[April 6 iS88 



SCIENTIFIC NEWS. 



315 



small island, it iS most desirable that we should continue 

 to import petroleum oil from other parts of the world in 

 order to diminish the extravagant demand upon our coal 

 which arises from gas making. I fear, however, that the 

 present rate of working the American wells will ere long 

 exhaust them. We may then obtain supplies from Baku 

 on the Caspian, and also by distillation of the vast deposits 

 of Scotch shale, but it will be more costly than at 

 present, and both Russian oil and shale oil are inferior 

 to that which is obtained from the American oil wells. 

 The above applies equally to the supplies of natural gas 



The simplest form of primary battery is a pair of 

 plates — the one of zinc, the other of copper — in a vessel 

 of dilute sulphuric acid. When a current of electricity 

 is allowed to flow from the copper to the zinc, a chemical 

 action is set up, and the acid attacks the zinc, forming 

 sulphate of zinc, while hydrogen gas is given oiT at the 

 copper. If, by forcing a more powerful current in the 

 opposite direction, we could undo this action, and deposit 

 the zinc on the plate again, as in electrotyping, we should 

 have a secondary battery ; but this is not practicable. 



If, however, we take two lead plates and coat them, 



Accumulator Room at Broomhill, the Residence of Sir David Salomons, Bart., F.R.S. 



which of late has been as largelj' used in America both 

 as fuel and for lighting. 



ELECTRIC ACCUMULATORS. 



ELECTRIC accumulators, or storage batteries, are 

 supposed by many people to contain, when 

 charged, a store or supply of electricity, much in the 

 same way as a Leyden jar is said to; be charged. The 

 expression, " storage of electricity," is convenient, but it 

 is not accurate. The same may be said of the " flow- 

 ing" of an electric " current." The name, "secondary 

 battery," is more accurate, but it is seldom used. 



one with peroxide of lead and the other with monoxide 

 of lead or litharge, and place them in dilute sulphuric 

 acid, we shall have a powerful battery which has the 

 great advantage of retaining its force until nearly ex- 

 hausted, instead of gradually running down. The 

 chemical changes which take place during the discharge 

 have formed the subject of a considerable amount of dis- 

 cussion, and the leading authorities dilfer very consider- 

 ably in their views. One theory is that both the 

 coatings become sulphate of lead ; another that there is 

 merely a change in the quantity of oxygen in the oxides ; 

 and again, that one plate becomes so reduced by the 

 hydrogen that the oxide becomes spongy metallic lead. 



