« iepriekšējāTurpināt »
that sugar dissolves in water, alkalies unite with acids, metals dissolve in acids; and he inquires whether these effects are not occasioned by an attraction between their particles? Copper dissolved in aquafortis is thrown down by iron. Is not this, he inquires, because the particles of the iron have a stronger attraction for the particles of the acid than those of copper, and do not different bodies attract each other with different degrees of force?
From the seventeenth to the commencement of the present century little further advancement was made in this science; but from that period to the present time chemistry has received a marked impulse from the unremitting attention of the most eminent men of nearly all nations; discoveries have been made, inventions brought out, and systems promulgated, which would have astonished the world had they occurred at an earlier period; and this, too, not only as applied to the purposes of medicine, manufacture, &c., but also, and that to a very great extent, as connected with agriculture.
In a commercial point of view, chemistry has also made some very rapid strides. Within the last twenty years the manufacture of caustic and carbonate of soda has originated and developed itself to a degree almost unparalleled in the history of commerce. The fires of the kelp business on the coasts of the islands of Scotland are scarcely now extinct, when vast factories, employing large numbers of individuals, produce, in enormous quantities, the same alkali which, until recently, was derived from the fused ashes of marine plants. The manufacture of this alkali, by an ingenious decomposition of common salt, by the simple aid of sulphuric acid, chalk, saw-dust, and coal, is now prosecuted to a vast extent for the supply of the industrial arts generally, the quantity used in medicine being comparatively insignificant. At some alkali works, fifty and sixty tons, and upwards, of common salt are decomposed every week, and converted into caustic and carbonate of soda. The alum factories are not less extensive; at these establishments crystallizations, on a scale emulating those of nature, are constantly in progress. The manufacture, also, of sulphuric acid, and of the compounds used by the dyer and calico printer, occupies a prominent feature of commercial enterprise.
The prussiates of potash, forming large masses of yellow and red crystals, and the green but perishable crystals of copperas, are substances largely used in the arts, and the colors and dyes produced by their assistance present themselves in every direction when textile printed fabrics are examined.
Amongst the varied specimens of chemical and pharmaceutical products displayed, were many worthy of notice, and, taken throughout, they formed a valuable collection, and furnish remarkable illustrations of the extensive applications of chemistry to modern arts and manufactures.
Crystal of Copperas, or Sulphate of Iron.-T. Bramwell & Co., Newcastle-upon-Tyne.
This substance, so largely used in the arts for dyeing, &c., and also in chemistry and pharmacy, is obtained, as a natural product, from aluminous chalybeate springs, as well as by the spontaneous decomposition of certain native sulphurets of iron, or iron pyrites; and is prepared in
large quantity by the action of air and water. The sulphur and iron are thus both oxidated; and sulphate of iron, or copperas, is obtained by crystallizing the lixiviated masses.
Crystallization, and the circumstances under which it takes place, form an interesting subject of inquiry. Not having the operations of nature open to our inspection, our only sources of information relative to the formation of crystals are those afforded by the process of artificial crystallization; and here, until very recently, our experiments were circumscribed by a very few modes of operation: that of the deposit of crystals from solution in some fluid; their production while gradually cooling from a state of fusion; and their volatilization by heat, or otherwise. Latterly, however, by the aid of that universal agent-electricitynew methods of producing crystals have been pursued; and there can now be little doubt that all the phenomena of crystallization are governed, in a greater or lesser degree, by electric influence.
Specimens of Crystallized Alum and Bicarbonate of Soda.-W. Patterson, Newcastle upon-Tyne.
The first of these products is also extensively used in the arts, as well as in chemistry and medicine. It is an earthy salt, and occurs in a native state only in small quantities. In a great measure, however, it is prepared artificially from alum slate-a rock belonging to the coal formation, and containing a considerable proportion of sulphur, iron, and alumina. The slate is broken in pieces, roasted, exposed to air and moisture; and, the soluble parts being dissolved in water, crystals of alum are obtained as the solution cools.
Bicarbonate of soda is chiefly used in medicine, and may be obtained by passing carbonic acid through a concentrated solution of the carbonate.
Camphor and Borax.-Howards & Kent, Shatford, London.
