the dissolved soda and aluminate of soda is drawn off, and the residue is properly washed. The solution will, on an average, mark 26° to 28° Beaumé.

The lye, being a strong solution of soda, carbonate of soda, and aluminate of soda, is treated with carbonic acid in order to produce carbonate of soda and alumina. The carbonic acid is produced by the combustion of coke, and the products of combustion are drawn off by means of a fan, and passed through stacks filled with coke, down which water is made to trickle; and in this way the carbonic acid is washed and purified. The purified gas is passed from these stacks into a large horizontal cylinder, from 40 to 50 feet long, through the middle of which a shaft with paddles rotates. The cylinder is about half filled with liquor, the paddles are put in motion, and the gas is let on through one end of the cylinder, the unabsorbed gases escaping at the other end. When the solution is saturated with carbonic acid it is run off into settling-boxes capable of holding one charge. In about from four to six hours the alumina will have separated from the liquor which is drawn off, and the deposited alumina is freed from the adhering soda by washing it with water and filtering upon proper filters. The clear solution first drawn off has a density of about 31° Beaumé, and the alumina is left in the form of a granular powder. In this way two valuable products are produced from the cryolite-carbonate of soda and alumina. The latter contains but a trace of soda, and is a valuable material for the manufacture of alum and sulphate of alumina.

Considering the nature of the mineral and its impurities, sometimes amounting to 10 or 15 per cent., the carbonate of soda is remarkably pure, its only impurity being one or two per cent. of sulphate of soda, the sulphuric acid having been formed from the sulphides that are associated with the cryolite.

THE WET PROCESS.-If cryolite be boiled with six equivalents of lime, the decomposition which takes place. is similar to what occurs in the dry process; but if two equivalents of cryolite be boiled with 15 equivalents of lime, the resulting product will be caustic soda, aluminate of lime, and fluoride of calcium.

2

2 (Al2 Fl3 + 3 Na Fl) + 15 Ca 0=6 Apparatus used for the decomposition of Na 0+2 Al1⁄2 O3 3 Ca 0+12 Fl Ca. In either case the decomposition is effected as follows: Into a large vertical cylinder, a, Fig. 2, scale, pro

Cryolite in the wet way.

vided with a perpendicular shaft having paddles, b, and a steam-pipe, c, ending close to the bottom in a perforated ring, is introduced milk of lime, made from about 15,000 pounds of good lime. The paddles are now put in motion, and the mass is agitated for a little time, and the liquid is then assayed and measured, so as to ascertain the exact amount of lime present. The cryolite is then added in fine powder in the proportion desired to accomplish a given result. Two equivalents of cryolite and 12 equivalents of lime will produce, as already stated, caustic soda and aluminate of soda. Fifteen equivalents of lime will furnish all the soda as caustic soda, with aluminate of lime. Fluoride of calcium is formed in both cases.

After two or three hours' boiling and agitation the decomposition is generally completed, (testing will indicate the liberation of all the soda,) and the contents of the agitator are discharged on a suitable filter. The clean liquor which will form on top of the sediment is drawn off, and the sediment is treated with water as long as the filtered liquid contains soda. If the first proportion of lime has been used and aluminate of soda has been formed, the liquid is treated with carbonic acid, as in the dry process, and all the soda is converted into carbonate, and the alumina is deposited as an insoluble residue. If the latter proportion of lime is used, and all the soda be in the solution as caustic soda, all that it is necessary to do is to evaporate the liquid to dryness in pans or kettles. In this manner caustic soda containing 75 per cent. of NaO is manufactured on a very large scale at Natrona.

It is evident that the wet process is decidedly the simpler of the two, there being less handling and less costly apparatus; but the feeble strength of the lye produced (10°B) by this process, and consequently the large amount of water to be evaporated, is a great drawback to it. Where alumina is of but little value and caustic soda is much sought after, the wet process with 15 equivalents of lime may be most profitably employed. Where the contrary is the case, the dry process is to be preferred, producing a lye of 26° to 28°B, and requiring but little concentration in order to crystallize.

