on the "Terra, Ponderofas &cw \/ 305 
H. The falt, formed with the nitrous acid (E), thot reasllgh 
into beautiful permanent cryftals, of a rough bitterifh tafte. 
2: Some of this falt was deflaorated swith nitre and charcoal, 
and the alkaly afterwards wafhed away. 
3. The refiduam, being ‘theearth ‘of the imarmor, metalli- 
cum, was very white, burnt to lime, and‘again formed an ans 
foluble compound with acid of vitriol... | 
I. roo grains of terra ponderofa aérata were diflolved in di- 
luted marine acid. Vitriolic acid was‘dropped into this {folu- 
tion, until no-more precipitation errfued. ‘The precipitate, after 
very careful wafhing and drying, was’expofed to.a red heat in 
@ covered tobacco-pipe “for half an ‘hour: when cool, it 
weighed 117 grails. OG G14. 
2. 50 grains of terra ponderofa aérata in a lurmp were put 
into diluted. vitriolic acid; but the action of the acid Bone it 
was hardly fenfible, ‘even’ when made het. , 
Marine acid was then added, “and after Yome time-an effer= 
vefcence appeared. The terra ponderofa’ vitriolata, thus. formed, 
after proper wafhing’and ‘drying, ‘was expofed to-a: red heat for 
an hour : | Sts then weighed 5854 a | 
CONCLUSIONS 
ft, It appears that;the marmor metallicum is compofed of 
vitriolic acid and terra ponderofa, D. E. F. G.H. 
_ 2dly, That this compound, though probably foluble in wa- 
ter, has fo little folubility as valmoft to efeape detedtion by the 
niceft chemical tefts, B. 1. 2. 
3dly, That at is not Hite in acids of the ufual ftreneth ; 
but that ‘it perfe@ly and entirely diffolves in’ highly concen- 
Vor, LXXIV. St trated 



