3 tons of
fine copper (by dry assay) brought ?2591 12s., the standard would be
?83 15s. This is calculated as follows:--The returning charge is fixed
at 55s. per ton of ore. This on 985 tons will amount to ?2708 15s.
Add this to the actual price paid, and there is got ?5300 as the value
of the fine copper present. The weight of copper in these 985 tons being
63.3 tons, the standard is ?5300/63.3, or ?83 15s. (nearly).
The value of a parcel of 150 tons of a 6 per cent. ore on the same
standard would be arrived at as follows:--The 150 tons at 6 per cent.
would contain 9 tons (150?6/100) of fine copper. This, at ?83 15s.
per ton, would give ?753 15s. From this must be deducted the returning
charges on 150 tons of ore at 55s. per ton, or ?412 10s. This leaves
?341 5s. as the value of the parcel.
At Swansea the returning charge is less than in Cornwall, and varies
with the quality of the ore. This appears equitable, since in smelting
there are some costs which are dependent simply on the number of tons
treated, and others which increase with the richness. The returning
charge then is made up of two parts, one fixed at so much (12s. 2d.)
per ton of ore treated, and the other so much (3s. 9d.) per unit of
metal in the ore. In this way the returning charge on a ton of ore of
8-3/4 produce would be (12s.
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