THE CORRELATION OF THE PHYSICAL FORCES 83 



tion of indigo, and the power of electricity has come 

 through these wires and made itself evident by its chem- 

 ical action. There is also another curious thing to be 

 noticed now we are dealing with the chemistry of electricity, 

 which is, that the chemical power which destroys the color 

 is only due to the action on one side. I will pour some 

 more of this sulphindigotic acid( 2a ) into a flat dish, and 

 will then make a porous dike of sand separating the two 

 portions of fluid into two parts (Fie. 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 can not perceive any action 

 none has taken place. 



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 precipi- 

 tated 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 



93 Sulphindigotic acid. A mixture of one part of indigo and fifteen parts 

 of concentrated oil of vitriol. It is bleached on the side at which hydrogen 

 gas is evolved in consequence of the liberated hydrogen withdrawing oxygen 

 from the indigo, thereby forming a colorless deoxidized indigo. In making 

 the experiment, only enough of the sulphindigotic acid must be added t 

 give the water a decided blue color. 



