366 
ELEMENTARY CHEMICAL MICROSCOPY 
From drops containing moderate amounts of mercury, the 
metal may be separated by a fragment of magnesium, or it may 
be deposited upon a bit of copper. If in the latter case the spot 
of deposit be rubbed it becomes silvery white. If the coated 
copper is placed in a subliming tube and heated the mercury 
will be volatilized and will condense in characteristic globules. 
EXPERIMENTS. 
a. Test several mercurous and mercuric salts by heating them with Na2C03. 
Examine the sublimates. Rub them gently with a hair-like glass rod and note 
that the globules unite. 
i. Obtain a deposit of Hg upon a tiny bit of Cu foil— i millimeter by 3 milli¬ 
meters— by heating in a drop of a solution of an Hg salt acidified with HCl. 
Dry and sublime. 
c. Introduce a fragment of iodine in one or more of the tubes, warm gently and 
allow to stand about five minutes. Examine for crystals of HgD. 
B. Differeniiaiing between Mercurous and Mercuric Salts. 
Add Hydrochloric Acid. — With mercuric salts there is no 
precipitation. Mercurous salts give an immediate amorphous 
precipitate of a white chloride HgCl. Under unusual conditions 
and exceedingly dilute solutions, mercurous chloride may some¬ 
times be obtained in the form of slender needles. To charac¬ 
terize the white precipitate, draw off the supernatant solution 
and add to the residue a drop of dilute ammonium hydroxide. A 
black compound of the formula NH2Hg2Cl is immediately formed. 
Examined with a \ inch or an 8 millimeter objective the black 
compound is seen to consist of a mass of tiny acicular crystals, 
tiny squares, crosses and fusiform grains. 
EXPERIMENTS. 
a. Precipitate HgCl, examine with the microscope. 
h. Add NH4OH to the white precipitate and examine again. 
Add Potassium Bichromate and Nitric Acid. — To the drop to 
be tested add nitric acid. Place nearby, a drop of solution of 
bichromate. Warm the drops over the micro-flame and while 
