30 ELECTRIC LIGHTING. 



circuit has little resistance, and that of 100 to 150 metres 

 when the resistance is large. The values which we have 

 just given relate only to a cell with fresh liquids; but these 

 are rapidly changed as the nitric acid becomes deoxidized 

 and the acidulated water becomes charged with sulphate of 

 zinc from the corrosion of the metal. To restore the con- 

 dition of the cell it often suffices to pour a little water into 

 the outer liquid, and to add to the nitric acid some concen- 

 trated sulphuric acid, which, having great attraction for water, 

 dehydrates the spent nitric acid. 



I enter into many details on this battery, and on all others, 

 in the first volume of my Expose des applications del'ekctricite^ 

 and this renders it unnecessary to speak more about them 

 here. Their profound study would be altogether beyond the 

 purpose of this work ; it is sufficient for us to describe the 

 mode of arranging the foregoing battery, in order that in the 

 application which may be made of it to electric lighting it 

 may be known upon what we have to rely. 



In order to obtain the electric light with a Bunsen's bat- 

 tery, it is necessary to group together a certain number of 

 cells, and the mode of grouping these cells depends upon 

 the kind of light which it is desired to obtain. If the light 

 is to be supplied by a voltaic arc, that is to say, with a gaseous 

 interval between carbon electrodes, it is necessary to group 

 the cells for tension, that is to say, by their opposite poles, a 

 positive pole with a negative pole, as shown in Fig. 5, and at 

 least 30 cells are necessary ; generally 60 are used for most 

 of the experiments that are made at theatres, or for the 

 lighting of works by night, and even then only" one lamp 

 can be lighted. When it is desired to light several, a much 

 more powerful battery must be used with certain lamps. 

 \Ye shall speak of this farther on. 



If the light is to be the result of art incandescent effect, 

 the battery gains by being arranged for quantity ; that is to 

 say, arranged in such a manner that all the cells are joined 

 by their like poles. The calorific effects are then increased 



