14 



Mi: CLIVE CUTHBERTSON AND MAUDE CUTHBERTSON ON THE 



the acid on phosphorus pentoxide and proceeding as in the case of hydrobromic acid. 

 The solid obtained on free/ing was colourless, but the liquid was usually a pale pink, 

 owing to a trace of dissolved iodine. As the boiling point of HI is far below that of 

 imline the quantity of iodine subliming, at the boiling point of HI, from this mixture 

 was negligible. 



Tests for impurity, similar to those in the case of HBr, were equally satisfactory. 



Rtfractinty, \ = 5461. In this case also measurements of refractivity had to be 

 supplemented by those of density as this has not previously been determined carefully. 



In three trustworthy experiments the following figures were obtained for the 

 refractivity at the green mercury line : 



a 76 



. . . . 9237, 9277, 9260. Mean 9258. 



The mean is taken as the best value. 



Dispersion. From seven experiments the following values were obtained for the 

 dispersion : 



TABLE VII. Dispersion of Hydriodic Acid. 



Using SELLMEYER'S equation the refractivity can be expressed by the formula 



Qu-1) D 57900 xlO 27 



K76) 6556-4 xlO"-n'' 



Fhe calculated values are shown in column 3 and the differences in column 4. 



** of Hydnodic ^.-The density of this gas also has not been accurately 

 Umlated m the same way as in the case of hydrobromic acid three 

 i gave for the weight of a litre 5789, 5791, 5793, mean = 5791 gr 

 we,ght is 57151, taking H == 1'008 and I = 126-97, and the weight 

 ot a litre of oxygen as 1 '4290 gr. 



