This diminished figure, however, does in no way reduce the value as a tanning agent of Neradol D; it merely shows how inadequate is the hide powder method of analysis when applied to substances of the composition of Neradol D. This is further confirmed by the Loewenthal permanganate method, which yields the following figures:—
Tanning matters 7.2 per cent.
Soluble non-tannins 59.1 [Footnote: Collegium, 1913, 521,487.]
If, on the other hand, completely neutralised Neradol is acidified with an organic acid, such as acetic acid, till the acidity, (1 gm.= 10 c.c. N/10 NaOH) is reached, the resulting product is in all respects similar to Neradol D and yields a corresponding leather.
It is permissible to assume that the irregularity exhibited by Neradol D as regards the analytical estimation of its tannin contents is connected with the low molecular weight of the tanning principle. Whereas all tannins so far isolated from the natural tanning materials possess rather high molecular weights, that of Neradol D deviates considerably from this rule, as is shown by the following table:—
Neradol D tannin Cl_5H_16S_2O_8 358
Mangrove " C_24H_40O_2l 670
Oak bark " C_28H_28O_23 840
Myrabolam " C_54H_48O_35 1256
Dividivi " C_54H_46O_35 1270
Malletto " (C_4lH_50O_20)_2 1724
This low molecular weight may mainly account for the figures obtained by the incorrect oxymetric estimation with permanganate; the apparent tannoid property of the tannoid-inactive neutral salt of dicresylmethanedisulphonic acid may be explained by assuming that though it is, probably, in the colloidal state, and as such adsorbed by hide powder, it is still devoid of astringent properties.
G. Different Methods of Condensation as Applied to Phenolsulphonic Acid
In addition to formaldehyde, many other substances may, theoretically, induce condensation of phenolsulphonic acid; condensation takes place either with the elimination of water or, in addition to this, with the introduction of methane group.
So far, the following condensing agents have been investigated:—
(1) Heating in vacuo. (2) Sulphur chloride. (3) Phosphorus compounds. (4) Aldehydes. (5) Glycerol.