Page:Proceedings of the Royal Society of London Vol 69.djvu/123

Rh 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.

Percentage.

/t-l/rflO- 5. Observed.

M 2 -i/( M 2 + 2)<no- s.

Observed.

Mj = M-Ojo). Calculated.

Difference.

2-19 3'85

33228 33169

20507 20453

M = 20360, a = -4-1

6-79 9-29 11-88 16-11 18-27

33012 33093 32597 32472 32356

20339 20222 20118 199935 19853

20329 20225 20118 19946 19857

+ 10 - 3 - 7 -11

- 4