Acidity: 1 gm. = 40 c.c. N/10 NaOH.
According to its chemical constitution, this product may be considered to be dinaphthylmethanedisulphonic acid.
Samples of this crude, strongly acid material were partly neutralised, and the following figures obtained on analysis:—
Acidity. Tanning Soluble Water.
Matters. Non-tans.
Per Cent. Per Cent. Per Cent. 1 gm. = 35 c.c. N/10 NaOH 61.8 7.0 31.2 1 " = 30 " " 58.9 7.1 34.0 1 " = 25 " " 50.1 7.9 42.0 1 " = 20 " " 42.2 8.9 48.9 1 " = 15 " " 37.4 10.4 52.2 1 " = 10 " " 31.6 13.6 54.8 1 " = 5 " " 26.3 16.6 57.1
Experimental tanning tests which were carried out with the various partly neutralised samples yielded leathers which, on an average, were nearly white, but which in comparison with a leather tanned with Neradol D appeared rather more greyish and were much harder.
A solution of the half-neutralised substance (1gm. = 20 c.c.
N/10 NaOH) gives the following reactions:—-
Gelatine—Precipitate, partly soluble in excess tannin solution.
Ferric chloride——-No coloration.
Barium chloride——-Precipitate, insoluble HNO_3.
Bromine water——-No reaction.
Silver nitrate——-No reaction.
Aniline hydrochloride——Precipitate, dissolves when solution
is heated.
This condensation product is very soluble in water, but insoluble in most solvents, excepting methyl and ethyl alcohols. The above reactions show the similarity of this dinaphthyl derivative to the dicresyl derivative, and the absence in the former of characteristic reactions with iron salts is mainly accounted for by its lack of phenolic groups. The absence of this reaction does not, of course, influence the tannoid character of dinaphthylmethanedisulphonic acid in the least, and is of no importance in practice, since the various stages of tannage may be demonstrated by means of a solution of indigotine.
From a technical point of view the absence of this reaction is advantageous to this extent, that it eliminates the exceedingly great care to avoid the contact of tan liquors and tanned pelt with iron particles which has to be observed when tannins of phenolic character are employed.