Prof. R. Bunsen's Spectral- Analytical Researches. 421 



active ziuc surface of about 48 square centims. Fig. 2, Plate II. 

 shows a battery of four such elements. If this battery be closed 

 with a connecting wire of low conduction-resistance, the forma- 

 tion of a dark-coloured film of liquid, extending outwards from 

 the dissolving zinc plate, is observed ; this dark liquid gradually 

 sinks, and at last collects, in the form of a well-defined layer, at 

 the bottom of the glass cylinder. The original liquid has a spe- 

 cific gravity of 1*140, while the liquid laden with zinc sulphate 

 which collects at the bottom has a gravity of 1272. While the 

 latter liquid sinks gradually downwards, its place is continuously 

 supplied by fresh quantities of liquid which have not undergone 

 electrolysis ; constant circulation is hereby ensured, upon which 

 the constancy of the current greatly depends. 



I have not considered it superfluous to inquire how far the 

 proportion of 1 equivalent of free chromic acid to 6 equivalents 

 of free sulphuric acid is maintained in the liquid while under- 

 going exhaustion by electrolysis. The exhaustion of the liquid 

 w 7 as allowed to proceed until the absolute intensity of the current 

 had diminished from 36 to 6 ; for this purpose the battery was 

 closed by a connecting wire of not very great resistance during 

 a period of fourteen days. The composition of the liquids, referred 

 to an equal weight of hydrated sulphuric acid, was as follows 

 (A represents the original, and B the exhausted liquid) : — 



A. 



B. 



H 2 O.S0 3 100-0, 2-041 equiv. 



H 2 O.S0 3 100-0, 2-0410 equiv. = a. 



K a O.Cr 2 6 . 50-2, 0-340 „ 



Cr 2 O b . 4-5, 0-0447 „ =b. 





Cr 2 3 21*7, 0-2833 „ = c. 





K 2 15-9, 0-3383 „ =d. 





ZnO 340, 08395 „ = <?. 



If the electrolytic process occurs in the battery in the manner 

 already supposed, then the following equations must nearly hold 

 good : — e = 3c and 6b = a — (e + d+ 2c) ; i. e. for every equivalent 

 of reduced chromic acid (Cr 2 6 ) three equivalents of zinc are dis- 

 solved, and the proportion between the two acids yet combined 

 with bases during electrolysis of the liquid remains nearly con- 

 stant. That this is really the case appears from the following 

 numbers : — 



3c= 0-850, 65 = 0-268, 



e = 0-840, a-(e + d + 2c) =0-297. 



If all the bases present be supposed to be in combination with 

 sulphuric acid, then the proportion of free sulphuric to free 

 chromic acid is in the original liquid 1 : 0'424, and in the nearly 

 exhausted liquid 1 : 0'320. In the last instance, the rather too 

 small value actually found for chromic acid may be accounted for 

 by the formation of a small quantity of mercurous chromate by 



