4:4:2 A. L. Day and J. K. Clement — Gas Thermometer. 



from one clay's observations to another, inj9 , — the pressure of 

 the gas at 0°, — which will be found to vary irregularly within 

 narrow limits. 



The Pressure Coefficient of Nitrogen. — A number of deter- 

 minations of the pressure coefficient of nitrogen, under differ- 

 ent initial pressures, were made by observing the pressure 

 inside the bulb when it was immersed alternately in ice and in 

 steam, and with the following results : 



• Pioo — Po 



Initial Pressure a ^ru] No. of Observations 



314 mm 0-003665 4 



550 -003668 5 



744 '003610 6 



985 -003673 12 



Chappuis has obtained the following values of a : 



Initial Pressure 



Pioo — Pc 



des Poids et des Mes- 

 ures, vols. 6 and 12. 



100 



529 mm - 0-00366811 Traveaux et Memoires 



533 -00366846 du Bureau International 



793-5 -00367180 



995-95 -00367477 



Computation of Results. — The formula for the constant 

 volume gas thermometer may be written in the form, 



P Y , P v , , pv 9 _ v p v, , p v 9 



In * o ' 



+- at 1 + at l 1 + a£ 2 " " I ° ° 1 + at\ 1 + at\ 



In this equation : 



V o = volume of bulb at 0° 195-547 cc . 



V — volume of bulb at t° . 



p = initial pressure, i. e., pressure when bulb is at 0°. 



p = pressure at temperature of t°. 



v^ = portion of " unheated space" enclosed in furnace 

 (in which temperature varies from the tempera- 

 ture of the bulb to that of the room) 0*161 cc . 



v 2 = portion of " unheated space" outside of furnace . . 0*1 28 c . 



t l == estimated mean temperature of v 1 when bulb is at t°. 



t\ = estimated mean temperature of v x when bulb is at 0°. 



£ 2 = temperature of v 2 when bulb is at t°. 



t' = temperature of v 2 when bulb is at 0°. 



a = expansion coefficient of nitrogen under constant volume. 



ft — linear coefficient of expansion of platinum-iridium alloy. 



/y 



Writing A = -^j~- + 



and 



B 



1 + at\ 



«,/v. 



1 + at', 

 t.'/Yi 



