214 Dr. C. R. A. Wright and Mr. C. Thompson. [Mar. 31,. 



tained, amounting under favourable conditions to 0*5 or 06 volt.. 

 The maximum E.M.F. thus capable of development varies considerably 

 with the strength of the ammoniacal solution, being the less the 

 weaker the fluid; addition of common salt or of sal-ammoniac to the 

 liquid notably increases the E.M.F. and diminishes the internal resist- 

 ance of the cell. Spongy platinum in a thin layer as the aeration 

 plate gives higher values than thin platinum foil ; the highest num- 

 bers thus obtained, using pretty concentrated ammoniacal brine, fell 

 but little short of 0*8 volt ; or somewhat less than the E.M.F. corre- 

 sponding with the heat of formation of cuprous oxide,* since, accord- 

 ing Julius Thomsen, Cu 2 ,0 = 40810 = about 0*88 volt, 



It is obvious that this copper atmospheric oxidation cell has a close 

 connexion with the " air-battery " described in 1873 by Gladstone 

 and Tribe ('Roy. Soc. Proc.,' vol. 21, p. 247) in which what is virtually 

 an "aeration plate," consisting of a tray fall of crystals of silver is 

 used, opposed to a copper plate immersed in a solution of copper 

 nitrate. Cuprous oxide is formed in both cases, in virtue of the 

 indirect combination brought about between the oxygen of the air 

 and the copper : but there is this great difference between the two 

 (apart from the cuprous oxide being deposited as such in Gladstone 

 and Tribe's arrangement, and being kept in solution in ours), that in 

 the one the cuprous oxide is formed at the surface of the copper plate 

 itself, and in the other at the surface of the aeration plate. This, 

 essential difference is embodied in the above depicted scheme as 

 compared with the following one which represents the action in 

 Gladstone and Tribe's cell : — 



^] Copper. 



i Silver I ol Cu I ^°3)2Ch I (N0 3 ) 3 Cu I 

 ^toilver | U| 0u | (N03 ) 2Cu | (NQ 3 ) 2 Cu | Lo PP er ' 



One result of this difference is that the surface of the aeration plato 

 in the ammonia cell is kept constantly the same, whereas in the 

 nitrate cell it is continually changing its character through deposition 

 of solid cuprous oxide on the silver : in consequence of this deposition,, 

 whilst the E.M.F. of the ammonia cell, cceteris paribus, is constant, 

 that of the nitrate cell is continually varying. Gladstone and Tribe, 

 moreover, only obtained an E.M.F. of ¥ % to ±± of a Daniell, or about 

 0T04 to 0T43 volt, even under the most favourable conditions, viz., 

 when the cell was connected with an electrometer ; whilst four or five 

 times this amount is indicated by the cells examined by us. 



* The actual chemical change going on in the cell is the synthesis of cuproso- 

 ammonium hydroxide, so that the (unknown) heat of solution of cuprous oxide in 

 ammonia should be added to this to obtain the total heat development. 



Silver + 



Cu(NO s ) 

 Cu(N0 3 ); 



CufN0 3 ) 2 



Cu(rto 3 )o 



