Nitrogen monoxide, NO; Nitrogen tetroxide, NO.; 66 dioxide, NO2; 66 trioxide, NO3; pentoxide, N2O5. (2) They are also called acid, basic, or neutral, according to the reactions which they have. What is ozone, O? It is oxygen intensified in activity and modified in its nature. discovered by Schönbein, of Basle, in 1840. Where does it occur? It is found in the air, especially after electric disturbances. Give its mode of preparation. It was (1) It may be prepared by the passage of a current of electricity through a tube containing oxygen; (2) By slow oxidation of phosphorus, ether, and turpentine : Phosphorus burned in air combines as a pentoxide: (3) By the action of sulphuric acid on barium dioxide : 3H2SO,+3Ba02 = 3BaSO,+3H20+03. 2 What are the chemical and physical properties of ozone? It is a gas of peculiar metallic odor, insoluble in water and in solutions of acids or alkalies. By heat it reverts to the less active oxygen. It is a powerful oxidizing agent, corroding cork, rubber, and other organic substances, and rapidly oxidizing iron, silver, and copper, besides possessing potent bleaching and disinfecting properties. What is the test for ozone? It decomposes potassium iodide, liberating iodine, which may be detected by starch solution, the iodine turning the solution blue. How do we know that it exists in air? There is no direct test for the detection of ozone in air. The potassium iodide test is fallacious, as air contains H2O, and HNO2, which affect the test. Similarly, the metallic silver test, which is based on the fact that ozone will tarnish silver, cannot be used, as the sulphur with the reaction. BOSTOunds existing in air (HS) will attack the surface of silver and in By deductions based on experiments of Andrews, who found that the constituent of air which separates iodine from potassium iodide is deMAY 25 911 IBRARY stroyed by the same reagents which destroy ozone (peroxides), we are led to regard its presence in air as certain and not doubtful. What is the composition of water? Water is the monoxide of hydrogen, H,O. It always contains impurities, either in solution or in suspension, or in both. What impurities are found in various forms of water? Rain-water contains gaseous impurities washed from the atmosphere, together with traces of solid matter. River, spring, well, and lake waters contain a variety of mineral substances dissolved from the soil. Sea-water, salt lakes, and mineral springs contain saline substances in large quantities. Effervescent waters are either naturally or artificially charged with carbon dioxide gas, CO2. Water containing much lime in solution is called "hard" water; if little or no lime is present, the water is said to be "soft." Perfectly pure water is tasteless, and palatable only after aëration. Suspended impurities may be separated from water by filtration; dissolved impurities by distillation. How can water be prepared synthetically? By passing an electric spark through a mixture of oxygen and hydrogen gas enclosed in a eudiometer, the gases unite to form water. The apparatus consists of a strong glass tube, closed at one end and supported over a trough of mercury, into which the open end projects. It is also adjusted to receive the electric spark. Water is always a product of combustion whenever the substance burned contains hydrogen. How may water be decomposed? The two constituent gases of water may be obtained by passing an electric current through a vessel of water and collecting the gases which form and escape from the two poles of the battery. FIG. 1. + How may the exact proportions be calculated? Hydrogen is passed over copper oxide contained in a strong glass tube heated to redness. The hydrogen seizes the oxygen of the oxide, forming water and converting the oxide into metallic copper. The weight of the copper oxide before and after the experiment with the weight of the water produced furnishes data for calculations. What per cent. does the analysis give? Practically, there are by weight eight parts of oxygen to one part of hydrogen, or by volume one of oxygen to two of hydrogen. On what does the commercial analysis of water depend? The analysis of 1000 grains of water from the British Channel gave the following: Classify some of the mineral waters. (1) Saline: Containing sodium chloride (common salt); as the sea, salt springs and lakes; sodium sulphate-Glauber's salt, springs at Ems. (2) Alkaline: