A. L. Day and J. K. Clement — Gas Thermometer. 423 



and Petavel,* and pumped into bombs at a pressure of about 

 1,000 pounds per square inch. One of these bombs could be 

 readily connected with the furnace through appropriate port- 

 able connections whenever desired. A pressure gage con- 

 necting with the inside of the furnace bomb enabled the 

 pressure within the bomb and outside the bulb to be read at 

 any time. If the advance in pressure outside the bulb did not 

 proceed as rapidly as that within, additional nitrogen could be 

 admitted as required. In general, it can be said of the oper- 

 ation of this arrangement for the adjustment of pressure within 

 and without the bulb, that if the furnace is perfectly tight the 

 two pressures advance together and are never very far apart. 

 Attention to this detail is therefore not burdensome unless the 

 bomb is leaking, in which pase the losses must be supplied by 

 the addition of small quantities of nitrogen from time to time. 

 An effort was made to keep the pressure outside the bulb 

 within one-half pound of the inside pressure as read on the 

 manometer. 



After the current had brought the temperature to the point 

 where it was proposed to make a reading, about three-quarters 

 of an hour was required to adjust the three resistance coils so as 

 to produce a permanently uniform temperature along the bulb, 

 which limited the number of temperature readings in one 

 working day to six or seven. It was therefore our habit to 

 make readings, at 50° or 100° intervals, so as to cover a consid- 

 erable range of temperatures each day. On following days 

 intermediate temperatures were selected in such a way that the 

 whole Held between 250° and 1200° would eventually be can- 

 vassed in steps of 25°. In order to provide a sufficiently rigid 

 control of the conditions within the bulb, however, each day's 

 readings began with a new determination of the ice point. 



It is interesting to note in passing that the variation of the 

 ice point after heating, which was a conspicuous feature in all 

 gas thermometric work previous to 1900, has now substan- 

 tially disappeared with the return to the platinum bulb. Our 

 ice points (column 3, Table II) from day to day showed no 

 disagreement of greater magnitude than that produced by 

 the somewhat irregular contraction of the bulb due to slight 

 variations in. the rate of cooling, to which attention has been 

 explicitly called in the chapter on the expansion coefficient of 

 platin-iridium (p. 436). 



When the temperature had become constant over the entire 

 length of the bulb, one observer took his position at the tele- 

 scope of the manometer and the other at the galvanometer, 

 and simultaneous readings were made of the group of ther- 



* Hutton and Petavel, Preparation and Compression of Pare Gases for 

 Experimental Work, Journ. Soc. Chem. Ind., xxiii, Feb. 15, 1904. 



