Effect of Varying Bulk.—As before, 20 c.c. of the iron solution, and 10 c.c. of the dilute acid were diluted to the required volumes and titrated.
| Bulk | 30 c.c. | 100 c.c. | 500 c.c. | 1000 c.c. |
| Permanganate required | 20.4 " | 20.3 " | 20.8 " | 21.5 " |
The variation due to difference in bulk here, although only equal to an excess of 0.7 milligram of iron for each 100 c.c. of dilution, are about three times as great as those observed in a sulphuric acid solution.
Effect of Free Hydrochloric Acid.—In these experiments 20 c.c. of the ferrous chloride solution were used with varying quantities of acid, the bulk of the assay in each case being 100 c.c.
| Dilute acid present | 5 c.c. | 10 c.c. | 50 c.c. | 100 c.c. |
| Permanganate required | 20.2 " | 20.2 " | 20.5 " | 21.0 " |
The last had a very indistinct finishing point, the brown coloration being very evanescent. The effect of the acid is modified by the presence of alkaline and other sulphates, but not by sulphuric acid. Repeating the last experiment we got—
| Without further addition | 21.0 | c.c. | |||
| With | 100 | c.c. | of dilute sulphuric acid | 22.0 | " |
| " | 10 | grams | ammonic sulphate | 20.5 | " |
| " | 10 | " | sodic sulphate | 20.0 | " |
| " | 10 | " | magnesium sulphate | 20.4 | " |
| " | 10 | " | manganese sulphate | 20.2 | " |
The results with these salts, in counteracting the interference of the acid, however, were not a complete success, since the end-reactions were all indistinct, with the exception, perhaps, of that with the manganese sulphate.
Effect of Varying Amounts of Iron.—In these experiments the bulk of the assay was 100 c.c., and 10 c.c. of acid were present.
| Ferrous chloride used | 1 c.c. | 10 c.c. | 20 c.c. | 50 c.c. | 100 c.c. |
| Permanganate required | 1.1 " | 10.3 " | 20.3 " | 50.4 " | 100.1 " |