^2 A SYSTEM OF 
SECT. XIII, 
B* Satiated or united with the Acid of Vitriol^ 
Sierra calcar ea acido vitrioli faturat'a, Gyp~- 
fum. Plafter-ftone or Parget. 
This is 
1. Loofer and more friable than a pure cal- 
careous earth. 
2. Either crude or burnt, it does not excite 
any effervefcence with acids, or at moft it 
effervefces but in a very flight degree, and 
then only in proportion as it wants fome 
of the vitriolic acid to compleat the fatu- 
ration. 
3. It readily falls into a powder in the fire. 
4. If burnt, without being red-hot, its pow- 
der readily concretes with water into a 
mafs, which foon hardens ; and then 
5. h^o heat is perceived in the operation. 
6. It is nearly as difficult to be melted by 
itfelf as the limeflone and fhews moftly 
the fame effiefls, with other bodies, as 
the limeflone : the acid of vitriol feems, 
however, to promote its vitrification. 
7. When melted in the fire with borax, it 
puffs and bubbles very much, and for a 
long while, during the fufion, owing to 
the nature of both the falts f, 
* I have found moH: of the gy6reous kind, and particularly 
the fibrous, to melt pretty eafily by themfelves in the fire. 
t When a fmall quantity of any gypfum is melted to- 
gether with borax, the glafs becomes colourlefs and tranfpa* 
rent ; but I have found fome forts of alabafter and fparry gyp- 
fa that, when melted in fome quantity with borax, yield a 
fin# yellow tranfparent colour, refembling that of the bell 
topafes. This phoenomenon might probably happen with 
every one of the gypfeous kind. But it is to be obferved, 
that if too much of fuch gypfum is ufed in proportion to the 
borax. 
