1883.] 655 [Barker. 



solution is prevented, first, by keeping a crystal of copper sulphate in the 

 copper solution, and second, by the deposition of the excess of zinc sul- 

 phate in crystals. Since the zinc solution is the heavier, any hydrostatic 

 transfer will be into the copper solution where no damage is done. When 

 the cell is on open circuit, no diffusion takes place, communication being 

 cut off. And since the apparatus is wholly closed to the air, no change- 

 in the conditions can arise from evaporation. Provided therefore the 

 temperature be uniform, the electromotive force of the cell may be ex- 

 pected to be constant within narrow limits. 



2d. Its transportability. In the use of the ordinary Daniell cell, par- 

 ticularly of the gravity pattern, any change of position disturbs more or 

 less the conditions of equilibrium, and so varies the electromotive force. 

 After moving such a cell, therefore, or after altering in any way its normal 

 state, as bj^ adding water lost by evaporation, it is necessary to allow 

 twenty-four hours or more of rest, before the battery can be trusted to give 

 proper measurements. But in the cell now preposed, no change can take 

 place in its conditions by being moved from place to place. Hence for 

 local testing in circumstances where a permanent battery cannot be had, 

 its value is considerable . 



3d. Its convenience and cheapness. The common form of Daniell bat- 

 tery requires to be especially prepared for use. If set up anew, twenty- 

 four nours are needed before it comes into good working action. Even 

 the improved forms of standard cell above described are more or less in- 

 convenient, since they require something to be done to put them in action. 

 But in the form now proposed the cell is always ready for use, no matter 

 how long a time may have elapsed since it was used before. Tlie opening 

 of a stop-cock puts it in full operation. Moreover, this cell is readily con- 

 structed from apparatus and material at hand in every laboratory. And 

 it douche bottles are used, the cost is not over a dollar. 



It is evident that the form of apparatus now described has a much wider 

 range than has yet been claimed. By its means not only may the effect of 

 using various solutions in contact with either plate of a Daniell cell be ac- 

 curately studied, free from many of the disturbing causing hitherto en- 

 countered, but by the use of various metals also, the innumerable ques- 

 tions of importance, concerning not only primary but also secondary bat- 

 teries, may be conveniently investigated. One of these for example, is the 

 question whether the zinc of a Daniell cell should be amalgamated. The im- 

 pression is very generally in favor of amalgamation, since in a zinc sulphate 

 solution amalgamated zinc is said not to become polarized ; and since the 

 electromotive force is one or two per cent, higlier. But experiments have 

 shown, that while amalgamated zinc should be used when the solution is 

 acid, yet that when it is neutral, local action is greater with amalgamated 

 than with unamalgamated zinc. 



Experiments now in progress with this new form of cell, it is hoped, 

 will enable some of these doubtful points to be satisfactorily settled. 



Philadelphia, January 18, 1883. 



