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28 CHEMISTRY AND TECHNOLOGY OF EXPLOSIVES

Vandoni [72] repeated the experiments of Sapozhnikov on the vapour pressure

of HNO 3 over mixtures of HNO 3 -H 2 SO 4 -H 2 O using an improved technique. In

the main, he confirmed the earlier results, but he introduced some corrections to

the figures obtained by Sapozhnikov. Thus he used nitric acid free from nitrogen

oxides which were present in the acid used by Sapozhnikov. Vandoni has shown

FIG. 11. Vapour pressure and activity H/H 0 of HNO 3 in the solution HNO 3 -

-H 2 SO 4 -H 2 O containing 21.9% HNO 3 (Vandoni [72]).

that the absorption of vapours of nitric acid by potassium (the method applied

by Sapozhnikov) is not complete. Instead of HNO 3 vapour pressure values, Van-

doni utilized the activity of HNO 3 , i.e. the ratio H/H, between the vapour pres-

sure of HNO 3 over the surface of the solution (H) and the vapour pressure of pure

HNO 3 (H 0 = 14.1 mm Hg at 0°C).

Vandoni’s diagrams of the activity of HNO 3 and H 3 O, when the content of

HNO 3 is 21.9 and 50% (i.e. in the most common nitrating mixtures) are given

in Figs. 11 and 12 respectively.