Notwithstanding the improvements in the manufacture of artificial soda, Leblanc's process is still continued in practice with few changes, furnishing hence very large residues of oxysulphuret of calcium and preventing the sulphur of the sulphuric acid from serving several times.

This is owing to the great degree of perfection to which the manu facture of sulphuric acid is now carried; the very perfect condensation of the hydrochloric acid and its applications; the low price of the materials used, the lime and combustibles, and the simplicity of the apparatus required for transforming the sulphate of soda into the carbonate; and finally the fact that the manufacture of sulphuric acid in connection with that of artificial soda, constitutes a complete and symmetrical work in which nearly all the products are utilized. Improvements that have been proposed have not been adopted, either because they derange this symmetry of operations, or else because of the cost of introducing them, or they are adapted only to certain circumstances or localities. The process now brought forward escapes these objec

It is by M. Emile Kopp, formerly Professor in the School of Pharmacy of Strasburg, and has already been put into practice in a manufactory in Lancashire, England, at Church near Manchester.

The process consists in decomposing sulphate of soda by a mixture of oxyd of iron and carbon, and treating the product of the reaction in the way described below. The proportions employed are as follows: Sulphate of Soda (SO3NaO), 125 kilograms. Peroxyd of Iron (Fe2O3) Carbon,

80

66

55

66

The sulphate of soda may without inconvenience contain some common salt; but then the oxyd of iron and carbon should be proportioned only to the pure and dry sulphate of soda present in the crude material. A furnace for calcination is used, taking care to break up the larger lumps. The oxyd of iron should be weighed dry and in a fine pow. der, and should be as pure as possible.

For the first operation, instead of the artificial or native peroxyd of iron, the carbonate (spathic iron) may be employed, or the magnetic oxyd, or even iron filings. But in the case of the last, the quantity of carbon should be diminished, since metallic iron acts as a reducer of the sulphate of soda. It will be soon seen, that whatever the compound of iron used, there will be shortly only the peroxyd, and this is regenerated constantly in the operation.

The mixture of sulphate of soda and oxyd of iron which is obtained as a residue in the process of decomposing common salt by the sulphate of iron, is readily adapted to Kopp's process, since, if the proportions are correctly taken, it is only necessary to add the requisite quantity of carbon. This carbon may be coke, or any other organic reducing substance; but the quantity will vary with its reducing properties. In England they use ordinary coal.

The amount of oxyd of iron must be such as will combine with all the sulphur of the sulphate of soda to form SFe. For 9 of the pure and dry sulphate, not less than 5 parts of the pure and dry oxyd of iron are required; a smail excess of oxyd of iron is advantageous. If the oxyd contains lime it should be removed by treating with hydroSECOND SERIES, Vol. XXI, No. 61. Jan., 1856.

16

chloric acid and washing; for the lime would give rise to CaS, then CaO SƆ3, and then again CaS, increasing unnecessarily the volume of material under manipulation, and causing a loss of carbon and heat. The carbon should not be in excess, as it favors the formation of sulphuret of sodium, and because also of this excess remaining with the sulphuret of iron, will afterwards afford, in the roasting of the latter, some sulphurous acid mixed with the carbonic acid. The proportion of carbon should hence be diminished until there is a minute proportion of the sulphate of soda left undecomposed in the blocks of crude ferruginous soda.

The quantity of the mixture that may be put into the calcining furnace at one time will depend of course on its size: but the amount may be full twice as large as in the Leblanc process, since the ferrugi nous soda works more easily than the ordinary soda.

For calcination, the furnace may be similar to that for the calcareous soda: but to economise heat, there had better be two or three stories, the lowest nearest the fire. The furnace then holds three charges at once, which are moved downward in succession, another being added above when one is taken out below.

The treatment in the furnace is like that for the crude calcareous soda, and the phenomena are nearly the same. The whole softens, becoming pasty, and the fluid as the action goes on disengages a yellow flame; then the action, which has been very bright, diminishes as the flames become less abundant, and when the mass is homogeneous, it is finished. It is then removed immediately from the furnace, being run while still red into a waggon on wheels in which it cools and solidifies, having been partially covered for security from contact with the air. When cold, it is a block in the form of a parallelopiped, blackish in color and more or less porous, very hard and of considerable density. The surface has a coppery reflection. In fracture, it has a uniform aspect, a crystalline texture, and a greenish and brilliant metallic reflection.

