863.  A dilute sulphuric acid, made by adding about one part by measure of oil of vitriol to thirty parts of water, will act energetically upon a piece of zinc plate in its ordinary and simple state:  but, as Mr. Sturgeon has shown[A], not at all, or scarcely so, if the surface of the metal has in the first instance been amalgamated; yet the amalgamated zinc will act powerfully with platina as an electromotor, hydrogen being evolved on the surface of the latter metal, as the zinc is oxidized and dissolved.  The amalgamation is best effected by sprinkling a few drops of mercury upon the surface of the zinc, the latter being moistened with the dilute acid, and rubbing with the fingers or two so as to extend the liquid metal over the whole of the surface.  Any mercury in excess, forming liquid drops upon the zinc, should be wiped off[B].

  [A] Recent Experimental Researches, &c., 1830, p.74, &c.

[B] The experiment may be made with pure zinc, which, as chemists well know, is but slightly acted upon by dilute sulphuric acid in comparison with ordinary zinc, which during the action is subject to an infinity of voltaic actions.  See De la Rive on this subject, Bibliotheque Universelle, 1830, p.391.

864.  Two plates of zinc thus amalgamated were dried and accurately weighed; one, which we will call A, weighed 163.1 grains; the other, to be called B, weighed 148.3 grains.  They were about five inches long, and 0.4 of an inch wide.  An earthenware pneumatic trough was filled with dilute sulphuric acid, of the strength just described (863.), and a gas jar, also filled with the acid, inverted in it[A].  A plate of platina of nearly the same length, but about three times as wide as the zinc plates, was put up into this jar.  The zinc plate A was also introduced into the jar, and brought in contact with the platina, and at the same moment the plate B was put into the acid of the trough, but out of contact with other metallic matter.

[A] The acid was left during a night with a small piece of unamalgamated zinc in it, for the purpose of evolving such air as might be inclined to separate, and bringing the whole into a constant state.

865.  Strong action immediately occurred in the jar upon the contact of the zinc and platina plates.  Hydrogen gas rose from the platina, and was collected in the jar, but no hydrogen or other gas rose from either zinc plate.  In about ten or twelve minutes, sufficient hydrogen having been collected, the experiment was stopped; during its progress a few small bubbles had appeared upon plate B, but none upon plate A. The plates were washed in distilled water, dried, and reweighed.  Plate B weighed 148.3 grains, as before, having lost nothing by the direct chemical action of the acid.  Plate A weighed 154.65 grains, 8.45 grains of it having been oxidized and dissolved during the experiment.