The sensitiveness to alkalies of Neradol D is considerably greater than in the case of natural tannins, and it appears that a vegetable tan liquor neutralised with lime will not even surface-tan when acting upon pelt and will neither impart a dark colour to the leather nor remove from it any appreciable amount of protein. Similarly, a Neradol D liquor neutralised with lime exerts no tanning action, but in contradistinction to the vegetable tan liquor similarly treated, will impart a blue or blackish-blue colour to the pelt, from which it removes larger quantities of protein. The author examined two such liquors relating to their contents of tanning matters and protein and obtained the following results:-- Reaction. Bark. Tans. Non-Tans Insol. Proteins Per Per Per Per Cent. Cent. Cent. Cent. Vegetable Slightly 12° 0 2.93 0.35 0.01 tan alkaline liquor Neradol " " 10° 0 4.43 0.17 0.17 These figures do not only show the higher protein contents of the Neradol D liquor, but do also show higher contents in soluble non-tannins, which consist mainly of lime (2.12 per cent.) and sodium salts (1.8 per cent.), thus establishing the fact of the sensitiveness of Neradol D to alkalies in addition to its lime-solubilising effects. The sensitiveness towards alkalies is also noticeable on a large scale where the tanpits have been built of cement; though the pelt may be quite free from lime, the Neradol D is quickly neutralised by the cement, with results similar to those enumerated above. The blue coloured soluble compound of Neradol D and iron salts, to which frequent reference has been made, is very important from a practical standpoint. Whereas the catechol tannins (_i.e._, fir, gambir, hemlock, cutch, mangrove, and quebracho) are coloured black, those of the pyrogallol class (_i.e._, algarobilla, dividivi, valonea, gallotannic acid, myrabolams, and sumac) bluish-black, and the "mixed" tannins (_i.e._, canaigre, oak, and mimosa bark) bluish-purple by iron alum, Neradol D is coloured a pure blue. How sensitive this reaction is, the following comparative analyses illustrate: to each litre of tan liquor containing 4 gm. tanning matter prepared from (_a_) quebracho extract and (_b_) Neradol D, 10 c.c. of a 10 per cent. iron alum solution were added, the solutions heated to 100° C., cooled and filtered, and the colour of the filtrates and the weight of the precipitates determined:-- (_a_) Quebracho solution: light reddish-brown filtrate, 3.22 gm. precipitate. (_b_) Neradol solution: deep blue filtrate, 0.02 gm. precipitate.