Prof. Daniell 07i the Constant Voltaic Battety. 299 



is necessary that they should slowly mingle; and the diaphragm 

 is placed to regulate the mixture. In his own words it is ne- 

 cessary " que I'on approche les deux diaphragmes de telle sorte 

 que I'acide nitrique de la case zinc puisse passer le?iteinent dans 

 la case cuivre." 



The purpose which the nitric acid is said to effect, is to me 

 perfectly incomprehensible, namely, that of " taking up the 

 copper of the solution, which after having traversed the dia- 

 phragms is deposited upon the zinc.*' 



According to my experience, under these circumstances 

 the deposited copper would be untouched and the local solu- 

 tion of the zinc greatly promoted : but my present object is 

 not to controvert M. E. Becquerel's statements further than 

 is necessary to show that the principles which he has derived 

 from his father's experiments are not the principles of my 

 "constant battery." 



M. Edmond Becquerel, however, seems to have some mis- 

 givings that the premises upon which he has founded his fa- 

 ther's claim may not be deemed sufficient for the purpose; 

 for he proceeds, — 



" Ainsi ces experiences montrent la possibilite d'obtenir un 

 courant constant en detruisant le courant secondaire ; c'est-a- 

 dire en faisant plonger les lames dans des liquides differents. 

 Plus tard monpere a resolu complelement la question." (P. 440.) 



This complete solution of the problem is comprised in the 

 apparatus which M. Becquerel has named " chaine simple a 

 oxygene." It consists of two small glass vessels, of which one 

 contains a concentrated solution of caustic potassa, and the 

 other a solution of strong nitric acid. These two vessels are 

 connected together by a bent glass tube fitted with porcelain 

 clay wetted with a solution of sea salt. In each vessel is placed 

 a small plate of platinum; and when a metallic communica- 

 tion is made between the two, a current is established of suffi- 

 cient energy to cause the evolution of oxygen from the plate 

 in the potassa, while the equivalent hydrogen is absorbed by 

 the nitric acid at the opposite plate. When the communica- 

 tion is made between the plates by means of a galvanometer, 

 the needle is deflected. This slow current will remain con- 

 stant for twenty-four hours, or longer ; but it ceases when the 

 nitrate of potassa formed in the connecting-tube crystallizes. 



Now, it will be observed, that the porous diaphragm is here 

 again employed, not to produce, as in my "constant battery," 

 as complete a separation as possible between the liquids, but 

 to regulate their mixture, which is essential both to the pro- 

 duction of the primary current and, according to M. Becque- 

 rel, to the destruction of the secondary one. 

 X 2 



