THE MELTING POINT OF CAST IRON. 345 tially of two pieces of wire of a slightly varying composition, a heating of the junction of which produces a current of electricity proportioned to the degrees of heat applied. The amount of this current is measured by a suitably calibrated galvanometer, and thus we can read off the heat at any convenient distance rapidly and with a surprising degree of accuracy. "Unfortunately, this wonderful instrument, one wire of which is of platinum, the other of an alloy of platinum and 10 per cent, of the rare metal rhodium, cannot be immersed directly in the melted iron — there would soon be an end to this expensive thermo-couple. The long porcelain tube which protects it when used in kilns is worse than useless in a ladle full of metal, and so at the suggestion of the writer the Pittsburg representatives, the Vulcan Mfg. Co. set about to remedy the matter and devise some protective cover which would allow experiments of this kind to be carried out readily. The outcome, while not having the advantage as yet of an extended period of trial, was nevertheless so happy a solution that it is presented, for the first time, with the hope that much of value may be learned from it, not only in our daily work but also in connection with the many intricate problems still before us which await solution at the hands of those willing- to give their time and energy to such an exacting study. '' Fig. 64 shows a section through the instrument. The platinum wire will be noticed running from the terminal box through an iron pipe ending at the inner side of the point of the clay tip. Here is the button made by the fusion to the other wire of platinum and rhodium alloy which runs back, parallel to the platinum wire, to the terminal box. Both wires are covereda short time, compared to that generally occupied in ordinary shop practice. The longer heated or semi-molten iron remains in contact with incandescent fuel or is exposed to gases, the more sulphur will be absorbed — up to the limit of the iron'sding its mate.. 2111 3Os i m. mi 3os 3OS. 3111. im ^os Jill l^S i in.