cru 
‘black. From the Brafilian soe = it is eafily diftin- 
guifhed by not being ele€tric ex y friGtion, while the 
tourmaline becomes eleGtric by ins 
‘The more tranfparent varieties of the Vefuvian or ido- 
crafe are cut and polifhed by the Neapolitan lapidaries, who 
fell them to — as objects of ariel under the name 
Pefuvian a but they are of little value and feldom 
mployed as articles of jewellery. Dr. Sona has lately 
deferibed a be aa Mand ea this fubftance, under the 
cate green 
arene ae fometimes into vellowithered or wit 
aad SS 
nown, nor n the count 
t he ae — he ae folite, though not vivid, are 
chafte and pleafing; but the hardnels of this ftone is fo 
inconlider ons that it foon becomes ine and unfightly when 
ufed for ornament ; hence it has never been much v 
for, indeed, secnting to a faying among French lapidaries, 
«© Oui a ape ai 
naun 
What is not efleemed is renerally negledted, and confe- 
uently confounded with other things it may refemble 
thus the chryfolite (which name was probably given by the 
ancients to our topaze), has been jumbled together with 
the Plone oe fome of them more, others lefs pre- 
cious than itfe . Chryfoberil, either fimply or with the 
epithets of nae and opalefeent ; 2. Light-green ziri ug ay 
Ceylon ; 3. Yellowifh-green topaze, from Saxo 
lowith-green beryl, from Siberia ; 5.Piftachio-green pa malin 
from Brafil; 6. Prebnite, from the rey 7. Tranfpa: 
. Pittachio-green apatite; 13. Fluor-/par ; not to mention 
the oltvine with Vwhich the rch is ed by the French 
antiquity. ‘The eve in poffeffion 
of this art, as feveral alte relics have fufficiently proved. 
equally fkilful in imitating emeralds an 
ftones, by colouring cryftals ; they alfo manufactured onyx 
nd dark coloured to a 
I rdeuyx, by cementing red a kc 
white layer of chalcedeny. Their pattes or eer of 
engraved gems, their c ubes, Sc. for mofaic pavement, their 
beautiful vafes with figures in bas relief, are ftill fubjeéts of 
admiration to the curious. But alfo at this prefent day we 
the no ble op _— 
they are fubftituted; and the difficulty o difcriminating 
them increafes in proportion as it becomes impra¢tica 
of common gla e fureft criteria by whict 
thefe artificial produCtions may be difting uifhed. With regard 
o the laf of thefe characters, however, it fhou Id e ob- 
mel exc ept in 
their ie tran{parent. Enamel i ae ane ea ae on 
account of the oxyd of tin which generally forms the bafe, 
and which is ue difficult to vitrify. (See ENAMEL. The 
coloured glaffes, on the contrary, aa their tran{parency, 
au the aan fubitances 
tely combine 
he tga A Sood 
artificial precious ftones confift in their being a d as 
polfible, without velicles, of a perfect antparerey aE in 
the brilliancy and elma of the colou laft-men- 
tioned quality depen e eka Geta before fufion. 
The longer the pina ee are expofed to the ation of 
the fire, the harder they become, and the more they are 
freed from veficles. But this long continued ation of the 
fire deftroys and Seino the colouring sagen with the 
exception of the colour ma cobal t, which refifts 
ay beste a fire, sad ah which, therefore artificial ae 
high degree of hardnefs can be prepared. It is this 
impoiblty of fixing the other Slane. “ hich renders tthe 
difficult, and obliges moft artiits 
art in queftion fo 
fatisfed with for Pee mich lofes its polifh ae the — 
bbin; 
ments, which are faid to have been fre equently repeated with 
the re nasi and to deferve more attention than thefe 
of ot 
The ‘fet objeCt of M. Fontanieu’s refearches, was to pro- 
duce a perfectly colourlefs cryftal, proper to take the pa 
intended for it, and this he calls fondant or bafe. They 
five in number. 
Firft Bafe.— <1 we parts and a half of lead in feales, one 
and a qua 
parts’? the anthor merece WUNECS, 
hence in this et the peer of the eens 18, lead in 
feales 203, rock-cryftal 12%, nitre 432 5 rax 438, arfenic 
23) being well pulverized and mixed, ona the compofition 
of 
the 
vials a arfenic, (by ‘ 
U 
