Proceedings of the Royal Society of London/Volume 2/An Account of some Experiments with a large Voltaic Battery
The battery with which these experiments were made, has 21 cells, each containing about 40 gallons of water, to which was added a mixture of nitric and sulphuric acids, at various intervals, beginning with 140th, and ending with 120th part of the water. Into each cell was immersed a zinc plate, with a pair of copper plates, one on each side, but connected together at the bottom, and also duly connected to the zinc in the cell adjacent. Each plate had 16 square feet of surface.
The first series of experiments were on the comparative liability of different metals to be ignited by the power of this battery, by joining equal lengths of any two wires in the same line, and making the circuit through both thus connected. In the comparison of platina and iron, which of all metals are most easily ignited, the difference was so little, that their comparative ignition altered during the experiment in consequence of apparent difference in their capacities, as well as conducting powers. Of other metals, gold and copper were nearly equal, and far less easily ignited than the former. After them stood zinc; and last of all silver. Mr. Children observes, that the order of these metals, as conductors of electricity, nearly follows that of their powers to conduct heat.
When this battery was excited to its utmost, it ignited 512 feet of platina wire one ninth of an inch in diameter.
A bar of platina, one sixth of an inch square and 214 inches long, was heated red, and fused at each end.
A round rod, one fourth of an inch in diameter and 212 inches long, was heated bright red throughout.
Oxide of tungsten was partially reduced.
Oxide of tantalum was partly fused, and of a reddish brown colour.
Oxides of uranium and titanium were fused, but not reduced.
Oxide of molybdena was fused and reduced.
Oxide of iridium, with osmium, was fused to a globule.
Pure iridium was fused into an imperfect globule, having specific gravity 18·68.
Of earthy bodies, ruby and sapphire were not fused.
Blue spinel ran to a slag.
Magnesia was agglutinated.
Quartz was not affected.
This opportunity was taken by Mr. Pepys of attempting the conversion of iron into steel by union with diamond, which appeared to have been accomplished. A wire of good soft iron, having been slit longitudinally with a fine saw, the slit was filled with diamond powder, and the whole having then been wrapped round with a piece of muscovy talc, was bound together with a fine iron wire. Although the wire thus prepared was by no means intensely ignited, and for no longer a time than six minutes, no part of the diamond powder was to be found after the experiment, and the iron was found converted into a sort of blistered steel; for it was hardened by quenching while hot, so as to resist the file, and to scratch glass with facility.
Beside the experiments above made with three plates connected in succession as a powerful battery by the action of acids on their surfaces, a trial was made whether at the moment of contact between very large metallic surfaces, any degree of ignition could be rendered visible. All the zinc plates were connected together as one zinc plate, and also all the copper plates connected as one copper plate. A communication was then made between the two sets of plates thus connected, but not immersed in a fluid, and all the electricity supposed to move in consequence of the contact, was made to pass through a wire of platina 15000th of an inch in diameter, and about 130th of an inch in length; but there was no appearance of ignition, although the same wire may be instantly ignited by a single pair of one inch plates immersed in a weak acid.