Containing bicarbonate of sodium or lithium-Vichy, seltzer, and apollinaris. (3) Acid: Sulphuric and hydrochloric acid, as at Rio Vinagre. (4) Acidulous: Carbonic acid and bicarbonates of lime and magnesium -High Rock Spring, Saratoga. (5) Chalybeate: Iron bicarbonate-Saratoga. (6) Alum: Aluminium and potassium sulphate (alum)-Virginia. Borax: Sodium borate (borax)-California and Italy. (8) Sulphur: Hydrogen sulphide (sulphur spas)-Virginia, Arkansas, and Harrowgate. (9) Silicious: Hot geysers-Iceland and Yellowstone Park; generally alkaline. Water containing forty grains or less of mineral matter per gallon is termed sweet or fresh. An excess of this amount renders the water a mineral water. Give an average analysis of Croton water. Croton water contains the following mineral substances in solution : Parts in 100,000— : Calcium bicarbonate, CaH2(CO3)2 Sesquioxide of iron, Fe,O, Sesquioxide of aluminium, Al,O, Calcium sulphate, CaSO4 Sodium sulphate, Na,SO, Potassium sulphate, K,SO, Sodium chloride, NaCl. What are the physical properties of water? 4.53; 3.25; 1.05; trace; trace; 0.26; 0.44 0.30; 0.68 1.13; 11.64. Pure water in small quantities is transparent, tasteless, odorless, and colorless. In masses it assumes a bluish tint. It may exist in the solid, liquid, or aëriform state. Ordinarily it freezes at 0° C., boils at 100° C., and evaporates at all temperatures. It is practically incompressible, but contracts regularly from the boiling-point to about 4° C., its maximum density; then expands until 0° C. is reached, at which point it undergoes further and sudden expansion to become ice. It is this expansive force which ruptures water-vessels and water-pipes and disintegrates rocks. Because ice is expanded-water solidified, it is lighter than the same volume of water, and therefore floats. If water had its maximum density at the freezing-point, ice would form at the bottom of rivers and lakes and thus destroy fish and other aquatic life. When vapor is suddenly chilled, snow is formed. What are the chemical properties of water? It is the best solvent known, and its solvent power for most solid substances increases with its temperature. For this reason, hot, saturated solutions on cooling deposit their excess of solid matter in the form of crystals. Water also dissolves gases, but with a power increasing with pressure and a diminution of temperature. Some solids, like common salt, dissolve equally well in hot or cold water. How may dissolved gases be freed from water? (1) By exposure under exhaust pump; (2) By heating to boiling-point of water; (3) By freezing the water, thus eliminating the gas. This is shown by the presence of air-bubbles in ice, which consist of the air dissolved from the atmosphere and set free by solidification. Pure water dissolves gases more copiously than water containing salts in solution, except in some cases where the dissolved salt forms a chemical combination with the gas absorbed. What standards are based on the properties of water? (1) Standard of weight : 1 cubic centimetre of water at 4° C. weighs 1 gram. (2) Standard of temperature: The Centigrade thermometer has zero-point at temperature of freezing and 100° at temperature of boiling water. Réaumur has zero-point at temperature of freezing and 80° at temperature of boiling. Fahrenheit has 32° at temperature of freezing and 212° at temperature of boiling. (3) Standard of amount of heat : The heat-unit is called a caloric. The French unit is the amount of heat necessary to raise 1 kilogram of water 1° C. The British heat-unit (B. H. U.) is the amount of heat necessary to raise 1 pound of water 1° F. (4) Standard of specific gravity : Solids and liquids are referred to water as the unit of comparison. If the substance is twice as heavy as water, bulk for bulk, its specific gravity is said to be 2, etc. (5) Standard of specific heat : The specific heat of water being 1, the specific heat of gases, liquids, and solids is referred to it. What is the action of water on oxides? Water acts on many oxides, both basic and acid, with great energy and considerable evolution of heat, producing compounds called "hydroxides," which contain hydrogen and oxygen not actually existing as water, the elements undergoing a different arrangement in combining :K,O+H,0=2KOH, potassium hydroxide (potash); CaO+H2O=CaO,H2, calcium SO, HOSH,O,, sulphur PO+H,O=2PHO, phosphorous 66 66 66 (slaked lime); |