Being a sulphonic acid derivative, the chemical constitution of Neradol is obviously considerably different from that of the natural tannins, and the question has been asked: Will Neradol D, in its concentrated form, attack the hide substance?[Footnote 1: _Collegium_, 1913, 521, 487.] Bearing in mind that concentrated extracts of vegetable tannins in some circumstances effect a "dead" tannage (_cf_. case-hardening) and hence reduce their practical value, and that for this reason it is impossible to allow either concentrated extracts or concentrated Neradol D to act upon pelt, the author still decided to carry out some experiments in this direction. Concentrated Neradol D (33° Bé.) and strong aqueous solutions of this material in strengths of-- 30° 25° 20° 15° 10° 5° 3° 1° Bé. were therefore allowed to remain in contact with pelt for a period of ten days, when the pelts were taken out and washed in running water for twenty-four hours, and then dried. The resultant leathers possessed the following properties:-- 33° Bé. solution: completely gelatinised.[Footnote 2] 30° " " " [Footnote 2] 25° " two-thirds gelatinised; surface tanned. 20° " one third gelatinised; surface "dead" tanned. 15° " pelt was glassy throughout. 10° " rather cracky leather, but well tanned. 5° " normal tannage. 3° " " " 1° " " " [Footnote 2: Impossible to subject the pieces to a proper washing out.] The interiors of the leathers obtained from the 25° and 20° Bé. solutions were completely gelatinised; this may be accounted for by assuming that the surface was "dead" tanned, and that hence the free dissociated sulphonic acid diffused into the leather, towards which it exhibited hydrolysing rather than a tannoid effect with the consequent result described above. Above 10° Bé. the effect is more that of an acid with concentrations below 10° Bé.--the only ones of technical importance--however, no ill-effects may be observed. For tanning purposes, Neradol D solutions of 2° Bé. are quite satisfactory, and it has been found [Footnote 1: _Technikum_, 1913, 80, 324.] that solutions of this strength do not dissolve out any protein of the hide. [Footnote 2: The translator cannot agree with the author on this point. He has, for instance, found that solutions of analytical strength dissolve considerable amounts of hide substance, and his practical experience confirms results arrived at in the laboratory.] A purely Neradol D tanned leather may be produced by immersing a bated pelt, free from lime, in a 2° Bé. Neradol D liquor for about four days; the resultant leather being nearly white and otherwise very similar to a leather tanned with vegetable tanning materials.