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POPULAR SCIENCE REVIEW. 
soda (salt cake), 16 cwt. of concentrated sulphuric acid (oil of 
vitriol) are required, and it therefore follows that with an 
active development of this new industry the demand for 
sulphuric acid and for the materials requisite for its production 
rapidly increased. In the preparation of this acid upon a 
large scale, sulphurous acid, obtained by burning sulphur or 
pyrites, is converted into sulphuric acid by means of a power- 
fully oxidising agent. The substance now universally employed 
for this purpose is nitric acid, although the greater portion of 
the oxygen utilised is not derived directly from the acid, but 
indirectly from the air ; the result of complex chemical changes 
which take place in extensive leaden chambers supplied with 
watery vapour by means of steam jets. 
Previous to 1838, sulphur was the material almost univer- 
sally made use of in the production of oil of vitriol, but in that 
year the King of Naples having granted a monopoly of Sicilian 
sulphur to a French firm at Marseilles, it resulted in the gra- 
dual introduction of iron pyrites as a substitute for brimstone 
in the manufacture of sulphuric acid. 
From that date to the present the consumption of this 
mineral has gone on steadily increasing ; the mines of Cornwall 
and those of Wicklow in Ireland having been, during many 
years, the chief sources of supply. A certain amount was also 
obtained from Norway. 
About the year 1853 small quantities of pyrites containing 
a little copper found their way into this country from mines 
worked by a French company in the South of Spain, but as 
their transit, on mule -back, to the shipping port was long, the 
supply was limited, and the results are believed to have been 
financially unsatisfactory. 
A few years subsequent to this (1859), Mr. James Mason 
opened out the now celebrated mines of San Domingos in 
Portugal, and having connected it by railway with the river 
Guadiana, near the town of Pomaron, commenced an active com- 
petition with the pyrites from Cornwall, Wicklow, and Norway. 
The comparative freedom of this ore from arsenic, and the 
small proportion of gangue which it contains, caused it to be 
generally preferred to pyrites from other localities, so that the 
quantity imported into Great Britain in 1868 from this mine 
alone amounted to no less than 83,000 tons. 
At this period the Tharsis Sulphur and Copper Company, who 
had now taken over the mines formerly worked by the French 
Company, already referred to, had not only commenced export- 
ing pyrites from Spain, but had also erected various extensive 
works in this country for the extraction of copper, by a humid 
process, from the cinder, or residue, remaining in the kilns of 
sulphuric acid manufacturers after the removal of sulphur 
