On the Thermo-electric Position of Aluminium

By William Thomson

Brit. Assoc. Rep., 1855. Part 2.
From reprint in Mathematical and Physical Papers, Vol. II, Art. LXXXIX, pp. 181-182

The author, through the kindness of Baron Liebig, having been enabled to make experiments on a bar of aluminium with a view to investigating its thermo-electric properties, found that it gave currents when its ends were at different temperatures, and an inch or two of its length was included in the circuit of a galvanometer by means of wires of copper, of lead, of tin, or of platinum, bent round it. These currents were in such directions as to show that the Aluminium lies, in the thermo-electric series, on the side towards bismuth, of Tin, Lead, Copper, and a certain platinum wire (P2); and, on the side towards Antimony, of another platinum wire (P3). They were in the same direction as regards the higher and lower temperatures of the two junctions of the aluminium with the other metal in each case, whether the whole bar was heated so much by a spirit-lamp that it could scarcely be held in the hand, or no part of it was heated above the temperature of the air, and one end cooled by being covered with cotton kept moistened with æther. Taking into account the results of previous experiments which the author had made on a number of different metals, including three specimens of platinum wire (P1, P2, P3), probably differing from one another as to chemical purity, which he used as thermo-electric standards, he concluded that at temperatures of from 10° to 32° Cent., the following order subsists unchanged as regards the thermo-electric properties of the metals mentioned:—Bismuth, P3, Aluminium, Tin, Lead, P2, Copper, P1, Zinc, Silver, Cadmium, Iron. As he had found that a brass wire, on which he experimented, is neutral to P3 at -10° Cent., and to P2 at 38°, he infers that at some temperature between -10° and 38° Aluminium must be neutral either to the brass or to P3. He intends, as soon as he can procure a few inches of aluminium wire to experiment with, to determine this neutral point, and others which he infers from the experiments already made, will probably be found at some temperatues not very low, between Aluminium and Tin, and Aluminium and Lead; and to look for neutral points which may possibly be found between Aluminium and P3 and Aluminium and P2, at either high or low temperatures.