2.94. When the surface was brushed with the feathery part of a quill, metallic iron was rendered visible, penetrating the general mass of the wood in a pulverulent form, or in the state of scales and angular and rounded grains. This structure was more clearly seen by means of a magnifying glass or of a microscope, which showed the fibres of the wood separated by the pulverulent iron. Here and there these grains of iron were of an appreciable magnitude, and were joined together like beads in a rosary. A group of five such grains was about a millimetre in length. In other portions of the specimen they might be detached, leaving cavities resembling the organic cellules. The specific gravity of this iron (in consequence, probably, of its admixture with organic matters) is very inconsiderable. In two trials it was found to be 6.248 and 6.4972; in a third and last experiment instituted with a grain of iron flattened by the blow of a hammer, it was found to be 6.6255.

M. Bahr analyzed these grains of iron, having first freed them as much as possible from all organic substances, and the results that he obtained are stated below. The solution was effected by means of very dilute nitric acid, and the portion thus dissolved amounted to 80-16 per cent. of the total weight of the grains, and contained the following substances calculated in the form of oxides ::

The residue, insoluble in very dilute nitric acid, contained also portions which obeyed the action of the magnet; and these in like manner were subjected to analysis, and gave the following results calculated in the state of oxides:

So far M. Bahr, the original source of whose paper I am unable to, state, as it is not given in the Spanish version of it. In conclusion I may observe, that I possess in my collection of minerals a specimen of limonite from Passau in Bavaria, containing small threads and veins of iron in the metallic state.

Madrid, Sept. 23, 1852.

On the Production of Photographs on Glass. By J. PUCHER.* According to this process, a thin film of iodide of sulphur is formed upon plate glass, by covering the glass, which must be perfectly clean,

From the London Chemical Gazette, August, 1852.

with a very thin coating of sulphur, and then impregnating this for a few seconds with the vapor of iodine. The glass plate is then placed in the camera, where at the same time the vapor of some quicksilver in an iron cup in the bottom of the camera acts upon the iodide of sulphur with which it is coated, and it receives the photographic image within a minute. The glass plate, when taken out of the camera, only exhibits a trace of the picture, but this immediately comes out on exposure to the action of the vapor of bromine. If the picture be now held over alcohol, and some of the same liquid be poured upon it, it will be fixed. Not more than from five to eight minutes are required for the whole operation.

The glass plates must be breathed upon and well rubbed with soft linen rag several times before use. They are coated with sulphur by burning sulphur sticks, made on purpose, in a proper tube, and holding the plates over it at a distance of about 3 inches. These sulphur sticks are prepared by dipping pieces of rush-pith into a melted mixture of sulphur and mastic, with which they become incrusted. For use, these sulphur sticks, which are about the size of a lucifer match, are stuck on a brass needle, introduced into the middle of a glass tube and kindled, so that the vapor of the sulphur may come in contact with the glass plate held over it.

These glass plates are so sensitive, that the coating of iodide of sulphur becomes instantly changed on exposure to direct sunlight, and give a Moser's image within five minutes when laid in a book. The figures thus obtained are most easily read by candlelight. In daylight, the blue letters can be recognised on the yellow ground only by looking through the plate towards the middle of the window, or towards a sheet of paper fastened in that place, the sulphur not having been removed either by vapor of bromine or by alcohol.

If a glass plate, covered with a solution of gum and exposed to the vapor of iodized sulphur, be placed in the camera, a positive picture, with all its details, is obtained, the outlines of which can be laid bare by an etching-point capable of scratching the glass. If a glass plate, so marked, be rubbed in with printing ink, the outlines will be filled, and the ink will remain in them when the glass is freed from the coating of gum by means of water. The picture is then easily transferred to paper, which is to be laid on the plate and rubbed over with a paper-knife.Archiv der Pharm., lxix. p. 301.

