the seventeenth century, when German workmen replaced them by “reverberatory” furnaces, which in turn were superseded in 1646 by aludel or Bustamente furnaces.  There is an anonymous description of the working with xabecas as practiced at Almaden in 1543, and later accounts in 1557 and 1565.  The ore was put into egg-shaped vessels with a lid, the mineral being covered over with ashes.  The vessels were packed in a furnace heated with wood, about 60 pounds being used per pound of quicksilver made.  This system was also applied at the Guancavelica mines, discovered in Peru in 1566, where the xabecas were abandoned in 1633, being replaced by the furnaces invented by Lope Saavedra Barba, which there were called “busconiles,” while in Spain they were named Bustamente furnaces, and elsewhere aludel furnaces.  They were introduced at Almaden thirteen years after their first use in Peru by Juan Alfonso de Bustamente, Barba and his son having been lost at sea on their way to the Peninsula.  In 1876, there were at Almaden, at the works at Buitrones, twenty such aludel furnaces and two Idria furnaces.  D. Luis de la Escosura y Morrogh, from whose work we take the above notes, has followed the historical details of the growth of Almaden closely, and from his account of the method of working in 1878 we take some data: 

It is not an easy matter to explain the classification of the ore at Almaden. Metal is there called the richest mineral, composed of quartz impregnated with crystalline cinnabar. Requiebro are middlings of medium richness, China are smalls, and Vaciscos the finest ore.  Besides native mercury, which the ores of Almaden contain in greater or smaller quantity, the most abundant mineral is cinnabar, which is always crystalline and is often crystallized.  The ores have, besides, a small quantity of selenium and iron pyrites intimately mixed with the cinnabar.  The gangue is quartz, occasionally argillaceous and bituminous.  The following are assays of some of the ores made by Escosura: 

Metal.  Requiebro.  Vaciscos.  China.
1 2 3 4 5 6 7 8
Cinnabar 29.1 21.2 13.3 10.2 5.1 2.8 1.2 0.86
Iron pyrites. 2.2 2.0 2.0 1.9 12.3 1.5 2.1 2.80
Bituminous matter 0.6 1.0 1.0 1.2 4.6 0.7 3.4 0.90
Gangue 67.5 74.8 82.1 76.5 77.5 93.3 90.2 93.50
---- ---- ---- ---- ---- ---- ---- -----
Total 99.4 94.0 98.8 98.9 99.5 98.3 98.7 98.06
Quicksilver 25.05 18.28 11.47 8.64 4.40 2.41 1.03 0.75

It appears to be a difficult matter to determine the average percentage of the various grades of ore.  In 1872, a commission classified and sampled a lot of 300 tons with the following results: 

Quantity, Per cent.  Average of
Grade.  No. kilos. mercury. grade.