perature immediately before making the observation. Isothermal distillation within the apparatus furnishes a very sensitive test for the purity of the liquid. As the result of observations made on acetic acid, bromine, benzene and carbon tetrachloride, it may be concluded that the vapor pressure of a sample of liquid rapidly elevated to the boiling point is identical with that which it exerts after remaining for several hours at the boiling point. Delay in attaining internal equilibrium is therefore not a factor of influence in the measurement of boiling point or vapor pressure of these liquids, and observations may be made as soon as temperature equilibrium is established.
The rate of production of vitamin D is directly proportional to the number of light quanta absorbed by ergosterol and independent of the wave length of the light used. 4. Vitamin D absorbs in the same wave length region as ergosterol and is destroyed by light of the same wave length as that which forms it.5. The highest concentration of vitamin D which can be produced by direct irradiation of ergosterol is 35%. This is an absolute maximum and the probable value is lower.6. The quantum efficiency is 0.3 molecules of vitamin D per quantum of light absorbed.
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