1 8 Mr. woulfe’s Experiments on 
was only 59 grains. Hence it is clear, that the calcareous 
earth of the gypfum contains a greater proportion of 
acid of vitriol than that of the cauk. 
According to this rule, the deflated fpar from Slieppy 
fhould have afforded 84^ grains of tartar of vitriol, but 
it produced only 58 grains. 
The erica , formed fpar by the fame rule, fhould have 
afforded 65-—- grains of tartar of vitriol, but the quantity 
was only 38 grains. 
As I fufpedted that the felenitical fpars contained fome 
calcareous earth, not united to the acid of vitriol, I di- 
gefled fome of them with redtified pure acid of nitre, 
and afterwards well wafhed and dried them ; but the lols 
of weight was very trifling, except in the cauk and erica 
formed fpar; the firft probably containing fome marcaf- 
fitical particles of copper, and the laft an ochre of iron. 
Dr. lewis, in his tranflation of newman’s Che- 
miftry, quotes from the Philofophical Tran fadt ions fome- 
what remarkable about cauk, that when wetted with 
antimony it gives it a fhining furface like fteel. 
I repeated the experiment as follows : I powdered and 
mixed ^ ff. of cauk with iij. of antimony, and put the 
mixture into a red hot crucible; and when melted, which 
readily happens, I ftirred it with an iron rod, and poured 
it 