Camphor is one of the principles arising from the separation of the volatile oil of two trees: the one, a native of Japan and China; the other, a native of Borneo and Sumatra. From these it is procured by different processes. It exists in every part, root, stem, branches, and leaves of the first-mentioned tree, which is chopped into pieces sufficiently small to be thrown into iron vessels. These vessels are afterwards covered with earthen hoods, in which are placed rice, straw, and rushes; heat being subsequently gradually applied. The camphor is volatilized, and afterwards condenses on the straws, rushes, &c. This, after being purified from the intermixture of straw, is found in commerce under the name of crude camphor; but it still retains many impurities, and on arrival in Europe is refined. The tree is familiarly known in this and other temperate countries as an ornament of conservatories. It is a graceful evergreen tree, whose wood and leaves emit, when bruised, an agreeable camphoraceous odor. In the camphor tree of Borneo, on the contrary, the volatile oil is not procured by distillization. The camphor here occupies the place of the pith of the tree, existing in its stem, in a crude solid form, along with camphor oil.
Camphor has been long and extensively used in medicine; but even yet its physiological and therapeutic actions have not been fully discov. ered, from the fact that more systematic inquiries have not been made as to its medicinal results.
Borax is, in reality, a compound of boracic acid and soda, correctly termed biborate of soda. It is chiefly brought from the East Indies, Persia, and Ceylon, and also from a lake in Thibet entirely supplied by springs, where it is collected by the natives from the edges in a state of crystallization. It is imported under the name of tincal. The crystals are bluish, or greenish-white, and sometimes nearly transparent, as well as soft and brittle. It is purified by solution in water and crystallization, and is then sold as borax.
On the continent, borax is prepared by decomposing carbonate of soda with the boracic acid of Tuscany, and purifying the biborate by various processes. Its chief use
Little is yet known of the medicinal actions of borax. in the arts is for glazing porcelain and making green fire.
Ferrocyadine of Potassium, used for Dyeing Blue, in place of Indigo.T. Bramwell & Co., Newcastle-upon-Tyne.
This is perhaps one of the most important chemicals used in the art of dyeing, and calico printing. Its preparation consists in projecting a mixture of pearl ashes with hoofs, horns, and other animal matters, in the proportion of two to five, into a red-hot iron crucible, and stirring diligently the pasty mass thus formed until fetid vapors cease to arise from it. When the product has cooled, it is lixiviated with cold water, filtered and concentrated, upon which yellow crystals of ferrocyadine of potassium are formed. By the addition of a salt of iron to ferrocyadine of potassium, that most beautiful blue, called Prussian blue, is produced.
A Pyramid of best Table Salt, with several other specimens of salt.— F. Cheshire, North witch.
These specimens of salt were from the extensive mines of Northwitch, in Cheshire, where there are also brine springs. They are of two kindsthe one white and transparent, the other of a reddish-brown. The rock salt is found from 28 to 48 yards beneath the surface of the earth. The first stratum is from 15 to 20 yards in thickness, extremely solid and hard, resembling sugar candy. Many tons at a time are loosened by blasting with gunpowder.
The second stratum is of hard stone, from 25 to 35 yards in thickness. The salt lies beneath this stratum in a bed above 40 yards thick, generally perfectly white, and clear as crystal. It is stated that the annual production of salt in England is upwards of 800,000 tons, and the population engaged in its manufacture 11,000 to 12,000. The sources of supply are said to be inexhaustible; and latterly the salt manufacturers have so far extended their works that the opening of a new market would be of the greatest advantage. Common salt, for ordinary purposes, can now be obtained at about 20 shillings sterling per ton. In India the British government monopolizes both the manufacture and sale of salt, and the exportation of British salt to India is prohibited. Attempts have been
made by the salt manufacturers and ship owners to obtain admission for British salt into the ports of India at a moderate duty; and the latter, especially, complain of disadvantage of not being allowed to take so convenient an article of merchandise to that part of the British empire. The salt monopoly had existed in India long before the sway of the East India Company commenced; and its modification, or total abolition, is considered only as a question of time. It is believed that a moderate duty on salt would soon yield quite as large a revenue if the monopoly were abolished, while commerce would be benefited by the exchange of sugar and other commodities for salt; smuggling in salt, which is extensively carried on, would cease; and, in place of arbitrary and harsh restrictions, the consumer would obtain a better article at a much cheaper
Refined Indigo.-John Marshall, Leeds.
