[Greek: b]aCl_2 is added. The barium sulphate indicates the sulphuric acid present in the leather as water-soluble sulphates. Whether the latter be sulphates or bisulphates may be indicated by the aqueous extract of the above residue, since neutral reaction would indicate the absence of bisulphates, acid reaction their presence in addition to possible normal sulphates; the quantitative estimation of the metals would decide this point definitely. 10. Properties of Leathers Tanned with Neradol D Whereas the colour of leathers tanned with Neradol D only is nearly a pure white, those tanned with mixtures of Neradol D and vegetable tanning materials are more or less light coloured according to the quantity of Neradol D present, as has been explained when discussing the phlobaphene-solubilising action of Neradol D. In any case, all leathers tanned with Neradol D possess fibre of remarkable length, which explains their increased tensile strength and elasticity. The tensile strength of a leather tanned with a mixture of Neradol D and vegetable tannins was 3.7 per cent, as compared to 3 per cent when no Neradol was used; the extension was 56 per cent, when tanning with Neradol D as against 36 per cent, without the latter. The sensitiveness to light of leathers tanned with Neradol D may be mentioned. Exposed to direct sunlight, the surface of the leather assumes a yellowish colour after two days' exposure, and assumes a pure yellow colour after a further three days. A further fifteen days' exposure only darkens the leather slightly, the final colour being very little different from the one obtaining after five days' exposure. In passing, it may be remarked that this yellow colour is observed on the surface only, the grain otherwise possessing that pure white colour characteristic of Neradol D tanned leather. Further, it may be noted that leathers tanned--with Neradol D fix basic coal-tar dyes excellently, whereas acid and substantive dyestuffs are fixed with other than their natural shades. The author has analysed a leather exclusively tanned with Neradol D, and has obtained the following results:--[Footnote: _Collegium_, 1913, 521, 478.] Moisture - - - - - 15.53 per cent. Ash - - - - - - 0.93 per cent. Fats- - - - - - 1.26 per cent. Extraneous matters - - - 0.00 per cent. Leather Substance |Tanning matters- 36.92 per cent. Leather Substance |Hide substance - 45.36 per cent. --------------- 100.00 per cent. [Footnote: Sp. gr., 0.642.] From these figures, those of "degree of tannage" and "yield" (pelt-->leather) are calculated as 81.4 and 220 respectively.