. Carnegie Institution of Washington publication. ENERGY CHANGES INVOLVED IN THE DILUTION OF ZINC AND CADMIUM AMALGAMS. By Theodore William Richards and George Shannon Forbes. INTRODUCTION. Nearly half a century ago a French physicist named Gaugain published a note 1 on his investigation of a voltaic pile whose " negative metal " was a dilute amalgam of zinc or cadmium. At first the electromotive force rose very rapidly when the proportion of oxidizable metal was increased, but beyond a certain point the introduction of fresh quantities of zinc caused no further variation. He conclud
. Carnegie Institution of Washington publication. ENERGY CHANGES INVOLVED IN THE DILUTION OF ZINC AND CADMIUM AMALGAMS. By Theodore William Richards and George Shannon Forbes. INTRODUCTION. Nearly half a century ago a French physicist named Gaugain published a note 1 on his investigation of a voltaic pile whose " negative metal " was a dilute amalgam of zinc or cadmium. At first the electromotive force rose very rapidly when the proportion of oxidizable metal was increased, but beyond a certain point the introduction of fresh quantities of zinc caused no further variation. He concluded that these phenomena were occasioned by the affinity of the mercury for the amalgamated metal, an affinity which varied with the proportions of the amalgam. He also found that cadmium always had an electromotive force greater than its amalgams, no matter whether these contained cadmium in mere traces or in sufficient quantities to form a solid compound. Shortly after, M. E. Becquerel2 published an exhaustive and scholarly treatise on the " Disengagement of electricity in voltaic ; His experi- mental skill and his logical interpretation of results appear remarkable when we consider the limitations of exact knowledge at that time. In this paper he suggested the probable existence of an approximate relation between the heats of combustion of different metals and their electromotive forces, and pointed out the importance of further work in this direction. Among the many substances examined by him were amalgams of zinc, manganese, ammonium, barium, calcium, sodium, and potassium. The dependence of electromotive force upon concentration was noted over a wide range, but no attempt was made to explain it. Very little improvement in the experi- mental or theoretical treatment of amalgams was made for thirty years after the publication of this work. In 1863 Crova 3 concluded that amalgams containing from 1 to 5 per cent of zinc could be substituted for the zinc in a Da
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