Fig. 10.—Electrometric Apparatus.
The following table shows some results obtained on puer liquors before and after skins have been put through. p+H has been called by Sorensen the exponent of the hydrogen ion concentration C, and is defined by the equation
p+H = log 1/C
i.e. it is equivalent to the logarithm of the reciprocal of the factor of normality of the solution with respect to the hydrogen ions.[69] p+H for pure water or a neutral solution is 7, corresponding to 0·69 volts. The measurements were made on filtered puer liquors, using a N/1 KCl calomel electrode as auxiliary, the capillary of the electrode being filled with 3·5N potassium chloride:—
No. | Before goods. | After goods. | ||
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].