Influence of Pro-portions in Electrolytes. 171 



cause of their departure from this simplicity of composition, 

 that boracic acid, ammonia, perchlorides, periodides, and many 

 other direct compounds of elements, are indecomposable. 



698. With regard to salts and combinations of compound 

 bodies, the same simple relation does not appear to hold good. 

 I could not decide this by bisulphates of the alkalies, for as 

 long as the second proportion of acid remained, water was 

 retained with it. The fused salt, therefore, conducted, and 

 was decomposed; but hydrogen always appeared at the ne- 

 gative electrode. 



699. A biphosphate of soda was prepared by heating, and 

 ultimately fusing, the ammonia-phosphate of soda. In this 

 case the fused bisalt conducted, and was decomposed ; but a 

 little gas appeared at the negative electrode, and though I be- 

 lieve the salt itself was electrolyzed, I am not quite satisfied 

 that water was entirely absent. 



700. Then a biborate of soda was prepared ; and this, I 

 think, is an unobjectionable case. The salt, when fused, con- 

 ducted, and was decomposed, and gas appeared at both elec- 

 trodes : even when the boracic acid was increased to three 

 proportionals the same effect took place. 



701. Hence this class of compound combinations does not 

 seem to be subject to the same simple law as the former class 

 of binary combinations. Whether we may find reason to 

 consider them as mere solutions of the compound of single 

 proportionals in the excess of acid, is a matter which, with 

 some apparent exceptions occurring amongst the sulphurets, 

 must be left for decision by future examination. 



702. In any investigation of these points, great care must 

 be taken to exclude water ; for if present, secondary effects 

 are so frequently produced as often seemingly to indicate an 

 electro-decomposition of substances, when no true result of 

 the kind has occurred (742. &c). 



703. It is evident that all the cases in which decomposition 

 does not occur may depend upon the want of conduction (677. 

 413.); but that does not at all lessen the interest excited by 

 seeing the great difference of effect due to a change, not in the 

 nature of the elements, but merely in their proportions, espe- 

 cially in any attempt which may be made to elucidate and ex- 

 pound the beautiful theory put forth by Sir Humphry Davy*, 

 and illustrated by Berzelius and other eminent philosophers, 

 that ordinary chemical affinity is a mere result of the electri- 

 cal attractions of the particles of matter. 



* Philosophical Transactions, 1807, pp. 32, 39; also 1826, pp, 387, 389. 

 [or Phil. Mag. first series, vol. xxviii. pp. 114, 220; also Phil. Mag. and 

 Annals, N.S., vol. i. p. 31-199.— Edit.] 



Z 2 



