Hydrochloric acid almost completely removes the colour, which, however, is restored by the addition of a few crystals of potassium iodide.
Effect of Alkalies.—Ammonia, soda, or potash destroys the colour, but it is restored on acidifying with nitric or sulphuric acid.
Effect of Ammonic Salts.—The following table shows the results after addition of ammonic salts:—
| C.c. present. | With 10 grams Ammonic Nitrate. | With 10 grams Ammonic Sulphate. | With 10 grams Ammonic Chloride. |
| 1.0 c.c. | 0.9 c.c. | 1.1 c.c. | — |
| 2.5 " | 2.5 " | 2.7 " | — |
| 5.0 " | 5.0 " | 5.5 " | — |
Ammonic chloride, like hydrochloric acid, removes the colour, which may be restored on the addition of more potassium iodide. Nitrates and sulphates do not thus interfere.
Effect of Foreign Salts.—Sodic hyposulphite almost completely removes the colour. Copper salts liberate iodine; but when this has been removed by boiling and the cuprous iodide has been filtered off there is no further interference. Dilute solutions of lead salts give no colour.
PRACTICAL EXERCISES.
1. A fusible alloy is made up of 8 parts of bismuth, 5 of lead, and 3 of tin. What weight of oxide of bismuth, Bi2O3, would you get on the analysis of 1 gram of it?
2. What weight of bismuth can be got from 2 grams of the subnitrate BiONO3.H2O?
3. How would you detect and separate arsenic, lead, and copper in a sample of bismuth?