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Updated: May 16, 2025
The heavier lines in their spectrum indicate more absorption of light, and tell us that the vapours are thickening about the globe; while compounds like titanium oxide make their appearance, announcing a fall of temperature. Below these, again, is a group of dark red or "carbon" stars, in which the process is carried further.
If the residue is white, or known to be free from iron, it may be neglected and need not be removed by filtration. Mix the ash with five times its weight of sodium carbonate and heat to fusion; cool, and disintegrate the fused mass with boiling water in the crucible. It is a native, hydrated oxide of iron.
Oxide of copper is black, and so in this decomposition what is called a "black precipitate" of that oxide is produced on adding the caustic soda. But it might not suit us thus to deposit the copper from our solution; we might desire to remove the sulphuric acid from the copper sulphate, and leave the copper dissolved, say in the form of a chloride.
In view of the sequel, Davy's experiments merit full attention. Here is his own account of them, as written in 1799: "Immediately after a journey of one hundred and twenty-six miles, in which I had no sleep the preceding night, being much exhausted, I respired seven quarts of nitrous oxide gas for near three minutes. It produced the usual pleasurable effects and slight muscular motion.
We add, as you have seen, a great proportion of slag to the melting of the calcined ore, which consists chiefly of the oxide of iron; while at the same time we derive the additional advantage of employing an excellent flux an advantage which metallic iron does not possess.
Trachyte, which consists chiefly of feldspar, with some hornblende and oxide of iron, has a specific gravity of about 2.45; whilst basalt, composed chiefly of augite and feldspar, often with much iron and olivine, has a gravity of about 3.0. This order of eruption has been observed by Beudant, Scrope, and by other authors; three instances, also, have been given in this volume.
The answer may be found in the fact that the thin film of oxide of iron, or "skin," as it is popularly called, which always forms on the surface of molten iron, was caught in these fine meshes, and thus prevented the molten metal from joining through the holes.
The metallic copper produced separates in the form of a red coating on the iron scraps. But we may also, relying on the fact that oxide of copper is insoluble in water, arrange for the deposition of the copper in that form.
Whether this tale be true or no, it is certain that even at the present day, in what are called "new countries," valuable metals often show themselves on the surface of the soil, either in the form of metalliferous earths, or of rocks which shine with spangles of a metallic character, or occasionally, though rarely, of actual masses of pure ore, sometimes encrusted with an oxide, sometimes bare, bright, and unmistakable.
Chloroform, nitrous oxide gas, and ether had been placed at the service of the physician in saving life, and the revolver, guncotton, and nitroglycerine added to the agencies for slaughter. New metals, chemicals, and elements had become available in large numbers, gases had been liquefied and solidified, and the range of useful heat and cold indefinitely extended.
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