Properties Of Pure Liquids Research Articles

Viscoelastic relaxation of supercooled liquids. II

In addition to the six liquids for which the results of viscoelastic measurements are reported in part I, studies have also been made on a further eight liquids which differ widely in molecular composition, namely: squalane, tri( β -chloroethyl) phosphate, tri( o -tolyl) phosphate, tri( m -tolyl) phosphate, tris(2-ethyl hexyl) phosphate, tetra(2-ethyl hexyl) silicate, m -bis( m -phenoxy phenoxy) benzene and bis( m -( m -phenoxy phenoxy) phenyl) ether. It has been confirmed for each liquid that the limiting shear modulus, G ∞ , varies with temperature according to the relation previously found, 1/ G ∞ = 1/ G 0 + C ( T - T 0 ). Plotting the quantities R L ( ρG ∞ ) 1/2 and X L /( ρG ∞ ) 1/2 against log 10 ( ωƞ / G ∞ ), where R L and X L are the resistive and reactive components of the shear mechanical impedance, shows that the results for six of these liquids are indistinguishable within experimental error. Moreover, the curves drawn through the experimental points represented in this manner are identical with the corresponding curves found for five of the liquids for which results are described in part I. The results for these eleven liquids show a striking agreement. A new theoretical model is put forward from which the viscoelastic properties of pure liquids in the supercooled region can be predicted within experimental error. This is regarded as a limiting case for liquids which follow the free volume description of steady flow viscosity. In the light of available evidence, it is envisaged that the viscoelastic relaxational behaviour approaches that represented by a single (Maxwell) relaxation process as the degree of co-operative motion of the molecules decreases. Only three of the fourteen liquids investigated show a behaviour which does not follow the theoretical prediction. The observed deviations are not great but are outside the limit of experimental error. Measurements on mixtures of liquids which individually exhibit behaviour in agreement with theory show that an impurity content of less than 2% can result in similar departures from theory. The lack of agreement for the three liquids in question is therefore attributed to impurities in the samples measured.

The Properties of Pure Liquids

By a semiempirical approach, a method is found to calculate the specific heat of a normal pure liquid at constant pressure form the specific heat of the gaseous state at the same temperature. It is also found that the coefficient of thermal expansion, the compressibility, and the velocity of sound of the liquid can be calculated accurately if the density, the molecular weight, and the normal boiling temperature of the liquid at atmospheric pressure are known. Finally, a method of computing the thermal conductivity of all liquids, except liquid metals, from compressibility and density is developed. For normal liquids, the thermal conductivity can again be determined if only the normal boiling temperature, the density, and the molecular weight are known.

Reduced temperature and general properties of pure liquids

Reduced temperature and general properties of pure liquids

Dieletric Properties of Pure Liquids.

Dieletric Properties of Pure Liquids.

IV. On evaporation and dissociation.— Part VIII . A study of the thermal properties of propyl alcohol

In continuation of our investigations of the thermal properties of pure liquids, we have now determined the vapour-pressures, vapour-densities, and expansion in the liquid and gaseous states, of Propyl Alcohol, and from these results we have calculated the heats of vaporization at definite temperatures. The range of temperature is from 5° to 280°, and the range of pressure from 5 mms. to 56,000 mms. Preparation of pure Propyl Alcohol.—A sample of propyl alcohol was procured from Kahlbaum, of Berlin. It was dried with barium oxide, and then with small quantities of sodium; but in this case the results were not nearly so satisfactory as with methyl and ethyl alcohol, for propyl alcohol is soluble in water, forming a mixture or “hydrate,” which boils constantly at a lower temperature than the pure alcohol. It is not completely decomposed by sodium, and can be separated only by repeated fractional distillation. This hydrate was first described by Chancel (‘Comptes Rendus,’ vol. 68, 1867, p. 659), who, observing that it boiled with perfect constancy, assumed that it possessed a definite composition, and gave it the formula C 3 H 8 O, H 2 O. It has more recently been examined by Konowalow (Wiedemann’s ‘Annalen,’ vol. 14, 1881, p. 34), who has determined the vapour- pressures of varying mixtures of propyl alcohol and water at definite temperatures. Konowalow finds that the composition of the mixture, the vapour of which exerts the greatest pressure, is not the same at different temperatures, but that the mixture contains more alcohol at high temperatures than at low. From this it has been concluded that the composition of the “hydrate” must depend on the pressure under which the liquid is distilled. We have proved experimentally that this is the case (but we reserve a discussion of this interesting substance for a future paper), and we give the results of our experiments in an Addendum to this paper.