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CHEMICAL APPARATUS.

Dcstription of tlte Ptale. Our plate to-day represents a gasometer of somewhat different construction to those we have before given; and there are still others, but which we shall not describe, as they are all on the same principles, though some of them may have a different and, perhaps, a more convenient adaptation. The two figures are different views of the same instrument, the same letters referring to both. Like the other, this is made of japanned tin: a a is the outer vessel with a spout at top; d and e are two tubes firmly soldered to the side of the pail, each of them having a stopcock; d penetrates at the bottom of the vessel, and proceeds to the centre, where it joins e, which enters from the top, and proceeds downwards; the place of junction, the upright tube, g, rises through the middle of the pail a little above the upper rim; 6 is a cylinder, open only at the bottom, and of less diameter than the vessel, a a, in which it moves up and down freely; e is a solid stem, which passes from it through the hole in the wooden cross bar of the frame, and serves both to indicate the quantity of gas in the vessel, it being graduated, and to keep the cylinder in a perpendicular direction. There is a scale-dish connected with the top of the cylinder by a cord and pulley, and weights put into this dish serve to balance the weight of the cylinder. There is an opening at f, which has a stop-cock, where the water may be drawn off. To use this gasometer, let the cylinder fall to the bottom. of the outer vessel, and pour water into the latter till it is quite full; then shut the cock, e, open d, and connect it with the vessel supplying the gas; though, if it be more convenient, d may be shut, and e opened. The gas rises through g to the top of the cylinder, b, which it gradually lifts up, care being taken to have weights in the scale-dishto enable it to rise easily. When the supply is complete, shut the stop-cock, and the gas may be kept till wanted. To take away

gas, connect a bent tube with one of the stop-cocks, insert the mouth of it in the vessel which is to receive the gas, open the cock, take the weights out of the scale, and the weight of the cylinder, b, will press out as much gas as is wanted. As the cylinder rises, weight must be continually added to the scale, otherwise the gas would be more and more compressed, and would at last cease to enter.

SKELETON OF A MAMMOTH. The entire skeleton of a large mammoth, or fossil elephant, of the same species as those found in Siberia and in various parts of Europe, has been recently discovered at Ilford, Essex, near Stratford and Bow. It lay buried 16 feet in a large quarry of diluvial loam and clay, which is digging up for inaking bricks. Mr. Gibson, of Stratford, has been diligent in collecting the bones of this skeleton, and a few days back Professor Buckland and Mr. Clift assisted him in digging up the bones, which he had purposely left in the first discovered position. These gentlemen found a large tusk and several of the largest cylindrical bones of the legs, many ribs and vertebrae, with the smaller bones of the feet and tail lying close to one another, making, with those before found by Mr. Gibson, very nearly an entire skeleton, fifteen feet high. They were embedded in tenacious clay, being part of that great superficial covering of diluvial clay, sand, and gravel, which is spread over a large portion of Essex, Suffolk, and Norfolk, and along the whole east coast of England at intervals, and in which has been frequently found remains of ante* diluvial animals.

WATER SPRINGS.

Where the snow melts first in spring, where no dew lies in summer and no frost glitters in autumn, and where no plants but short grasses grow, while the rest of the field bears a good crop, there you may expect concealed beneath the surface a spring of water.

CHEMISTRY AS A SCIENCE. Art. XII.

METALS FORMING, WITH OXYGEN, EARTHY AND NOT ACID SUBSTANCES.