Besides working out all the details of this process, Julius Thomsen has devised volumetric processes of analysis adapted to different stages of the operation. Weber & Bro., of Copenhagen, not only furnished all the means necessary for conducting his experiments, but established a factory in Copenhagen and sent vessels to Greenland for the cryolite. Their factory has been the model on which others have been erected.

There are four establishments in Germany, consuming annually about 2,000 tons of cryolite; and in 1867 the one in this country was erected by the Pennsylvania Salt Manufacturing Company, having a capacity for working up about 6,000 tons of cryolite. This company, in 1867, imported 8,000 tons, and sent out to Greenland during the summer 19 vessels of an average capacity of 450 tons, of which two were lost in the ice. The approach to the coast is considered dangerous on account of

the fields of ice, which sometimes form a thick and impenetrable belt of 80 to 100 miles in width. Off the western coast of Greenland the wind scatters the ice, and a good navigator can penetrate the openings without delay. No loss of life has yet occurred in this trade, as the ice affords a refuge for a shipwrecked crew until removed by the Esquimaux or until they escape by their boats to the settlements. The mines are worked, from May to October, by about 150 men. In the salt works of Natrona, Pennsylvania, more than half a million of dollars have been invested, and employment has been given to 500 men. The alumina manufactured there in connection with the soda is supplied to the largest makers of alum in this country; but this will be referred to again under alumina. The various manufactures from cryolite have a market value of oyer $1,500,000 in gold.

There has been no important improvement on Thomsen's processes, except it be one by G. A. Hagemann, on which a patent has just been obtained.

Beauxite (a mineral containing 80 per cent. of alumina) is sometimes mixed with the cryolite to increase the yield of alumina, and this process will be referred to under the part of the report relating to alumina.

Much space has here been devoted to this manufacture of cryolite soda, from the fact that cryolite and its products were conspicuous in the Exposition, and that the value of cryolite and its treatment as a sodayielding substance, is but little understood and appreciated by technical chemists generally.

PURE SODA FROM SODIUM.

One of the most curious triumphs of modern chemistry is the production of pure soda from the metal sodium at a price cheaper than the same article can be made by any other process previously adopted. It was made and exhibited by the firm of Messrs. Johnson & Matthey, of London. The bars of sodium, as they are now made by several European chemists, after the method of Deville, are cut into fragments of about a cubic inch in size. One of these fragments is thrown into a silver dish, floating on a stream of cold water; a little distilled water is poured on the sodium, and the vessel is agitated by the hand, which prevents explosions. After the first lump is dissolved another lump is thrown into the silver capsule and treated in the same way; and so on successive lumps are added. After a deposit of soda forms at the bottom and on the sides of the vessel the tendency to explode diminishes, but it is important to keep the vessel agitated to prevent the burning sodium from being scattered. The solution is somewhat milky, and must be filtered and evaporated, and then fused in a silver capsule or crucible, until the moisture is driven off and the mass is transparent; it requires a dull-red heat for this purpose. It is removed from the crucible while hot, broken up, and put in well stopped bottles. The operation is a slow one, and is disagreeable from the odor of the vapors and the danger of explosion. A steady

workman can treat in this way one and a half pound of sodium, or, with two dishes, two pounds of sodium. Pure soda is thus made and sold for $1 75 in gold per pound, including bottle and packing case, the metal sodium being sold by the same parties at $1 30 per pound, including the tin canister and packing case.

OTHER COMPOUNDS OF SODA.

BISULPHITE OF SODA.

There is no improvement in the ordinary way of making this material, viz., by passing sulphurous acid, made in any way found cheapest and most convenient, into a solution of carbonate of soda. Its use is extending more and more every day, frequently under the name of leucogene, for bleaching wool; also for bleaching vegetable textile matters, as cotton, linen, hemp, jute, phormium, &c. It gives a silky white color to threads and tissues that cannot be obtained by hypochlorites. M. Chaudet, of Rouen, manufactures annually 140 tons of leucogene, representing 2,000 tons of white wool. In 1866 he first applied bisulphite of soda and indigo to the blueing of wools. The process is to add to the ordinary leucogene from three to five parts by weight of blue dye for every 100 parts of wool to be bleached. The bleaching and dying take place at the same time.

