[ 21 ]■ 
If a quantity Jalfs be added in the prepara -• 
tion, they will, by attenuating the mixture, and 
confequently lejfening its fpecijic gravity^ make the 
glafs incline to blue, tbe colour next in order [/] ^ 
but this happens only when the fire is. moderate for 
in a greater degree of heat, the redundant falts, even 
thofe of the mofi: fixed nature, are expelled \u\. 
It is true.,' that> copper is mentioned by feme- 
writers, as an ingredient: in red glafs and enamel i 
but the redy which is the colour of the metal not 
difiblved or mixed with the glafs, remains only 
while the compofition is expofed to fuch a degree 
of heat as is too fmall to melt and incorporate it; 
for, if it be fufiered to remain in the furnace afew^ 
minutes ^ after the copper is added, the mafs will 
turn green inftead of red [w] : in efied, the pre- 
paration of copper recommended on this occafion, 
is exadly the lame as. that ufed in tinging glafs 
green^ 
[/] Flora Saturnizans, chap, xu art. 6-.. When a , green, 
colour IS to be given to glafs, care muft be taken «<?/ to ufe loo 
much fait in the compofition of the glafs-; otherwife the colou? , 
will be blueljh^ and bordering on the colour of the aiguc marine. 
Neri, chap. 32. An emerald colour in glafs-. 
In making green- you muft obferve that the metal have not : 
much fait I with metal -that hath much fait, as cryffcal and rochetta- 
have, you cannot make a fair- green, but only a fea green ; for r 
the fait confumes the green, and always inclines the colour to a 
blue ; wherefore, when you- would make a- fair green, put commons 
metal. 
Shaw’s Le£lures, p. 2g. Copper precipitated with commart 
fait out of aq-ua fortis gives the torquois- colour t© vtdiite glafs; 
when melted therewith. 
Kunkel’s- Remarks on Merret’s Notes,, p, 299.. 
f-wj Ncri, chap. 127. This chapter deferibes the method of 
JWaking red -gkfsjJ-n the cGmppfuioa- of which copper is ufed ; and 
i I.RQN;. 
