entirely of its silver by far the largest portion of the lead operated upon, while the remainder becomes an exceedingly rich alloy of both metals, so as to contain fifty times its original proportion of silver. This rich lead is subsequently exposed in a refining furnace to a strong blast of air at a high temperature, fresh supplies of lead being constantly introduced as the operation proceeds. By this means the lead becomes rapidly oxidized and converted into litharge, which partly runs off in the fluid state, and is partly (about 10 per cent.) lost by sublimation, while the silver forms a cake at the bottom of the cupel. The brightening of the silver, which lustrously shines forth at the moment of the separation of the last traces of lead, indicates the precise period at which the operation should be ended, and the blast is then turned off and the fire removed from the grate. Before the introduction of Pattinson’s ingenious process, the separation of the silver from the lead was attended with a much greater loss of the latter metal, as greater quantities had to be cupelled to effect the same result. The economy obtained amounts to no less than 98 per cent.; for where formerly 100 cwt. of lead were lost by sublimation, the same quantity of silver is now obtained with a loss of no more than 2 cwt., and at the same time with a considerable saving of fuel. Ores very poor in silver, as for instance those of Alston Moor or Derbyshire, which formerly could not be profitably cupelled, are now advantageously treated by the Pattinson process. This is but one example of the valuable practical results which may be obtained from a single scientific discovery. But chemistry has introduced thousands of similar technical improvements in almost all branches of manufacturing industry, and were we to add together the profits thus obtained, we should find that a great part of our wealth is due to the laboratory. CHAPTER XXX. MERCURY. Not considered as a true Metal by the Ancients—Its Properties and Uses— Almaden—Formerly worked by Convicts—Diseases of the Miners—Idria—Its Discovery—Conflagration of the Mine—Its Produce—Huancavelica—New Almaden. Among the metals known to antiquity mercury was the last discovered. It is mentioned neither in the Bible nor in Homer, who accurately, though briefly, describes the characters and uses of all the other ancient metals; but we learn from the works of Aristotle that its discovery must have preceded the times of Alexander the Great.