In the island of Milo there are likewise numerous caverns the walls of which are incrusted with sulphur and alum. A visit to these grottoes, which annually yield about five hundred tons of pure sulphur, is not without danger from the suffocating fumes that issue from their crevices.
Some of the Arabian volcanoes also produce considerable quantities of sulphur, such as the Dufan, which is called Djebel-el-Kebril, or ‘Sulphur Mountain’ by the Arabs, and is mentioned in the writings of Herodotus.
Though the craters of volcanoes are generally almost inaccessible, yet history mentions a curious instance where the most extraordinary exertions were made for collecting sulphur above the regions of perpetual snow. During the wondrous campaign which ended in the overthrow of the empire of Montezuma, Cortez, being in want of powder, sent a party under Francisco Montaño, a cavalier of determined resolution, to gather sulphur from the smoking throat of Popocatepetl, which rises, with its silvery sheet of everlasting snow, to the height of 17,852 feet above the level of the sea. After traversing the lower region, which was clothed with a dense forest, so thickly matted that in some places it was scarcely possible to penetrate it, the track of the Spaniards opened on a black surface of glazed volcanic sand and of lava, the broken fragments of which, arrested in its boiling process in a thousand fantastic forms, opposed continual impediments to their advance. They now came to the limits of perpetual snow, where new difficulties presented themselves, as the treacherous ice gave an imperfect footing, and a false step might precipitate them into the frozen chasms that yawned around. To increase their distress respiration in these aërial regions became so difficult that every effort was attended with sharp pains in the head and limbs. At length they reached the edge of the crater, which presented an irregular ellipse at its mouth more than a league in circumference. A lurid flame burned gloomily at the bottom, sending up a sulphurous steam, which, cooling as it rose, was precipitated on the walls of the cavity. The party cast lots, and it fell on Montaño himself to descend in a basket into this hideous abyss, into which he was lowered by his companions to the depth of four hundred feet! This was repeated several times, till the adventurous cavalier had collected a sufficient quantity of sulphur for the wants of the army.
Many mineral springs owe their medicinal properties to the hydrosulphuric acid which they contain, and whose decomposition frequently gives rise to the formation of sulphur. When the large marble slab which covers the imperial source at Aix-la-Chapelle is removed at the end of every twenty years, about two hundred pounds of sulphur are collected from the walls above the spring.
Combinations of sulphur with metals, particularly with iron and copper (pyrites), occur in much more considerable masses and in a far greater number of localities than the pure uncombined mineral. Formerly the sulphides of iron (52½ per cent. sulphur, 47½ per cent. iron) and copper served only for the fabrication of vitriol and alum; but since the progress of chemical science has allowed them to be profitably used for the manufacture of sulphuric acid, they have acquired a far greater importance. Our own mines, which are situated chiefly in the county of Wicklow, produced in 1866 at least 135,000 tons of iron pyrites, besides which an additional quantity of about 100,000 tons was imported from other countries.
In Southern Spain the mines of cupriferous pyrites—particularly in the province of Huelva, and in the Sierra de Tharsis, which on account of the copper they contain were already worked in times anterior to the Roman occupation, and give proof of their ancient importance by the vast dimensions of their excavations—produced in 1863 no less than 246,137 tons. In Portugal the mines of San Domingos, in the province of Alentejo, likewise afford a remarkable example of the mining industry of the Romans, in the ancient adit which served for draining the works. They merely used the ores that were richest in copper, and rejected the poorer qualities, which form the immense mounds of scoriæ round the mouth of the excavations. After having been abandoned for many centuries the mines of San Domingos are once more diligently worked. Their newly acquired importance is due chiefly to the enterprise of Mr. James Mason, now Baron of Pommorão. A railroad nine miles long unites the mine with the left bank of the Guadiana, which has been rendered navigable for larger vessels for a length of ten miles. Moreover the port of Pommorão has been excavated in the steep bank of the river for the convenient shipping of the pyrites. Before 1858 a solitary hermitage was the only dwelling at San Domingos, which is now a thriving village of five hundred houses, with a handsome church and a railroad station. The number of the workmen employed in 1866 amounted to two thousand, and large works were being erected for the separation of the copper. In 1859 the produce of these mines amounted to 7,887 tons, and in 1866 it had already risen to 167,028 tons, which formed the cargo of 544 ships. Such are the wonderful changes which can be brought about when the right man finds the right place for the employment of his energies. France produced in 1866 about 100,000 tons of pyrites, Prussia 38,248 tons, and Belgium 28,956 tons, so that the total production of Europe now probably amounts to more than a million tons. In Canada the ore of a vast deposit of pyrites is exported to the United States, where it serves for the fabrication of sulphuric acid. Thus a substance scarcely noticed twenty years ago has become an important article of commerce in both hemispheres.
CHAPTER XXXVI.
AMBER.
Various Modes of its Collection on the Prussian Coast—What is Amber?—The extinct Amber Tree—Insects of the Miocene Period inclosed in Amber—Formidable Spiders—Ancient and Modern Trade in Amber.
Amber is a resinous substance, the produce of extinct forests that now lie buried in the earth or under the bottom of the sea.
It is found abundantly on the Prussian coast of the Baltic, where it is collected in many ways. After stormy weather it is frequently cast ashore by the surf, or remains floating on the water. The amber-fishers, clothed in leather dresses, then wade into the sea, and secure the amber with bag-nets, hung at the ends of long poles. They conclude that much amber has been detached from its bed when they discover many pieces of lignite floating about. In some parts the faces of the precipitous cliffs along the shore are explored in boats, and masses of loose earth or rock, supposed to contain the object of search, are detached with long poles having iron hooks at their ends. It is also dredged for on an extensive scale at the bottom of the Frische and Curische Haffs, and further inland large quantities are dug up out of the earth. That which is washed ashore generally consists of small pieces, more or less damaged, while the specimens obtained by digging or dredging are frequently of large size and of a tuberous form, so that, though inferior in quantity to the former, their value is probably ten times greater.