50 SMITHSONIAN" MISCELLANEOUS COLLECTIONS VOL. 54 



I II 



(RX.nT)L RL 



^^— (l + a)(l — &) (l + ao)(l — bo) 



Equation I applies to the permanent gases, that is, to those which are 

 liquefiahle only below 0°. Equation II applies to the easily liquefiable 

 gases. E is the gas constant, and according to Berthelot ^ its value is 

 22.412. The constant m, of equation I, is given by Guye the value 

 0.0000623. T represents the critical temperature, on tlie absolute scale; 

 L is the weight of one litre of gas at 0°, 7G0 mm., sea level, and latitude 

 45° ; and M is the molecular weight. The symbols a and h are the con- 

 stants of the Van der Waals equation, which vary for different gases, and 

 in II are brought to the standard temperature and pressure. 



In any given case the use of these formulge requires a knowledge of 

 the constants a and h. These can be deduced from the compressibilities 

 and coeflBcients of expansion of a gas, or from the critical constants. The 

 latter method is the one adopted by Guye, and with one exception it will 

 be followed here. Guye gives the required data in form ready for use,^ 

 and they yield results which appear to be trustworthy. Applied to the 

 densities given in the preceding pages they give the following reductions : 



Nitrogen, Chemical L=1.25066. T = 127.5°. (1 + a) (!-&) = 

 1.00100. Hence N = 14.0058, ±.00085. From the figures given for at- 

 mospheric nitrogen, N= 14.0074, ±.00022. The weighted mean is N" = 

 14.0073, ±.0002. 



Nitrous Oxide. L=1.97775. (1 + ao) (l-&o) =1-00733. Hence 

 ^20 = 44.0028, ±.0021. The crude density ratio gives 44.2895, ±.0021, 

 showing that the correction is large. This reduced value combines with 

 other values for NgO ^s follows : 



From density of gas N^O = 44.0028, ± .0021 



From gravimetric analysis " = 44.0150, ± .0066 



From volumetric analysis " = 44.0417, ± .0060 



General mean N^O = 44.0074, ± .0019 



Nitric Oxide. L= 1.34012. T = 179.5°. a= 0.00257. & = 0.00115. 

 Hence NO = 30.0073, ±.00065. Gray's analyses of the gas gave N"0 = 

 30.0104, ±.0011. The general mean is 30.0083, ±.00055. 



Ammonia. The crude density ratio gave ]SrH3 = 17.2619, ±.00065. 

 This has been reduced by means of compressibility data. Perman and 

 Davies, who measured the compressibility, give the multiplying factor 



1 Zeitsch. Elektrochem., 1904, 621. In Journ. Physique (3), 8, 527, Berthelot gives values of 

 a and b for several gases. 

 " When Guye gives two or more figures for (1 + a) (1 — b) I take the average. 



