09 milligram, and a similar
sphere of gold weighs 0.167 milligram.
It is safer, however, to compare with a micrometer the diameter of the
button whose weight has to be determined with that of a standard button
of nearly equal size whose weight is known. The weights of the two
buttons are proportional to the cubes of their diameters. This plan of
working is described more fully in Appendix B., page 440.
~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 Ore taken.
Weight of |----------+----------+-----------+-----------+------------
Metal got. | 3 grams. | 5 grams.
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