Note 53 bis — Chapter XX · SULPHUR, SELENIUM, AND TELLURIUM

Judging from the best existing determinations (of Marignac, Kremers, and Pickering) for solutions of sulphuric acid (especially those containing more than 5 p.c. H2SO4) within the limits of 0° and 30° (and even to 40°), the variation of the sp. gr. with the temperature t may (within the accuracy of the existing determinations) be perfectly expressed by the equation St = S0 + At + Bt2. It must be added that (1) three specific gravities fully determine the variation of the density with t; (2) ds/dt = A + 2Bt—i.e. the factor of the temperature is expressed by a straight line; (3) the value of A (if p be greater than 5 p.c.) is negative, and numerically much greater than B; (4) the value of B for dilute solutions containing less than 25 p.c. is negative; for solutions approximating to H2SO43H2O in their composition it is equal to 0, and for solutions of greater concentration B is positive; (5) the factor ds/dp for all temperatures attains a maximum value about H2SO4H2O; (6) on dividing ds/dt by S0, and so obtaining the coefficient of expansion k (see Note 53), a minimum is obtained near H2SO4 and H2SO44H2O, and a maximum at H2SO4H2O for all temperatures.