I will pour some more of this sulpho-indigotic acid[23] into a flat dish, and will then make a porous dyke of sand, separating the two portions of fluid into two parts (fig. 50); and now we shall be able to see whether there is any difference in the two ends of the battery, and which it is that possesses this peculiar action. You see it is the one on my right hand which has the power of destroying the blue--for the portion on that side is thoroughly bleached--while nothing has apparently occurred on the other side. I say _apparently_, for you must not imagine that, because you cannot perceive any action, none has taken place. [Illustration: Fig. 50.] Here we have another instance of chemical action. I take these platinum plates again, and immerse them in this solution of copper, from which we formerly precipitated some of the metal, when the platinum and zinc were both put in it together. You see that these two platinum plates have no chemical action of any kind--they might remain in the solution as long as I liked, without having any power of themselves to reduce the copper;--but the moment I bring the two poles of the battery in contact with them, the chemical action, which is there transformed into electricity and carried along the wires, again becomes chemical action at the two platinum poles; and now we shall have the power appearing on the left-hand side, and throwing down the copper in the metallic state on the platinum plate; and in this way I might give you many instances of the extraordinary way in which this chemical action, or electricity, may be carried about. That strange nugget of gold, of which there is a model in the other room--and which has an interest of its own in the natural history of gold, and which came from Ballarat, and was worth £8,000, or £9,000, when it was melted down last November--was brought together in the bowels of the earth, perhaps ages and ages ago, by some such power as this. And there is also another beautiful result dependent upon chemical affinity in that fine lead-tree[24]--the lead growing and growing by virtue of this power. The lead and the zinc are combined together in a little voltaic arrangement, in a manner far more important than the powerful one you see here; because, in nature, these minute actions are going on for ever, and are of great and wonderful importance in the precipitation of metals and formation of mineral veins, and so forth. These actions are not for a limited time, like my battery here, but they act for ever in small degrees, accumulating more and more of the results.