128 A. L. Day and R. B. Sosman — 



In addition to the fixed points which have just been 

 described, two other metal melting points, cadmium and alu- 

 minum, were incidentally determined. Only one measurement 

 of the cadmium point was made on the gas thermometer, and 

 this chiefly for the purpose of checking the extrapolation 

 below the zinc point. The conditions of melting were the same 

 as for zinc. The sample was obtained from Eimer and Amend, 

 and its analysis has been given in a paper by Day and Allen. * 

 The charge weighed 215 grams. 



A sample of pure aluminum obtained from the Aluminum 

 Company of America was melted in a graphite crucible of the 

 usual size in an atmosphere of carbon monoxide. On account 

 of the sensitiveness of aluminum to silicon contamination, the 

 tube carrying the thermoelement was also provided with a thin 

 protecting cover of graphite so that the metal came in contact 

 only with pure graphite. The freezing point was sharp and 

 constant. The melting point was less sharp but lay within 

 0*5° of the freezing point. 



The effect on the final temperature of all the errors and 

 corrections which have been discussed in this section, is shown 

 in summarized form in Table IV. 



The figures of Table IV serve to emphasize the statements 

 already made, that the greatest present uncertainty in the high 

 temperature gas scale arises from the lack of uniformity in an 

 air bath, which not only leads to uncertainty as to what is the 

 true temperature of the gas in the bulb, but also to errors in 

 the transference by the thermoelement. The next largest 

 uncertainty, due to the limitations of the materials used for 

 fixed points, is not directly chargeable to the gas thermometer. 

 In this connection, considerably more work needs to be done 

 on the high thermometric points, comparable in thoroughness 

 to the work in low temperature thermometry of Richards, 

 Dickinson, and others, on the sodium sulphate transition point. 



4. Experimental Data and Calculated Results. 



A. Expansion Coefficient — In Table Y are given the experi- 

 mental data on the expansion coefficients of the alloy 80 per 

 cent platinum, 20 per cent rhodium. In the first column is 

 given the date of the series, in the second and third columns 

 the readings of the thermoelements at the middle of the bar, 

 corrected for zero error and the temperature of the cadmium 

 ceil. The 12 other readings taken with each element at each 

 temperature at different points along the bar cannot be given 

 here, but the fourth and fifth columns contain the readings of 

 the thermoelement corrected to represent the integrated tem- 



* Arthur L. Day and E. T. Allen, Phys. Eev., xix, 180, 1904. 



