[A.n abstract of a Lecture on " Sodium and its Compounds," delivered before the Mechanics' Institute, at Cincinnati, Ohio, by Prof. Chas. W. Wright.1 The equivalent of sodium (natrium) is 23'27, and its symbol Na. This metal, like potassium, was first obtained by means of the galvanic battery, by Sir H. Davy; but when a large quantity is desired, the same process is had recourse to as in the preparation of potassium, which was fully described when treating of that substance. Sodium is a white metal closely resembling potassium, and is so soft at common temperatures that it yields to the pressure of the fingers. It floats upon water, and has so great an affininity for oxygen, as to abstract it from that body, with the evolution of much heat, but the re-action is unattended with light, unless the water be heated. It is kept under the surface of naphtha, which contained no no oxygen, to protect it from the atmospheric oxygen. Salts containing sodium communicate a yellow color to flame. Hydrate of Soda, or Caustic Soda : Na.O.H. 0.—This substance is prepared in the same way, as caustic potash, the whole operation being conducted in the same manner as when that substance is made. Like caustic potassa, this substance, when in solution, is caustic, and a powerful solvent for organic matter, and is used in the arts and manufactures for the same purpose as that body. With fatty matters, soda unites and forms a class of salts commonly known as " soaps," which are solid at ordinary temperatures, differing in this respeet from the potash, soaps, which, under the same circumstances, are fluid. As soda is an article largely consumed in the arts, the following table, by Dalton, will be found of great value in determining the strengfcirwf a solution of this substance, approx-imatively, by its specific gravity. TABLE OP DENSITY. Density. Percentage of real Soda. 2 00 . . . 778 185 . . . 636 T72 . . . 538 163 . . . 466 1-55 . . . 41-2 1-50 . . . 36 1-47 . . :. 340 1'44 . . . 310 1-40 . . . 290 136 . . . 260 1-32 . . 23 0 129 . . . 19 0 1'23 . . . 16 0 1-18 . . 13'0 1-12 . . .90 106 . . .47 Carbonate of Soda: Na.O. CO8.—Almost all of the carbonate of soda of commerce is prepared from common salt, very little keing obtained from the ashes of sea-weeds, wkich, in former times, furnished all ot the carbonate of soda in the market. The preparation of carbonate of soda from common salt being one of the most interesting and useful applications of chemistry to the arts, I cannot give a better idea of the process than by quoting the graphic description ot it by Prof. Graham, it being borne in mind that sulphate of soda is formed as a step in the process of preparing carbonate of soda from common salt:— " 1. The sulphate of soda is prepared by throwing 600 pounds of common salt into the chamber ot a reverberatory furnace, already well heated, and running down upon it, from an opening in the roof, an equal weight of sulphuric acid of density 1,600, in a moderate stream. Hydroehloric acid is disengaged and carried up the chimney, and the conversion of the salt into the sulphate oi soda is completed in lour hours. 2. The sulphate of soda thus prepared is reduced to powder, and 100 parts of it mixed with 103 parts ot ground chalk, and 62 parts of small coal ground and silted. This mixture is introduced into a very hot reverberatory furnace, about two hundredweight at a time. It is frequently stirred until it is uni- formly heated. In about an hour it fuses ; it is then well stirred for about five minutes, and drawn out with a rake into a cast-iron trough, in which it is allowed to cool and solidity. This is called ball soda, or black-ash, and contains about 22 per cent, of alkali. 2. To separate the salts from insoluble matter, the cake of ball soda, when cold, is broken up, put into vats, and covered by warm water. In six hours the solution is drawn off irom below, and the washing repeated about eight times, to extract all the soluble matter. These liquors being mixed together are boiled down to dryness, and afford a salt which is principally carbonate of soda, with a little caustic soda and sulphide of sodium. 4. For the purpose of getting rid of the sulphur, the salt is mixed with one-fourth of its bulk of saw-dust, and exposed to a low red heat in a reverberatory iurnace for about four hours, which converts the caustic soda into the carbonate, while the sulphur also is carried off. This product contains about 50 per cent, of alkali, and forms the soda-salt of best quality. 5. If the crystallized carbonate is required the last salt is dissolved in water, allowed to settle, and the clear liquid boiled down until a pellicle appears on its surface. The solution is then run into shallow boxes of cast-iron, to crystallize in a cool place; and atter standing for a week, the motker liquor is drawn off, the crystals drained, and broken up for the market. 6. The mother liquor, which contains the foreign salts,is evaporated to dryness,fora soda salt, which serves for soap or glass making, and contains about 30 per cent of alkali." In the above re-action, the sulphate of soda is converted into the sulphide of sodium, by the coal, thus:—Na.O. S.O3.-f-2C=2C.O.-f-Na.S.; and the chalk or carbonate of lime converts the sulphide of sodium into the carbonate of soda, with the formation of the sulphide of calcium, thus:—Na.S.+Ca.O. C.O. =N.O. C.OM-Ca.S. "When carbonate of soda is prepared by the above process it contains ten equivalents of water of crystallization, and when heated, undergoes the watery lusion. Its solution has an alkaline re-action and taste. It is soluble in Jtwo parts of cold, and less than its own weight of boiling water. Nitrate of Soda, Cubic Nitre : Na.O.N.O'.— This salt forms a regular stratum Of great extent in the Pacific coast of South America. It is a deliquescent salt, used in the preparation of nitric acid, and for manure. From its attracting moisture from the atmosphere, and not so readily parting with its oxygen as nitre, it cannot be used as a substitute for that body in the preparation of gunpowder.