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Atomistry » Phosphorus » Physical Properties » Liquid Phosphorus | ||||||||||||||||||||||||||||||||||||||||
Atomistry » Phosphorus » Physical Properties » Liquid Phosphorus » |
Liquid Phosphorus
Values of the densities and specific volumes up to the boiling- point have been determined and are as follows:—
Densities and specific volumes of liquid phosphorus
Hence the expansion of the liquid is expressed by the formula vt = v50[1 + 0.035167(t - 50) + 0.06370(t - 50)2] In another investigation, on 0.7669 gram of phosphorus contained in an evacuated glass dilatometer, the increase of volume between 50° and 235° C. was found to be expressed by: vt = 0.5733[l +0.03505(t - 50) + 0.06118(t - 50)2] The agreement between the two expressions is good at the lower temperatures, and the differences at higher temperatures are about the same value as the coefficient of expansion of glass. Thus at 200° C. the second equation gives the specific volume as 0.6180 c.c. per gram. Without the correction for expansion of glass the apparent specific volume becomes 0.621 c.c. The specific volume at the boiling-point, determined by the method of Ramsay, was 0.6744 c.c. The corresponding atomic volume. Is 20.9 ± 0.4. This constant thus lies between 20 and 21, with a tendency to diminish on keeping the phosphorus at this boiling temperature, owing to the formation of the denser Pβ molecules, which are shown by the cherry-red colour of the liquid. Vapour Pressures of Liquid Phosphorus
The vapour pressures of liquid phosphorus are tabulated overpage in three sections, namely—
log p (mm.) = -3585.96/T – 3.59 log T + 19.2189 This was found to give pressures lower than those experimentally determined between 44° and 150° C. by MacRae and Voorhis, who have altered the constants to fit this range also, as follows:— logp(mm.) = -2898/T – 1.2566 log T + 11.5694 These formulae express the pressures of the liquid from 44° C. to 634° C. The latent heat of vaporisation of liquid yellow phosphorus at its boiling-point has been given as 4 Cals. or 3.89 Cals. Surface Tension of Liquid Phosphorus
The values of the surface tension σ and density D at two temperatures were determined with the object of calculating the molar surface energy σ(M/D)2/3, and its change with temperature.
Then, by comparison with the normal temperature coefficient, the molar weight in the liquid state can be deduced.
The molar weight M used in this calculation corresponded to a molecule P4, and since the temperature coefficient calculated on this assumption is normal, the molar weight in the liquid state is thus found to be the same as in the gaseous state. The molar weight in the dissolved state at the boiling-point of carbon disulphide, and at the freezing-point of benzene, also corresponds very closely to P4. |
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