Prof. R. Bunsen's Specti-aU Analytical Researches. 425 



under the above conditions, apparent and not real. Polarization 

 is therefore not prevented in the chromic battery to so great 

 an extent as in the Daniell or Grove battery ; and the conditions 

 on which equations (2) and (3) are based are not rigidly fulfilled 

 during the increasing exhaustion of the exciting fluid. The ex- 

 traordinarily large value of e for the chromic battery cannot, 

 therefore, be received without doubt. That this value, however, 

 is not due to errors of experiment is evident when we find 

 that an equally high value is derived from an estimation of the 

 electromotive force by Lipmann's electrometer in the unconnected 

 battery. Experiment gave the proportion between the electro- 

 motive force of the chromic battery and of Grove's as follows : — 

 Grove _ 18-45 



Chromic battery 21*18 



The chromic battery was allowed to remain at rest for a little 

 time before the experiment. A solution of potassium dichromate 

 and sulphuric acid, in those proportions which we have seen to be 

 the best, is possessed of considerably lower conduction-power 

 than the sulphuric and nitric acids used in the Grove cell. This 

 disadvantage, however, is completely counterbalanced by the 

 absence of the proportionally large conduction-resistance caused 

 by the clay cells of the ordinary batteries, and by the small dis- 

 tance which may therefore be maintained between the exciting 

 plates. 



For the purpose of comparison, a couple, consisting of a coal 

 rod and zinc plate (covered on the back with wax and amalga- 

 mated on the other side) was placed, first in a Grove's battery 

 with clay cells, and then in a chromic battery without clay cells — 

 the distance between the carbon and zinc being 15 millims., and 

 the surface exposed 400 square millims., in each case. 

 The conduction-resistance of the two elements was as follows: — 



Grove's battery with clay cells . =0*6401 B.A. 

 Chromic battery without clay cells =0*5575 „ 



That a just view of the economical effect of the chromic bat- 

 tery may be attained, it will be necessary to examine somewhat 

 closely into the chemical processes which take place in this bat- 

 tery. In an unconnected freshly filled Grove's battery the zinc- 

 consumption is extremely small ; it is only when, after long use, 

 an electrolytic and endosmotic exchange has been established 

 between the exciting liquids, that a consumption of zinc inde- 

 pendent of the production of the current becomes marked. In 

 an unconnected chromic battery, on the other hand, the con- 

 sumption of zinc is the same as is required for current-produc- 

 tion in the connected battery. In order to avoid this waste of 



