1868. | On the Iron-pyrites Mines of Andalucia. 40% 
have been met with; and those Roman remains whose date can be 
fixed belong to the times of the emperors Nerva and Honorius.* 
Strabo’s remarks on Spanish minesf are vague, and none of the 
localities he mentions can be identified with those treated of in this 
paper. In one passage, however, he mentions, quoting Posidonius, 
that the people of Turdetania (nearly the same as Andalucia) drive 
their levels zigzag and deep; and to get rid of the streams of water 
they encounter, employ Egyptian spiral pumps.t The levels and 
water-wheels at the Coronada, already described, agree so closely 
with this description, that we can have no doubt about referring 
them to the Roman period. The ore was worked by these early 
miners for the small percentage of copper which it contains, and 
the metal extracted by smelting: their industry is shown by the 
immense heaps of slag they have left, especially at Rio Tinto, which 
Mr. Thomas suggests may have been a centre of smelting; and an 
examination of these slags shows that their skill was far superior to 
that of the Spaniards during the first half of the present century. 
Leaving these uncertain traces of the old mimers, we find that 
the mine of Rio Tinto was reopened about 1727, and has been 
worked since 1849 by the Spanish Government. Before the latter 
date the metal was extracted by smelting ; but since 1849 a process 
has been employed known as Cementation, which is as follows :— 
The ore is first calcined in heaps in the open air: a small quantity 
of brushwood and roots of trees is used as fuel to light the pile, 
which, when once on fire, burns of itself. By this means a certain 
amount of the insoluble sulphide of copper is converted into soluble 
sulphate. The calcined ore is then placed in tanks of water, and 
when the latter has become saturated with the salts of copper and 
iron, it is run off into another tank, where the copper is precipitated 
on lumps of pig-iron. When a sufficient thickness of precipitate 
has accumulated, it is scraped off, and made into balls, which are 
dried in a kiln: these are reduced in a German blast-hearth, and 
the proceeds refined in a reverbatory furnace and cast into pigs. 
The results are far from satisfactory, as little more than half the 
copper contained in the ore is extracted; a far better method is 
that of “kernel roasting,” as practised at Agordo in the Venetian 
States, for an account of which the reader may consult Dr. Percy’s 
‘ Metallurgy of Copper.’ We may also note that the water flowing 
from the mine is strongly impregnated with salts of copper: it is 
collected in long wooden troughs, and the metal precipitated by 
iron. 
By the cementation process all the sulphur in the ore is lost, 
* See Mr. Thomas’s pamphlet, p. 5. 
+ ‘Geographia,’ book iii. 
t{ Ihave to thank my friend, the Rev. T. C. H. Croft, of Caius College, Cam- 
bridge, for directing my attention to this passage. 
