Page:Scientific Papers of Josiah Willard Gibbs.djvu/381

and sometimes cold is produced.^[1] When neither is produced, of course the electromotive force of the cell is exactly equal to its diminution of energy per unit of electricity transmitted. But such a coincidence is far less significant than the fact that an absorption of heat has been observed. With acid containing about seven equivalents of water $({\text{HNO}}_{6}+{\text{7HO}})[{\text{HNO}}_{3}+3{\tfrac {1}{2}}{\text{H}}_{2}{\text{O}}]$, M. Favre has found

$(V''-V')\Delta e=46781^{\text{cal}},$⁠$\Delta \epsilon =-41824^{\text{cal}},$⁠$\Delta Q=4957^{\text{cal}};$

and with acid containing about one equivalent of water

$({\text{HNO}}_{6}+{\text{7HO}})[{\text{HNO}}_{3}+{\tfrac {1}{2}}{\text{H}}_{2}{\text{O}}],$ $(V''-V')\Delta e=49847^{\text{cal}},$⁠$\Delta \epsilon =-52714^{\text{cal}},$⁠$\Delta Q=-2867^{\text{cal}}.$

In the first example, it will be observed that the quantity of heat absorbed in the cell is not small, and that the electromotive force is nearly one-eighth greater than can be accounted for by the diminution of energy in the cell.

This absorption of heat in the cell he has observed in other cases, in which the chemical processes are much more simple.

For electrodes of cadmium and platinum in hydrochloric acid his experiments give^[2]

${\begin{aligned}(V''-V')\Delta e&=9256^{\text{cal}},&\Delta \epsilon &=-8258^{\text{cal}},\\\Delta W_{\text{P}}&=-290^{\text{cal}},\qquad &\Delta Q&=1288^{\text{cal}}.\end{aligned}}$

In this case the electromotive force is nearly one-sixth greater than can be accounted for by the diminution of energy in the cell with the work done against the pressure of the atmosphere.

For electrodes of zinc and platinum in the same acid one series of experiments gives^[3]

${\begin{aligned}(V''-V')\Delta e&=16950^{\text{cal}},&\Delta \epsilon &=-16189^{\text{cal}},\\\Delta W_{\text{P}}&=-290^{\text{cal}},\qquad &\Delta Q&=1051^{\text{cal}};\end{aligned}}$

and a later series,^[4]

${\begin{aligned}(V''-V')\Delta e&=16738^{\text{cal}},&\Delta \epsilon &=-17702^{\text{cal}},\\\Delta W_{\text{P}}&=-290^{\text{cal}},\qquad &\Delta Q&=-674^{\text{cal}}.\end{aligned}}$

In the electrolysis of hydrochloric acid in a cell with a porous partition, he has found^[5]

$(V'-V'')\Delta e=34825^{\text{cal}}$⁠$\Delta Q=2113^{\text{cal}},$

1. Mém. Savants Étrang., loc. cit., p. 93; or Comptes Rendus, t. lxix, p. 37, and t. lxxiii, p. 893.
2. Comptes Rendus, t. lxviii, p. 1305. The total heat obtained in the whole circuit (including the cell) when all the electromotive work is turned into heat, was ascertained by direct experiment. This quantity, 7968 calories, is evidently represented by $(V''-V')\Delta e-\Delta Q$, also by $-\Delta e+\Delta W_{\text{P}}$. (See (691 ).) The value of $(V''-V')\Delta e$ is obtained by adding $\Delta Q$, and that of $-\Delta \epsilon$ by adding $\Delta W_{\text{P}}$, which is easity estimated, being determined by the evolution of one kilogramme of hydrogen.
3. Ibid.
4. Mém. Savants Étrang., loc. cit., p. 145.
5. Ibid., p. 142.