REFRACTION AND DISPERSION OF THE HALOGENS, HALOGEN ACIDS, ETC. 1 1 



It was not considered worth \vhilr to s|x'ii<l further time in multiplying observations 

 which could never command great confidence, owing to the fewness of the bands 

 read. We hope to return to this rlnnent, using the method of crossed prisms, which 

 is more suitable than that of the interferometer. 



HYDROCHLORIC ACID. 



Previous Determinations. DULONG obtained 1*000447 for white light, and 

 MASCART 1 '000444 for the D line. The dispersion has never before been 

 attempted. 



Preparation. The gas was prepared by dropping sulphuric acid on pure sodium 

 chloride. After passing through two drying bulbs filled with sulphuric acid it was 

 condensed in liquid air and allowed to boil off. When the gas had flowed through 

 the connecting tubes for 15 minutes so as to displace the air, it was admitted to the 

 refractometer and allowed to flow till the pressure was atmospheric. The following 

 table gives the experimental values found, reduced to C. and 760 mm. by the 



formula 



/ .x Tx760 

 } 



Experiment . 1, 2, 3, 4, 5, G, 7. 



(,u-l)l0 7 . . 4514, 4513, 4508, 4512, 4510, 4509, 4510. 



Mean 451 1. 



This value requires correction for the density of the gas. GRAY and BURT* found 

 that the volume of hydrogen from two volumes of hydrochloric acid is 1'0079. 



LEDUC gives the mean coefficient of expansion of the gas at constant pressure as 

 003736. 



The average temperature of our experiment was 16 C. 



Hence the experimental value must be multiplied by 



lx(l + 16x'003736) 



1'0079 x(l + 16 x '00366)' 

 whence we obtain 



Dispersion. Assuming this value the dispersion was determined from six experi- 

 ments. The following table shows the results: 



* 'Trans. Chemical Society,' 95, II. of 1909, p. 1604. 

 C 2 



