Metallurgy; an introduction to the study of physical metallurgy . e purpose of taking heating and cooling curves thethermo-electric couple is in almost universal use, as it possessesindisputable advantages over any other device. Most fre-quently the couple employed consists of a fine wire of pureplatinum and one of platinum alloyed with 10 per cent, ofeither rhodium or iridium. The latter has the advantage ofbeing rather more sensitive, and in the authors hands it hasproved extremely constant in its indications, even underdifficult conditions. The opinion is, however, widely heldthat the rhodi
Metallurgy; an introduction to the study of physical metallurgy . e purpose of taking heating and cooling curves thethermo-electric couple is in almost universal use, as it possessesindisputable advantages over any other device. Most fre-quently the couple employed consists of a fine wire of pureplatinum and one of platinum alloyed with 10 per cent, ofeither rhodium or iridium. The latter has the advantage ofbeing rather more sensitive, and in the authors hands it hasproved extremely constant in its indications, even underdifficult conditions. The opinion is, however, widely heldthat the rhodium couple is more reliable in its indications. For temperatures above 500° or 600° C. the platinum typeof thermo-couple is the only one sufficiently permanent to besuitable for laboratory use. For lower temperatures, however, base metal couples can be employed with considerableadvantage—such a couple as that of copper with the alloyknown as Constantan being very satisfactory as regardspermanence and constancy of indications, while it 3deld8 more PLATE Fig. 27. h^-T-^-^-^ ^^n^ -T-=P=^ 1 1 1 1 1 tm 1 1 -^v -^-T-^ 1^1 1 II 1 \ ? w Y^ I^T 1 [ I jsi i!i H B| s 1 ^ ^^^^^^^^^H Fig. 36. [Tnface p. SO. THERMAL STUDY OF METALS AND ALLOYS 81 than three times the electro-motive force per degree of tempera-ture which is obtainable from a platinum-iridium couple. The action of the thermo-couple consists in setting up anelectro-motive force which is proportional to the differencebetween the temperatures of the hot and cold junctions. Lithe case of cooHng or heating-curve work in the laboratory, thehot junction is placed in the specimen of metal under examina-tion, care being taken to insure that the junction is properlyplaced as nearly as possible at the centre of the mass of cold junction is always kept at a temperature of 0° being placed in a glass tube, which is itself plunged into amass of melting ice. The ice-box usually employed in theauthors laboratory consis
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectmetals, bookyear1922
