E. B. TUSTIN, JR. Worcester Salt Company, New York City
SonIuM CHLORIDE, or "saltn in the common vernacular, is the modern philosopher's stone with which untold generations of mankind has preserved and seasoned food. Rich mineral deposits of salt, left by evaporation of great lakes in prehistoric days, have proved themselves to be invaluable in times of peace and a terrible weapon in war. More than one volume might be written regarding the history, properties, and uses of salt, but in this article wifl be indicated something of the wonderful series of products to which salt gives rise. For sodium rhloride is the starting point in the preparation of all sodium compounds as well as of chlorine and hydrochloric acid. Discoveries of Scheele and Leblanc. Just before the year 1800 salt commenced the new epoch in its career, when the magical touch of the Swedish chemist Scheele and the genius of the Frenchman, Leblauc, succeeded in extracting two of its most important secrets. Scheele discovered that salt contains a suffocating yellow gas called chlorine which possessed bleaching properties, while Leblanc a short time afterwards proved that salt could he converted to soda ash, which had hitherto been extracted only from vegetable materials, such as the ashes of wood and seaweed. So valuable is soda ash that nowadays 7,000,000 tons of salt-almost half of our national production-is used yearly in its manufacture. These two discoveries became the foundation of the great alkali industry, but they remained undeveloped for many years because of the heavy tax on salt in Europe, which in England amounted to $150 per ton, taxes due to the Napoleonic wars and the consequent financial stringency in Europe. Salt Tax Removed. In 1823 the salt tax was removed in England and the evolution of salt was allowed to take place under unfettered conditions. James Mnspratt realized what the removal of the salt tax meant to industry and in that same year erected the first works, a t Liverpool, for the manufacture of alkali by the Leblanc method. Twenty-five years previously Charles Tennant had been experimenting with chlorine gas, discovered by Scheele, and had shown how it could be converted into a harmless, but potent form of bleaching powder. This important method for the conveyance of chlorine was achieved in 1799 a t St. Rollox, but Tennant's work was greatly impeded by the enormous duty on salt. Upon its removal in 1823 the price of salt fell from about $160 per ton to $10 per ton and the manufacture of bleaching powder and alkali began in earnest.
lea
*
m. 40
-
1931
. 1935
1945
1940
Salt Ua. Follows the 1nd.x of Bu.in-
Activity
Increased production in recent yesra is due to new app1icstioan: Solid line, salt produoed in the U. 8. in 100.000 tons. Bmken line. New York Time8 Index of Bllriness Activity. Estimated normhl. 100.
From that date to the present time the uses of salt have performed an extraordinary series of evolutions, but nothing has eclipsed the work of those pioneers, Muspratt and Teunant, who first harnessed the powerful forces set free by Scheele and Leblanc. In order to realize adequately what the introduction of the Lehlanc process and the consequent large supplies of alkali meant, one has only, for example, to picture the soap industry which was formerly dependent for its alkali on wood ashes and the ashes from seaweed. There was a large business with Spain in this residue obtained from burning seaweed, or "harilla" as it was called, and the soap trade had to rely on this crude raw material for its alkali, as did the glass, pottery, and paper manufacturers. In like manner the cotton and linen trades were in difficulty. A large factor in cost was the expense of bleaching; most Irish linen, for example, was bleached in Holland by an air and salt water process, which required six months. The introduction of Tennant's bleaching powder opened enormous possibilities of expansion and revolutionized the whole textile industry. Ramifications of Alkali Industry. When in the manufacture of alkali James Muspratt converted salt to sulfate of soda by means of sulfuric acid, huge quantities of hydrochloric acid were allowed to escape up the chimney, much to the annoyance of the nearby inhabitants and to the detriment of local vegetation. It was not until 1836 that Gossage succeeded in condensing this acid, and what was formerly regarded as a waste product and great drawback to the process proved to be a valuable new substance for the manufacture of Tennant's bleaching powder. From 1836 the new industry expanded by leaps and bounds. Salt began to play an important part in