HYPOSULPHITE OF SODA.

The use of this substance, which commenced with the art of Daguerre, has since extended to a variety of uses. As an antichlor, it is introduced into paper pulp to decompose the last traces of bleaching powder, which, if allowed to remain, attacks the paper and renders it brittle and friable; in the manufacture of antimony vermillion by the action of this hyposulphite or the salts of antimony, especially the terchloride; in metallurgy, after treating silver ores so as to form the chloride of silver, this chloride is dissolved out by the hyposulphite of soda. So much of this salt is now used that one establishment alone in Lancashire makes three to four tons a week. This salt is made in two or three ways. Kopp's method is to form it by a double decomposition with carbonate of soda and hyposulphite of lime. This substance can be readily obtained by oxidizing the soda-waste and submitting it to the action of carbonate of soda and evaporating the resulting solution of hyposulphite of soda to the point of crystallization. It is also formed by first converting the sulphate of soda into the sulphide by heating with carbon, dissolving in water, and treating by a current of sulphurous acid until the reaction is acid, neutralizing with a little caustic soda and evaporating to crystallization. Sometimes stacks of coke are used to bring the sulphide of sodium and sulphurous acid in contact, the solution of sulphide trickling downwards and the sulphurous acid gas ascending.

CHAPTER III.

POTASH AND ITS COMPOUNDS.

PRINCIPAL SOURCES AND USES OF POTASH AND ITS COMPOUNDS-POTASH FROM FELDSPAR-METHOD OF DECOMPOSING SILICATES-EXTRACTION OF POTASH-SALTS FROM SEA-WATER BY BALARD'S PROCESS-MERLE'S IMPROVEMENT-POTASH-SALTS FROM THE ROCK-SALT MINES OF PRUSSIA-GEOLOGY OF THE STASSFURT DEPOSITS-LIST OF THE MINERAL SPECIES FOUND AT ANHALT AND AT STASSFURT-THEORY OF THE ORIGIN OF THE DEPOSITS-EXTRACTION OF THE POTASH-SALTS-SULPHATE OF POTASH-NITRATE OF POTASH-POTASH FROM ORGANIC SOURCES-EXTRACTION FROM WOOD ASHES-EXTRACTION FROM ASHES OF SEA-WEED-EXTRACTION FROM SUINT IN SHEEP'S WOOL-USE OF POTASH-SALTS IN AGRICULTURE.

PRINCIPAL SOURCES AND USES OF POTASH AND ITS COMPOUNDS.

In years gone by, potash was the cheapest of the alkalies used in the arts, but that time has passed, and this alkali is now the most expensive of all, and consequently soda and ammonia have taken its place to a great extent. It is still, however, essential for some purposes where soda cannot be used, as for example, in the preparation of pure crystalglass, to which soda gives a greenish hue, as potash-nitre in the forma tion of gunpowder, and in the formation of chlorates and cyanides. In the last series of compounds, the cyanides, baryta may in the future take the place of potash to a considerable extent.

Potash is furnished to commerce from the mineral, vegetable, and animal kingdoms; it is procured from products both from the land and from the water. The method of obtaining potash from the incineration of terrestrial plants is so well known, and was for so long a time the only way of obtaining this alkali, that any notice of it further than a mere mention is unnecessary.

POTASH FROM FELDSPAR.

There have been many attempts to separate potash from feldspar, (in which it exists in considerable quantities,) so as to produce it, economically, in large quantities for commerce, but no one has come so near accomplishing this successfully as Mr. F. O. Ward, in 1861. At the Exposition in London there were specimens of potash manufactured according to his process. He called the process of decomposing the feldspar the calefluoric attack, and he describes it as follows: "The feldspar, or other alkaliferous silicate which it is proposed to treat, is ground to the fineness of ordinary Portland cement, and mixed with a due proportion of fluorspar or other fluoride, also in powder. With this mixture a certain quantity of chalk, or preferably of a mixture of chalk