Soda.— The old standard method of produc ing soda (sodium carbonate) from salt (sodium chloride) was by the process of Nicholas Le blanc, who in 1789 developed his invention and presented the discovery to his patron the Duke of Orleans, whose domestic physician he was. The Duke provided capital for the start of the industry, but the French Revolution came along and the industry, as is the way with such things in times of disorder, moved over to England where the process is still in operation in some works. It consisted in treating salt with sul phuric acid, producing salt cake (sulphate of sodium) and muriatic (hydrochloric) acid. The salt cake was heated with coal and lime stone (calcium carbonate) until the mass had fluxed, when the reaction took place; that is, there was an exchange of adds and bases, the sulphate of sodium becoming the carbonate and the lime becoming the sulphate. We need con cern ourselves no further with the details of the process because it is practically obsolete.
In 1861 Ernest Solvay of Brussels patented the so-called Ammonia process, which is that by which the major portion of the soda used to-day is made, although we shall soon note another process that is crowding it wherever there is abundant power for electricity. In the Solvay process, salt (sodium chloride) is treated with ammonium bicarbonate, or suc cessively with ammonia and carbon dioxide, at a low temperature. Sodium bicarbonate and ammonium chloride are formed and the former being nearly insoluble in a solution of the latter, it precipitates out. The mother liquor (of ammonium chloride) is drawn off, treated with caustic lime, which frees the ammonia which is recovered and produces calcium chloride.
By using magnesia instead of lime the chlorine may be saved and the magnesia used continu ously. The bicarbonate of soda is changed to the carbonate by heating. Caustic soda is made by treating the carbonate with quicklime.
The still newer method, resulting in caustic soda as the first product, and a very successful one, is the electrolytic process, which is by no means as simple as it looks. Methods differ in detail, but in principle the salt brine is led into an electrolytic cell, through which a current of electricity is passed which splits the sodium from the chlorine, each element approaching its opposite pole. The sodium combines with the water to form caustic soda and the chlorine is collected. A very lively industry is developed at Niagara Falls, N. Y., and elsewhere, under several modifications of this process. See ELECTROCHEMICAL INDUSTRIES.
Chlorine.— The electrolytic production of soda and improved methods of transporting gases hi iron containers has facilitated the use of chlorine in bleaching, in chemical manufac ture and in the destruction of noxious bacilli in supplies of drinking water. A surprisingly
small amount of the gas dissolved in water seems effectively to destroy them. Since the water supply of New York City has been chlo rinated, no single case of typhoid fever has been traced to this source. The gas, condensed to a liquid, is shipped in cylinders under pressure and it has replaced the use of bleaching powder in many instances. It was the first German °poison gas)) of European warfare.
Flotation.— An improved method of con centrating ores has been found to consist in grinding the rock to a very fine powder and then feeding it into a tank containing water and a slight amount of oil. As bubbles are caused to rise in the water, the metal-bearing particles attach themselves to the bubbles and float to the top, while the lighter gangue of limestone or other rock falls to the bottom. The phenome non is regarded as due to the fact that the oil wets at once the metallic surfaces and the sur faces of the bubbles, which carry the oil and the metal to the top. The particles of rock, on the contrary, not being wetted by the oil, do not so attach themselves, and so fall to the bottom. By this means a 20 per cent concentrate may be obtained from a 2 or 3 per cent ore. The process has come into very widespread use.
Artificial Precious Stones.— small diamonds are produced by heating a piece of iron, as pure as possible, with sugar charcoal in a carbon crucible in an electric arc furnace, according to the discovery of Moissan. Under these conditions the iron melts and dissolves a great deal of carbon. At about 4,000 degrees Centrigrade, when the iron volatilizes in clouds, the crucible is plunged in cold water. The sud den cooling solidifies the outer layer so that the inner core becomes solid at enormous pressure. This separates some of the carbon from the iron and when the latter is dissolved away by means of an acid, a few microscopic diamonds are found, with graphite, in the residue. No large diamond has been produced synthetically. Greater success has been attained in the pro duction of other precious stones. Rubies and white,yellow and blue sapphires are among the principal stones made. They are syntheti cally correct, consisting of alumina fused with additions of chromium-and iron oxides, titanic acid and other materials, according to the con tent of the stones as found in nature. They cannot be distinguished from natural gems.