29t Royal Society. 



In the third section of the paper, the primary or secondary charac- 

 ter of the bodies evolved at the electrodes is discussed. It is shown 

 that they are secondary in a far greater number of cases than has 

 usually been imagined ; and that laws have been deduced w-ith regard 

 to the ultimate places of substances, from the appearance of the se- 

 condary products ; so that certain conclusions, true in themselves, 

 have hitherto been obtained by erroneous reasoning, since the facts 

 which were supposed to support them have in truth, no direct relation 

 with those conclusions. The methods of distinguishing primary and 

 secondary results from each other are explained, and the importance 

 of this distinction towards the establishment of the law of definite 

 electro-chemical action is insisted upon by the author. 



The fourth section is entitled, "On the definite Nature and Extent 

 of Electro chemical Decomposition," and is considered by the author 

 as by far the most important of this or indeed of the whole series of 

 investigations of which he has now presented the results to the Royal 

 Society. He adverts to the previous occasions on which he has al- 

 ready announced, more or less distinctly, this law of chemical action ; 

 and also to the instrument just explained as one of the examples of the 

 principle about to be developed. He next refers to experiments de- 

 scribed in another part, in which primary and secondary results are di- 

 stinguished as establishing the same principle with regard to muriatic 

 acid j the results showing, that not only is the quantity of that acid 

 decomposed constant, for a constant quantity of electricity, but that, 

 when it is compared with water, by making one current of electricity 

 pass through both substances, the quantities of each that are decom- 

 posed are very exactly the respective chemical equivalents of those 

 bodies. The same current, for example, which can decompose nine 

 parts bv weight of water, can decompose thirty-seven parts by weight 

 of muriatic acid, these numbers being respectively the chemical equi- 

 valents of those substances, as deduced from the phaenomena of ordi- 

 nary chemical action. 



Cases of decomposition are then produced, in which bodies ren- 

 dered fluid bv heat, as oxides, chlorides, iodides, &c, are decomposed 

 by the electric current, but still in conformity with the law of con- 

 stancy of chemical action. Thus the current which could decompose 

 an equivalent of water, could also decompose equivalents of muriatic 

 acid, of proto-chloride of tin, of iodide of lead, of oxide of lead, and 

 of many other bodies, notwithstanding the greatest differences in their 

 temperature, in the size of the poles, and in other circumstances ; and 

 even changes in "the chemical nature of the poles or electrodes, and 

 in their affinities for the evolved bodies, occasioned no change in the 

 quantity of the body decomposed. 



The author proceeds, in the last place, to consider a very important 

 question with relation to chemical affinity, and the whole theory of 

 electro-chemical action, namely, the absolute quantity of electricity 

 associated with the particles or atoms of matter. This quantity he 

 considers as precisely the same with that which is required to sepa- 

 rate them from their combination with other particles when subjected 

 to electrolytic action, and he brings many experiments to bear upon 

 this point 5 describing one, in particular, in which the chemical action 



