Dr. Schroeder van dcr Kolk on Gases. 129 



That the influence of adhesion on the formula? obtained is inap- 

 preciable, follows also from the examination of the law of volumes 

 given in the fourth section. 



§ III. Determination of -=-« 



J dr 



Regnault's determinations of Mariotte\s law and of the coeffi- 

 cients of expansion give, as already observed, values only for the 

 two temperatures 4° and 100°. But llegnault has compared 

 with each other thermometers filled with different gases, and 

 has found that two thermometers filled with air and hydrogen 

 were quite parallel if, in both, the fixed points for 0° and 100° 

 were first determined. The temperatures were inferred from 

 the increase of pressure under constant volume. He extended 

 these investigations to between — 87° and 300°, between which 

 limits the thermometers were parallel. At the lowest tempera- 

 ture the difference was only o, 2*, and in this calculation quite 

 to be neglected. Supposing, now, three determinations of air 

 and hydrogen at 0°, 100°, and n degrees, the condition of these 

 gases in these three cases will be given by the formula 



Air. Hydrogen. 



/>!»=*! 273, p l v = k l 273, 



p 2 v = k 2 373, p n v = Jc u 373, 



p 3 v = k 3 {273 + n), p in v = k lu (273-\-n) • 



and as llegnault considered the temperatures proportional to the 

 pressures, the proper expression of his result is 



P3-P1 'Pi-P\=Piu-Pi'-Pi-Pi> 

 or 



k 3 {273-\-n)-273k l : 373^-273/q 



= k lu {273 + n)-273k { : 373k tl -273k r 



Since k may, in the case of hydrogen, be considered to be inde- 

 pendent of the temperature, k t , k jp and k JU may be calculated by 

 means of the formula given for hydrogen in the preceding sec- 

 tion ; for the pressure may in each case be calculated with suffi- 

 cient accuracy from the temperatures, which in this case is suf- 

 ficient, for the pressure is only implicitly contained in the value 

 of k. For air, k x and k 2 may be calculated by means of the for- 

 mulae already found, and hence k 3 alone remains to be determined. 

 In this way, for instance, is found the value of k for 50° and 

 1 metre pressure. 



* Daguin, Traite de Physique, vol. i. p. 833. 



