Paragraph 4 REAGENTS
Hydrochloric acid solution, 50% (V/V): dilute an appropriate volume of hydrochloric acid (ρ = 1.18 g/ml) with an equal volume of water.
Sulfuric acid, 0.05 M solution } for variant (a) (see page 21)
Sodium or potassium hydroxide, 0.1 M solution, carbonate free } for variant (a) (see page 21)
Sulfuric acid, 0.1 M solution } for variant (b) (see page 21)
Sodium or potassium hydroxide, 0.2 M solution, carbonate free } for variant (b) (see page 21)
Sulfuric acid, 0.25 M solution } for variant (c) (see page 21)
Sodium or potassium hydroxide, 0.5 M solution, carbonate free } for variant (c) (see page 21)
Sodium hydroxide solution, approximately 2 M.
Arnd’s alloy — powdered to pass through a sieve with square apertures less than 1.00 mm.
Magnesium chloride solution, 20% (W/V):
Dissolve 200 g magnesium chloride (MgCl2.6H2O) in approximately 600-700 ml water in a one litre flat bottomed flask. To prevent frothing, add 15 g magnesium sulfate (MgSO4.7H2O). After dissolution add 2 g magnesium oxide and a few anti-bump granules of pumice stone and concentrate the suspension to 200 ml by boiling, thus expelling any trace of ammonia from the reagents. Cool, make up the volume to 1 litre and filter.
Indicator solutions:
Mixed indicator:
Solution A: dissolve 1 g methyl red in 37 ml 0.1 M sodium hydroxide solution and make up to 1 litre with water.
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Solution B: dissolve 1 g methylene blue in water and make up to 1 litre. Mix 1 volume of A with 2 volumes of B.
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This indicator is violet in acid solution, grey in neutral solution and green in alkaline solution. Use 0.5 ml (10 drops).
Methyl red indicator solution:
Dissolve 0.1 g methyl red in 50 ml 95% ethanol, make up to 100 ml with water and filter if necessary. This indicator may be used (4 to 5 drops) instead of the preceding one.
Congo red indicator solution:
Dissolve 3 g Congo red in 1 litre warm water and filter if necessary after cooling. This indicator may be used, instead of the two described above, in the neutralisation of acid extracts before distillation, using 0.5 ml per 100 ml of liquid to be neutralised.
Anti-bump granules of pumice stone, washed in hydrochloric acid and ignited.
Sodium nitrate.