1725 SummaryThe compressibility isotherms of helium have been measured a t -70, -35, 0, 50, 100 and 200" up to 1000 atmospheres pressure.

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Conclusions.The refractive indices and the densities of a number of organic liquids belonging to different classes were determined for a large number of temperatures between 1 5~ and ;5O, and the curves plotted showed the refractive index to be a linear function of the temperature within the experimental error in every case.The refractive powers were calculated for temperatures from IO-80'; the expression (n2 -~) / d gave decreasing values as the temperature increased, (a2 -1 ) / ( n 2 + 2 ) d gave increasing values for normal (not tautomeric) substances, (n -I ) / d in some cases gave increasing, in others decreasing values.It is shown that the molecular refractions calculated by using Briihl's values for atomic refractions gave results agreeing with the experimental values as well a t high as a t low temperatures.The state of the equilibrium between the two forms of tautomeric substances can only be arrived a t qualitatively by means of refractive powers.

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