Perhaps we should have placed magnesium, the first article to be treated of in the present paper, in the last; but magnesia, the earthy compound of magnesium and oxygen, is so innocuous compared with lime, and has so much more resemblance to earth than to the acid alkalies, that wc thought the single circumstance of its changing very delicate^ blues to green, did not authorize us to place it among them. Magnesia is probably known to most of our readers, as it is a very common medicine. It exists, combined with sulphuric acid, and is then called sulphat of magnesia, in salt water, and in many springs, particularly in some about Epsom, whence sulphate of magnesia has been named Epsom salts. If this salt be dissolved in water, and half its weight of potash be added, the magnesia is immediately precipitated. It is to be washed with water, and dried and exposed to a red heat. In shops, what is called magnesia is a carbonate of magnesia, and calcined magnesia is the earth in a pure state. Magnesia is usually procured on a large scale by acting on magnesian limestone with what is called bittern, or spirit of salt, it being the uncrystallized residuum, after all the common salt has been made. This is an impure muriate of magnesia, and being mixed with the magnesian limestone, the acid combines with the lime, forming a soluble salt, and leaves behind the magnesia both of the stone and the bittern. Or a crude subcarbonate of ammonia is obtained by distilling bones in iron cylinders: with this the bittern is decomposed, and muriat of ammonia and subcarbonate of magnesia result. The former is evaporated to dryness, mixed with chalk, and sublimed, by which subcarbonate of ammonia is recovered, to be again employed in decomposing a new quantity of bittern.

Magnesia is a white soft powder, having very little taste, and no

smell. This was considered up to the time when Sir Humphrey Davy discovered the metallic base of potassium, as a simple undecompounded substance ; from that discovery he was Jed to suppose that all the earths had.some metallic base, and at length he succeeded in decomposing magnesia. Sulphate of magnesia was moistened and exposed to the action of a galvanic battery, in contact with mercury, the earth was reduced, and its base amalgamated with the mercury. It was found to be a white solid metal, looking like silver, and being considerably heavier than water. When exposed to the air it absorbed oxygen, and was converted into magnesia. To this metal Sir Humphrey Davy gave the name of magnesium, and since then magnesia has been classed as a compound substance, and the metal magnesium as a simple elementary substance. Nothing more than this is known of magnesium. When it is combined with 40 parts in the 100, constituting magnesia, it forms a very considerable portion of the stony crust of the globe; and a large portion of all the matters held in solution by its different waters, is magnesia in combination with some acid.

Yttria is an earth, like magnesia, but it has only been obtained by subjecting two minerals, both of which are found in Sweden, to an elaborate chemical analysis; and it has been made only probable that yttria, like magnesia, has a metallic base, but whether the fame or a different metal is not ascertained.

From the beryl, a transparent green stone of considerable hardness, called also aqua marina, and from the emerald, a white powder is obtained by a long process, which is called glucina. It has been supposed that this earth is a metal combined with oxygen, and to this metal the name of glucinum has been given. Neither the eaith nor the metal has ever been put to any use, and no further knowledge of the least value has ever been acquired of either of them.

Alum is a substance which is probably known to our readers, and has been used for various domestic purposes for many centuries . If this substance be dissolved in water, and ammonia be added to the solution, a precipitate falls down, which, having the fluid poured oil'it, and being washed in water, is alumina. Still it contains, however, a quantity of sulphuric acid, with which it was combined, forming the alum, and this must be driven off by exposing it to a strong heat in a platinum crucible. The earth thus obtained, or alumina, has little taste, and, when pure, no smell; if it contains oxide of iron, however, which it very frequently does, it has that peculiar smell which is called earthy. At first this earth, being known to constitute the plastic principle of clays and loams, was called argil, or argillaceous earth; but subsequently, being obtained in the greatest purity from alum, it was called alumina. It was considered an elementary earth till Sir Humphrey Davy's researches led to the conjecture, that, like barytes and lime, it was a metallic oxide. This conjecture has, in some measure, been verified by some experiments of this chemist, but nothing is known of the properties of the metal which forms the base of alumina. It has, however, been named aluminum, and is considered, with no very good reason, we think, a peculiar elementary substance. It has never been obtained in a separate state, and of course has been put to no use; but the earth alumina is widely diffused through nature, and is extensively employed in the arts. It constitutes a large portion of all clays, and, together with silica, another earth, is the principal ingredient in all porcelain and earthenware. Bricks and crucibles are also made chiefly of alumina. Fullers'-earth, ochres, pipe-clays, are all composed principally of alumina, and derive their valuable properties from it. It is used both in dyeing and scouring, and, as will be seen in another part of our journal, may

be employed to bleach sugars, as well as woollen cloth. Almost all soils, certainly all good soils, contain a considerable quantity of alumina, and derive from it their property of retaining moisture, which is so necessary to the nourishment of plants. Many rocks and minerals consist principally of alumina. It forms also the basis of several gems or precious stones; and as the diamond is crystallized carbon, so the sapphire and the ruby consist, in a great measure, of pure alumina in a state of crystallization.

