Since π = (0·283 + 0·0575 log(1/C) volt) log(1/C) = _p__{H+} = (π - 0·283)/0·0575 π = potential difference found C = concentration of hydrogen-ions. ---+------------------+--------+--------- | Before goods. | After goods. +--------+---------+--------+--------- No.| Volts. | _p__{H+}| Volts. | _p__{H+} ---+--------+---------+--------+--------- 1 | 0·560 | 4·7 | 0·755 | 8·16 2 | 0·585 | 5·16 | -- | -- 3 | 0·600 | 5·4 | 0·658 | 6·44 4 | 0·595 | 5·35 | 0·710 | 7·35 5 | 0·600 | 5·4 | 0·725 | 7·6 6 | -- | -- | 0·770 | 8·35 ---+--------+---------+--------+--------- No. 6 was a very old “spent” liquor. The mean hydrogen ion concentration before goods was 0·588 volt, i.e. the concentration was 10^{-5·32} normal equivalent to 0·00000479 grm. per litre of hydrogen ions. Therefore the value of _p__{H+} was 5·32. A solution of hydrochloric acid of the same strength by titration consumed 0·7 c.c. N/1 alkali per 100 c.c. Measured by the electrometric apparatus, it showed 0·410 volt, corresponding to _p__{H+} = 2·1, or a hydrion concentration of ·0079N. In other words, the HCl solution has an acidity or strength 1600 times that of the puer liquor. The mean hydrogen ion concentration of the liquors after goods was 0·000000076 grm. per litre, corresponding to 0·715 volt and _p__{H+} = 7·12, i.e. the liquor was alkaline to a slight extent. For comparison saturated lime-water gave a reading of 1·01 volt, corresponding to _p__{H+} = 12·5. The hydrogen ion concentration is of the greatest importance for the proper action of the enzymes in the bate;[70] we shall, however, treat of this in Chapter VII. [70] _Vide_ Sœrensen, Sur la mesure et l’importance de la concentration des ions hydrogène dans les réactions enzymatiques. Comp. rend. Lab. de Carlsberg, 8me. vol. 1^{ere} livraison, Copenhagen, 1909. *Conductivity of Puer Liquors.*--It was thought of interest to examine the electrical conductivity of puer liquors in actual use, in the hope that the numbers obtained might give some useful indications. It was found that the conductivity increased, as might be expected from the lime going into solution, but the difficulties of the method render it of less use than ordinary chemical analysis. The results of a typical liquor are given here as a record-- Conductivity (K) of liquor before goods 0·00316(1/(ohm × cm.)) Conductivity (K) of liquor after goods 0·00423(1/(ohm × cm.))