3© Mr. woulfe’s Experiments on 
colour, reddifh, and of different fhades of brown and 
yellow, fome of them being like gold, brafs, and copper. 
It has always a peculiar glofs or brightnefs. May not the 
green and yellow glimmers from Johngeorgenfladt be 
of this kind ? , 
The fpecimen I made ufe of for the following experi- 
ments is in Dr. hunter’s collection, and feemed to be 
well adapted for this purpofe, it being perfectly free from 
any matrix or heterogeneous matter. The whole fub- 
ftance of it is a cruft compofed of rhomboids, which 
grow out of one another, and form a variety of cavities : 
its colour is white and femi-pelludd, and on one fide 
there was a flight marcafitical coating. This fubftance 
comes from Joachimfthal, and is harder than any of 
thofe mentioned before, except the cryftal, quartz, and 
feld fpar. 
EXPERIMENT i. 
Three drams of this fpar, with an equal quantity of 
fixed alkaly of cream of tartar, melt with a moderate de- 
gree of tin; but the mixture foon becomes thick and 
cakes. It was after an hour’s calcination fuffered to cool, 
then was powdered and deprived of its faline part with 
boiling diftilled water. This faline part, treated as in the 
other 
