28 Mr woulfe’s Experiments on 
affords when added to oil of vitriol made hot, which 
exadtly refembles that of acid of fait. It is found of 
various colours, as green, blue, purple, crimfon, whiter 
and alfo yellow. When cryftallized it forms perfect 
cubes ; the only exception I ever met with was a fpeci- 
raen of the green fort, which was fent me by Mr. soper, 
of St. Cohimb in Cornwall, who has difting-uiflietl him- 
felf by his fkill in natural hiftory and mineralogy. This 
fpecimen was compofed of two- quadrangular pyramids 
united together at their balls. 
Selenitical fpar is found cryftallized in a great variety 
of forms; is heavier than the foregoing fubftance; does 
not cffervefce or dilfolve with acids, nor is it fo hard as 
the phofphoric fpar. 
Calcareous fpar is ealily diftinguilhed from other fub- 
ftances by its effervefcences and folution in the acids of 
nitre and fea fait. Acid of vitriol, added to thefe folu- 
tions, caufes a felenitical precipitation: this fpar is nei- 
ther fo hard nor fo heavy as the foregoing fubftances, 
and cryftallizes in a great variety of forms. 
Gypfum is lighter than any of the foregoing fub- 
ftances, and is fo foft as to be eafily fcratched with one’s 
nail; it does not effervefce nor difloVe with acids, and is 
the only fubftance that forms plafter when burnt; it 
"cryftallizes in a great variety of forms. 
5 
Mica 
