MERCURY. 
§§ 864-866.] 
Spots on linen, and, generally, very small quantities of silver, may 
be detected by a simple galvanic process :—The substance is treated 
with solution of cyanide of potassium, and submitted to a weak galvanic 
current, using for the negative plate a slip of copper, for the positive, 
platinum ; the silver is deposited on the former. 
5. MERCURY. 
§ 864. Mercury, Hg = 200 ; specific gravity, 13-596 ; boiling-point, 
350° (662° F.) ; it becomes solid at —39-4°( —39°F.). This well-known 
and familiar fluid metal evaporates and sublimes to a minute extent at 
all temperatures above 5°. 
When precipitated or deposited in a finely divided state, the metal 
can be united into a single globule only if it is fairly pure ; very slight 
fatty impurities especially will prevent the union. It is insoluble in 
hydrochloric acid, soluble to a slight extent in dilute cold sulphuric 
acid, and completely soluble in concentrated sulphuric and in nitric 
acids. It combines directly with chlorine, bromine, and iodine, which, 
in presence of free alkali, readily dissolve it. It is unalterable at 100°, 
and, when exposed to a high temperature, sublimes unchanged. 
Mercurous Chloride (Calomel, HgCl = 235-5; specific gravity, 
7*178 ; subliming temperature, 111-6° ; Hg, 84-94 per cent., Cl, 15-06 
per cent.), when prepared in the wet way is a heavy white powder, 
absolutely insoluble in cold, but decomposed by boiling water. It may 
be converted into the mercuric chloride by chlorine water and aqua 
regia. Chlorides of ammonium, potassium, and sodium all decompose 
calomel into metallic mercury and mercuric chloride. It is easily 
reduced to metal in a tube with soda, potash, or burnt magnesia. 
§ 865. Sulphide of Mercury (HgS; Hg, 86-21 per cent., S, 13-79 per 
cent.) is a black powder, dissolving in nitromuriatic acid, but very in¬ 
soluble in other acids or in water. It is insoluble in alkaline sulphides, 
with the exception of potassic sulphide. 
§ 866. -Medicinal Preparations of Mercury. —Mercury in the liquid 
state has been occasionally administered in constipation ; its internal 
use is now (or ought to be) obsolete. Grnelin has found samples con¬ 
taminated with metallic bismuth—a metal which only slightly diminishes 
the fluidity of mercury ; the impurity may be detected by shaking the 
mercury in air, and thus oxidising the bismuth. Mercury may also 
contain various mechanical impurities, which are detected by forcing 
the metal by means of a vacuum pump through any dense filtering 
substance. Tin and zinc may be dissolved out by hydrochloric acid, and 
all fixed impurities (such as lead and bismuth) are at once discovered 
on subliming the metal. 
Mercury and Chalk (Hydrargyrum cum creta). —Mercury, 33-33 
per cent. ; chalk, 66-67. 
