KF.FRACTION AND DISPERSION OF THE HALOGENS, HALOGEN ACIDS, ETC. 21 



AMMONIA. 



Previous Determination.*. Previous determinations of the refractivity of ammonia 

 are us follows : 



It would occupy too much space to analyse the causes of these discrepancies, which 

 are chiefly due to differences in the standard conditions assumed and in the coefficients 

 of thermal expansion and compressibility adopted. But the figures in the last 

 column give approximately the figures corrected for the theoretical density. 



Preparation. Our gas was prepared by warming a mixture of ammonium chloride 

 and calcium oxide in a flask. After passing over red hot lime and cold dry lime it 

 was condensed at 80 C. and allowed to boil off, the middle fraction being collected. 

 Three samples were used. 



Calculation of Jtesitltx. In reducing the results the figures given below were used, 

 following GUYE* : 



Coefficient of thermal expansion (l + '003914<). 

 Coefficient of compressibility 



l_ll = A (/>,-), A = -0002(1- -0000030. 

 Poo 



Weight of a litre of ammonia at C. and 760 mm., "7708 gr. Theoretic 



density, '7605 gr. 

 Thus the equation for reduction is 



D 



(dJG) 



NX 7605 

 L 7708 



x 76 



W3914*, 



1 + -003914*., 



where N is the number of bands observed, X the wave-length, L the length 

 of the tul>e, and p t p. t t t. 2 the initial and final pressures and temperatures. 



Refraction. The determinations for X 5461 were, as usual, made by pairs of 

 experiments, witli pressure rising and falling. 



The mean of nine such experiments, whose extremes were 1 '0003782 and 1 '0003790, 



Me"m. Soc. de Phys. et d'Hist. Nat. de Geneve,' vol. 35, 1908. 