Extracts from Lectures on the Results of the Great Exhibition of 1851, delivered before the Society of Arts, Manufactures, and Commerce, at the suggestion of His Royal Highness Prince Albert, President of the Society.*

I. SIR HENRY DE LA BEche.

1. Amount of British Iron.-The Exhibition may be said to have given rise to the most complete view of the iron produce of this country * From the Edinburgh New Philosophical Journal, 1852.

which we possess. Mr. Samuel Blackwell, himself an ironmaster, accompanied the collection of iron ores by a statement of great value. He estimates the gross annual production of iron in Great Britain to be now upwards of 2,500,000 tons. Of this quantity, South Wales furnishes 700,000 tons; South Staffordshire, (including Worcestershire), 600,000 tons; and Scotland 600,000 tons. The remainder is divided among the various smaller districts. The iron of England and Wales was produced by 336 furnaces in blast in 1850. Though a considerable quantity of British iron is exported, a very large proportion remains to be variously employed in our own industry.

2. Desilverizing of Lead.-As to lead, the illustrations were chiefly British. There was an excellent exhibition of Pattinson's important process for desilverizing that metal-a process which has been of such service to lead-mining generally, rendering many lead-mines workable with profit which must otherwise have been abandoned. The chief ore whence lead is extracted is that known as galena, or the sulphuret of lead, furnishing from seventy-five to eighty-three parts of the metal, according to purity. It usually, though not always, contains silver in variable proportions. Upon the quantity of silver often depends the profitable raising of the ore. Previous to the invention of Mr. Pattinson, (of Newcastle-upon-Tyne,) about twenty ounces of silver in the ton of lead were required to render the extraction of that metal worth the cost; since then as little as three and four ounces in the ton of lead will repay extraction. Now, as so many ores contain small quantities only of silver, the importance of the process is evident. In a scientific point of view, it is one of much interest, as it consists in so conducting the work that portions of the lead can crystallize, by which the silver becomes excluded, in the manner in which, in many crystallizing processes, foreign substances are excluded during crystallization. Thus, by degrees, a mass of mixed lead and silver is left, extremely rich in the latter. When this richness in silver arrives at the point desired, that metal is extracted in the usual manner by cupellation. The lead-smelting at the Allenhead's mines, and at the Wanlockhead Hills, Dumfrieshire, both excellently displayed, are both founded on Pattinson's process. While touching on the Wanlockhead Hills exhibition, we should not pass over the arrangements by which the fumes from the furnace are prevented from escape, and from damage to the surrounding country, while lead, to the amount of thirty-three per cent. from the deposits or "fume," is obtained.

III. DR. LYON PLAYFAIR.

*

1. Iron Smelling.-Let us select the smelting of Iron, as an example of the teachings of chemistry. If practice, unaided by science, be sufficient for the prosecution of manufactures, this venerable art must be thoroughly matured, and science could scarcely expect to be of much use to it in its present state. But while we find much to admire in the triumphs of practical experience, there is yet great room for the improvement of this art. The cheapness of iron ore, and of the coal used in its smelting,

Although the smelting of iron is not strictly within the division of Manufactures, according to the classification, its importance to this country will authorize an exception in its favor.

has been so great that, regardless of their capital importance to this country, we, like careless spendthrifts, use them without thought of the future.

The mode of smelting iron consists in mixing the ore with lime and coal; the former producing a slag or glass with the impurities of the ore, while the coal reduces the oxide of iron to its metallic state. Much heat is required in the process of smelting, but the cold air blown in, as the blast, lowers the temperature, and compels the addition of fuel, as a compensation for this reduction. Science pointed to this loss, and now the air is heated before being introduced to the furnace. The quantity of coal is wonderfully economized by this application of science; for instead of seven tons of coal per ton of iron, three tons now suffice, and the amount produced in the same time is nearly sixty per cent. redly this was a great step in advance. Could science do more?

