428 Prof. R. Bunsen's Spectral- Analytical Researches. 



and the amount of zinc, Z , required for the current-production 

 during the experiments, by the equation 



rj Zn 



Z « = HTO W ' 



In experiments carried out by Dr. Gabriel the following values 

 were obtained : — 



w = 2714, 



hence 



t =14400, 

 J = 20; 



Z =9802. 



The actual loss of weight for each zinc cylinder was, in milli- 

 grammes, 



18129 

 16972 

 20481 

 19221 



Mean . 18701 



While, therefore, in the chromic- acid battery, arranged as already 

 described, the loss of zinc averaged 22 per cent., in the nitric-acid 

 battery employed in these experiments the mean loss amounted 

 to 48 per cent. 



The economical superiority of the chromic battery for regular 

 work is confirmed by the results obtained in practice. I am 

 possessed of a battery of 40 pairs with an active zinc surface of 

 only 40 square centims. in each plate; by a simple handle- 

 arrangement the plates are immersed in and withdrawn from the 

 liquid when required. This battery has served for all lecture ex- 

 periments throughout eight semestres, during which time neither 

 the zinc plates, the covering of wax, nor the exciting liquid has 

 been renewed, nor have the conducting connexions been cleaned ; 

 it has only been necessary occasionally to bestow a few minutes' 

 labour upon the renewal of the amalgamation of the zinc plates, 

 and from time to time to replace the water lost by evaporation. 

 The apparatus, to this day, gives an electric arc between carbon 

 points — not, it is true, sufficiently steady for optical projection, 

 but perfectly serviceable for photochemical lecture experiments. 

 The currents obtained from this battery after four years' use are 

 yet, and are likely for some time to remain, strong enough for 

 electrolytic demonstration, production of spark-spectra, decom- 

 position of gases by induction- sparks, &c. I need scarcely repeat 



