p 
Add of wolfram, in a dry ftate 
15 grains. 
Prepared filex, i dram. 
Glacial phofphoric add, 2 drams 
Acid of wolfram, in a dry ftate, 
10 grains. 
1 found both melted to a glafs in a 
proper degree of heat: (a), was of a 
fine cryftalline colourlefs glafs j (b) 
was alio of a clear, tranfparent glafs 
tinged with a fine fapphire blue 
9 
9 
As therefore cobalt is not the only 
fubftance which communicates a blue 
colour to glafs j this circumftance mull 
not be overlooked, in determining the 
difpute wit! refped to the material the 
antients ufei in preparing their blue 
glafs 1 cobalt as fome affert, having been 
unknown to them. 
% 
I 
1 
'Jv 