Assu

Professor Bunsen, in an inquiry in which I was glad to afford him aid, has shown that she can. We examined the furnaces, in each portion of the burning mass, so as fully to expose the operations in every part of the blazing structure. This seemingly impossible dissection was accomplished by the simplest means; the furnaces are charged from the top, and the materials gradually descend to the bottom; with the upper charge a long graduated tube was allowed to descend, and the gases streaming from ascertained depths were collected and analyzed. Their composition betrayed with perfect accuracy the nature of the actions at each portion of the furnace, and the astonishing fact was elicited, that, in spite of the saving produced by the introduction of the hot blast, no less than 81 per cent. of fuel is actually lost, only 18 per cent. being realized. If, in round numbers, we suppose that four-fifths of the fuel be thus wasted, no less than 5,400,000 tons are every year thrown uselessly into the atmosphere; this being nearly one-seventh of the whole coal annually raised in the United Kingdom. This enormous amount of fuel escapes in the form of combustible gases, capable of being collected and economized; yet in spite of these well-ascertained facts, there are scarcely half-a-dozen furnaces in the United Kingdom where this economy is realized by the utilization of the waste gases of the furnace.

Large quantities of ammonia are annually lost in iron smelting, which might readily be collected. Ammonia is constantly increasing in value, and each furnace produces and wastes at least 1 cwt. of its principal salt daily, equivalent to a considerable money loss. With the low price of iron, this subsidiary product is worthy of attention. As I write, a Welsh smelter has visited me, to say that he has adopted this suggestion with advantageous results. I might adduce other improvements introduced by chemistry in the smelting process; but these will suffice to show you that she has added to human power by increasing production, while she has also economized both the time and the materials employed.

On a new Yellow Dyeing Agent for Silk and Woolen, discovered by M. Guinon, of Lyons. By ROBERT Warington.*

In the early part of last year, (March 2, 1851,) a specimen of a material for dyeing silk of a fine clear yellow color, without the aid of a From the London Chemical Gazette, July 15th, 1852.

mordant, was put into my hands for examination. It had been obtained in France, and was for the time supposed to be kept a secret. It was of the consistence of a soft extract, dissolved almost entirely in hot water, with the exception of a small quantity of brown resinous matter; and on the addition of a little tartaric acid, produced a fine clear yellow on silk by its being immersed in it for a short time; if a mordant be used, the color is much faster. This substance proved, on chemical examination, to be the picric, nitropicric or carbazotic acid in an impure state.

As the parties for whom the investigation was undertaken, wished to be informed as to a process for its manufacture, I made a series of experiments on this subject, and found that the action of nitric acid upon the resins of Xanthorrhea hastilis and X. arborea afford an excellent product for this purpose. These gums are known in commerce, the first as gumflavum, or yellow gum, and gum-acaroides, and that from the latter as black-boy gum, or grass-tree gum. The former was suggested some years since by Dr. Stenhouse, as likely to prove the best source of carbazotic acid. As thus prepared, a very pure, dry, crystalline carbazotic acid is readily obtained, and at a very cheap rate, the resin yielding about half its weight of crude acid.

In October of last year, I made application, through Dr. Playfair, to the Industrial Exhibition, to endeavor to obtain a small specimen of these gums, as exhibited in the Australian department, for the purpose of identification, and to ascertain their value, but unfortunately without success, having received a polite note from the Executive Committee, stating that my application would be taken into consideration when all public institutions had been supplied. Failing in this direction, I have since been able to ascertain that it can at present be obtained in the drug market in small quantities at from 36s. to 40s. the cwt.; and I have also learnt, that if there were a sufficient demand, it could be imported at from 14s. to 20s. the cwt., making the cost of carbazotic acid about 6d. the pound.

I may state that I also communicated this investigation and process to Professor Magnus, of Berlin, during his sojourn in London in September, 1851, and have since forwarded him a small parcel of the resin.

The process employed in France has since been published by M. J. Girardin, of Rouen, and consists in treating coal-tar with nitric acid. The price of the impure acid, as examined, is 25 francs the kilogramme, or about 9s. 6d. the pound avoirdupois.

Method of Crystallization by means of an uninterrupted Circulation. By M. PAYEN.

To procure substances in larger and more regular crystals than is possible by the ordinary processes, the author has made use of a very simple apparatus, in which a constant current is produced by a slight difference of temperature. An alembic is furnished at the top with a head, and • Memoirs and Proceedings of the Chemical Society, vol. iii. p. 10.

† Journal de Pharmacie et de Chemie, vol. xx., Jan. 1852.

From the London Chemical Gazette, July 15th, 1852.