Lapas attēli

of them in manure, that plants are enabled to appropriate from the air and water the elements of which they are chiefly formed. The quantity per cent. and the composition of the ash vary in different plants and grain; but the ash of any particular plant is always essentially the same, whether the plant be grown on chalk, clay, or sand. By using, therefore, manures similar in composition to the ashes of plants, we are en. abled to produce good crops on all soils-to grow wheat year after year on the same land, and to render poor soils gradually as productive as rich. That the inorganic manures do enrich the land, and that these principles are correct, is fully proved by the accumulated evidence of upwards of ten years' use; and they were the first and only manures offered to the farmer based on a true and scientific principle, which has been since approved and recommended by the highest authorities.

These manures require no mixing for use; nor is any other matter needful. They are lasting in their effects, and any portion not taken away in one crop remains to benefit the next; so that, when once on the land, they must always effect good more than equal to their cost. They should be sown generally broadcast, or drilled, so as not to be in contact with the seed; on stiff land, it is desirable to harrow or hoe them well in, or to plough them lightly. The effect of any dressing of this manure will be found quite equal to dung, and the continued use of them must make the land cleaner, and free it from vermin.

The price is £7 per ton, and the quantity per acre three to six hundred weight. A farmer, writing from Tunbridge Wells, Kent, says:

"I have used in one year nearly £250 worth of your inorganic manures for wheat, oats, and peas, and confidently assert, and feel it my duty to confess, that the benefits in the several crops where it was duly applied so far exceed all other kinds of manure, that I have much satisfaction in recommending it to my friends and the public generally. I also witnessed its effects on hops, where different manures were tried. The land was divided into three parts-one portion manured with sprats, another with rotten dung, and the third with your inorganic manure. The result is manifestly much in favor of your valuable invention."


Mining, Quarrying, Metallurgical Operations and Mineral Products.

The objects exhibited in mining and metallurgy were extremely varied and interesting. They comprehended specimens not only of all the more important mineral ores, building stones, gems and native metals, but also numerous illustrations both of their useful applications and of the several processes by which the natural productions of the mineral kingdom are made subservient to the daily wants of man.

On the west end of the building, extending along the southern wall, was placed the mining and metallurgic collection of Great Britain. These were found a very excellent educational collection of minerals, together with a set of apparatus necessary to enable the student to examine chemically the substances brought under his notice.

Plumbago. This plumbago was from the mines of Borrowdale, England, which produce the best black lead for the manufacture of pencils. This substance is found in irregular deposits, which usually occur in granite, gneiss, mica, slate, or graywacke; as also sometimes, though more rarely, in the coal formations. At Borrowdale, in order to prevent robbery, it is found necessary to protect the entrance to the pit by a strong building, where the men change their clothes on leaving the mine, and where they are carefully watched by proper superintendents, to prevent their taking with them any portion of the valuable commodity. This mine is usually worked for a period of six weeks only during the year. Its net produce has often amounted to £40,000 per annum.

China Clay, or Kaolin, from St. Stephen's, Cornwall. This substance is produced by the decomposition of the feldspar occurring in granite rocks, which, by losing a portion of its alkaline constituents, leaves a substance rich in silica and alumina, but retaining a very feeble percentage either of potash or soda. This kaolin is separated from the silicious sand, with which it is invariably associated, by being exposed to a current of clear water, which leaves the sand behind, while the clay is carried off in suspension, and subsequently deposited in deep pits, in which it is allowed to settle. In connexion with the kaolin are exposed specimens of what is called China stone, which appears to be feldspar in a less decomposed state than where it exists as kaolin. This stone, from still retaining a large amount of the alkalies originally contained in the feldspar, is fusible at a high temperature, and it is consequently used in forming the transparent glaze with which the surface of the object previously formed in clay is covered, before being brought to a finished state. The works employed in extricating and preparing the China clay give labor to a large portion of the population of St. Stephen's.

Various models illustrating the methods of working and ventilating Coal Mines. One of these consisted of a very simple contrivance, by which wagons passing through a level are made to open and shut the various doors established in different places to facilitate a free circulation of air. By this contrivance the constant attendance of a man to open the door on the approach of the wagons is obviated; and as the work is so much more surely and readily done by the wagons themselves, one great cause of accidents is thereby avoided. Another machine for the ventilation of the collieries involves a principle seldom resorted to for this purpose. The current of air is obtained by the rapid motion of a wheel, having a series of radiating tubes, connected with a hollow axle, forming the extremity of the pipe by which the contaminated air is to be exhausted. When this mechanism is made to revolve with great rapidity, by means either of steam or water power, a current of air is by centrifugal force established from the centre of the periphery, and a corresponding movement of exhaustion is induced in the central column, forming the prolongation of the axis of the apparatus connected with the upcast shaft to be ventilated.