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supplying alkali and bleaching powder to a large number of industries and from this time there began to be available good supplies of sulfuric acid, saltcake, hydrochloric acid, caustic soda, sodium and chlorine compounds, all derived from the Leblanc process. New business activity sprang up; shipping, canals, and railroads were required to bring sulfur and pyrites, coal, and limestone for the alkali industry. In addition, large quantities of lead, iron, bricks, and stone were required to build plants. In fact, so many industries were affected that people began to wonder where the new force, set free by Leblanc, was going to end. Solvay and Electrolytic Processes. The Leblanc process had no rival for more than fifty years, but in 1868 the Belgian chemist Solvay succeeded in overcoming the technical and engineering difficulties of an ammonia-soda process. This idea of converting salt to alkali by carbonate of ammonia had been patented in 1838 by the London chemists Dyar and Hemming, the advantage being the direct conversion of sodium chloride into carbonate, but such were the obstacles connected with the method in preventing a reverse reaction that thirty years elapsed before a practical manufacturing process was evolved. From about 1880, however, the ammonia soda he-. came a strong competitorrwith Lehlanc alkali, but such was the vitality of the older process that it continued to exist for another forty years. Its salvation during such a long period was its large numher of by-products, and time after time what appeared to be waste material became the source of new wealth. One has only
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to mention the recovery of manganese by the Weldon process, Deacon's conversion of weak hydrochloric acid gas to chlorine and bleaching powder, the recovery of sulfur by the Chance-Claw process, Claudet's silver process, Henderson's copper extraction method, etc., to realize how many separate chemical processes were brought about by the Lehlanc method of decomposing salt. The death knell of this old process was sounded, however, when it became possible to generate electrical energy at a low cost. It had been known for many years that a solution of salt was susceptible of decomposition by a current of electricity, giving off chlorine and forming caustic soda in the water. The gas could be liquefied or converted into bleaching powder and the solution of caustic soda concentrated for the soap manufacturer. The great advantage of the electric decomposition is that it produces in a single operation the same, materials that required three cumbersome stages by the Leblanc process. Great advances in the economic production of electrical energy has now made it possible to use large quantities for the conversion of salt into caustic soda and chlorine. We have two successors to the Leblanc process: the Solvay or ammonia method for the manufacture of carbonate and bicarbonate of soda, and the electrolytic method for soda and chlorine for bleaches. Although the Leblanc process is dead as far as alkali or chlorine manufacture is concerned, there still remains the very important step for the manufacture of sulfuric acid, called into existence for the production of immense quantities of sodium sulfate. This portion
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of the Leblanc process is still employed to produce pure sulfate of soda, or saltcake, used in the manufacture of glass of high quality, while a considerable quantity of saltcake is converted to sodium sulfide for the leather and dyestuffs industries. Salt i n Warfare. When war came it was realized what a terrible weapon we possessed in our immense deposits of salt, the sodium and chlorine from which could be made the raw material for the manufacture of such deadly products as phosgene, chloropicrin, arsenious chloride, mustard gas and many others-to be held in readiness against any employment of gases by the enemy. In addition to these noxious substances, chlorine could also be consumed in thousands of tons for the manufacture of explosives such as dinitrophenol and picric acid. When salt goes to war it literally does so with both hands, for besides supplying chlorine it gives immense
JOURNAL OF CHEMICAL DUCATION
quantities of caustic soda for making soap and high explosives, the former an essential ingredient for the manufactme of glycerin, the base of nitroglycerin and cordite. In fairness to salt, it must be stated that although it is ruthless in time of war it is vital to our existence a t all times, and there is hardly a single industry which is not dependent on it or on the important series of products to which it gives r i s e i n recent. years, notably: plastics, sulfa drugs, deodorants, nylon and rayon yarns, compounds for case hardening, insecticides, degreasers, films, tetraethyl lead, and synthetic mbber. The chemical and metallurgical induatries of the U. S. employ about 11,000,000 tons of salt yearly of a total production in this country of over 15,000,000tons. The United States produces approximately 43 per cent of the world total.
