 drug. Chloral hydrate is the common ingredient, along with alcohol, in what are popularly known as knockout drops or Mickey Finns; the combination can induce acute
..... Click the link for more information. , which are used in medicine. It is also employed in the extraction of bromine from seawater. It is used in preparing some synthetic rubbers, in petroleum refining, and to prepare pure hydrochloric acid (see hydrogen chloridehydrogen chloride,
chemical compound, HCl, a colorless, poisonous gas with an unpleasant, acrid odor. It is very soluble in water and readily soluble in alcohol and ether. It fumes in moist air. It is not flammable, and the liquid is a poor conductor of electricity.
..... Click the link for more information. ).
Cl, a chemical element in Group VII of Mendeleev’s periodic system. Atomic number, 17; atomic weight, 35.453. A member of the halogen family.
Under normal conditions (0°C and 0.1 meganewton/m2, or 1 kilogram-force/cm2), chlorine is a yellowish green gas, with a pungent, irritating odor. It occurs naturally in the form of two stable isotopes: 35Cl (75.77 percent) and 37Cl (24.23 percent). A number of radioactive chlorine isotopes have been obtained artificially, with mass numbers 32, 33, 34, 36, 38, 39, and 40, which have a half-life of 0.31 sec, 2.5 sec, 1.56 sec, 3.1 × 105 yr, 37.3 min, 55.5 min, and 1.4 min, respectively. 36Cl and 38Cl are used as isotopic tracers.
History. Chlorine was first obtained in 1774 by K. Scheele by the reaction of hydrochloric acid with pyrolusite (manganese dioxide). However, it was only in 1810 that H. Davy established it as an element and named it chlorine (from Greek chloros, “yellowish green”). In 1813, J. L. Gay-Lussac proposed the French name chlore for this element from which the Russian name khlor is derived.
Distribution in nature. Chlorine is found in nature only as a component of compounds. The average content of chlorine in the earth’s crust (clarke) is 1.7 × 10–2 percent by weight. The average content in acidic igneous rocks, such as granites, is 2.4 × l0–2, and in basic and ultrabasic rocks, 5 × 10–3. Water migration plays a major role in the history of chlorine in the earth’s crust. In the form of the Cl– ion, chlorine is a component of the earth’s oceans (1.93 percent), underground brines, and salt lakes. There are 97 chlorine minerals, primarily natural chlorides, the most important of which is halite, NaCl (see and ROCK SALT). Numerous extensive deposits of potassium and magnesium chlorides and mixed chlorides are known: sylvite, KCl, sylvinite, (Na,K)Cl, carnallite, KCl · MgCl2 · 6H2Ó, kainite, KCl · MgSO4 · 3H2O, and bischofite MgCl2 · 6H2O. The migration of HCl contained in volcanic gases into the upper portions of the earth’s crust was of great significance in the earth’s geological history.
Physical and chemical properties. The boiling point of chlorine is –34.05°C, and the melting point –101°C. The density of chlorine gas at normal conditions is 3.214 g/liter (g/l), while the density of the saturated vapor at 0°C is 12.21 g/l. The density of liquid chlorine at its boiling point is 1.557 g/cm3, while the density of solid chlorine at –102°C is 1.9 g/cm2. The pressure of saturated chlorine vapor is 0.369 meganewton/m2 (MN/m2), or 3.69 kilograms-force (kgf/cm2), at 0”C, 0.772 MN/m2 (7.72 kgf/cm2) at 25°C, and 3.814 MN/m2 (38.14 kgf/cm2) at 100°C. The heat of fusion is 90.3 kilojoules/kg (kJ/kg), or 21.5 cal/g, while the heat of evaporation is 288 kJ/kg (68.8 cal/g). The heat capacity of chlorine gas at constant pressure is 0.48 kJ/(kg · °K), or 0.11 cal/(g · °C). The critical constants of chlorine are as follows: critical temperature, 144°C; critical pressure, 7.72 MN/m2 (77.2 kgf/cm2); critical density, 573 g/l; and critical volume, 1.745 × 10–3l/g. The solubility of chlorine at a partial pressure of 0.1 MN/m2 (1 kgf/cm2) in water is 14.8 g/l at 0°C, 5.8 g/l at 30°C, and 2.8 g/l at 70°C, while in a 300 g/l NaCl solution, its solubility is 1.42 g/l at 30°C and 0.64 g/l at 70°C.
Below 9.6°C in aqueous solutions, hydrates of chlorine are for