24 'Mr. woulfe's Experiments on 
diffolved part weighed § v. and gr. xxxvi. This fpar 
does not boil up in its fufion with the alkaly near fo 
much as the other, and therefore the lofs in the opera- 
tion is trifling compared to it, and on that account it 
affords a greater proportion of allum. 
Shir l frequently , though erroneoujly , called bafaltes. 
The fhirl I tried is of a brown colour, forms a mafs of 
long minute prifms clofely adhering together, and comes 
from Bohemia. Its brown colour is owing to iron. 
'This fhirl, treated in the fame proportion and manner as 
the Feld fpar, afforded no neutral fait. The quantity of 
allum was § ij. 7 j. and gr. xxiv.; but I mud obferve, 
that the two laft cryftallizations contained iron, and the 
mother water that remained w 7 as of an oily confidence, 
had a dyptic tafle, and refembled that obtained in mak- 
ing green copperas. The earthy matter here remaining 
weighed ^ ij. and gr. lii ; was light and of a grey colour. 
Hence it is evident, that fhirl contains nearly as much 
earth of allum as the Cornifh porcellane clay. 
Mr. ..its em an, an ingenious apothecary and chemifl 
at Claudhal in the Hartz, has allured me, that he ob- 
tained from pumice done and fhirl a fal catharticus 
mmarus. He has, I prefume, made his trials on fhirl 
5 which 
