[ 27 ] 
tranfparent hilled not diftinguilhable from that which 
cobalt imparts to glafs. 
Iron vitrified per fe is converted into a blue 
glafs [d]. 
In fhort, it is indubitable that iron is the only 
metaly which will, without any addition, impart to 
the matter of glafs a blue colour for copper will not 
communicate that colour, without the addition of 
a confiderable quantity of [alts, or fome other mat- 
ter that attenuates it j and the other metals cannot 
by any means be made to produce it at all. 
Having fhewn that the metals exhibit colours,, 
invariably in the order of their denfities, when 
melted with in a proper proportion, without 
any other ingredient, and expofed to a fuficient heat ; ; 
I fhall proceed to fliew that the other preparations 
of the metals, viz. their folutions, precipitates, , 
cryfials, &c. do for the moll: part exhibit the fame 
colours, in the order of their denfities, though not fo 
invariably as their glafies ; fome fmall variation of 
colour happening in the more imperfect metals, 
probably from a change of denfity in their difterent 
preparations. 
[<3^j Lewis’s Courfe of Chem. p. 49. The fpecific gravity of 
iron is to that of gold as 7,645 to 19,640. This metal requires 
a great degree of heat to melt it, when it throws out fparkles, lofcs . 
confiderabiy of its weight, and is. at length converted into a dark . 
t>lue glafs. 
El 2 ' 
GOLD 
