Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/153

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143
Mr. William Phillips on the Veins of Cornwall.

are national institutions for the education of those intended to conduct the working of mines, in the three important branches of science before alluded to, and which are so intimately connected with their occupation, in this country all is left to accident, and the rich gifts which nature has bestowed upon us, are consequently often neglected, or lavishly thrown away.

The ores of copper, as sold at the mine, though some of them are richer, do not in most instances contain more than one-twelfth of copper, frequently not one-fifteenth, some of them not one twentieth. The accompanying substances are a heterogeneous mixture of earths and metals, amongst which arseniates of various kinds often bear a considerable proportion. It needs not to be insisted upon that much attention ought to be given to free copper from arsenic, which is so very liable to render it brittle. When a pound or two of the ore is given to the sample-trier, as a fair sample of 50 or 100 tons, his report is but too often grounded on the weight of the prill he has obtained from a given quantity of the ore, without reference to the substances with which it may be alloyed, which indeed his skill does not enable him to detect. When the ore is taken from the mine, it is for the most part deposited, not that of each mine separately, but mixed with that of many others, without regard to the great difference that must of course exist in the ore of veins, circumstanced so variously as are those of Cornwall.[1] And strange as it may seem, it is notwithstanding true, that even the interest of the buyer seldom tempts him to swerve from

  1. In reply to this observation, it has been said that the ores of some mines are found to smelt more easily when mingled with those of certain other mines than alone. This will not perhaps be doubted. All that is now contended against is, the common practice of mixing indiscriminately ores of copper of any, or rather of every description.