It now remains to treat this crude ferruginous soda, so as to draw off on one side the soluble carbonate of soda, and on the other the insoluble sulphuret of iron. The method used with the crude calcareous soda would give only bad results. In fact, the mass expands on the action of water, becomes very voluminous, difficult to wash, and affords a liquid containing much caustic soda and also sulphuret of sodium.

The washing is however easy after a preparatory operation which M. Kopp calls "délitation." It is as follows.-The crude ferruginous soda left exposed to the air under a shed, undergoes a change, which is the more rapid if the air be charged with moisture and carbonic acid. The lustre fades, the block breaks to pieces and becomes covered with an abundant blackish pulverulent material; and this goes on so rapidly that in a few hours it is reduced to a hillock of this powdered sub

stance.

This change is due to the absorption of oxygen, water and carbonic acid, while heat is given out, which without care may rise even to ig nition, in which case the powder has a reddish aspect, and contains sulphate of soda with 10 to 15 p. c. of carbonate of iron and a little sulphuret. But this high heat is prevented by removing the powder from

the surface as it accumulates, so as to leave the interior open to the air and carbonic acid. Water then separates from it carbonate of soda, and the residue consists principally of sulphuret of iron.

M. Kopp aids the process by an artificial supply of cold and moist carbonic acid, as the action of the air is very slow. This process, which he calls "carbonation," is as follows. In a chamber, at a height of two and a half meters, a grating of cast-iron is placed, whose spaces are one and a half centimetres. The earth is removed to about a depth of one meter. The roof of the chamber is about two and a half me. ters above the grating. The walls have numerous holes for the passage and circulation of the air. In the lower part, the carbonic acid is introduced. The blocks of crude ferruginous soda are placed on the grating, on their small face; and as they crumble, the powder falls below where it encounters and rapidly absorbs the carbonic acid. A block of 250 kil. requires as a maximum a space of a meter, and the process is complete in eight or ten days. Consequently a space of 20 meters by 10, will answer for 200 blocks, which will furnish more than 50,000 kilograms in 10 days, equivalent to 5000 kilograms a day. Ten metric quintals of coke, worth in England 7 to 8 francs, suffices to carbonate 90 to 100 quintals of dry and pure carbonate of soda.

The material when ready for lixiviation should be pulverulent, fine, gray or blackish-gray in color, and without hard fragments. It is well to use a course seive to remove the stony matters present, retaining them to be lixiviated apart, taking care to reject the insoluble residue. The sifted powder forms with water a lye which is clear in five to ten minutes, holding a heavy deposit, with often a coppery reflexion.

Weak so

The lixiviation should be carried on methodically either by filtration or decantation, by means of warm water at 30° to 40° C. lutions are used in lixiviating new portions of the powder.

When the exterior temperature is not too high, the solutions furnish after 24 to 48 hours, without concentration, an abundance of finely crystallized limpid carbonate of soda. By dropping in a bit of dry carbonate of soda, the crystallization is often hastened.

The residue, principally sulphuret of iron, is received on a filter or porous surface. In this state, it alters slowly. It is dried by heat or pressure and made into a brick. It is so combustible that it will take fire below 100° C., when the drying is nearly complete. This sulphuret affords the sulphur for making sulphuric acid, in which change, the iron becomes peroxyd and is then ready to be used again. It is thus seen that a single proportion of sulphur may be utilized a large num ber of times, in transforming common salt into sulphate of soda. But the oxyd of iron gradually becomes impregnated with the impurities of the common salt, the sulphate of soda and coal, and it must then be renewed; yet it may be used when it contains even 40 p. c. of impurities.

When the oxyd of iron contains sulphate of soda, it is necessary to change the proportions of the mixture for the crude soda. It has been found by experiment that the proportions most convenient are

Sulphate of soda,

125 kilograms.

Peroxyd of iron, proceeding from the sulphuret, 140
Carbon,

66

70 to 75"

and these proportions should be preserved for the subsequent opera tions, as long as the rotation of the same oxyd and same sulphuret of iron continues.

