REFRACTION AND DISPKRSION OF THE HALOGENS, HALOGEN ACIDS, KTC. 13 



l>i*persion. Assuming this value the following values of the dispersion were 

 obtained from eight 



TAHLE VI. Dispersion <>f Jlydrobromic Acid. 



Using SELLMEYEK'.S formula the refractivity can be expressed by the equation 



_.v D 5'1446 xlO-' 7 



''(d a 76) 8668-4xl0 27 -N, a ' 



Calculated values are shown in column 3 and differences in column 4. 



Density of Itydrobromic Acid. As the density of the gas at temperatures higher 

 than C. does not appear to have been previously measured the following values are 

 perhaps worth recording. The degree of accuracy was not carried beyond one part in 

 a thousand, since errors in reading the refractivity were not less than this amount. 



The gas was weighed at atmospheric pressure and the temperature of the room, 

 which averaged 19 C., and the values were reduced to C. and 760 by the formula 



T 76 

 D ' = D * X 273 X P- 



Three experiments gave, for the weight of a litre, on these assumptions, 3'648, 

 :i '(' 17, and 3'650 gr., the mean of which is 3'6484. 

 The theoretical weight is :n>l(i:'.:!. 



HYDRIODIC Acm 



Previous Determination*. MASCART found /x 1 = '000906 for the D line. The 

 dispersion has not been attempted. 



Preparation. The gas was prepared by slowly dropping pure aqueous solution of 



