[68] It is necessary to use pure hydrogen. This may now be obtained commercially from the Knowles’ Oxygen Co., Wolverhampton.
[69] The formula for calculating p+H for the N/1 auxiliary electrode used is as follows:—
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.
[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. 1ere livraison, Copenhagen, 1909.
[71] Minot, Address to Amer. Assoc. for Advancement of Science, Minneapolis, Dec. 29, 1910. Nature, 1911, p. 96.
[72] The apparatus was constructed by Mr. W. Linney, of the University College, Nottingham.
Since this apparatus was constructed Professor H. R. Procter has informed me that an appliance devised by Mr. Anderson, of the Leeds University, for measuring the thickness of leather under varying pressures, has been in use in the leather industries department for some months for the purpose of measuring the proportion of the permanent to elastic compression.