Effect of Varying Potassium Iodide.—An excess of iodide is always required to keep the iodine in solution; a larger excess has little effect.
| Iodide added | — | 1 gram | 20 grams |
| "Hypo" required | 20.4 c.c. | 20.5 c.c. | 20.6 c.c. |
The 20 c.c. of iodine used, itself contained 0.5 gram of potassium iodide.
Effect of Foreign Salts.—
| Bicarbonate of soda added | — | 0.5 gram | 1.5 gram | 5.0 grams |
| "Hypo" required | 20.4 c.c. | 18.2 c.c. | 17.1 c.c. | 16.0 c.c. |
The solution obviously must be free from bicarbonate of soda. This should be remembered, since when titrating arsenic assays with iodine it must be present; and students must avoid confounding the two titrations.
In some other experiments, in which 10 grams each of the salts were taken, the following results were obtained:—
| Salt added | — | AmCl | AmNO3 | Am2SO4 |
| "Hypo" required | 20.4 c.c. | 20.5 c.c. | 20.3 c.c. | 20.2 c.c. |
| Salt added | NaCl | NaNO3 | Na2SO4 |
| "Hypo" required | 20.3 c.c. | 20.4 c.c. | 20.4 c.c. |
Effect of Varying Iodine.—