These show clearly the interference of free mineral acids, although very dilute hydrochloric acid (1 c.c. in 500 of water) has no effect.
Effect of Acetic and Citric Acids.—A similar series of experiments with these acids gave the following results:—
| Acetic acid present | 0.0 | c.c. | 5.0 | c.c. 50.0 | c.c. 100.0 | c.c. | ||
| "Baric chloride" required | 20.0 | " | 20.0 | " | 20.0 | " | 20.0 | " |
| Citric acid present | 0 gram | 1 gram | 5 grams |
| "Baric chloride" required | 20.0 c.c. | 20.0 c.c. | 20.0 c.c. |
These acids do not interfere.
Effect of Sodic Acetate and Acetic Acid.—In each of these experiments 5 c.c. of acetic acid was present.
| Sodium acetate added | 0 gram | 1 gram | 10 grams | 50 grams |
| "Baric chloride" required | 20.0 c.c. | 20.0 c.c. | 20.0 c.c. | 20.0 c.c. |
As sodic acetate and acetic acid did not interfere, it became desirable to make some experiments on the finishing point. The first object sought for was the smallest amount of the standard baric chloride in 500 c.c. of water, required to give an indication when tested in the manner already described.
| Conditions of Assay Solution. | Baric Chloride required. |
| Water only | 0.05 c.c. |
| With 10 grams of sodium acetate and 5 c.c. of acetic acid | 0.05 " |
| The same with 5 grams of nitre | 0.10 " |
| Like the last, but with 5 grams of salt instead of nitre | 0.10 " |
These show that as small an amount of baric chloride solution as is equal to only 0.000002 gram of sulphur in the 2 c.c. of solution tested yields a decided precipitate on the addition of 3 drops of sulphuric acid.