Original Puer The same Liquor After Goods π (volts) 0·61 0·69 π after 10 c.c. formalin 0·53 0·54 N (Kjeldahl), grm. per litre 0·3136 0·5936 Increase of N -- 0·2800 N/10 soda for 50 c.c. to original voltage 7·0 11·6 c.c. increase N/10 soda -- 4·6 ∴ 1 c.c. N/10 soda = mg N -- 3·05 A preferable method is to add decinormal acid or alkali to the original liquor until the P.D. of 0·69 is reached, at which point the liquor will be neutral to phenolphthalein, and, after adding formaldehyde, to titrate with N/10 soda until the P.D. of 0·69 is again reached. The factor which connects the amount of decinormal soda required for the titration, after the addition of formaldehyde, with the total nitrogen as determined by Kjeldahl’s method, will afford information as to the extent of the hydrolysis undergone by the proteid matter, in the same manner as Stiasny (loc. cit.), has proposed to differentiate the dissolved proteid matter in lime liquors. As hydrolysis proceeds the percentage of nitrogen in the molecule increases, being at its maximum in the ultimate nitrogenous product ammonia; the factor, therefore, becomes less as hydrolysis becomes more advanced. For ammonia 1 c.c. N/10 soda = 1·4 mg. N " hydrolized gelatin[39] = 2·9 " " Witte peptone completely hydrolized[39] = 3·6 " " lysin = 2·8 " " arginin = 5·6 " " histidin = 4·2 " [39] Stiasny. Collegium 1910, p. 184. We may conclude that the skin substance dissolved in the puer liquor is hydrolized almost as completely as gelatin is by boiling with sulphuric acid. I have previously pointed out that dilute acids dissolve a certain amount of skin substance (see p. 157), and in this connexion, Dr. Georges Abt has given me the results of some experiments, on the solubility of skin in various organic acids, which he made in Vienna. Pieces of skin, weighing 40 grm. in the wet state, were allowed to remain for one month in N/10 solutions of the acids. The N was then determined, by Kjeldahl’s method, with the following results, expressed as per cent. of the wet skin dissolved:-- Per cent. Acetic acid dissolved 0·645 Lactic " " 2·27 Butyric " " 0·577 Formic " " 1·47 It will be seen that butyric acid dissolved the least amount of skin, lactic acid dissolving close upon four times as much. *Scud.*--A certain amount of skin substance comes away in the “scud.” This is the liquid squeezed out of the skin by the pressure of the scudding knife after puering.