-----------------+------------+-----------+------------------ Copper present. | Dry Assay. | Margin. | Loss on 100 | | | Parts of Copper. -----------------+------------+-----------+------------------ Per cent. | Per cent. | Per cent. | 100 | 98 | 2.0 | 2.0 95 | 92-1/2 | 2.5 | 2.6 90 | 87-3/8 | 2.6 | 2.9 85 | 82-3/8 | 2.6 | 3.0 80 | 77-3/8 | 2.6 | 3.2 75 | 72-3/8 | 2.6 | 3.5 70 | 67-1/2 | 2.5 | 3.6 65 | 62-1/2 | 2.5 | 3.8 60 | 57-5/8 | 2.4 | 4.0 55 | 52-3/4 | 2.3 | 4.2 50 | 47-3/4 | 2.2 | 4.4 45 | 43 | 2.0 | 4.5 40 | 38-1/8 | 1.8 | 4.6 35 | 33-1/4 | 1.7 | 4.8 30 | 28-1/2 | 1.50 | 5.0 25 | 23-1/2 | 1.50 | 6.0 20 | 18-1/2 | 1.56 | 7.8 18 | 16-1/2 | 1.53 | 8.5 16 | 14-1/2 | 1.48 | 9.3 14 | 12-5/8 | 1.40 | 10.0 12 | 10-5/8 | 1.37 | 11.4 10 | 8-3/4 | 1.28 | 12.8 8 | 6-7/8 | 1.14 | 14.3 6 | 5 | 1.05 | 17.5 5 | 4 | 1.00 | 20.0 4 | 3 | 1.00 | 25.0 3.75 | 2-3/4 | 0.97 | 26.0 3.50 | 2-9/16 | 0.94 | 27.0 3.25 | 2-5/16 | 0.91 | 28.0 3.00 | 2-1/8 | 0.87 | 29.0 2.75 | 1-15/16 | 0.82 | 30.0 2.50 | 1-3/4 | 0.77 | 31.0 2.25 | 1-1/2 | 0.72 | 32.0 2.00 | 1-5/16 | 0.66 | 33.0 -----------------+------------+-----------+------------------ The wet assay being known, the dry assay can be calculated with the help of the above table by deducting the amount in the column headed "margin" opposite the corresponding percentage. For example, if the wet assay gives a produce of 17.12 per cent., there should be deducted 1.5; the dry assay would then be 15.62, or, since the fractions are always expressed in eighths, 15-5/8. With impure ores, containing from 25 to 50 per cent. of copper, the differences may be perhaps 1/4 greater.