of sulphur? What would be the effect on the price of an error
of 0.25 per cent. in the assay?
2. Pyrites carries 50 per cent. of sulphur, and on calcining yields 70
per cent. of its weight of burnt ore. Supposing the burnt ore carries
3.5 per cent. of sulphur, what proportion of the sulphur will have been
removed in the calcining?
3. How would blende compare with pyrites as a source of sulphur for
sulphuric acid making?
4. How would you determine the percentage of sulphuric oxide in a sample
of gypsum? What is sulphuric oxide, and what relation does it bear to
sulphur?
5. A mineral contains 20.7 per cent. of water, 32.4 per cent. of lime,
and 18.6 per cent. of sulphur. What is its probable composition? What
experiment would you try to determine the accuracy of your conclusion?
SELENIUM
occurs in nature combined with copper, mercury, and lead, in certain
rare minerals. In small quantities it is found in many ores. It is
detected in solution by the red precipitate produced on boiling the acid
solution with sodium sulphite. This reaction is used for its
determination.
~Solution.~--The solution is effected by boiling with nitric acid or
aqua regia, or by fusing with nitre. To separate the selenium, the
solution is evaporated with an excess of hydrochloric acid and a little
sodium or potassium chloride.
Pages:
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699