168 DAY and sosman: nitrogen thermometer scale 



The chief source of present uncertainty [in high temperature gas- 

 thermometer measurements] is the temperature distribution over the 

 surface of the bulb in an air bath. It would be possible to eliminate this 

 error in the lower portion of the scale by substituting a liquid bath which 

 could be stirred. In fact, this was done for temperatures below 500° 

 in the earlier work of Holborn and Day, but has not, so far, been tried 

 in the present investigation because of the relatively secondary importance 

 of the lower temperatures to the ultimate purpose of the investigation 

 (the study of silicates) . For the higher temperatures, no sarisfactory 

 liquid bath has been found. 3 (Publication of the Carnegie Institution 

 of Washington No. 157, p. 115. 1911). 



It was nevertheless thought wise to establish the identity and 

 the magnitude of the error in these low temperature measure- 

 ments which may have been due to this cause. 



2. APPARATUS 



No attempt will be made to describe in detail the gas thermom- 

 eter and accessories used in this investigation. A full descrip- 

 tion of the apparatus, with illustrations, will be found in the pub- 

 lications to which reference has been made. No change whatever 

 was made in the gas thermometer system for these measurements, 

 except for the substitution, about the bulb, of a liquid bath, made 

 up from potassium and sodium nitrates in eutectic proportions 

 (55 per cent KN0 3 , 45 per cent NaN0 3 ). This bath was intro- 

 duced into the furnace bomb described in connection with the 

 earlier apparatus in place of the platinum-wound furnace pre- 

 viously used. The insulating material was dry magnesia, as 

 heretofore, and the bomb was water jacketed thruout to protect 

 the manometer. The heating apparatus amounted, briefly, to 

 one bath within another, that is, the tube containing the stirrer 

 was continued across the bottom of the tank and upward about 

 the bulb, which it fitted with but little clearance (10 mm.) in order 

 to insure the very rapid circulation of a thin layer of liquid past 

 the bulb, while the remainder of the bath remained at an approxi- 

 mately uniform temperature without. With this arrangement, 

 no systematic temperature differences greater than the errors of 

 observation of the thermoelement (0?1) were observed. 



3 Professor Holborn has directed attention to the same limitations in our 

 results at these temperatures (Ann. Physik., 35: 761-774. 1911). 



