176 
MERCURY. 
ores, in the same manner as at present. Being the 
heaviest of all fluids of which we have any knowledge, 
and not congealing in the temperature of our climate, 
it has been preferred, before all others, for barometers, 
as a measure of the weight of the atmosphere. And, as 
heat dilates mercury similarly to other fluids, it is like- 
wise made into thermometers. Mercury is sometimes 
used in medicine in its pure metallic state. 
The combinations of mercury with other metals are 
termed amalgams. That of mercury and gold is formed 
so readily, that if gold be dipped into mercury, its sur- 
face immediately becomes as white as silver. An 
amalgam of mercury and gold is employed for the gild- 
ing, and of mercury and silver for the silvering of me- 
tals. 
Mercury and tin combined together form the sub- 
stance that is used for the silvering of looking-glasses. 
The process is as follows : A quantity of tin-foil,, equal 
in size to the glass, is evenly placed on a flat stone or 
table ; and mercury, in which some tin has been dis- 
solved, is poured upon it, and spread with a feather, or 
bunch of cloth, until its union has covered every part. 
A plate of glass is then cautiously slided upon it, from 
one end to the other, in such manner that part of the 
redundant mercury is driven off, or swept away before 
its edge. The remainder is now united to the tin. The 
glass is then loaded with weights all over, so as to press 
out still more of the mercury. By inclining the table, 
this remaining mercury becomes discharged ; and, in a 
few hours, the rest of the tin-foil and mercury adhere 
so firmly to the glass, that the weight may be removed 
without any danger of its falling. About two ounces 
of mercury are requisite for covering, in this manner, 
three square feet of glass. 
By means of mercury a fulminating powder is made, 
which, when struck with a hammer on an anvil or flat 
iron, such as is used by laundresses, explodes with a 
stunning and disagreeable report, and with such force 
