Pulverised charcoal was diffused through dilute sulphuric acid, and subjected with the solution to the action of a voltaic battery, terminated by platina poles; but not the slightest tendency of the charcoal to the negative pole could be observed. Sublimed sulphur was diffused through similar acid,, and submitted to the same action, a silver plate being used as the negative pole; but the sulphur had no tendency to pass to that pole, the silver was not tarnished, nor did any sulphuretted hydrogen appear. The case of magnesia and water (231, 269), with those of comminuted metals in certain solutions (282), are also of this kind; and, in fact, substances which have the instant before been powerfully determined towards the pole, as magnesia from sulphate of magnesia, become entirely indifferent to it the moment they assume their independent state, and pass away, diffusing themselves through the surrounding fluid.
284. There are, it is true, many instances of insoluble bodies being acted upon, as glass, sulphate of baryta, marble, slate, basalt, etc., they form no exception; for the substances they give up are in direct and strong relation as to chemical affinity with those which they find in the surrounding solution, so that these decompositions enter into the class of ordinary effects.
285. It may be expressed as a general consequence, that the more directly bodies are opposed to each other in chemical affinity, the more ready is their separation from each other in cases of electro-chemical decomposition, i.e. provided other circumstances, as insolubility, deficient conducting power, proportions, etc., do not interfere. This is well known to be the case with water and saline solutions; and I have found it to be equally true with dry chlorides, iodides, salts, etc., rendered subject to electro-chemical decomposition by fusion (138). So that in applying the voltaic battery for the purpose of decomposing bodies not yet resolved into forms of matter simpler than their own, it must be remembered, that success may depend not upon the weakness, or failure upon the strength, of the affinity by which the elements sought for are held together, but contrariwise; and then modes of application may be devised by which, in association with ordinary chemical powers, and the assistance of fusion (130, 153), we may be able to penetrate much further than at present into the constitution of our chemical elements.
286. Some of the most beautiful and surprising cases of
