CHLORIDES OF PHOSPHORUS. 77F
further purified by another fractionation. The yield is almost
theoretical.
Sulphur chloride, S 2 C1 2 , as ordinarily obtained, is a yellowish-
red, heavy liquid which fumes a little in the air, has an unpleas-ant odor, and attacks the mucous membrane. When distilled in
vacuum it has a pure yellow color. This preparation should be
Fig. 14carried out in a room reserved especially for working with nox-
ious compounds, and the liquids should be transferred from one
vessel to another only when under the hood.
- Chlorides of Phosphorus.
Chlorine combines with phosphorus to form either the liquid trichloride or
the solid pentachloride according to whether the phosphorus or chlorine is
present in excess. Phosphorus trichloride boils undecomposed at 76° C; on
heating phosphorus pentachloride, it vaporizes without passing through the
liquid phase. Density determinations of the gas show that the pentachloride
is appreciably dissociated at 180°, and practically completely so at temper-
atures above 290°, into phosphorus trichloride and chlorine; the latter can be
identified by its yellowish-green color. On cooling, the dissociation products
recombine and again form the pentachloride.
Phosphorus oxychloride is most conveniently prepared by oxidizing phos-
phorus trichloride with potassium chlorate.
3 PC1 3 + KCIO3 = 3 POCI3 + KC1.