The standard solution of manganese is made by dissolving 0.1435 gram of
permanganate of potash (KMnO_{4}) in a little water acidulated with
nitric acid, and diluting to 1 litre. One c.c. will contain 0.05
milligram of manganese.
PRACTICAL EXERCISES.
1. What percentage of manganese (Mn) is contained in permanganate of
potash (KMnO_{4})?
2. Ten c.c. of a solution of permanganate of potash is found to oxidise
10 c.c. of an acid solution of ferrous sulphate. The manganese is
determined in the titrated solution by precipitation as dioxide and
titrating. How much of the ferrous solution will be oxidised in the
second titration?
3. What weight of potassium iodide would be just sufficient to absorb
the chlorine evolved by 0.5 gram of pure dioxide of manganese?
4. What weight of iron must be dissolved up so as to have an excess of
0.25 gram after oxidation by 1 gram of pure dioxide?
5. What weight of the brown oxide, Mn_{2}O_{4} will be left on igniting
1 gram of the pure dioxide?
CHROMIUM.
Chromium occurs in nature chiefly as chromite or chrome iron ore
(FeO_{2}Cr_{2}O_{3}, with more or less MgO and Al_{2}O_{3}), which is
the chief ore. It is a constituent of some silicates, and is frequently
met with in very small quantities in iron ores. It occurs as chromate in
crocoisite (PbCrO_{4}), and some other rare minerals.
Pages:
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573