of Nitric Acid Solutions. 115 



It will be observed that the values for p D increase slowly with 

 increase of percentage up to 70 per cent., the maximum value ; from 

 this point the values decrease up to 98'67 per cent., when there is a 

 slight but apparent reversal. The value for the anhydrous acid is 

 approximately equal to that of a mixture in equal proportional 

 weights of acid and water, a somewhat curious coincidence. This 

 maximum value appears to have escaped the notice of previous 

 workers on the refractive indices of nitric acid. 



In the following table the values are given for (/X D - l)jd, Gladstone 

 and Dale Vformula, and for p-^ 2 - I/(^D~ + 2) d, Lorentz's formula ; the 

 ratio of the two values is approximately 1'63 to 1, the densities in both 

 cases have been interpolated from our results, the fifth decimal place 

 being dismissed as inconsequent, and the assumption being made that 

 at least for small differences in percentages the values may be repre- 

 sented as on straight lines. 



In the case of both factors the values decrease with increase of 

 percentage, the variations for that of Gladstone and Dale amounting 

 to 21*4 per cent., and for that of Lorentz to 23 per cent, of the whole 

 values. 



Gladstone (loc. dt., suprti) has shown previously that the molecular 

 refractive energies of nitric acid, as determined from aqueous solution, 

 and after taking into account the water present, are not constant, 

 though the variations deduced by this method of representation are 

 not of the same order of magnitude. 



The observed results for one of the above factors (Lorentz) are 

 compared with results calculated from formula of straight lines 

 MI = M - a (A/>), wherein MI is the deduced value, and M the 

 values for /Jt D 2 - I/(/*D" + 2) d for the several origin of co-ordinates, 

 <i is a constant and Ap the percentage differential. Neglecting the 

 first two values, which stand by themselves, the value for M from 

 6 to 20 per cent, is taken at 0'20360, and for the remaining portion 

 at 0-19750. 



