It is a greyish-coloured substance, melting at low red beat, and uudergoing volatilization at a higher temperature. Its specific gravity is 2.80. The dioxide is pure white, turning yellow when heated. It is not decomposed by heat, but is very unstable in the air. It absorbs moisture and carbon dioxide, and becomes converted into carbonate. Neither of the oxides are of any considerable importance in manufacturing or industrial operations.
Carbonate of Sodium. (Fa., Sonde, Carbonate de Soude ; GER., Soda, Kohlensaures Natron.) Formula, important salt exists in nature, but to no very great extent. A mineral, the sesqui carbonate, is found in several localities, notably in Egypt and South America, going by the names of trona, or latroni, and urao. It forms an incrustation half an inch or so in thickness, and The Salsola soda is especially esteemed as yielding a good product, and the cultivation and treat-, ment of this and other species is still au important industry- in Spain, France, and other countries. The well-known Narbonne soda is the product of the Salicornia annua, and contains 15 per ceut. of carbonate.- Many of the marine and saline plants are of course chiefly valuable for the potash salts and iodine which they yield. Of carbonate of soda they contain down to 2 per cent. and as high as 40. The preporation is of the roughest character, very little in the way of purification being attempted. For a description of the process usually employed, the reader is referred to the article upon Potash—more particularly to that portion of it treatiug of " Kelp-salt." Many processes for the artificial production of soda have heen from time to time proposed, but, nothing of any importance was done until about the dose of the eighteenth century, when Scheele, Guyton, Carey, aud Hodgson worked out various methods for the decomposition of common salt by caustic lime, hy lead oxide, by alum, and felspar. Of these, the oxide of lead process was worked for long by Losh, at Walker-upon-Tyne, more especially for the sake of the pigment known as " Turner's yellow," which was obtained. The use of sulphuric acid was first proposed by Higgings in 1781, who, after decomposing the salt, reduced the sulphate of soda formed to sulphide, hy fusing it with coal, and, decomposing the sulphide by iron or lead, formed caustic soda and sulphide of lead, &c.,
The process known as Le Blanc's was patented in France in the year 1792, in response to an invita tion from the French Government to the chemists of the day to provide a substitute for the barilla soda when the supply of that article was cut off by the wars with Spain. Of thirteen processes proposed, that of Le Blanc was selected. It consisted in the decomposition of salt by sulphuric acid, the conversion of the sulphate of soda formed into carbonate of soda and (roughly speaking) sulphate of lime, by means of carbonate of lime or chalk and coal, and the lixiviation and preparation of the soluble oarbonate. The first establishment for carrying out the process on a large scale was set up in 1804, at St. Denis, by Le Blanc and his part leis, Dize- and Slade, hut was by no means a success, the proprietors eventually being forced to appeal for English aid in order to enable them to prosecute their enterprise. In this country the process was not adopted until the olose of the French war, when Losh, in conjunction with Lord Dundonald, established the first works at Walker-upon-Tyne. The alkali trade, however, was of exceedingly small importance until the repeal of the salt-tax, in the year 1823, sufficiently reduced the cost of the staple raw material to enable the products to bccome of wide application in the industrial life of the world. The introduction of pyrites in place of the Sicilian sulphur, as a source of sulphuric acid, gave a second great impetus to the trade about twenty years ago.
At the present time nearly the whole of the carbonate of soda of commerce, in various forms, is manufactured by Le Blane's process, which has undergone, for such an intricate method, remark ably little modification.
The first part of the process consists in the manufacture of sulphate of soda, or " salt cake," from common salt and sulphuric acid, inasmuch as it is cheaper for the alkali-maker to produce his own material than to buy it. Some reference has already been made to this process when treating of hydrochloric acid, but it will probably be found useful to give further details here. The action of sulphuric acid upon &lorido of sodium is extremely simple; thus: 2NaC1 + = 2HC1.