enough crystal out of the small tube for measuring change of resistance with temperature. The actual crystal measured was taken from a tube such as the one just described. Even when the tube was suspended for a long time in the furnace it was noted that the arsenic did not all distil into the small tube at the bottom, and at first it seemed surprising that the crystal referred to above was formed near the top of the small tube at all. It was concluded that if the furnace had been made of one piece instead of a number of small pieces this could not have happened; but because of the particular way in which our furnace was accidentally constructed, cool parts existed at the junctions of the heated coils. The temperature at such a point must have been sufficiently high for the slow formation of the crystal, and not too high to cause it to distil away again from that part of the tube. Subsequently the furnace was turned into a horizontal position and merely a straight tube containing arsenic at one end was pushed in. The arsenic sublimed from the warmer part of the tube to the cooler part which lay opposite a junction of two coils in the furnace. Various methods were employed to try and improve on the type of tube for forming the crystal, such as introducing a current of air in an inner tube inside the tube containing the arsenic; the condensation, however, was too rapid, with the result that a number of small crystals were formed instead of a single large one. The improvement that seemed necessary was to construct a furnace with two chambers which could be regulated separately and fitted with thermometers to tell just the correct temperatures for the best formation of crystals, but as our object was mainly to get a single crystal for electrical measurements and not to grow large crystals, we did not continue farther with the work. The crystal to be measured was clamped between two copper jaws at either end. Four wires leading to the four jaws comprised the two current leads and the two potentiometer leads. Crystals formed from the vapour of a substance display their facets and thus differ as a general rule from crystals formed by slow cooling of molten metal. In one of our crystals the direction of the hexagonal axis could be easily seen. Measurements were made on this crystal between room temperature and the temperature of liquid. helium along the hexagonal axis. Antimony. No trouble was experienced in making a crystal of antimony from molten metal. In spite of the fact that antimony has a melting-point nearly as high as pyrex glass, it was found that a fine bore tube did not cave in at the temperature of molten antimony and that it was possible to obtain a long thin single crystal by the method used by Bridgeman in pyrex glass. The temperature resistance curves of a crystal of antimony prepared in this way and also of a chip off a mass of metal were investigated between room temperature and the temperature of liquid helium. Results of Measurements. In the work previously published by the authors, graphs, showing the variation of electrical resistance with temperature, have been constructed measuring specific resistances along the resistance axis. In this communication, however, the more usual practice of using the ratio of the resistance at any temperature to the resistance at 0° C. will be adopted. We do this because we wish to compare our results with Clay's *. The results of the measurements are given in the table, and these are presented in graphical form in the diagram. By studying the diagram below we can reach some rather interesting conclusions. (1) The resistance temperature curve of the antimony crystal is not very different from that of the piece off the mass of metal. (2) The curves arrange themselves as would be expected from the arrangement of the metals in the periodic table. (3) The temperature resistance curve for arsenic resembles that of many other pure metals. At the same time there is a very decided departure from the law stating that the electrical resistance is proportional to the absolute temperature. (4) Our results show that in the case of both arsenic and antimony resistance at low temperatures approximates to a definite residual value. This property is common to most pure metals. The arsenic crystal was measured to 2:42° K., and the antimony crystal to 2.43° K.; neither was found to be superconducting. On the graph we have drawn the curve for bismuth according to Clay's results; bismuth appears to be unique in its behaviour, since, so far as is known, it is the only pure metal that has a value of R/R。 greater than 0.3 at the temperature of liquid air. The value 0-3 is what would be expected if the linear relation connecting resistance and temperature held good. In general, metals have a value of R/R in liquid air less than 03, and in this respect both arsenic and antimony follow the general behaviour of other metals. The Physical Laboratory, University of Toronto. LXIV. The Resistance of Cersium, Cobalt, and Chromium at Low Temperatures. By Prof. J. C. MCLENNAN, F.R.S., C. D. NIVEN, M.A.*, and J. O. WILHELM, Casium. .A. † ALTHOUGH a great deal of work has been done on the conductivity of the alkali group of metals in regard to variation with both temperature and pressure, yet data were not available on caesium and rubidium below the temperature of liquid air at the time when Onnes and Tuyn published their "Data concerning the Electrical Resistance of Elementary Substances at Temperatures below -80° C." Last year the authors of this communication published some data on rubidium at low temperatures, so that only cæsium remained to be measured. The caesium was run into a fine capillary tube similar to that used in measuring potassium and sodium, as described in another paper §. Measurements were made at room temperature and at the temperature of liquid air, liquid hydrogen, and liquid helium. By assuming the value for the specific resistance given in Smithsonian Tables and by neglecting any change in the dimensions of the caesium due to contraction with change of temperature, the values of the specific resistances were calculated. The results are given in Table I. and reproduced graphically in the diagram (p. 674). *This work was carried out with the aid of a Fellowship from the National Research Council of Canada to C. D. Niyen. + Communicated by the Authors. Leiden Communications Supplement, No. 58. P. W. Bridgeman * found that cæsium was very com pressible, and also that the electrical resistance passed through a minimum with increasing pressure, and on this account cesium appeared to be an interesting member of the alkali group to measure at low temperatures. The resistance of nearly all pure metals, other than superconductors, approaches a certain limiting value, so that in general at very low temperatures the resistance of a pure metal is independent of the temperature. In this respect cæsium stands out as different from most pure metals. A glance at the diagram shows that the resistance of cæsium continues to decrease with temperature below 4° K. In Table II. values of R/R-i.e., the ratio of the resistance at any temperature to the resistance at 0° C.-are Am. Acad. Proc. lx. pp. 385-421 (Oct. 1925). |