The effect of varying conditions on the assay may be seen from the following experiments.
Effect of Varying Temperature.—The effect of increased temperature is to slightly decrease the colour, but this can only be observed when a fair quantity of copper is present.
| 1.0 | c.c. at 15° | showed the | colour of | 1.0 | c.c. at 70° |
| 2.5 | " | " | " | 2.7 | " |
| 5.0 | " | " | " | 5.0 | " |
| 10.0 | " | " | " | 9.0 | " |
Effect of Varying Ammonia.—The solution must, of course, contain free ammonia; about 5 c.c. of dilute ammonia in 50 c.c. bulk is the quantity to be used in the experiments. A larger quantity affects the results, giving lower readings and altering the tint. With small quantities of ammonia the colour approaches a violet; with larger, a sky-blue.
| 2.5 | c.c. with | 25 | c.c. of | strong ammonia | read | 2.2 | c.c. |
| 5.0 | " | " | " | " | " | 4.0 | " |
| 10.0 | " | " | " | " | " | 8.0 | " |
Effect of Ammonic Salts.—The following table shows the results after addition of ammonic salts:—
| C.c. Present. | With 10 grams Ammonic Nitrate. | With 10 grams Ammonic Chloride. | With 10 grams Ammonic Sulphate. |
| 2.5 | 2.5 | 2.5 | 2.0 |
| 5.0 | 5.0 | 5.3 | 4.3 |
| 10.0 | 10.0 | 10.0 | 8.5 |
These show that sulphates should be avoided, and either nitrate or chloride solutions be used in the standard as well as in the assay.
Determination of Copper in a Manganese Ore.—Treat 3 grams of the ore with 20 c.c. of hydrochloric acid, and evaporate to dryness. Take up with 10 c.c. of hydrochloric acid; dilute to about 200 c.c., and pass sulphuretted hydrogen until the solution smells of the gas; filter, burn, take up with 5 c.c. of dilute nitric acid, add 10 c.c. of dilute ammonia, and filter into the Nessler tube, and make up with the washings to 50 c.c. Into the "standard" tube put 5 c.c. of dilute nitric acid and 10 c.c. of dilute ammonia. Make up to nearly 50 c.c. with water, and run in the standard copper until the colours are equal. In a determination 4 c.c. (= 2.0 milligrams of copper) were required; this in 3 grams of ore = 0.07 per cent.
Determination of Copper in "Black Tin."—Weigh up 3 grams of the dried ore, boil with 10 c.c. of hydrochloric acid, and afterwards add 1 c.c. of nitric; boil off nitrous fumes, evaporate to about 5 c.c., dilute to 50 c.c., add 20 c.c. of dilute ammonia; stir, and filter. If much iron is present, dissolve the precipitate of ferric hydrate in acid, and reprecipitate with ammonia. Mix the two filtrates, and dilute to 100 c.c. Take 50 c.c. for the test. A sample of 3 grams of an ore treated in this way required 5.2 c.c. of standard copper to produce equality of tint. This gives 0.35 per cent.