Circular Buddle.-A very valuable and interesting contrivance for the dressing or separation of metallic ores from the many earthy impurities with which they are invariably found associated. It is intended to effect the final separation of the slime or pounded earthy matter from the metalliferous particles, with which it is more or less mixed. It consists of a hollow shaft, carrying two brushes, which continually sweep the

surface of the circular space, of which the extremities of the brushes describe the circumference. The mineral, in the form of a thin paste, suspended in water, is allowed to enter this area through the hollow spindle in the centre, and as it is then constantly brushed over the floor, which is higher in the middle than towards the edges, it is evident that the metallic or heavier portions will arrange themselves nearly in the order of their respective densities, and accumulate on the central part of the buddle.

Patent Fuel.-There are several specimens of this. It is composed of coal-screenings, mixed either with pitch or coal tar, and then lightly forced into a proper mould, usually in the form of bricks. In some instances the excess of pitch and tar is subsequently eliminated by the bricks being heated to about 600' Fahrenheit in ovens properly constructed for that purpose; while in other cases the coal dust is made to assume solid and regular forms by great pressure only. The advantages of this fuel are that it is less likely to crumble than common coal during a long voyage, and it also stores into less space; but, from the impurities which are always associated with the small coals employed, it is nevertheless liable to produce a large quantity of ash and clinker on the base of the furnace.

Coal.-Pit coal, which is now raised in England to the annual amount of more than 35,000,000 tons, and the applications of which are daily becoming more extended, was but little known in England, as an article of commerce, prior to the commencement of the thirteenth century. In the year 1238, the first researches for this mineral were commenced on the high ground in the neighborhood of Newcastle-upon-Tyne. These were followed in the year 1330 at the coal field at Colliery, near Lanchester; in 1343, at Merrington and Ferry Hill; and in 1500 the several collieries at Gateshead, Whickham, and Tynemouth were first opened. At this period the principal demand was for the use of blacksmiths and limeburners, who appear to have been in the habit of employing this fuel long before it came into anything like general use for household purposes. The mechanical resources of the miner were of a very limited nature, and the principal part of the coal extracted was consequently raised from such situations as afforded considerable facilities for the removal of the water which naturally drains into all subterranean excavations. In the earliest periods of coal-mining, this was drawn off through the level, or gallery, by which the fuel itself was carried to the surface; but as the demand for the latter became more extensive, the mines were gradually worked at greater depths. This was effected either by extracting the water by an endless chain, carrying a series of properly arranged buckets, or by a system of pumps, worked by a water-wheel. The aid of horses was also frequently called in; but these were only employed in situations where water-power could not be obtained; and they were subsequently superseded by windmills, which either raised the water by an endless chain, passing over pulleys, or by pumps, worked by a due arrangement of cranks. The discovery of the steam engine has, however, produced by far the most important revolution in this branch of industry; for, by means of this machine, the working of the mines is not only in a most remarkable degree facilitated, but, from the immense demand thus created for fossil fuel, the extraction of coal has become a most important branch of national industry in all those countries which

have the good fortune to possess large deposits of this invaluable production.

England and Belgium are, in proportion to their extent, the richest with regard to the coal fields which they contain. In the former country, the coal deposits are estimated at of the total superficies of the Kingdom; whilst in Belgium they are supposed to occupy about of the entire surface of the country. In France, all the known deposits scarcely occupy part of the soil; and all the other European States are much poorer still in this respect. Sweden, Norway, Russia, Italy, and Greece are almost entirely without these formations. Bohemia is, in this particular, the richest part of Germany, although its annual productions are far from being considerable. Spain, Portugal, Austria, and Poland have likewise their beds of coal; and the mineral is also more or less abundant in India, China, Madagascar, Van Dieman's Land, Borneo, and the other East India islands, New Holland, and at Conception Bay, in Chili.

