with Boiling Point of Sulphur. 531 



In Table V are brought together all the gas thermometer 

 determinations of the boiling point of sulphur since 1890 with 

 the necessary information for an intelligent comparison of the 

 determinations. Column 5 contains the initial pressure of the 

 gas used, and column 6 the original value published by the 

 author with a reference to the place of publication. Two 

 of these determinations were subsequently corrected by the 

 authors themselves. These corrections (with the reference) 

 are given in column 7. 



Inasmuch as these various determinations were made under 

 somewhat different gas conditions, the results are not directly 

 comparable without reduction to some common unit. The 

 four columns which follow contain such reductions for pur- 

 poses of convenient comparison. Our own observations are 

 directly comparable with the numbers contained in the column 

 " Const, vol. nitrogen scale, p Q = 500." The fairest compar- 

 ison is afforded by reduction to the thermodynamic scale, in 

 view of the fact that the different gases used by the various 

 observers depart in varying degree from the behavior of a per- 

 fect gas expanding at constant volume from the same initial 

 pressure. It should be noted that the small differences between 

 the four columns are really arithmetical and not experimental, 

 since none of the original determinations can claim an accuracy 

 closer than 0'05°. 



The Callendar and Griffiths determination above, which is 

 often quoted as direct, is in reality indirect. In his first inves- 

 tigation (Phil. Trans. 1887) Callendar showed that his parabolic 

 formula represented within 1° the variation of the resistance of 

 platinum with the temperature as determined by the constant 

 pressure air thermometer as far as 600°. In this later work 

 (Phil. Trans. 1891) he showed by a comparison of two resist- 

 ance thermometers with the air thermometer, using sulphur 

 merely as a constant temperature bath, that his original value 

 of 8 = 1*57 would still represent the results for these ther- 

 mometers within the limits of error. This value of 8 was then 

 used to calculate the sulphur boiling point determined with 

 several platinum thermometers in the usual (Meyer) form of 

 sulphur boiling tube.* 



* The air thermometer observations of Callendar and Griffiths in sulphur 

 vapor comprise fourteen readings, made between 4:52 and 5:30 p. m. on 

 Friday, September 12, 1890, and between 8:25 and 9:07 the following morn- 

 ing, as follows (Phil. Trans., 182 A, 1891, p. 139) : 



Saturday, Sept. 13, 1890. 



Friday, 



Sept 



12, 1890. 



Time 



Temperature 



4:52 





444-52° 



5:02 





444-90 



5:06 





444-68 



5:18 





444-77 



5:21 





444-79 



5:26 





444-94 



5:30 





44498 



Time 



Temperature 



8:25 



444*51° 



8:28 



444-51 



8:38 



444-52 



8:42 



444-53 



8:48 



444-54 



8:50 



444-52 



9:07 



444:61 