The same process may be used with the oxyds of manganese and zinc, but with greater difficulties, as the "délitation" and "carbonation" in these cases are more complicated.

Bibliography.-Recueil des Travaux Scientifiques de M. EBELMEN, Professeur de Docimasie à l'ecole des Mines de Paris, Administrateur de la Manufacture de Sèvres, etc., publié par M. Salvetat. 2 vols. in 8vo. Paris: chez Mallet-Bachelier.-Ebeimen died on the 2nd of April, 1852, at the age of 38 years, having been born in 1814. He passed through the Polytechnic school and the School of Mines, and finally became one of the Professors in the latter. He there made his important researches on the gas of high furnaces, on boracic and silicic ethers, on artificial hyalite, etc. Appointed afterward " Administrator" at the manufacture of Sèvres, he entered upon a fruitful line of dis covery in his researches on compounds crystallized by the dry way; he made artificially several minerals such as spinel, chrysoberyl, chrysolite, corundum, Brookite, Perofskite, and also glucina.

The process which he employed in his investigations are described in the work just published. His labors are presented under the heads of Ceramic Chemistry, Reports on Ceramic Industry, Geological researches, Metallurgical researches, Metallurgy of Iron, and Heating of Locomotives. Some of his labors rank among the highest in the scientific world, especially his synthesis of minerals, in which he devised methods of making even some of the gems. His publications will be welcomed both by men of science and those interested in the industrial arts.

Leçons de Cosmographie; par M. FAYE, Membre de L'Institut. 1 vol. in 8vo, 2de edition. Paris: chez Hachette & Co.-The first edition of this work has been promptly exhausted. The new edition has been adapted to the programme on Cosmographie made out for the candidates at the Polytechnic school. M. Faye adds to his knowledge of astronomy, the talent of a distinguished writer. The chapters of greatest interest are those relating to the construction of geographical charts, in which the methods used in the chart of France are described with full details. Other subjects of special interest are Comets, Zodiacal Light, the Milky Way, Nebulæ, Solar Spots, the Tides.

Elements de Physique expérimentale et de Météorologie, par POUILLET, Membre de l'Institut. 2 vols. in 8vo, with an Atlas. Paris: chez Hachette & Co.-M. Pouillet was one of the most eloquent professors of Paris, and had the happy talent of making the most abstruse subjects clear to his audience. His work exhibits the same characteristics. The sixth edition is just issued, and the sale of it is far from coming to and end.

SCIENTIFIC INTELLIGENCE.

I. CHEMISTRY AND PHYSICS.

1. On the direction of the vibrations of the ether in the case of polar. ized light.-HAIDINGER has made a communication from Stokes the occasion of an interesting examination of the long mooted question whether the vibrations of the ether take place in the plane of polarization or at right angles to it. The former opinion it will be remembered was held by Maccullagh and Neuman and at one time by Cauchy; the latter is the view taken by Fresnel, Cauchy, Beer and the majority of physicists who have written upon the subject. Our readers will remember that the question considered from the mathematical point of view amounts to this. Is the density of the ether to be considered constant and its elasticity variable; or is the elasticity to be considered constant and the density variable? the former supposition leads to the conclusion that the vibrations are at right angles to the plane of polarization; the latter that they are in this plane. It is only an appeal to experiment which can decide the question, or rather it is only this appeal which can throw the weight of probability upon the one side or the other. Haidinger supports Fresnel's view and bases his reasoning upon the phenomena of pleochroism in doubly refracting crystals. We shall simply translate the author's succinct expression of his own argument. I. Let the object be a dichroöus crystal and let equal thicknesses of its substance be investigated.

II. The following positions are considered as demonstrated.

a. The vibrations of the luminiferous ether are transverse.

b. To the same colors belong equal wave lengths; to different colors different wave lengths.

III. Mode of investigation.

(1.) Observation.-In the horizontal zone (of a uniaxial crystal) whose edges are parallel to the axis in all azimuths, one ray or bundle of rays, (an image of the dichroscopic lens or of any doubly refracting prism,) viz., the ordinary ray, is polarized parallel to the axis with the color A, and one ray or bundle of rays, the extraordinary ray, is polarized perpendicular to the axis with the color B.

Inference. The vibrations are either perpendicular to the plane of polarization or in this plane.