110 A. L. Day and B. B. Sosman — 



porcelain bulbs formerly used, where both changes of volume 

 and emission or absorption of gases by the walls occurred. 

 The restoration of the platinum metals to favor as materials 

 for the gas thermometer bulb has practically eliminated this 

 uncertainty. During the present work small changes in the 

 value of p have frequently occurred after heating to a high 

 temperature, which seem not to be due to any change in volume, 

 for the determinations of the volume, Y , given above (p. 109), 

 show a total change after a year's work corresponding to less 

 than 0*l mm in jv Iu the early part of the work, the passage 

 through the bulb wall of hydrogen or some other gas produced 

 by the reducing action of wood fiber in an asbestos board insu- 

 lator within the furnace, was suspected as being the cause of 

 irregularity, particularly in view of the fact that Holborn and 

 Valentiner had difficulties from this cause. Further, it was 

 several times observed that heating the furnace and bulb to a 

 higher temperature than they had reached before, caused a 

 slight increase in the value of p , — whether due to some gas 

 passing in from the outside, or coming out of the wall of the 

 bulb, is not known. Air dried over calcium chloride was 

 used outside of the bulb in the furnace enclosure throughout 

 the work, and no indication was ever obtained of the passage 

 of either oxygen or nitrogen through the wall of the bulb, 

 since measurements at a given temperature (after the first 

 heating to that temperature) gave the same value of p within 

 the error of measurement. 



On one occasion an almost inappreciable leak in the mano- 

 meter connection caused some uncertainty. All measurements 

 affected by this error, when it was discovered, were rejected. 



a. — Since the gas thermometer apparatus as arranged for 

 high temperature measurements is not suited to a determina- 

 tion of the value of a (the pressure coefficient of the gas from 

 to 100°) with an accuracy comparable to that attained by 

 Chappuis,* the value of a was treated as a constant. The 

 figures used were : 



For p = 345 — 347 mm , a = 3665*8 X lO" 6 

 For p = 217 — 221 ram , a = 3664*0 X 1CT 6 



A number of independent determinations of a for different 

 pressures were made by Day and Clementf with the platin- 

 iridium bulb, but they show no appreciable difference from 

 those by Chappuis within the experimental error of the appara- 

 tus. The probable error in Chappuis' results is not great 

 enough to affect the high temperature values. 



* Trav. Mem. Bur. Int., vi and xii, 1888 and 1902. , 

 •|Day and Clement, loc. cit., p. 442. 



