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.
Wet methods are gradually replacing the dry assay, and it is probable
that in the future they will supersede it; for stock-taking, and the
various determinations required in smelting works and on mines, they are
generally adopted, because they give the actual copper contents, and
since it is obvious that a knowledge of this is more valuable to the
miner and smelter.
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