RELATIVE INTENSITIES OF ELEMENTARY VOLTAIC ACTIONS. 433 



sition is prevented, the transmission of the electricity is prevented also ; and although 

 a battery of many plates may be used, yet if it be of that perfect kind which allows 

 of no extraneous or indirect action (1000.), the whole of the affinities concerned in 

 the activity of that battery are at the same time also suspended and counteracted. 



911. But referring to the resistance of each single case of decomposition, it would 

 appear that as these differ in force according to the affinities by which the elements 

 in the substance tend to retain their places, they also would supply cases constituting 

 a series of degrees by which to measure the initial intensities of simple voltaic or other 

 currents of electricity, and which, combined with the scale of intensities determined 

 by diffiirent degrees of acting force (909.), would probably include a sufficient set of 

 differences to meet almost every important case where a reference to intensity would 

 be required. 



912. According to the experiments I have already had occasion to make, I find that 

 the following bodies are electrolytic in the order in which I have placed them, those 

 which are first being decomposed by the current of lowest intensity. These currents 

 were always from a single pair of plates, and may be considered as elementary voltaic 

 forces. 



Iodide of potassium (solution). 



Chloride of silver (fused). 



Protochloride of tin (fused). 



Chloride of lead (fused). 



Iodide of lead (fused). 



Muriatic acid (solution). 



Water, acidulated with sulphuric acid. 



913. It is essential that in all endeavours to obtain the relative electrolytic intensity 

 necessary for the decomposition of different bodies, attention should be paid to the 

 nature of the electrodes, and the other bodies present which may favour secondary 

 actions (986.). If in electro-decomposition one of the elements separated has an 

 affinity for the electrode, or for bodies present in the surrounding fluid, then the 

 affinity resisting decomposition is in part balanced by such power, and the true place 

 of the electrolyte in a table of the above kind is not obtained : thus, chlorine combines 

 with a positive platina electrode freely, but iodine scarcely at all, and therefore I be- 

 lieve it is that the chloride stands first in the preceding Table. Again, if in the de- 

 composition of water not merely sulphuric but also a little nitric acid be present, then 

 the water is more freely decomposed, for the hydrogen at the cathode is not ultimately 

 expelled, but finds oxygen in the nitric acid, with which it can combine to produce a 

 secondary result ; the affinities opposing decomposition are in this way diminished, 

 and the elements of the water can then be separated by a current of lower intensity. 



914. Advantage may be taken of this principle to interpolate more minute degrees 

 into the scale of initial intensities already referred to (909. 911.) than is there sup- 

 posed ; for by combining the force of a current constant in its intensity, with the use 



