(1) 30 c.c. 15 c.c. 5 c.c. 2 c.c. 1 c.c. 1/2 c.c. -- c.c. = 53-1/2 c.c. (2) 30 " 15 " 1 " 1 " 1 " 1/2 " -- " = 48-1/2 " (3) 30 " 15 " 3 " 1 " 1 " 1/2 " -- " = 50-1/2 " (4) 30 " 15 " 5 " 2 " 1 " 1/2 " 1/2 " = 54 " (5) 30 " 15 " 2 " 1 " 1 " 1/2 " -- " = 49-1/2 " (6) 30 " 15 " 2 " 1 " 1 " 1/2 " 1/2 " = 50 standard Three grams of ore were taken, and the standard contained 0.480 gram of copper. In this series the difference of half a c.c. means about 0.15 per cent. on the ore; with a little practice it is easy to estimate whether the whole or half of the last addition should be counted. To get satisfactory results, the manner of finishing once adopted must be adhered to. 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. Nitric acid 5.0 c.c. 10.0 c.c. 15.0 c.c. Cyanide required 21.6 " 21.7 " 21.5 " On adding nitric acid to the solution it combines with a portion of the ammonia to form ammonic nitrate; it will be seen from the last series of experiments that the lessening of the amount of free ammonia will decrease the quantity of cyanide required; but, on the other hand, the ammonic nitrate which is at the same time formed will increase the amount required; under the conditions of the assay these two effects neutralise each other, and such differences in the quantity of acid as are likely to occur are unimportant.