2i 4 SCIENCE PROGRESS 



Zeitschrift fur physikalische Chemie as a vehicle for the concen- 

 trated inculcation of certain aspects of the subject, that even 

 English writers have formed the habit of discussing at length 

 the more superficial aspects of chemical change and of catalysis, 

 but have to all intents and purposes disregarded the profound 

 consequences that follow from the far-reaching observations 

 made in their own country. It is scarcely too much to urge 

 that the observations of Dixon and of Baker should be placed 

 in the very forefront of any discussion of chemical change 

 and that a casual reference to moisture as an " interesting 

 catalyst," of which " the mode of action is quite unknown," 

 does not form an adequate description of the most important 

 experiments that have yet been made in this branch of 

 chemistry. 



In the absence of any satisfactory alternative explanation 

 of the influence of moisture in promoting chemical change, the 

 electrolytic theory put forward by Armstrong in 1885 un- 

 doubtedly occupies the field ; it has received confirmation 

 amounting almost to positive proof from the observation 

 recorded by Baker 1 that the exceptionally pure water pro- 

 duced by the slow combination of hydrogen and oxygen, not 

 quite perfectly dried, by prolonged heating in a glass vessel, 

 is not a sufficiently active catalyst to initiate an explosion 

 even when present in considerable quantities. 



The essential feature of the electrolytic theory is the 

 formation of a circuit of not less than three components, of 

 which one at least must be an electrolyte. The typical battery 

 consists of two metals and a solution, but it is important to 

 recognise that the electrolyte may be discharged by electrodes 

 of other kinds, since otherwise the theory would be restricted 

 to a very narrow range of chemical changes. In an accumulator, 

 for instance, sulphuric acid is electrolysed in such a way that 

 the " sulphate " is discharged at a lead electrode, but the 

 hydrogen by means of lead peroxide, a metal grid being pro- 

 vided as a backing for the peroxide mainly in order to secure 

 mechanical strength and to diminish the electrical resistance 

 of the circuit. In a gas-battery the electrolyte is discharged 

 by means of hydrogen at one pole and oxygen at the other, 

 platinum being employed in order to provide a metallic circuit 

 of low resistance between the oxygen and hydrogen, which 



1 Trans. Chem. Soc, 1902, 81, 403. 



