360 



DE. J. A. HARKEK ON THE HIGH-TEMPERATURE STANDARDS 



fig. 6. The bulb of the gas thermometer, resting on a small piece of cork, occupies 

 the centre of the inner tube, through which steam brought direct from the boiler by 

 a well protected wide tube is circulated. The steam issuing from the outer jacket is 



Fig. 6. Steam bath. 



condensed and returned to the boiler as shown. The excess of the steam pressure 

 over that of the atmosphere, which in these experiments was seldom over 1 millim. 

 of water, is indicated by a small graduated water gauge. 



The sulphur-points of the platinum thermometers were taken in the usual manner 

 in the well-known Callendar form of boiling-point apparatus. The only departure 

 from previous custom being that for the glass boiling tube was substituted one of 

 thin weldless steel,* which is more durable and can be heated up quickly without 

 being removed from its asbestos cover. Careful comparisons of this form with the 

 older glass apparatus showed no systematic discrepancy. 



For the sulphur boiling-point CALLENDAR'S old value 444 '53 C. at normal pressure 



* An ordinary iron tube such as gas or steam pipe cannot be used for this purpose, as owing to 

 conduction from the flame of the burner upwards there is a tendency for the sulphur vapour to become 

 superheated. 