This substance is the innoxious and beautiful product of an interesting tribe of tropical plants, and is very extensively employed in dyeing and calico printing; being esteemed the most useful and substantial of all dyes. When the plant is in full flower it contains most coloring matter. It is then cut, dried, put into vats, and covered with water; fermentation takes place, accompanied with the evolution of carbonic acid, and other gaseous products, and the yellow liquor is covered with a froth. This froth, in a little time, becomes of a violet color, and a substance is evolved, which is rendered blue by absorbing oxygen of the air, and, being thus rendered insoluble, is precipitated. This, when collected and dried, is indigo.
Specimen of Ultramarine.-Gorton & Co., City road, London.
This is a well known blue pigment of extraordinary beauty. Until within the last few years it was entirely prepared from the lapis lazuli, or lazulite, and from the great costliness attending its preparation, its use was confined to the artist. It is now prepared artificially, at a very moderate rate, and equal in beauty to that obtained from the lazulite. It is stated that by adding freshly precipitated silica and alumina, mixed with sulphur, to a solution of caustic soda, evaporating the mixture to dryness, and placing the residue, in a covered crucible, and exposed to a white heat, where the air has partial access to it, a pure ultramarine is obtained. The product is then reduced to impalpable powder. The proportions of materials to be used are about 36 silica, 36 alumina, 24 soda, and 3 sulphur. Since this discovery, its value has become very much reduced, and it is now used extensively in the arts.
Specimen of Carmine.-J. Leichfield, Clapton, London.
This beautiful product is obtained from cochineal, and is so valuable an article as to be rarely met with in a state of purity. It is obtained by the following process: boil 12 pounds of filtered rain water in a tin vessel, and add to it four ounces of finely-powdered cochineal; boil for five minutes, constantly stirring with a glass rod; then add five scruples of alum in fine powder, perfectly free from iron; boil again for two minutes, remove the vessel from the fire, cover it, and allow the contents to settle.
As soon as the liquor is clear, pour it, while still hot, into glass or porcelain vessels, and suffer it to remain some days, covered from dust. The alum gradually precipitates the coloring matter, in combination with animal matter and a little alumina. The precipitate is put on a filter, washed, and dried in the shade. It is one of the most beautiful red colors used by painters.
Several Specimens of Wood preserved by Chemical Process.
All wood contains what is called albumen-an essential ingredient in vegetable bodies, entering largely into the composition of the sap. As long as this albumen is supplied with sufficient moisture, so long will it be liable to enter into a kind of fermentation, especially if placed in damp or ill-ventilated situations, and often even where the ventilation is perfect, and the atmosphere in its ordinary state of humidity. If a piece of green timber, containing this albumen in a perfect state of solution in the moisture of the wood, be employed in the construction of a house, the albumen undergoes fermentation, and the rot and decay of the wood speedily follow.
How is this waste and destruction of wood to be prevented? To a certain extent, by thoroughly drying the timber in a current of air. This, however, takes considerable time to effect. For instance, a large piece of oak requires exposure for eight or ten years to dry it completely. This is demonstrated by the fact that it loses weight for that period. We may apply heat to hasten the process of drying, but the wood, when exposed to the ordinary temperature of the atmosphere, absorbs moisture in quantity varying with the compactness of the wood. In a dry room, without a fire, the quantity of water reabsorbed by wood amounts, on an average, to ten per cent. As long as the albumen of the wood is supplied with sufficient moisture to render it soluble, so long will there be danger of dry rot. The best plan, therefore, to adopt is, to render this albumen perfectly insoluble, so that, however much moisture shall be absorbed, it cannot be brought into an active state again. For this purpose, Sir H. Davy recommended that the wood should be steeped in a solution of corrosive sublimate-a salt, called bichloride of mercury by chemists, which has the property of forming an insoluble compound with the albumen, and thus preventing its further action. This process was commercially applied by Wm. Ryan; but, from the great expense attending the preparation, and the fear that the use of this poisonous salt might prove deleterious to the health of persons coming in contact with it, the employment of corrosive sublimate has been abandoned. Creosote oil, obtained from wood and coal tar, has been used with great success; but this also possesses a disadvantage, as it imparts a disagreeable odor, and increases the inflammability of the wood.
Some of the specimens exhibited by Mr. Payne are prepared, first, by injecting a soluble salt of baryta into the pores of the wood, and then adding solution of sulphate of iron. By this means a compact solid sub. stance is formed, which remains in the wood, thereby increasing its weight, and partly converting it into stone. Sir W. Barnett & Co. have some specimens prepared by injecting chloride of zinc into the pores of the wood. This substance makes the albumen perfectly insoluble, even in sea water, does not communicate any color or odor to the wood,