As alumina is the basis of clays, and constitutes the retentive principle of soils, so silica is the chief ingredient in all sands, and may be considered as the filtering principle of all soils. When these earths are mixed together in proper proportions, the soil is neither too retentive of moisture, nor does it part with it too easily; and certainly Bo soil is good in which both these earths are not met with. Silica, like alumina, is also found crystallized in many parts of the world, and is called rock crystal, a substance resembling regular masses of glass, with which probably most of our readers are acquainted. Silica may be obtained pure by mixing one part of pounded flint or quartz and three parts of potash, and heating the mixture in a silver crucible till it is quite melted. The fused mass is to be dissolved in water; add to the solution as much acid as will saturate the potash, and evaporate to dryness. A white mass remains behind, which, after being washed with plenty of water, is silica in a state of purity. It is a fine white powder, without either taste or smell, with a harsh feel, as if consisting of grains of very fine sand. It may be exposed to a very intense heat without undergoing alteration; but some chemists have fused a small quantity of it. By passing the vapour of potassium over silica in an Ignited state, Sir H. Davy obtained a dark-coloured powder, which he concluded was formed with silicon, the supposed bnso of the earth silica. There is no other reason, except analogy, for believing that the earth silica is a metallic oxide, having for its base the peculiar undecompounded metal silicon.

Zirconia, like silica and alumina, is a primitive earth, but, unlike them, they being widely diffused through the globe, it has been found only in two precious stones, the zircon and the hyacinth, both of which come from the island of Ceylon, though some of the latter are found in other parts of the world. By mixing these stones, reduced to powder, with potash, and heating the mixture, as was mentioned of silica, zirconia is obtained, which possesses many of the characteristics of silica. The two precious stones from which it is obtained are found to consist of it and silica, with a small quantity of iron and nickel in a state of crystallization. Sir H. Davy subjected zirconia, as he did silica, to the test of potassium vapour, and there is the same evidence to conclude zirconia to be a metallic oxide, compounded of a metal, to which the name of zirconium has been given, as there is to conclude silica to be a metallic oxide. It is probable that both are metallic oxides, but not so probable that each has a different metal for its base.

Thorina is an earth obtained from only one or two minerals, and resembles zirconia. The earth has been put to no use; and it is a mere supposition that it has a metallic base to which the name of tltorinum has been given. We have perhaps detained our readers rather longer than we ought with this part of our subject; but in doing so we w»re guided by a wish to make them acquainted with the present state of the science, and shall pass over the remainder of the uninteresting portion of the undecompounded substances with a very slight notice. Among them, however, are those metals of which so much use is made in the arts, and on these we shall bestow a larger space. Iron will be the subjectTof our next article.

ON THE PREPARATION OF THE OXIDE OF URANIUM.

3y Messrs. Lecanu and Serbat.] The authors of this process, after having fused the pulverized mineral (pechblende) with half its weight of nitre, washed the mass which results from the operation, and heated the residuum with nitric acid; evaporated the solution to dryness, and re-dissolved in water acidulated with the same acid; they then added to the solution excess of carbonate of ammonia, which, while it is sufficient to re-dissolve the whole of the oxide of uranium, has no action on the. carbonates of lead and lime. Mr. Laugier, in commenting on the above process, reeommends the use of 14 parts of nitre instead of half a part. The solution containing the nitrate of ammonia and the carbonate of uranium is to be evaporated to a dry mass, and calcined to obtain the pure oxide. Mr. Laugier advises in preference, to wash away with hot water the nitrate of ammonia, and to calcine the remaining carbonate of uranium, which has in the filter a fine lemon yellow colour.—Journal de Pharmacie.

