The Origin of the Platinum Resistance Thermometer by L
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The Origin of the Platinum Resistance Thermometer By L. B. Hunt Johnsan Matthey & Co Limited Since the beginning of this century the platinum resistance therm- ometer has been relied upon as a most convenient means of temperature measurement and control in industrial applications, while its accuracy in precision thermometry has contributed largely to the definition of the International Temperature Scale. lts origin sterns, however, from the early years of the costly and hazardous attempts to Lay underwater telegraph cabks, before even a standard unit of resistance had been generally adopted. The many millions of platinum resistance platinum element and its temperature, and thermometers in use for the measurement of secondly upon the high purity and stability of temperatures from well below zero up to those the specially prepared platinum employed. of the order of rooo0C testify to the accuracy Neither of these factors was simple or easy to and the versatility of these instruments. Their establish, however, in their earlier years. reliability depends first upon the simple The discovery that the electrical resistance of relationship between the resistance of the a metal varies with temperature was first made Sir William Siemens 1823-1 883 Born Carl Wilhelm Siemens near Ifanovrr, he camp to England when not yet twenty and quickly made a reputa- tion in the early days of the electrical industry. In 1860 he devised the first resistance thermometer, using copper wire, to check the temperature-of coils of submarinc cnblrs, a SL~Jthat saved an cJxpwnizv calh from destruction by spontaneous overheating. Ten years later he introducrd a platinum resistance thermometer for the measuremrnt of high temperatures. He ioas the ,first president of the Society of Telegraph Engineers, later rr-named the Institution of Electrical Engineers, and shortly before his death was knightrd by Queen b’ictorin Reproduced bvcouricry ofrhc BBC Hulron Picture Library Platinum Metals Rev., 1980,24, (31, 10441 12 104 by Humphry Davy at the Royal Institution Science. Acting on a suggestion put forward in in 1821. In the course of a paper read to the a paper by Sir Charles Bright and his partner in Royal Society he reported that: the Atlantic Telegraph Company, Joseph “The most remarkable general result that I Latimer Clark, that names should be adopted obtained . was that the conducting power of for standards of resistance, current and metallic bodies varied with the temperature, and electromotive force, William Thomson, later was lower, in some inverse ratio, as the temperature was higher. Thus a wire of platinum Lord Kelvin, Professor of Natural Philosophy of 1/220 and three inches in length, when kept at Glasgow and also a director of the Atlantic cool by oil discharged the electricity of two Telegraph Company, proposed the formation of batteries, or of twenty double plates: but when a committee to report on standards of electrical suffered to be heated by exposure in the air, it barely discharged one battery.” (I). resistance. The committee appointed comprised This phenomenon was investigated some Thomson himself, A. W. Williamson, years later by Emil Lenz in St. Petersburg (2), Professor of Chemistry at University College, by Professor A. F. Svanberg at the University of London, Professor Wheatstone of King’s Uppsala (3) and by the Norwegian physicist College, London, Professor W. H. Miller of Adam Arndtsen (4), but the very low purity of Cambridge, H. C. Fleeming Jenkin, then in the the copper and other metals then available submarine cable industry and Dr. Augustus handicapped these workers in establishing a Matthiessen who had already carried out a relationship between temperature and increas- massive series of researches on the resistance of ing resistance. In any case the concept of metals and alloys in Kirchhoffs laboratory at “resistance” was then wreathed in uncertainty Heidelberg, an activity he continued after his and there was no unit or fixed standard in appointment as lecturer in chemistry at St. which to express it, while the simplest applica- Mary’s Hospital in London in I 862. tion of Ohm’s law to practical problems was In the following year the committee was hardly understood. strengthened by the addition of Sir Charles Bright, Professor Clerk Maxwell of Aberdeen Standards of Resistance University, Balfour Stewart, then Director of the Kew Observatory and later Professor of In 1860 Werner Siemens, much engaged Physics at Owens College, Manchester, and C. with the new electric telegraph in Germany and W. Siemens, while in 1863 Thomson’s elsewhere, proposed that a column of mercury collaborator J. P. Joule and C. F. Varley, also of of I square millimetre in cross section and I the Atlantic Telegraph Company, were co- metre in length at the freezing point of water be opted. adopted as the unit of resistance (5), while he The Committee’s report submitted to the also published a paper