3 io POPULAR SCIENCE MONTHLY. 



sired it is very doubtful whether the economy of the steam engine 

 can be superseded by any one of them. It is true that there is 

 no expenditure for fuel, but the interest on the extra cost of the 

 plant and the maintenance thereof, as well as the additional space 

 required, may more than offset this gain ; and the fact that so little 

 is done in the way of utilizing them would seem to show that up 

 to the present time their value has failed to make any great im- 

 pression upon engineers who have looked into the subject. It 

 does not follow from this that they will never come into use on a 

 more extensive scale than at present, but it does follow that the 

 dreams of those who believe that they will eventually supersede 

 all forms of prime movers that consume fuel will never be real- 

 ized. Through the increased value of fuel or the reduced cost of 

 construction of the apparatus, or both, they may become compet- 

 itors to a greater or less extent, but more than this can not be 

 expected. 



Considering, now, the effects of the solution of the problem of 

 obtaining electricity direct from coal, it can be said that it is far 

 more likely to revolutionize the affairs of the world than the utili- 

 zation of the natural forms of energy ; but it must also be said 

 that we are not justified, in view of what is now known in rela- 

 tion to the subject, in assuming that it will ever realize the pre- 

 dictions of the oversanguine prophets. If we could solve the prob- 

 lem according to our ideal, all that is expected of it would be 

 accomplished ; but such a solution is highly improbable, if not 

 actually impossible. Our ideal battery would be as simple as a 

 boiler, and be provided with a place where coal could be fed in 

 and another through which the residue could be removed. In a 

 boiler, the pressure of the steam, as well as the quantity generated, 

 can be increased by simply increasing the size of the fire box, but 

 this simplicity could not be obtained even in our ideal battery, 

 because the electromotive force would remain the same no matter 

 how much the size of the cell might be increased. To obtain an 

 electromotive force high enough for practical purposes it would 

 be necessary to use a large number of cells, and, to feed these with- 

 out too much trouble, it would be necessary to devise an auto- 

 matic feeder capable of operating with a degree of perfection 

 hardly obtainable without the aid of human intelligence. 



It may be permissible to dream of such perfection, but we are 

 not justified in assuming that it is possible. Electricity can be 

 obtained from chemical action only when the material acted upon 

 is in the electric circuit. If two metals are placed in a solution 

 that can decompose one of them, an electric current will flow in a 

 wire the ends of which are attached to the two metals. If two 

 solutions capable of acting upon each other are separated by a 

 porous partition, and into each a plate attached to a wire is im- 



