c.c. of water and 6 c.c. concentrated sulphuric acid added, the mixture shaken and a solution of 3 gm. of sodium nitrite in 25 c.c. of water plus 100 c.c. of water added, and the whole then filled up to 500 c.c. The solution should be stocked in the dark. 2. A less sensitive reaction for Neradol and wood pulp extract constitutes that of Appelius and Schmidt employing cinchonine, [Footnote: _Collegium_ 1914, 597.] while the presence of the substances in question yields characteristic precipitates. 3. Seel and Sander [Footnote: _Zeits. f. ang. Chem._, 1916, 333.] recommend the following method of detecting Neradol D:--