Effect of Varying Acid.—These experiments were under the usual conditions, the bulk being 100 c.c. The results were—
| Acetic acid | — | 1.5 | c.c. | 30.0 | c.c. |
| "Hypo" required | 20.4 c.c. | 20.7 | " | 20.7 | " |
| Hydrochloric acid | — | 1.5 | c.c. | 15.0 | c.c. |
| "Hypo" required | 20.4 c.c. | 20.6 | " | 20.9 | " |
| Sulphuric acid | — | 0.5 | c.c. | 20.0 | c.c. |
| "Hypo" required | 20.4 c.c. | 20.7 | " | 15.2 | "[86] |
| Nitric acid | — | 0.5 | c.c. | 10.0 | c.c. |
| "Hypo" required | 20.4 c.c. | 21.5 | " | could not be titrated. |
In the application of this titration to the assay of manganese ores, hydrochloric and hydriodic acids are the only ones likely to be present.
Effect of Alkalies.—On theoretical grounds the presence of these is known to be inadmissible. A solution rendered faintly alkaline with ammonia required only 11.2 c.c. of "hypo;" and another, with 0.5 gram of caustic soda, required 4.0 c.c. instead of 20.4 c.c. as in neutral solutions.
Effect of nearly Neutralising Hydrochloric Acid Solutions with Ammonia.—Provided care is taken not to add excess of ammonia, this has a good effect, counteracting the interference of excess of acid. Thus 20 c.c. of iodine (as before) required 20.4 c.c. of "hypo;" with 15 c.c. of hydrochloric acid 20.7 c.c. were required, but with 15 c.c. of acid, nearly neutralised with dilute ammonia 20.4 c.c. were used.
Effect of the Addition of Starch.—The addition of varying quantities of starch has no effect, provided it is added when the titration is nearly finished, as the following experiments show:—
| Starch added | 1.0 | c.c. | 5.0 | c.c. | 10.0 | c.c. | 50.0 | c.c. |
| "Hypo" required | 20.4 | " | 20.4 | " | 20.4 | " | 20.5 | " |
But if the starch is added before the titration, the results are liable to error.
| Starch added | 1.0 | c.c. | 50.0 | c.c. |
| "Hypo" required | 20.4 | " | 24.0 | " |
The starch should be used fresh, and is best made on the day it is used; after four days the finishing point is not so good.