joa Dr. Wituentne's Exporiments and Obfervations 
portion of the acid muft firft be tried in a diluted ftate, from 
whence we muft judge how much of the terra ponderofa falita 
the whole will require; or elfe the whole of the acid muft be 
diluted with water. Whether we ufe the terra ponderofa dif- 
folved in water or in marine acid; in either cafe the acid of 
vitriol immediately feizes upon it, ane bNalities ‘id it in form 
of an infoluble powder. ‘ 
As there are reafons for preferring the marine acid in fyi 
of the nicer and more important enquiries of chemiftry, this 
ready method of purifying it cannot but prove acceptable. 
So, (Cat an Oc aan 
Terra ponderofa vitriolata. BERcMan’s Sciagraphia, 
§§ 58. 89. . 
Variety,, Heavy Ghplite: Ponderous Spar. 
‘Marmor Metallicum. CronsTEDT Min. og 18. 2. 
19. C. 
F rom. 5, Rakeback -hills near Ghigo A fort, with ss 
cryftals, amongft the iron ore about Ketley in Shropfhire. Ta 
the lead mines at Alfton-Moor. 
More obvious Properties. ‘ 
White ; ; nearly tranf{parent, but has not the property of doue 
ble'refra@tion ; compofed of lamin of rhomboidal cryftals ; de- 
crepitates in the fire. Specific gravity from 4,402 to 4,440.) 
4 4 
v °° 
EX P Ee 

