Determinations of the density of phosphine gas
were carried out at the pressures of one atmosphere,
three_quarters atmosphere, one_half atmosphere, and
one-quarter atmospheres The gas was prepared by the
action of dilute potassium hydroxide solution on
solid phosphonium iodide, and purified by fractional
distillation. The value for the normal density thus
and the factor for compressibility between zero and
one atmosphere pressure was found to be
(1 + λ ) = (pv)₀ / (pv)₁ = 1.0091
The molar weight of phosphine is then 34.00(0), and
the atomic weight of phosphorus 30.97(7).
The accuracy claimed is of the order of 1 in 10,000.