Sulphur from Coal Gas.—ln the manufacture of gas from coal, sulphide of hydrogen is one of the products from which the gas must be purified; and, for several years, what is known as the oxide of iron process has been adopted in large towns. This process consists in passing the gas through layers of peroxide of iron, mixed with some inert material to give it the necessary mechanical subdivision. The peroxide of iron is reduced to protoxide of iron, and the sulphur is precipitated in the mass, remaining uncombined. Exposure to air reconverts the protoxide into peroxide of iron without altering the sulphur contained in it; and this revived peroxide is used a second, third, and fourth time, in fact until the accumulated sulphur interferes with its rapid action, when it is replaced by fresh material. After repeated use this oxide of iron often contains as much as 40 per cent of sulphur. Some snlphuric acid factories employ this residue thus char;;ed with free sulphur, and manufacture sulphuric acid from it a fter certain cyanides are extracted from it by other factories. The amount of - sul phur that could be thus furnished annual'y is vegreat, estimating the sulphur in coal as one per cent, when its average is actually much greater. In London and its suburbs alone the lIas produced annually would furnish 15,000 tans, equal to 30,600 tuns of sulphuric acid. !'. Lawes, near London, uses 2,180 'uns of this resiilue, caeh Van furnishing, one and a quartertuns of sulphuric acid. Sulphur from CWi/0r»irt.—'To the northeast of Borax Lake, in California, and about one mile from it on the borders of Clear Lake, is a large deposit of sul phur, where solfatric action is still apparent. Tlie amount of sul phur which has been deposited in this place is very large, csvering an area of several acres, and extending' to a depth not yet ascertained. From six to eiglit tuns of this sulphur are refined daily, and are used in the manufactureoi sulphuric acid, gunpowder, etc. A small quantity of cinnabar is associated with this sulphur. There is another large deposit two miles from this locality, at Chalk Mountain, and still another at Sulphur Springs further east ; but neither ol them contains cinnabar. These and other localities of sulphur in California were represented in the collection sent from California by the Commissioner. Pyrites.—The manufacture of sulphuric acid from pyrites is probably the most important improvement made in manufacturing chemistry since the production of carbonate of soda from sulphate of soda, by Leblanc ; and although it has been in operation for many years, it is instructive to review it in connection, together with the development of industrial chemistry in the past few year'!; for hardly fifteen or twenty years have elapsed since all sulphuric acid was manufactured from Sicilian sulphur, with but one 01' two insignificant exceptions, while now there is not more than one tenth of this acid made directly from sulphur. While the use of iron pyrites in the manufacture of sulphuric acid dates back prior to 1830, it was not until 1838 that the short-sighted policy of the King of Naples, granting the monopoly ot Sicilian sulphur to Messrs. Taijf&Co., of Marseilles, that it i use was fairly established, for the price of sulphur rose in England from $25 to $70 a tun, and in twelve months from that time, in England alone, not less than fifteen patents were granted for the manufacture of sulphuric acid from pyrites. And although the monopoly was soon withdrawn, by the persuasion of English vessels of war and the diplomacy of other governments, the pyrites had I secured a firm footing in supplanting sulphur in the manufacture of sulphuric acid; and since then its use has rapidly increased; giving a wholesome lesson to governments to exercise great caution in granting monopolies and in legislating so as not to thwart industries based upon a science that draws colors rivaling the tints of the rainbow from coal, and that is not to be confined in the manner and method of its creations so long as the elements in one shape or another are at its command. Since the first production of sulphuric acid from pyrites the establishment at Fahlun, in Sweden, has employed this process altogether, pyrites being very abundant in that locality. This example was followed by Perret, of Chessy. France, where the pyrites contains from three to four per cent of copper, which metal can only be extracted by desulphurizing the ore. From the mines of this locality 70,000 tuns of pyrites are burnt and exported annually, and the various lead chambers here for making sulphuric acid have a capacity of about 1,600,000 cubic feet. This process is carried on in all parts of France, whether the pyrites contains copper or not, and Sicilian sulphur is only employed for special purposes in France and England. In the middle of France the pyrites of d'Alais is principally employed, it being very abundant. In the North of France the Belgian pyrites is used. In England the Irish pyrites is sometimes employed, although containing not more than 30 per cent of sulphur; but most of the manufacturers use the pyrites coming from Huelva, in Portugal, containing 45 to 50 per cent of sulphur, where the deposits of pyrites are remarkable for their great extent, extending into Andalusia, in Spain. One of the mines that is worked in the province of Alem- tejo, in Portugal, has a deposit of massive pyrites nearly a half mile long by two hundred and fifty feet across the widest part, and contains from two and a half to four per cent of copper. Pyrites is frequently arsenical, and as the sulphuric acid produced from it contains arsenious acid, it is unfit for many purposes, especially where it is employed in the manufacture of products of domestic economy, such as acetic, citric, and tartaric acids, and also in some of the industrial arts, and in cleansing the surface of metals for alloying them with tin or other metal. In these cases add made from sulphur is to be used, or the pyrites acid is to be purified by means of sulphide of barium or by sul phide of hydrogen, when the aeil thus treated is equal in purity to any other. It is not to be supposed, howe v er, that sulphur is henceforth to be excluded from the manufacture of su phuric acid; on the contrary, it is more than probable that many factories will return to its use, as the sulphur in Sicily is almost ex- haustless, and if ever the country becomes opened to the world by good and numerous roads, the price of sulphur must diminish; and the diminution required is very small to bring it again in to more common use among the acid manufacturers of the world. The factories in Belgi um, in the North of France, and some in other parts of that country, those in Ger iany, and a number in England, will find it profitable in almost any state of the case to continue the use of pyrites. (To he continued.)
This article was originally published with the title "The Manufacture of Sulphuric Acid"