. Éléments de la chimie moderne . les ex-tremblements antérieurs sont con-nectés avec les pôles d'une batterie galvanique. Le courant-loyer passant par le liquide acidulé décompose la Fig 28. L'eau,^ et des bulles de gaz sont formés et augmentent rapidement à partir des two.platinum wiresqui constituent les pôles. Si deux petits tubes remplis d'eau sont inversés sur ces fils, les gaz peuvent être collectés,aud il sera constaté que le gaz désengagé au niveau du négativepole est sensiblement double dans le volume qui se dégage au niveau de la posi-tive. Le premier est l'hydrogène, et le second l'oxygène, et la proportion dans laquelle ces gaz sont fixés

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. Elements of modern chemistry . terior ex-tremities are con-nected with thepoles of a galvanicbattery. The cur-rent passing throughthe acidulated liquiddecomposes the Fig 28. water, ^ and bubbles of gas are formed and rapidly rise from the two.platinum wireswhich constitute the poles. If two small tubes filled withwater be inverted over these wires, the gases may be collected, aud it will be found that the gas disengaged at the negativepole is sensibly double in volume that disengaged at the posi-tive. The first is hydrogen, and the second oxygen, and theproportion in which these gases are set free would be exactlythat of 2 to 1, were it not that a small quantity of oxygen re-mains dissolved in the acid liquid, or, under certain condi-tions, combines with a portion of the water surrounding thenegative pole to form a trace of hydrogen dioxide, as will bementioned farther on. This experiment of the decomposition of water by the pilewas made for the first time, in 1801, by two English physi-cists, Nicholson and Carlisle.. ^ Under these conditions, it is really the sulphuric acid which is decom-posed; H^SO* breaks up into H^, which is liberated at the negative pole, and SO*, which separates at the positive pole, and is at once decomposedinto SO^ and 0. The 0 is disengaged, and the SO^ in the presence of thewater becomes again hydrated, reforming sulphuric acid. SO^ + H^O =H^SO*. The electrolytic action is thus confined to the sulphuric acid, which alone is decomposed. 72 ELEMENTS OF MODERN CHEMISTRY. 2. Eiidiometric Synthesis.—The composition of water canbe established by synthesis, that is, by the combination of thetwo elements, hydrogen and oxygen. The experiment, whichis made in an eudiometer, has already been described (page 28).It demonstrates that the two gases combine in the exact ratioof 2 volumes of the first to 1 of the second, and that these3 volumes of gas are condensed into 2 volumes of vapor ofwater. • These experiments establish the volumetric compositio

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