SUGAR BLEACHED BY CLAY. M. Pajot Des Charmes, whose name has before appeared in our journal as the discoverer of a mode of bleaching sugar by chlorine, has more lately announced that pure alumina may be used very advantageously for the same purpose.'To take away completely the colour of a cold solution of sugar of a course quality, he found it was only necessary to agitate this solution for a few minutes with the tenth part of its weight of pure alumina, mix it, after decantation, with a tenth part of its weight of animal black, and then subject it to agitation a second time, with half the quantity of pure alumina before used. This mode of managing the sugar, which is done without fire, and does not require the strainer to be used, is speedily and easily effected, and is very economical. The common coloured clays of the neighbourhood of Paris may be employed to obtain the alumina, if the salts extracted from it are turned to account. Alumina is easily recovered after the operation, by the action of liquid chlorine, or by that of the regulated heat of a reverberatory furnace. The author adds, that clay powdered, sifted, and subjected to a slight degree of ealcination, produces, in that state, a considerable efi'ect. Other coloured syrups may be advantageously bleached by the same method.

PRUSSIATE OF AMMONIA AND IRON.

{From a Correspondent.) Pour into a phial of the capacity of six ounces, three ounces of caustic ammonia upon half an ounce of the finest and purest Prussian blue, reduced to a fine powder. Stop the phial well, and leave the mixture to macerate in the cold for several days, taking care to shake it from time to time. If the deposited matter is become brown, add a new quantity of blue, and repeat this addition until the colour no longer changes. Filter the matter through paper, and pour, by little and little, on the residuum, an ounce of water, in order to separate all the salt. The filtered liquor is prussiate of ammonia and iron; it has a beautiful yellow colour, and a particular odour.

HEATING POWER OF COKE AND WOOD.

Some experiments have lately been made at Paris, where wood is consumed in immense quantities, and is very dear, on the different heating powers of it and coke. The following was the result:—In the Opera House of that capital there are two stoves, placed in two precisely similar situations; one of these stoves was heated with wood, the other with coke. A thermometer was placed near each stove, so as to show the temperature the air acquired. The temperature of the atmosphere was 41°, and that of the air in the neighbourhood of both stoves 62* whea the fire was

first made in them. Tlie fire was kept up in both for five hours, and the average temperature during this time was, of the air in the room of the stove heated by wood, 62°, of the other, 68", so that the heating effect of the coke was nearly double that of the wood. There were employed about 1601 bs. of wood, which cost 3 francs, 10 centimes, and about (itilbs. of coke, which cost 1 franc, 80 centimes, and about 141bs. of this remained, and might be afterwards burnt, while the whole of the wood was consumed. By employing a quantity of coke, therefore, which did not cost half so much money as the weod cost, nearly double the quantity of heat was obtained. As in most parts of England the difference of price between eoke and wood is greater than in Paris, it should be proportionately more advantageous to burn the former than the latter.

HISTORY OF SYMPATHETIC

INKS.

"Heaven (says Pope) first taught letters for some wretch's aid, Some Imuish'd lover, or some captive maid."

And so, on the authority of history, we can assert, Heaven, for much the same purpose, taught man, or rather maidens, the use of sympathetic ink. As long ago as the days of Ovid, we find him recommending the girls who wished to write secret love-letters, to use fresh milk, and the dried writing could be made visible by ashes or by rust. It is quite plain, that any colourless fluid, which is a little sticky when dry, would answer the purpose as well as milk. This is, however, a mechanical sympathetic ink, and hardly falls within the notice of the chemist. Pliny, who was more knowing in such matters than Ovid, though less disposed, it is thought, to put his knowledge into practice, recommended that the milky juice of certain plants should be used for writing such letters. In modern times, the juice of many such plants is known, but in use it is super

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