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H' at. wt. (natural) 1.007967
   at. wt. (H') 1.007822
   at. no. 1
   m.p. - 259.140C
   b.p. - 252.870C 
   density 0.08988 gm./l
   density (liquid) 70.8 gm/i. (-2530C)
   density (solid) 7016 gm/i. (-2620C)
   valence 1.

**Electronic configuration**
K	L	M	N	O	P	Q
1	2	3	4	5	6	7
s	s p	s p d	s p d f	s p d f	s p d f	s p d f
1

. MERCURY (Planet Mercury), Hg (hydragyrim, liquid silver); at. wt. 200.59, at. no.80; m~p. 38.870.C; b~p. 356.580C; sp. gr. 13.546 (2rnC); valence 1 or 2. Known to ancient Chinese and Hindus; found in Egyptian tombs of 1500 B.C. Mercury is the only common metal liquid at ordinary temperatures. It only rarely occurs free in nature. The chief ore is cinnabar (HgS). Spain and Italy produce about 50% of the world's supply of the metal. The com- mercial unit for handling mercury is the "flask," which weighs 76 lbs. The metatis obtained by heating cinnabar in a current'of air~and by~condensing the vapor. It is a heavy, silvery white metal; a rather poor conductor of heat, as compared with other metals; and a fair conductor of elec- tricity. The metal is widely used in laboratory work for making thermometers, barometers, diffusion pumps, and many other instruments. It is used in making mercury-vapor lamps and advertising signs, etc., and is used in mercury switches and other electrical apparatus. Other uses are for making pesticides, mercury cells for caustic-chlorine pro- duction, dental preparations, anti-fouling paint, batteries, and catalysts. The most important salts are' mercuric chloride (HgCl2, corrosive sublimate-a violent poison), mercurous chloride Hg2Cl2 (calomel- occasionally still used in med- icine), mercury fulminate '(Hg(ONC)2, a detonator widely used in explosives), and mercuric sulfide (Hg$, vermillion, a high-grade paint pigment). Organic mercury compounds are important. It has been found that an electrical discharge causes mercury vapor to combine with neon, argon, krypton, and xenon. These products, held together with van der Waals' forces, correspond to HgNe, HgAr, HgKr, and HgXe. It is not generally appreciated that mercury is a virulent prison and is readily absorbed through the respic- atory tract, the gastrointestinal tract, or through unbroken skin. It acts as a cumulative poison since only small amounts of the element can be eliminated at a time by the human organism. The maximum allowable concentration of mer- cury vapor in air has been set at 0.1 mg./cu. meter. Since B-20 mercury is a very volatile element, dangerous levels are readily attained in air. Air saturated with mercury vapor'at 200C contains a concentration which exceeds the toxic limit by more than 100 times. The danger increases at higher temperatures. It is therefore important that mercury be handled with utmost care. Containers of mercury should be securely covered and spillage should be avoided. If it is necessary to heat mercury or mercury compounds, it should be done in a well-ventilated hood.

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