120 
POPULAR SCIENCE REVIEW. 
by the Roman workmen, whereas at Rio Tinto they had been 
partially worked by the Spanish Grovernment up to the time of 
their transfer to the English company. The south lode is, how- 
ever, the only portion of the property which has been worked 
in modern times, and the portion which has been recently un- 
covered has to a considerable extent been honey-combed by 
Roman and Spanish workings as far down as the ninth floor. 
This has had the effect of, to some extent, bleeding the vein by 
the continual drainage of copper water which has for many 
years produced, by precipitation, about three-and-a-half tons of 
metallic copper weekly. 
That portion of the vein which was selected by the late Mr. 
David Forbes F.R.S. for an open cutting is about 200 fathoms in 
length and is, in the widest part, about 47 fathoms in width ; 
the outcrop of this deposit is 45 fathoms above the valley of 
the Rio Agrio, with which the workings communicate by a 
large drainage-tunnel in which a double line of rails has 
been laid down. The total yield of this portion of the lode to 
the level of the valley was, when first opened, calculated at 
about 11,000,000 tons. 
The open cutting is worked in stages, or steps, each con- 
nected by tunnels with a railway by which the richer ores, in- 
tended for exportation, are taken to the main line, by which 
they are sent to the port of shipment at Huelva ; while the 
poorer ores, destined for local treatment, are taken to the 
calcination grounds. The total length of these local railways, 
which are of the same gauge as the main line and are worked 
by locomotive power, is 17 miles. 
The illustration, Plate IV., from a photograph of a portion of 
the Rio Tinto cutting, looking north, shows some of the Roman 
and early Spanish workings which have been cut into during 
the progress of the work. 
On arriving on the calcination grounds the ores are built into 
heaps, or teleras , of the form of a beehive, each containing 
from 100 to 500 tons; these are lighted at bottom, either by 
the help of brushwood or of a little coal, and the sulphur of 
the pyrites, taking fire, a slow combustion is continued during 
several months. 
At the expiration of some eight or nine months the teleras 
have generally burnt out, and a large proportion of the copper 
has been converted into cupric sulphate, which is a salt soluble 
in water. 
The ore is now removed to large tanks, each some 60 feet long, 
1 6 feet in width, and 3 feet in depth, where it is lixiviated by 
successive additions of water which, after dissolving out the 
salts of copper, is run through an extensive labyrinth of tanks 
in which pig iron is regularly stacked in hollow piles. Here 
