subdivision of this series of Researches which contains the account of the volta-electrometer (439, etc.).
521. In the next place, I also consider the law as established with respect to muriatic acid by the experiments and reasoning already advanced, when speaking of that substance, in the subdivision respecting primary and secondary results (493, etc.).
522. I consider the law as established also with regard to hydriodic acid by the experiments and considerations already advanced in the preceding division of this series of Researches (502, 503).
523. Without speaking with the same confidence, yet from the experiments described, and many others not described, relating to hydro-fluoric, hydro-cyanic, ferro-cyanic, and sulpho-cyanic acids (505, 506, 507), and from the close analogy which holds between these bodies and the hydracids of chlorine, iodine, bromine, etc., I consider these also as coming under subjection to the law, and assisting to prove its truth.
524. In the preceding cases, except the first, the water is believed to be inactive; but to avoid any ambiguity arising
Fig. 28.
from its presence, I sought for substances from which it should be absent altogether; and, taking advantage of the law of conduction already developed (116, etc.), I soon found abundance, amongst which protochloride of tin was first subjected to decomposition in the following manner. A piece of platina wire had one extremity coiled up into a small knob, and, having been carefully weighed, was sealed hermetically into a piece of bottle-glass tube, so that the knob should be at the bottom of the tube within (fig. 28). The tube was suspended by a piece of platina wire, so that the heat of a spirit-lamp could be applied to it. Recently fused protochloride of tin was introduced in sufficient quantity to occupy, when melted, about one half of the tube; the wire of the tube was connected with a volta-electrometer (446), which was itself connected with the negative end of a voltaic battery; and a platina wire connected with the positive end of the same battery was dipped into the fused chloride in the tube; being however so bent, that it could not by any shake of the hand or apparatus touch the negative electrode at the bottom of the vessel. The whole arrangement is delineated in fig. 29.
525. Under these circumstances the chloride of tin was decomposed: the chlorine evolved at the positive electrode
