GOLD. 
486 ’ 
is very much impaired when the smallest quantity 
of arsenic or tin is mixed with the gold, a single 
grain of these metals being sufficient to alter a 
whole ingot. 
Gold has neither smell nor taste ; it is neither 
attacked by air, water, or even by fire, Boyle and 
Kunckel having exposed it during several weeks to a 
violent heat, without its having lost a single grain. 
It is true that when exposed to the focus of a large 
burning lens, it is evaporated, but without changing 
its metallic state. This evaporation was proved by 
exposing a plate of silver to the fumes of the melt- 
ed gold, which was soon found to be perfectly gilt. 
The operation, however, cannot be effected without 
the assistance of a most powerful burning glass, such 
as that belonging to Mr. Parker in Fleet-street, 
which is three feet in diameter. 
This valuable metal is not soluble in either of the 
mineral acids taken separately ; but when the nitrous 
and marine acids are united, they form a men- 
struum that dissolves gold, and which from thence 
has obtained the name of aqua regia. If a solution 
of gold in this liquor be properly mixed with tin 
dissolved in the same menstruum, a fine purple 
powder is precipitated, (called by the name of 
Cassius , its inventor,) which produces a beautiful 
lasting purple colour. This powder, when mixed 
with vitreous substances, is used in preference to all 
others by the painters in enamel and glass manu- 
facturers. 
If volatile alkali be added to the same solution of 
