290 Dr. C. R. A. Wright on the Determination of 



accounts, H 2 is greater than H x ; that is, the work gained in 

 the synthesis ZnO, S0 3 x aq. increases as x diminishes. Since 

 the net chemical action in a Daniell cell is equivalent to 

 the result of the actions (Zn, 0) + (ZuO, S0 3 x aq.)— (Cu, 0, 

 S0 3 ?/aq.), it finally results that the chemical action taking- 

 place in the cell develops an amount of energy which in- 

 creases, ccderis paribus, as x diminishes, i. e. is greater the 

 more concentrated the acid surrounding the zinc. 



On the other hand, when the zinc plate is surrounded by 

 zinc-sulphate solution instead of sulphuric acid, the effect of 

 variation in the strengths of the copper- and zinc-sulphate 

 solutions will be comparatively but small when both are of 

 the same degree of molecular concentration (which, as shown 

 above, is very nearly the case when they are of the game 

 density). If S0 4 Zn, ?iH 2 evolves, as before, hi on addi- 

 tion of (m— w)H 2 0, and S0 4 Cu, nH 2 evolves h 3 on a 

 similar addition, and if H 3 and H 4 are respectively the heats 

 evolved when zinc displaces copper from Cu S0 4 , ?iH 2 0, and 

 Cu S0 4 , niH 2 0, it results that, if zinc displace copper from the 

 stronger solution and the resulting S0 4 Zn, «H 2 be diluted to 

 Zn S0 4 ,?nH 2 0, the heat evolved will be H 3 + /<i ; whilst if the 

 copper- sulphate solution be first diluted and then the zinc 

 displaces the copper, the heat-evolution is H 4 + /* 3 . Since, of 

 necessity, lI 3 + hi = ~H. 4 + h 3 , it follows that H 3 = H 4 + /f 3 — 7^. 

 Now, since the solution of zinc and copper sulphates (crystal- 

 lized) is in each case accompanied by heat-absorption, it results 

 that h 3 and li x are both negative, and hence that h 3 —h x is 

 negligible if h 3 is any thing like comparable with h x in magni- 

 tude ; so that in this case the energy developed by the net che- 

 mical action taking place in a Daniell cell must be practically 

 independent of the degree of concentration of the solutions. 



114. The earlier calculations of J. Thomsen, referred to in 

 §16, as to the heat evolved in the displacement of copper 

 from copper sulphate by zinc, are for various reasons probably 

 less accurate than the later results obtained by him (Journ. 

 prak. Chem. [2] xi. p. 412, and xii. p. 271) ; these different 

 values may be thus contrasted, the values being gramme- 

 degrees per gramme-molecule : — 



Values from experiments by An- 

 drews, Dulong, Hess, Favre and 

 Silberrnarm, and J. Thomsen. 



Zn, 0, S0 3 aq. = 108460 



Cu, 0, S0 3 aq. = 56216 

 Difference = 52244 

 Corresponding in volts (per 

 gramme-equivalent) to T152 



Values from later experiments 

 of J. Thomsen. 



106090 

 55960 

 50130 



1-105 



