A pair of fine wires of iron and constantan are twisted together in the middle, and one pair of unlike ends are connected to a galvanometer.
In the inner space between the test tubes one pair of these platinum wires are connected by a fine constantan wire about 02 mm.
A b, constantan wire; c d, thermojunction; G G, galvanometer terminals; 0 0, antenna and earth terminals.
Nickel is used for the manufacture of domestic utensils, for crucibles, coinage, plating, and for the preparation of various alloys, such as German silver, nickel steels such as invar (nickel, 35.7%; steel, 64.3%), which has a negligible coefficient of thermal expansion, and constantan (nickel, 45%; copper, 55%), which has a negligible thermal coefficient of its electrical resistance.
For this purpose it must be an alloy such as manganin or constantan.