Note 47 — Chapter XX · SULPHUR, SELENIUM, AND TELLURIUM
George Kamensky translation
According to Regnault, the vapour tensions (in millimetres of mercury) of the water given off by the hydrates of sulphuric acid, H2SO4,nH2O, are—
t=5° 15° 30°
n=1 0·1 0·1 0·2
2 0·4 0·7 1·5
3 0·9 1·6 4·1
4 1·3 2·8 7·0
5 2·1 4·2 10·7
7 3·2 6·2 15·6
9 4·1 8·0 19·6
11 4·4 9·0 22·2
17 5·5 10·6 26·1
According to Lunge, the vapour tension of the aqueous vapour given off from solutions of sulphuric acid containing p per cent. H2SO4, at t°, equals the barometric pressure 720 to 730 mm.
p = 10 20 30 40 50 60 70 80 85 90 95
t = 102° 105° 108° 114° 124° 141° 170° 207° 233° 262° 295°
The latter figures give the temperature at which water is easily expelled from solutions of sulphuric acid of different strengths. But the evaporation begins sooner, and concentration may be carried on at lower temperatures if a stream of air be passed through the acid. Kessler's process is based upon this (Note 48).