IV 



ith Boiling Point of Sulphur. 525 



ture of the vapor within the aluminium shield compared with 

 the corresponding temperature in one of the sulphur baths 

 which Waidner and Burgess* have standardized and described 

 in connection with their measurements with the platinum 

 resistance thermometer. This comparison has been described 

 by Messrs. Dickinson and Mueller, f The differences amounted 

 in maximum to 0'04°, which may afford some measure of the 

 certainty with which the temperature of the sulphur vapor is 

 reproduced in an apparatus differing considerably from the 

 conventional form and dimensions. 



At the close of the measurements the gas thermometer bulb 

 and manometer were disconnected. In order to make certain 

 that our calculation of the volume of the unheated space con- 

 tained no unknown constant error, that portion of this space 

 lying outside the furnace was determined directly, as follows : 

 the mercury was brought np to the fixed point with the capil- 

 lary open to the air. The connection between the two arms 

 of the manometer was then closed, and a known volume of air 

 (about 0'1 CC ) was drawn in through the capillary by drawing 

 off a weighed amount of mercury from the short arm. The 

 open end of the capillary was then sealed, the manometer con- 

 nection reopened, and the mercury again brought up to the 

 fixed point. The pressure necessary to effect this is a measure 

 of the volume of the space in the capillary and connections. 

 The results were : 



Direct determinations ._ 0'159 cc 



0-164 cc 



Mean 0'162 cc 



Calculated in 1909 0'168 cc 



The difference is negligible. 



Finally, the location on the brass scale of the gas thermo- 

 meter of the "fixed point" which is situated in the top of the 

 short arm of the instrument and which defines its "constant 

 volume," was redetermined and found to have become dis- 

 placed by 0*18 mm since the initial determination in 1909. An 

 appropriate correction was accordingly made to this constant 

 in computing the results. 



These various checks and verifications complete the observa- 

 tions. The more important constants of the instrument and 

 the formula used in the calculations are reproduced below from 

 the previous paper.;); 



* Bull. Bur. Stds., vi, 150-230, 1909. 



\ J. Washington Acad., ii, 176-180, 1912. 



X Pub. No. 157, p. 52. 



