1137. Nature and strength of the acid.—­My battery of forty pairs of three-inch plates was charged with acid consisting of 200 parts water and 9 oil of vitriol.  Each plate lost, in the average of the experiments, 4.66 equivalents of zinc for the equivalent of water decomposed in the volta-electrometer, or the whole battery 186.4 equivalents of zinc.  Being charged with a mixture of 200 water and 16 of the muriatic acid, each plate lost 3.8, equivalents of zinc for the water decomposed, or the whole battery 152 equivalents of zinc.  Being charged with a mixture of 200 water and 8 nitric acid, each plate lost 1.85, equivalents of zinc for one equivalent of water decomposed, or the whole battery 74.16 equivalents of zinc.  The sulphuric and muriatic acids evolved much hydrogen at the plates in the trough; the nitric acid no gas whatever.  The relative strengths of the original acids have already been given (1127.); but a difference in that respect makes no important difference in the results when thus expressed by equivalents (1140.).

1138.  Thus nitric acid proves to be the best for this purpose; its superiority appears to depend upon its favouring the electrolyzation of the liquid in the cells of the trough upon the principles already explained (905. 973, 1022.), and consequently favouring the transmission of the electricity, and therefore the production of transferable power (1120.).

1139.  The addition of nitric acid might, consequently, be expected to improve sulphuric and muriatic acids.  Accordingly, when the same trough was charged with a mixture of 200 water, 9 oil of vitriol, and 4 nitric acid, the consumption of zinc was at each plate 2.786, and for the whole battery 111.5, equivalents.  When the charge was 200 water, 9 oil of vitriol, and 8 nitric acid, the loss per plate was 2.26, or for the whole battery 90.4, equivalents.  When the trough was charged with a mixture of 200 water, 16 muriatic acid, and 6 nitric acid, the loss per plate was 2.11, or for the whole battery 84.4, equivalents.  Similar results were obtained with my battery of twenty pairs of four-inch plates (1129.).  Hence it is evident that the nitric acid was of great service when mingled with the sulphuric acid; and the charge generally used after this time for ordinary experiments consisted of 200 water, 4-1/2 oil of vitriol, and 4 nitric acid.

1140.  It is not to be supposed that the different strengths of the acids produced the differences above; for within certain limits I found the electrolytic effects to be nearly as the strengths of the acids, so as to leave the expression of force, when given in equivalents, almost constant.  Thus, when the trough was charged with a mixture of 200 water and 8 nitric acid, each plate lost 1.854 equivalent of zinc.  When the charge was 200 water and 16 nitric acid, the loss per plate was 1.82 equivalent.  When it was 200 water and 32 nitric acid, the loss was 2.1 equivalents.  The differences here are not greater than happen from unavoidable irregularities, depending on other causes than the strength of acid.