fyiag3 4] 
XXIt. vee and Obfervations on the ‘Terra Ponderofa, 
&c. By William Withering, M. D.; communicated by. 
Richard Kirwan, Ef. FR. S. 
Read April 22) £784:. 
Seve. EE ONIN 
Terra ponderofa atratas. 
he fubftance was got out of a:lead-mine at Alfton-- 
| Moor, in Cumberland: I> firft: faw it in the valuable. 
«olleé&tion of my worthy and ingenious- friend MattrHew: 
Bouiton, Eig. at Seho; who, when he picked it up, con= 
jectured from its weight that it contained:fomething metallic. 
About two years ago I faw it in his poffeffion ; and partly from 
its appearance, being different from that-of any calcareous f{par- 
I had feen, and partly from: its great weight, I. fufpected it.to. 
be the {patum ponderofum. | 
A few experiments made at: the -moment:confirmed my fuf-- 
picions, at leaft fo far as to fhew that it contained a large pro-. 
portion of the terra ponderofa united to fixed air; but I-did not’ 
then flatter myfelf that it would prove fo pure as-I. See S: 
found it to be.. 
“Brofelides 
