Supplementary Figure captions
Figure S1. a) Extrapolated ratios between the density of a 1 molal aqueous Na2SO4 solution obtained
from Ref. 16 and the density of a NaCl aqueous solution containing 15 wt% NaCl
75
at 373, 473 and
673 K. At 0.4 GPa the ratios approach a value around 1.005 for the three isotherms. b) Coefficient of
determination R2 for the acoustic velocities of the 1m Na2SO4 solution as a function of the ratio
Na2SO4 / NaCl (15 wt% NaCl) at every temperature investigated in this work. The black symbols
represent R2 calculated from the tests with different initial ratios. The highest R2 value, corresponding
to the best fit, is obtained with a ratio of 1 at 293 K, 1.005 at 373 K and 1.012 at 473, 573, 673 and
773 K, respectively.