In Great Britain there are several extensive coal districts, among the most important of which may be named those of Wales, Newcastle, Lancashire, Derbyshire, Staffordshire, and Scotland. The veins are worked by means of shafts and galleries, in the same way that the metallic minerals are extracted from the lodes in which they are found; but, as the seams of coal are generally much more extensive than the metallic deposits, and as much larger masses are removed from the interior of the mines, the greatest care is required not only to prevent the crushing together of the workings, but also to introduce a current of air into every part of the colliery, so as to supply the workmen with fresh air for the purpose of respiration, and to prevent the accumulation of the explosive gases which frequently issue from the beds of coal. The very numerous varieties of coal have given rise to distinctions, founded partly on its age and appearance, and partly on its quality. In all kinds the structure of the wood from which they are supposed to have been formed is obliterated, although partial impressions of plants, indicating their origin, frequently occur. The coals form a more or less compact mass, of a dark-brown or black color, sometimes dull, but more frequently possessing a vitreous lustre, which often exhibit a decided iridescence. Their specific gravity is considerably above that of wood, and their structure decidedly granular. They are always distinctly stratified, and have generally a cleavage at right angles to the plane of deposition. The dif ferent laminæ of which they are made up are usually in close contact with each other; but are sometimes separated by thin layers of other minerals-such as iron pyrites, carbonate and sulphate of lime, galena, sulphate barytes, the soda salts, and still more frequently by a double carbonate of lime and iron. The fracture of the shining kinds of coal is conchoidal; that of the duller varieties is hackly. Common coal, and particularly that from the newer formations, is frequently observed to be made up of layers of very different appearance-the one kind, which is black and shining, with a conchoidal fracture, is rich in carbon; whilst the duller varieties are of a brown color.

The composition of the ashes of coal is in a great measure determined by the nature of the rock in the vicinity of the seam from which it is extracted; for, besides containing the inorganic elements originally forming part of the plants by the decomposition of which the coal has been pro


duced, they will also, to a certain degree, consist of earthy particles, posited in the pores of the coal by the infiltration of water from the overlying strata. The chemical composition of coals varies according to their different geological ages, and the localities from which they are obtained; but although they differ considerably in the relative amount of their various constituents, the nature of their ultimate elements is invariably found to be the same. All kinds of coal are, essentially, composed of carbon, hydrogen, and oxygen; but, besides yielding a certain portion of silicious and earthy residue and of sulphur, they usually afford traces of nitrogen, arising from the multitude of organic bodies, of which they contain the remains.

Among the specimens of coal exhibited, there was anthracite, from Tenby, South Wales; from the county of Tipperary, Ireland; and from the western side of the Vale of Neath, near Swansea. This substance is the oldest of all kinds of fossil fuel, and is chiefly found in the transition formation; its structure is perfectly homogeneous; its fracture, conchoi. dal; and its color of a jet black, with a vitreous lustre, which frequently shows a powerful play of colors. This coal contains an extremely large proportion of carbon, with but a small amount of volatile constituents, and is consequently totally unfit for the manufacture of gas, although well adapted for many purposes requiring intensity of heat and durability in the furnace. From the composition of this fossil, being more nearly allied to that of coke than to that of ordinary coal, it is frequently em. ployed in lieu of the former, and is extensively used in iron furnaces where the hot blast has been adopted.

The per centage composition of two of the above-mentioned specimens, as stated by Sir H. T. De la Beche and Dr. Lyon Playfair, in their first report on coals suited to the steam navy, is as follows: Anthracite from the Vale of Neath: carbon, 91.69; hydrogen, 0.79; and ash, 1.50. Anthracite from Tipperary, Ireland: carbon, 80.18; hydrogen, 2.21; oxygen, traces nitrogen, 0.23; sulphur, 6.76; and ash, 10.71. The specific gravity of the former specimen was found to be 1.357, and that of the latter, 1.590.

Among the specimens from the Welsh coal fields will be observed the Powell's Duffryn, the Aberdare Company's, Merthyr Nixon's, Merthyr and the Risca black vein, together with coal from the Llangenneck Company, whose mines are situated at a short distance from the port of Llanelly. The coals from the above districts are usually characterized by an irregular brilliant fracture, and many portions will be observed to possess a peculiar radiated appearance, seldom noticed in coals coming from other parts of the country. When used under a steam boiler, they are found to light easily and to blow off steam readily, with the production of but little smoke or soot. This variety of coal, which has also a very high evaporating value, is well adapted for the generation of steam, and is largely employed for this purpose in the navy, where its smokeless properties are evidently most useful.

The specific gravity of this class of coals usually varies from 1.29 to 1.35. In order to afford a general idea of the chemical constitution of the coals from this part of South Wales, we will select, as an example, from the report already quoted, the analysis of the Birch Grove Graigola, which, although one of the best varieties belonging to this class, very fairly represents the average per-centage composition of good Welsh coals.

« iepriekšējāTurpināt »