422 A. L. Day and J. K. Clement — Gas Thermometer. 



taining 20 per cent of iridium) of 200 cc capacity with nitrogen 

 as the expanding gas up to 1600° without discovering any 

 irregularity in its behavior. The porcelain bulb has therefore 

 probably disappeared permanently from gas thermometry. 

 Whether or not some other platinum metal than iridium will 

 not prove preferable with which to give the necessary stiffness 

 to the platinum is a question for the future to decide. It is a 

 matter of great difficulty and some uncertainty to make trust- 

 worthy measurements of temperatures above 1000° with 

 platinum thermoelements in the presence of iridium (see para- 

 graph on thermoelectric measurements preceding), even when 

 the iridium is present only in a low percentage ('005) alloy 

 with platinum. 



Parenthetically, it may be remarked that the platinum cruci- 

 bles and other ware as made up for laboratory use in this 

 country are usually stiffened with about 2 per cent of iridium, 

 a quantity amply sufficient to contaminate thermoelements if 

 exposed in the furnace with it to temperatures above 900°. 



The Measurements. — The method of procedure with the 

 system in adjustment for observation was then substantially as 

 follows : 



With the body of the furnace lowered so as to expose the 

 bulb, a pail of suitable size was brought up about the latter 

 and filled with distilled water and finely divided ice in such a 

 way as to enclose the bulb and so much of the capillary as was 

 included within the furnace when heated. Several readings 

 of the ice point were then made on the manometer, together 

 with simultaneous readings of one or both barometers. . To 

 control the expansion coefficient of the gas, these readings 

 were occasionally followed by a second reading at the temper- 

 ature of boiling water in which the ice pail was replaced by a 

 double-chambered boiling-point apparatus of standard type. 

 In general, however, it may be said that the expansion coeffi- 

 cient of pure nitrogen has already been so carefully determined 

 by Chappuis and others that this observation is superfluous, par- 

 ticularly as the sensitiveness obtainable in a bulb of a size 

 suitable for long ranges of temperature is not sufficient to admit 

 of a determination comparable with theirs. 



After the ice point had been determined, therefore, the gen- 

 eral procedure was to arrange the three thermoelements in posi- 

 tion at the top, middle and bottom of the bulb (fig. 1), to close up 

 the furnace gas-tight and to proceed with the heating. Before 

 turning on the current, however, it was first necessary to 

 exhaust the bomb and to replace the air with a nitrogen atmos- 

 phere, the nitrogen being supplied from a separate bomb under 

 high pressure. The nitrogen for this purpose was made in 

 large quantities in the laboratory by the method of Hutton 



