12 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 76 



hydrogen gas set free by the action of the sulphuric acid on the zinc, 

 and hence was the depolarizing agent. Hydrogen combining with 

 nitric acid forms nitrous peroxide and water. Part of the nitrous 

 peroxide is dissolved in the water, and the rest escapes as fumes 

 which, however, are very suffocating. 



The chemical equations of this cell are as follows: 



In outer glass jar: Zn + H2S04 = ZnS04 + H2 

 In inner porous jar: H2 + 2HN03 = N204 + 2H20 



An interesting thing about Grove's cell is that it was planned in 

 accordance with a theory. Grove knew that the electrical energy of 

 the zinc-sulphuric acid cell came from the chemical affinity of the two 

 reagents, and if the hydrogen gas set free could be combined with 

 oxygen (to form water — H2O), such chemical affinity should increase 

 the strength of the cell. As the hydrogen gas appears at the other 

 electrode, the oxidizing agent should surround that electrode. Nitric 

 acid was known at that time as one of the most powerful oxidizing 

 liquids, but as it attacks copper, he used platinum for the other elec- 

 trode. Thus he not only overcame the difficulty of polarization by 

 the hydrogen gas, but also increased the voltage of the cell by the 

 added chemical action of the combination of hydrogen and oxygen. 



grove's DEMONSTRATION OF INCANDESCENT LIGHTING 



In 1840 Grove made an experimental lamp by attaching the ends 

 of a coil of platinum wire to copper wires, the lower parts of which 

 were well varnished for insulation. The platinum wire was covered 

 by a glass tumbler, the open end set in a glass dish partly filled with 

 water. This prevented draughts of air from cooling the incandescent 

 platinum, and the small amount of oxygen of the air in the tumbler 

 reduced the amount of oxidization of the platinum that would other- 

 wise occur. With current supplied by a large number of cells of his 

 battery, he lighted the auditorium of the Royal Institution with these 

 lamps during one of the lectures he gave. This lamp gave only a 

 feeble light as there was danger of melting the platinum and platinum 

 gives but little light unless operated close to its melting temperature. 

 It also required a lot of current to operate it as the air tended to cool 

 the incandescent platinum. The demonstration was only of scientific 

 interest, the cost of current being much too great (estimated at 

 several hundred dollars a kilowatt hour) to make it commercial. 



