MERCURY. 
§ 889.] 
tube, sealed at one end, and applying heat. If mercury be present, a 
ring of minute globules condenses in the cool part of the tube. If the 
quantity of mercury is likely to be very minute, it is best to modify the 
process by using a subliming cell (p. 262), and thus obtain the sublimate 
on a circle of thin glass in a convenient form for microscopical examina¬ 
tion. If there is any doubt whether the globules are those of mercury 
or not, this may be resolved by putting a fragment of iodine on the 
lower disc of the subliming cell, and then completing it by the disc 
which contains the sublimate (of course, the supposed mercurial surface 
must be undermost) ; on placing the cell in a warm, light place, after a 
time the scarlet iodide is formed, and the identification is complete. 
Similarly, a glass tube containing an ill-defined metallic ring of mercury 
can be sealed or corked up with a crystal of iodine, and, after a few 
hours, the yellow iodide, changing to scarlet, will become apparent. 
There are few (if any) tests of greater delicacy than this. 
Mercury in solution can be withdrawn by acidulating the liquid, and 
then inserting either simply a piece of gold foil, gold wire, or bright 
copper foil; or else by a galvanic arrangement, such as iron wire wound 
round a gold coin, or gold foil attached to a rod of zinc ; or, lastly, by 
the aid of gold or copper electrodes in connection with a battery. By 
any of these methods mercury is obtained in the metallic state, and the 
metal with its film can be placed in a subliming cell, and globules 
deposited and identified, as before described. 
The Precipitating Reagents for mercury are numerous : a solution 
of stannous chloride, heated with a solution of mercury, or any com¬ 
bination, whether soluble or insoluble, reduces it to the metallic state. 
Mercurous Salts in solution yield, with potash, soda, or lime, a 
black precipitate of mercurous oxide ; Mercuric Salts, a bright yellow 
precipitate of mercuric oxide. 
Mercurous Salts yield black precipitates, with sulphides of 
ammonium and hydrogen. Mercuric Salts give a similar reaction, 
but, with sulphuretted hydrogen, first a whitish precipitate, passing 
slowly through red to black. 
Mercurous Salts, with solutions of the chlorides, give a white 
precipitate of calomel; the Mercuric Salts yield no precipitate under 
similar circumstances. Mercurous Salts, treated with iodide of 
potassium, give a green mercurous iodide ; Mercuric, a scarlet. 
§ 889. The Detection of Mercury in Organic Substances and 
Fluids. —Simple treatment of the organs or tissues with hydrochloric 
acid may give qualitative evidence of mercury, for distinct evidence of 
mercury in the liver has been obtained on a piece of copper gauze in a 
case where a child had been given 2 grains of calomel before death. 
“ Four ounces of the liver were treated with hydrochloric acid and water, 
and a small piece of pure copper placed in the acid liquid while 
