Answer:
FROM the magnetic point of view, phosphorus is an extremely interesting
substance because of its allotropic modifications. The ordinary forms are
the yellow (or white) and the red varieties. X-ray investigations indicate
that probably yellow phosphorus is analogous with the cubic forms of antimony and arsenic; and red phosphorus with monoclinic antimony and
arsenic (Mellor, 1928). The conclusions of different workers on the structure of red phosphorus are not in agreement. There is also Bridgman's black
phosphorus which is probably hexagonal (Linck and lung, 1925). Natta
and Passerini (1930) have studied the crystal structure of white phosphorus.
This substance when condensed at the temperature of liquid ammonia is
cubic. Atomic positions however are yet undetermined. Another and noncubic form is obtained by condensation at liquid-air temperatures. It is
thus clear that most likely white phosphorus is cubic in structure with a
probable superposition of another lattice.
The evidence from Raman effect also points to the same conclusion.
Bhagavantam (1930) investigated the Raman effect of white phosphorus in
the solid state. The characteristic frequencies obtained by him are 607, 468
and 374. Since the phosphorus molecule is known to contain 4 atoms,
Bhagavantam (1930) has shown that the tetrahedral structure fits the results
satisfactorily since such a structure would give only three frequencies. But
for the particular law of forces adopted, the frequencies should have the
ratio 2: 2: 1 but the observed frequencies deviate considerably.
