DETERMINATION OF ELECTRO-CHEMICAL EQUIVALENTS. 113 



835. X. Electro-chemical equivalents are always consistent ; i. e. the same number 

 which represents the equivalent of a substance A when it is separating from a sub- 

 stance B, will also represent A when separating from a third substance C. Thus, 8 is 

 the electro-chemical equivalent of oxygen, whether separating from hydrogen, or tin, 

 or lead ; and 103'5 is the electro-chemical equivalent of lead, whether separating from 

 oxygen, or chlorine, or iodine. 



836. xi. Electro-chemical equivalents coincide, and are the same, with ordinary 

 chemical equivalents. 



837. By means of experiment and the preceding propositions, a knowledge of 

 ions and their electro-chemical equivalents may be obtained in various ways. 



838. In the first place, they may be determined directly, as has been done with hy- 

 drogen, oxygen, lead, and tin, in the numerous experiments already quoted. 



839. In the next place, from propositions ii. and iii., may be deduced the knowledge 

 of many other ions, and also their equivalents. When chloride of lead was decom- 

 posed, platina being used for both electrodes (395.), there could remain no more doubt 

 that chlorine was passing to the anode, although it combined with the platina there, 

 than when the positive electrode, being of plumbago (794.), allowed its evolution in the 

 free state ; neither could there, in either case, remain any doubt, that for every 103'5 

 parts of lead evolved at the cathode, 36 parts of chlorine were evolved at the anode, for 

 the remaining chloride of lead was unchanged. So also when in a metallic solution 

 one volume of oxygen, or a secondary compound containing that proportion, appeared 

 at the anode, no doubt could arise that hydrogen, equivalent to two volumes, had been 

 determined to the cathode, although, by a secondary action, it had been employed in 

 reducing oxides of lead, copper, or other metals, to the metallic state. In this man- 

 ner, then, we learn from the experiments already described in these Researches, that 

 chlorine, iodine, bromine, fluorine, calcium, potassium, strontium, magnesium, manga- 

 nese, &c., are ions, and that their electro-chemical equivalents are the same as their 

 ordinary chemical equivalents. 



840. Propositions iv. and v. extend our means of gaining information. For if a body 

 of known chemical composition is found to be decomposable, and the nature of the 

 substance evolved as a primary or even a secondary result (743. 777-) at one of the 

 electrodes, be ascertained, the electro-chemical equivalent of that body may be de- 

 duced from the known constant composition of the substance evolved. Thus, when 

 fused protiodide of tin is decomposed by the voltaic current (804.), the conclusion 

 may be drawn, that both the iodine and tin are ions, and that the proportions in which 

 they combine in the fused compound express their electro-chemical equivalents. 

 Again, with respect to the fused iodide of potassium (805.), it is an electrolyte; and 

 the chemical equivalents will also be the electro-chemical equivalents. 



841. If proposition viii. sustain extensive experimental investigation, then it will 

 not only help to confirm the results obtained by the use of the other propositions, but 

 will give abundant original information of its own. 



MDCCCXXXIV. Q 



