114 



DR. FARADAY'S EXPERIMENTAL RESEARCHES IN ELECTRICITY. 



842. In many instances, the secondary results obtained by the action of the evolving 

 ion on the substances present in the surrounding liquid or solution, will give the 

 electro-chemical equivalent. Thus, in the solution of acetate of lead, and, as far as I 

 have gone, in other proto-salts subjected to the reducing action of the nascent hydrogen 

 at the cathode, the metal precipitated has been in the same quantity as if it had been 

 a primary product, (provided no free hydrogen escaped there,) and therefore gave as 

 accurately the nun^ber representing its electro-chemical equivalent. 



843. Upon this principle it is that secondary results may occasionally be used as mea- 

 surers of the volta-electric current (706. 740.) ; but there are not many metallic solu- 

 tions that answer this purpose well : for unless the metal is easily precipitated, hydrogen 

 will be evolved at the cathode and vitiate the result. If a soluble peroxide is formed at 

 the anode, or if the precipitated metal crystallize across the solution and touch the 

 positive electrode, similar vitiated results are obtained. I expect to find in some vege- 

 table salts, as the acetates of mercury and zinc, solutions favourable for this use. 



844. After the first experimental investigations to establish the definite chemical 

 action of electricity, I have not hesitated to apply the more strict results of chemical 

 analysis to correct the numbers obtained as elect rolytical results. This, it is evident, 

 may be done in a great number of cases, without using too much liberty towards the due 

 severity of scientific research. The series of numbers representing electro-chemical equi- 

 valents must, like those expressing the ordinary equivalents of chemically acting bo- 

 dies, remain subject to the continual correction of experiment and sound reasoning. 



845. I give the following brief Table of ions and their electro-chemical equiva- 

 lents, rather as a specimen of a first attempt than as anything that can supply the 

 want which must very quickly be felt, of a full and complete tabular account of this 

 class of bodies. Looking forward to such a table as of extreme utility (if well con- 

 structed) in developing the intimate relation of ordinary chemical affinity to elec- 

 trical actions, and identifying the two, not to the imagination merely, but to the con- 

 viction of the senses and a sound judgement, I may be allowed to express a hope, 

 that the endeavour will always be to make it a table of real, and not hypothetical, 

 electro-chemical equivalents ; for we shall else overrun the facts, and lose all sight 

 and consciousness of the knowledge lying directly in our path. 



846. The equivalent numbers do not profess to be exact, and are taken almost 

 entirely from the chemical results of other philosophers in whom I could repose 

 more confidence, as to these points, than in myself. 



847. Table of Ions. 



Anions. 



Oxygen 8 



Chlorine 35-5 



Iodine 126 



Bromine 78"3 



Fluorine IS? 



Cyanogen 26 



Sulphuric acid .... 40 



Selenic acid 64 



Nitric acid ........ 54 



Chloric acid 75*5 



Phosphoric acid .... 35 '7 



Carbonic acid .... 22 



Boracic acid 24 



Acetic acid 51 



Tartaric acid 6Q 



Citric acid 58 



Oxalic acid 36 



Sulphur (?) 16 



Selenium (?) 



Sulpho-cyanogen . . 



