The following experiments show the effect of variation in the conditions of the assay:—Use a solution of copper nitrate, made by dissolving 10 grams of copper in 50 c.c. of water and 35 c.c. of nitric acid, and diluting to a litre. 100 c.c. = 1 gram of copper.
Effect of Varying Temperature.—In these experiments 20 c.c. of copper nitrate were used, with 10 c.c. of nitric acid, 30 c.c. of dilute ammonia, and water to 200 c.c. The results were—
| Temperature | 15° | 30° | 70° | 100° |
| Cyanide required | 21.5 c.c. | 20.8 c.c. | 19.7 c.c. | 18.8 c.c. |
The temperature is that of the solution before titrating. These show the importance of always cooling before titrating, and of titrating the assay and standard at the same temperature.
Effect of Varying Bulk.—The quantities of copper, acid, and ammonia were the same as in the last-mentioned experiments. The results were:—
| Bulk | 100.0 | c.c. | 200.0 | c.c. | 300.0 | c.c. | 400.0 | c.c. |
| Cyanide required | 23.3 | " | 21.7 | " | 21.4 | " | 21.4 | " |
These show that large variations in bulk must be avoided.
Effect of Varying Ammonia.—The quantities of copper and acid were the same as in the series of experiments last noticed. The bulk was 200 c.c. The results were:—
| Dilute ammonia | 20.0 | c.c. | 30.0 | c.c. | 50.0 | c.c. | 100.0 | c.c. |
| Cyanide required | 20.9 | " | 21.7 | " | 22.3 | " | 24.6 | " |
Effect of Varying Acid.—The quantities of copper and water were the same as in the last-noticed set of experiments: 30 c.c. of dilute ammonia were used.