576 Dr. Armstrong and Prof. Armstrong. Studies on [June 13, 



respect. It has been contended, indeed, throughout this series of studies that 

 the doctrine itself is purely hypothetical and not in accordance with facts 

 generally. 



The upholders of the dissociation hypothesis assume that the characteristic 

 activity of acids is due to the constituent all acids have in common, the 

 hydrogen ion (H) and that of alkalies to the hydroxyl ion (OH). Everything 

 goes to show, however, that acids act as acids — that is to say that the 

 negative or acid ion is as much concerned as is the positive or hydrogen ion ; 

 in fact, that the characteristic properties of an acid are in the main due to 

 the negative radicle, the hydrogen radicle being no more characteristic of an 

 acid than it is of an alkali. 



Ex liypothcsi, the passage of an electrical current through a solution takes 

 place only through the agency of the dissociated ions. The slight con- 

 ductivity of highly purified water is therefore attributed to the presence of 

 a small proportion of free hydrogen and hydroxyl ions. The results are so 

 interpreted that about 1 molecule in every 10,000,000 (1-05 x 10~ 7 at 25°) is 

 supposed to be in this condition ; further, that if produced in a larger 

 proportion than this under any conditions, hydrogen and hydroxyl ions at 

 once unite to form neutral water. If a solution be acid, it is therefore 

 supposed that hydrogen ions are present in excess of the proportion in 

 winch they are contained in water : if it be alkaline, the assumption is made 

 that they are present in a smaller proportion. 



It is difficult enough for non-mathematical readers to appreciate values 

 stated in terms of the expression x x 10 -7 or 10 _J/ but it is still more difficult 

 for them to follow the method adopted by Sorensen* the first to introduce 

 order and one of the chief workers in this field, who uses the indices alone 

 (the y values) as the exponents of the hydrogen-ion-concentration, so that 

 values below 7 indicate alkalinity and those above 7 acidity. Such a system, 

 moreover, has the disadvantage that when curves are plotted to indicate the 

 relation between the effective acidity (or alkalinity) of the solution and 

 enzymic activity, as logarithmic values are used instead of actual values, an 

 altogether false and misleading shape is given to the graph. 



Eecognising the unsuitability of the method followed by Sorensen and 

 others, James Walkerf has recently advocated that acidity and alkalinity 

 be referred to water as a standard. He puts the acidity and likewise the 

 alkalinity of pure water as equal to 1 : hence the product of the acidity and 



* S. P. L. Sorensen, " Etudes enzymatiques. II. — Sur la mesure et l'importance de la 

 concentration des ions hydrogene dans les reactions enzymatiques," ' Comptes rendus des 

 Travaux du Laboratoire de Carlsberg.' 8me volume. Ire Livraison, 1909. 



t ' Journ. Soc. Chem. Ind., 5 1912, p. 1013. 



