The fact that a positive reaction is given with aniline hydrochloride [Footnote: This reaction is carried out as follows:—5 c.c. of the tannin solution to be examined (about 4 gm. tanning matter per litre) are shaken violently in a test tube with 0.5 c.c. aniline and 2 c.c. concentrated HCl added. All natural tannins are unaffected by this treatment, ligninsulphonic and other sulphonic acids cause opalescence. Note.—Employing formic acid in lieu of hydrochloric acid (Knowles) renders the reaction no more reliable.—Transl.] is very puzzling; none of the natural tannins are precipitated by this reagent, but only sulphite cellulose on account of its content of ligninsulphonic acid. One is justified in assuming that there is at least some connection between the constitution of ligninsulphonic acid and that of dicresylmethanedisulphonic acid.
Stiasny [Footnote: Collegium, 1913, 516, 142.] recommends the following reaction for the detection of and differentiation between Neradol D and wood pulp extract:—10 c.c. of a 5 per cent. solution of the extract to be analysed are violently shaken with 1-2 drops of a 1 per cent. alum solution and about 5 gm. of ammonium acetate. If only Neradol D is present no precipitate separates even after twenty-four hours, but if wood pulp be present, a precipitate is thrown down in a quantity corresponding to the amount of wood pulp present.
The official analysis gives the following figures:
[Footnote: Grasser, loc. cit.]
Tanning matters 32.5 per cent.
Soluble non-tannins 33.0 "
Insolubles 0.0 "
Water 34.5 "
——————-
100.0 per cent.
Ash 17.0 "
Acidity: 1 gm. = 10 c.c. N/10 NaOH.
Density: 33º Bé.
A comparison of its quantitative analysis to that of a natural tanning extract is illustrated by the following figures of a chestnut and a quebracho extract of same density (26º Bé):—
Chestnut Quebracho
Per Cent. Per Cent.
Tanning matters 32.0 34.0
Soluble non-tannins 12.0 8.0
Insolubles 1.5 2.0
Water 54.5 56.0
——- ——-
100.0 100.0
Ash 0.4 2.0
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.