when electrolyzed in a solution of ammonium sulphate.  The positive pole is formed of a plate of lead, pure or covered with a stratum of litharge, or pure oxide, or all these substances mixed.  These metallic plates are immersed in a solution containing 50 per cent. of ammonium sulphate.  Another arrangement is at the negative pole, sheet-iron; at the positive pole a cylinder of ferro-manganese.  The electrolyzed liquid contains 40 per cent. ammonium sulphate.

* * * * *

THE TREATMENT OF QUICKSILVER ORES IN SPAIN.

Though known from remote times, the date of the first opening of the famous mines of quicksilver of Almaden has not been precisely determined.  Almost all the writers on the subject agree that cinnabar, from Spain, was already known in the times of Theophrastus, three hundred years before the Christian era, although there is evidence in the writings of Vitruvius that they were worked at a still earlier date, Spanish ore being sent to Rome for the manufacture of vermilion.  Such ore constituted a part of the tribute which Spain paid to Rome emperors, and there are records of its receipt until the first century after Christ.  The history of Almaden during the reign of the Moors is so much involved in doubt that some writers deny altogether that the Arabs worked the deposit; still the very name it now bears, which means “the mine,” and many of the technical terms still in use, give evidence that they knew and worked that famous deposit.  As for their Christian conquerors, there are stray indications that they extracted mercury during the twelfth and thirteen centuries.  In 1417, Almaden was given the privileges of a city, and from 1525 to 1645 the working of mines was contracted for by the wealthy family of Fugger, of Augsburg, Germany.  Since then, the mine has been worked by the state, though the Rothschilds have controlled the sale of the product.

According to Vitruvius, the works for manufacturing vermilion from Spanish ore in Rome were situated between the temple of Flora and Quirino.  The ore was dried and treated in furnaces, to remove the native mercury it contained, and was then ground in iron mortars and washed.  In addition, small quantities of quicksilver and vermilion were made at Almaden.  The ancients describe other methods, among which Theophrastus speaks of using vinegar, which, however, appears from modern investigations to have been an erroneous account.  Nothing definite is known concerning the methods of the Moors; we possess only as a proof that they produced mercury, an account of a quicksilver fountain in the marvelous palace of Abderrahman III., at Medina-Zahara, and the works of Rasis, an Arab.  The Moors probably extracted mercury at Almaden, from the eighth to the twelfth century, by the use of furnaces called “xabecas,” which latter, in the fourteenth century, were still employed by the Christians, who continued them till