It
is separated and determined in the same way. Like it, it forms a
sulphide soluble in ammonium sulphide. It is distinguished from selenium
by the insolubility, in a solution of cyanide of potassium, of the metal
precipitated by sodium sulphite; whereas selenium dissolves, forming a
soluble potassic seleno-cyanide.[102]
For the determination, solution is effected by fusing with nitre and
sodium carbonate, dissolving out the tellurate of potash with water, and
boiling with hydrochloric acid. Tellurous compounds are formed, with
evolution of chlorine; and the solution, on treating with a reducing
agent (such as sulphurous acid or stannous chloride), yields metallic
tellurium; which is washed, dried at 100° C., and weighed.
FOOTNOTES:
[101] BaCl_{2} + Na_{2}SO_{4} = BaSO_{4} + 2NaCl.
[102] Se + KCy = KCySe.
CHAPTER XVII.
ARSENIC, PHOSPHORUS, NITROGEN.
ARSENIC.
The chief source of the arsenic of commerce is arsenical pyrites, or
mispickel, which contains about 45 per cent. of arsenic (As). Arsenic
also occurs as a constituent of several comparatively rare minerals;
and, as an impurity, it is very widely distributed. White arsenic is an
oxide of arsenic, and is obtained by roasting arsenical ores, and
refining the material (crude arsenic), which condenses in the flues.
Arsenic itself is volatile, and many of its compounds have the same
property.
Pages:
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701