at the same time on the British Association meeting in Newcastle in that effect of increasing temperature on electrical year includes for the first time the term “ohm”, resistance (6). The advent of the telegraph, the only or “ohmad” as it was originally called, this being defined as 109C.G.S. units. industrial application of electricity at that time, with many miles of copper wire of indifferent purity and poor conductivity strung alongside Carl Wilhelm Siemens the railway lines, and then the beginning of The first suggestion for making use of the international telegraphy by means of long and effect of temperature on the resistance of a expensive submarine cables, focused attention metal for the determination of that temperature much more actively on the problem of was due to Carl Wilhelm Siemens. Arriving resistance in conductors and the great need for penniless in London from Germany in 1843, an established and internationally agreed unit just before his twentieth birthday and after an was recognised in 1860 by the Council of the education in physics, chemistry and British Association for the Advancement of mathematics at Gottingen, Siemens had two Platinum Metals Rev., 1980, 24, (3) 105 ambitions in life-to make sufficient money to In the meantime Wilhelm became naturalised be able to support himself as an inventor and as Charles William Siemens in 1859, and was consultant and to support his five orphaned called upon to give evidence to the Commission young brothers in Germany, then aged between of Enquiry set up by the British Government seven and seventeen years, and then to be able into the failure of the first Atlantic cable. to indulge in scientific research. Finally laid in August 1858 after some Encouraged by his elder brother Werner, the unsuccessful attempts in the previous summer, primary object of his visit was to sell the latter’s this was in operation, with great difiiculty and invention of a process for gold plating to the delays in the transmission of signals, only until Elkingtons of Birmingham. In this he was the following October when the insulation had quickly successful, receiving the then consider- completely deteriorated. One result of the able sum of E1600, less EI10 for the costs of a enquiry was that in 1860 the Siemens Company British patent which the Elkingtons filed on his was appointed by the Government to behalf. His half share of this money with superintend the manufacture and laying of sub- Werner was enough to establish him in London. marine cables and it was in this context that the birth of the resistance thermometer took place. Underwater Telegraph Cables During the autumn a cable intended for laying between Rangoon and Singapore was His arrival in prosperous early Victorian made and loaded into the “Queen Victoria” for England could not have been timed to better despatch to the Far East. Siemens was on advantage. The great railways boom was at its board, and was concerned that spontaneous height, to be followed by the spectacular generation of heat in the coils of cable in the growth of the electric telegraph as we11 as the hold of the ship could possible lead to its replacement of sail by steam in the British deterioration. (In fact this cable never reached mercantile marine. In Berlin elder brother its destination; after the ship had been forced to Werner formed a company in 1847 with a seek shelter in Plymouth harbour the project young engineer called Johann Georg Halske to was abandoned and the cable was eventually manufacture telegraph equipment, a venture in laid from Malta to Alexandria in which they were immediately successful, and 1861.) Wilhelm was appointed their London agent. By 1850 the firm was well established in the The First Resistance Thermometer telegraph business, and had laid a line, among On his arrival back in London in December others, from Berlin to Cologne which involved Siemens wrote to Professor John Tyndall at the crossing both the Elbe and the Rhine with Royal Institution about his problem and its armoured underwater cables. Werner Siemens solution. The letter includes the following quickly became an acknowledged authority in paragraph: the new and exciting world of submarine “As it would have been impossible to introduce telegraphy, and encouraged his brother mercury thermometers into the interior of the Wilhelm, now heavily occupied with his mass, I thought of having recourse to an regenerative furnace, to give more of his time to instrument based upon the well-ascertained fact that the conductivity of a copper wire increases this fast growing industry. in a simple ratio inversely with its temperature.” In 1858 the firm of Siemens and Halske of The letter goes on to describe the instrument, a London was founded, the partners being the rod wound with silk-covered copper wire in Berlin company, Wilhelm Siemens and the several layers, covered with rubber, and con- cable manufacturer Newall and Company of nected to a battery and a galvanometer in the Birkenhead, but the Newall connection was not cabin.