Calculation of the Results.—After deducting for the silver added, and correcting for the cupellation loss, the calculation is made in the usual way; reporting as so many parts per thousand in the case of rich alloys and as so many ounces and pennyweights, or better as ounces and decimals of an ounce, in the case of poor alloys and ores.
In this last case, however, it is less fatiguing to refer to a set of tables which give, either directly or by means of simple addition, the produce corresponding to any weight obtained from certain given weights of the substance. The following table gives the produce in ounces and decimals of an ounce per ton of 2240 pounds:—
| Weight of Metal got. | Weight of Ore taken. | ||||
| 3 grams. | 5 grams. | 20 grams. | 50 grams. | 100 grams. | |
| 0.0001 | 1.09 | 0.65 | 0.16 | 0.06 | 0.03 |
| 0.0002 | 2.18 | 1.31 | 0.33 | 0.13 | 0.06 |
| 0.0003 | 3.27 | 1.96 | 0.49 | 0.20 | 0.10 |
| 0.0004 | 4.36 | 2.61 | 0.65 | 0.26 | 0.13 |
| 0.0005 | 5.44 | 3.27 | 0.82 | 0.33 | 0.16 |
| 0.0006 | 6.53 | 3.92 | 0.98 | 0.39 | 0.19 |
| 0.0007 | 7.62 | 4.57 | 1.14 | 0.46 | 0.23 |
| 0.0008 | 8.71 | 5.23 | 1.31 | 0.52 | 0.26 |
| 0.0009 | 9.80 | 5.88 | 1.47 | 0.59 | 0.29 |
| 0.001 | 10.89 | 6.53 | 1.63 | 0.65 | 0.33 |
| 0.002 | 21.78 | 13.07 | 3.27 | 1.31 | 0.65 |
| 0.003 | 32.67 | 19.60 | 4.90 | 1.96 | 0.98 |
| 0.004 | 43.56 | 26.13 | 6.53 | 2.61 | 1.31 |
| 0.005 | 54.44 | 32.67 | 8.17 | 3.27 | 1.63 |
| 0.006 | 65.33 | 39.20 | 9.80 | 3.92 | 1.96 |
| 0.007 | 76.22 | 45.73 | 11.43 | 4.57 | 2.29 |
| 0.008 | 87.11 | 52.27 | 13.07 | 5.23 | 2.61 |
| 0.009 | 98.00 | 58.80 | 14.70 | 5.88 | 2.94 |
| 0.01 | 108.89 | 65.33 | 16.33 | 6.53 | 3.27 |
| 0.02 | 217.78 | 130.67 | 32.67 | 13.07 | 6.53 |
| 0.03 | 326.67 | 196.00 | 49.00 | 19.60 | 9.80 |
| 0.04 | 435.56 | 261.33 | 65.33 | 26.13 | 13.07 |
| 0.05 | 544.44 | 326.67 | 81.67 | 32.67 | 16.33 |
| 0.06 | 653.33 | 392.00 | 98.00 | 39.20 | 19.60 |
| 0.07 | 762.22 | 457.33 | 114.33 | 45.73 | 22.87 |
| 0.08 | 871.11 | 522.67 | 130.67 | 52.27 | 26.13 |
| 0.09 | 980.00 | 588.00 | 147.00 | 58.80 | 29.40 |
| 0.1 | 1088.89 | 653.33 | 163.33 | 65.33 | 32.67 |
| 0.2 | 2177.78 | 1306.67 | 326.67 | 130.67 | 65.33 |
| 0.3 | 3266.67 | 1960.00 | 490.00 | 196.00 | 98.00 |
| 0.4 | 4355.56 | 2613.33 | 653.33 | 261.33 | 130.67 |
| 0.5 | 5444.44 | 3266.67 | 816.67 | 326.67 | 163.33 |
| 0.6 | 6533.33 | 3920.00 | 980.00 | 392.00 | 196.00 |
| 0.7 | 7622.22 | 4573.33 | 1143.33 | 457.33 | 228.67 |
| 0.8 | 8711.11 | 5226.67 | 1306.67 | 522.67 | 261.33 |
| 0.9 | 9800.00 | 5880.00 | 1470.00 | 588.00 | 294.00 |
| 1.0 | 10888.89 | 6533.33 | 1633.33 | 653.33 | 326.67 |
When, as in this table, the fraction of an ounce is expressed by two places of decimals, it may be reduced to pennyweights (dwts.) by dividing by 5. For example, 0.40 of an ounce is 8 dwts. The fraction of a dwt. similarly expressed may be converted into grains with sufficient exactness by dividing by 4. Thus, 1.63 ozs. equal 1 oz. 12.60 dwts., or 1 oz. 12 dwts. 15 grains. In England it is usual to report in ounces and decimals of an ounce.
The way to use the table is best shown by an example. Suppose a button of silver weighing 0.0435 gram was obtained from 20 grams of ore. Look down the 20-gram column of the table, and select the values corresponding to each figure of the weight, thus:—
0.04 = 65.33 ozs. to the ton
0.003 = 4.90 "
0.0005 = 0.82 "
——————
0.0435 = 71.05 "
Add these together. The produce is 71.05 ozs., or 71 ozs. 1 dwt. to the ton.
Or, suppose an ore is known to contain 1.24 per cent. of silver. Look down the 100-gram column, select the values, and add them together as before.
1.0 = 326.67 ozs. per ton
0.2 = 65.33 "
0.04 = 13.07 "
——————
1.24 = 405.07 "
This gives 405 ozs. 1 dwt. 10 grains to the ton.