USES OF MERCURY
Under normal conditions the chief uses of quicksilver (mercury) or its salts, stated in order of decreasing importance, are as follows: In the manufacture of drugs and chemicals, including calomel and corrosive sublimate; in the manufacture of certain chemicals, such as glacial acetic acid, phthalic acid and phthalic anhydride, into which mercury itself does not enter; as mercury fulminate ((C:N.O2)Hg, ¹⁄₂H2O), made by treating mercury with alcohol and nitric acid, which is used as a detonator for high explosives, and, though less than formerly, in small-arms ammunition.
The discovery of mercury fulminate by Howard in 1799 led to the invention of the percussion cap in place of the old flint-lock, and fulminate still remains the best-known and most-used detonator for gunpowder and high explosives. It is often combined with other substances, particularly an abrasive such as powdered glass, to increase its sensitiveness, and with compounds or mixtures that themselves have the property of detonating, such as sulphide of antimony and chlorate of potassium. Recently a large part of the mercury fulminate in detonators for modern high explosives has been replaced by picric acid, trinitrotoluene, or tetranitromethylamine, whereby a much stronger initial effect is obtained, and one part of mercury fulminate is made to detonate a charge that would have required six times as much fulminate used alone. Other substances have been found, which seem likely to replace mercury fulminate entirely for certain uses. One of these is lead azide, a salt of hydronitric acid. Large dry crystals of this salt are so sensitive as to explode when brushed with a feather, but smaller crystals are less sensitive.
As mercuric sulphide, mercury forms the brilliant red pigment vermilion. The metal is employed extensively in electrical apparatus, including rectifiers for changing alternating into direct current, mercury vapor lamps, and storage batteries. In the manufacture of felt hats from rabbits’ fur, mercuric nitrate is used to roughen the hairs so that they will adhere together, a process technically known as “carroting.” Metallic quicksilver is employed in the amalgamation of gold and silver ores, although of late years the wide application of the cyanide process has decreased this use. The metal is also utilized in the manufacture of instruments, thermostats, gas governors, and other appliances. Mercury enters into the composition of some anti-fouling marine paints for ship bottoms, a modern and at present rapidly increasing use. The mercury for this purpose is generally employed as red mercuric oxide, its efficiency depending upon the gradual conversion of the oxide to the poisonous bichloride by the sodium chloride of salt water. Mercury is also used in certain compounds for preventing boiler scale, in cosmetics, and in dental amalgam. Silver nitrate has to a large extent replaced mercury in silvering mirrors. A small quantity of quicksilver, not more than two or three flasks annually, is used in floating certain types of revolving lights in lighthouses. Quicksilver is also used as the cathode in certain electrolytic processes for manufacturing chlorine and caustic soda from common salt. Mercuric oxide parts with oxygen readily and is a useful oxidizing agent in certain chemical processes. An important modern utilization of this property is in the manufacture of glacial acetic acid by the oxidation of acetylene.
Experiments to determine the possible advantages of using mercury vapor with steam in turbine power generators are reported to have been encouraging and a 4,000-kilowatt unit has been built by the General Electric Co. to test further this application. Except for incidental losses, the mercury so used is recoverable, but if in practice the increase of power is as much as the experimental work has indicated a large consumption of the metal is likely to result.
The production of quicksilver in this country in 1917 was 35,954 flasks (of 75 pounds) and in 1918 it was 32,883 flasks.