Page:Proceedings of the Royal Society of London Vol 1.djvu/80

Rh The first experiments were made with tin, small plates, or arcs, of which were made to alternate with acid and water. About twenty sets of these produce a galvanic battery, in which the wire from the oxidating surface of the plates evolved hydrogen, and that from the non-oxidating surface (when of silver) deposited oxide. The second series consisted of plates, or arcs, of silver, copper, or lead, placed alternately between cloths steeped in water, and in solution of sul- phuret of potash. The effects of this combination were much more perceptible than those of the preceding. And a still more powerful battery was obtained by using metallic substances oxidable in acids, and capable of acting on solutions of sulphurets, and connecting them with oxidating fiuids, and solutions of sulphurets of potash, in such a manner that the opposite sides of every plate may undergo diffe- rent chemical changes. How this is to be effected is here explained at length, and an apparatus, contrived by Count Rumford, is lastly mentioned, for facilitating and giving permanency to the alternate succession of the different substances, so as to prevent, particularly in the fluids, the interference with each other, which would materi ally affect the results.

A short description is here premised of an apparatus for exposing luminous bodies to different kinds of air, which, in addition to the well-known glass phial or tube inverted in water, consists in a small stand, to the top of which the luminous substance is fixed, and thus inserted into the inverted phial, into which the species of air to be employed is previously let up to the quantity of about eight ounces.

With these instruments a copious set of experiments has been made, of which the following are the principal results.

In common or atmospherical air, all the objects which abound with spontaneous light in a latent state, such as herrings, mackerel, &c., do not emit it when deprived of life, except from such parts as have been some time in contact with the air. Nor does the blast of a pair of bellows increase this species of light, as it does that which proceeds from combustion

Oxygen gas does not act upon this kind of light so as to render it much more vivid than atmospherical air. And as to azotic gas, which is incapable of supporting light from combustion, it is remarkable that it should be so favourable to the spontaneous light emitted from certain fishes, as to preserve its existence and brilliancy when immersed in it, while it prevents the flesh of herrings and mackerel from becoming luminous, and extinguishes the light proceeding from rotten wood.