Foreign Laterature and Science. 357 
supposition of its being of a siliceous nature, mineralogists 
did not pay much attention to it, except On account ol some 
particles of sulphur which it sometimes contains in small 
cavities. M. Cordier, having submitted this breccia to dif- 
ferent trials, found that it yielded by heat a notable propor- 
tion of sulphuric acid ; and upon this important indication, 
he proceeded to make a complete analysis of it, by pe 
he found that this stone contained about twenty-eight 
cent. of silica, twenty-seven of sulphuric acid, thirty-one of 
alumine, six of potash, and a little water and iron. These 
are very nearly the same ingredients as are found in the 
celebrated ore of Tolfa, which yields Roman alum. In 
reality, ae treating this breccia from Mont D’or in the 
same manner as is practised at Tolfa, that is to say, by 
Grenking i neh it, and exposing it toa moist air, from 
ten to twenty per cent. of very pure alum was obtained 
from it ; and this breccia even yielded alum without being 
roasted, but merely by exposure in a damp situation. 
* It is probable, ee: the researches made upon the spot 
be decrenten: and that quarries may pests ss 
working of which cannot but be of advant taba 
“M. Cordier regards these sorts of stones as a minera- 
logical species consisting essentially of sulphuric acid, alu- 
mine, and potash. The silica found in it is not essential, 
for, quarries of a stone not containing any silica, but all the 
other constituent principles exist at Montrose, in Tuscany, 
and yield the same products as that at Tolfa. Those vari- 
eties of this species into which silica enters, are easily dis- 
tinguished by the jelly they form when they ar treated in 
succession with caustic potash and hiedénchlotic (muriatic) 
acid diluted with water 
“M, Cordier reduces to this species several volcanic 
patie hitherto vaguely designated iby geologists by the 
general denomination of altered Java.” 
Vou. IL....No. 2. 46 
