14 Mr. woulfe’s Experiments on 
it with acid of vitriol ; and hence it appears, that nearly 
two-thirds of the cryftal is changed into felenitical fpar. 
The folution which was obtained by the acid of nitre 
mixed with acid of vitriol, but efpecially with a folution 
of tartar of vitriol, precipitates copioufly, and forms a 
felenite. This evidently proves the exiftence of the cal- 
careous earth, and the tartar of vitriol mentioned above, 
that of the acid of vitriol in this altered cryftal. 
The unaltered part of this cryftal, treated in the fame 
manner as the altered part, afforded no marks of feleni- 
tical fpar. 
The change of this cryftal is, I fufpeft, owing to the 
lead ore which adheres to it; the fulphur of the lead 
ore furnifhing the acid of vitriol, and the cryftal the cal- 
careous earth. 
I have in the above manner treated a variety of the 
heavy fpars, commonly called felenitical or gvpfeous 
fpars, and found them all, as I firft judged by their ap- 
pearance and great weight (without being once miftaken) 
to confift of acid of vitriol, with calcareous earth and 
fome clayey matter. In fome, the calcareous earth was 
combined with a larger portion of this acid than in 
others; and in fome, the clayey matter was predominant. 
Among thefe were the following, fome of which were 
not before taken for felenitical fpars. 
i 
The 
