heat. When the iron turnings are raised to a white heat, the potash is melted by means of a chauffer, and suffered to pass slowly through the turnings. It is decomposed; hydrogen gas rushes out of the glass tube in abundance, and after the process is at an end, the potassium is found towards the extremity of the gun-barrel to which the glass tube is luted. This process has not hitherto succeeded in furnishing sodi

um.

3. Potassium possesses the following properties, as ascertained by Mr Davy. Its colour is white like that of mercury. At the temperature of 100° Fahrenheit, it is as fluid as mercury; at 50° it is a soft and malleable solid; while at 32° it is hard, brittle, and crystallized in facets. It is much lighter than any other metallic body known, swimming in all liquids, even the lightest oils. Mr Davy estimated its specific gravity at 0.770. Its affinity for oxygen is so great, that it cannot be left exposed to the atmosphere without instantly changing its state. The surface is immediately covered with a coat of potash, which absorbs water; this water is decomposed, new potash formed, and in a very short time the whole mass is converted into liquid potash. When thrown upon water, it decomposes that liquid with great rapidity, hydrogen gas is evolved, which holds a little of the potassium in solution, and, in consequence takes fire as soon as it comes in contact with the air. This combustion kindles the potassium, which instantly burns with a kind of explosion. One grain of potassium, when thrown into water, evolves 1.0625 cubic inches of hydrogen gas. Potassium, in like manner, decomposes the

water, with which alcohol, ether, and other similar fluids are always contaminated. The liquid, in which it can be preserved for the greatest length of time unaltered, is newlydistilled naphtha: Oil of turpentine likewise answers pretty well. Hydrogen gas dissolves it in considerable quantity when assisted by heat, and forms a compound gas, to which Davy has given the name of pot-assureted hydrogen.

It combines with various doses of oxygen, and of course forms different oxides. The peroxide is readily formed by fusing together potassium and potash. It has a brown colour when hot, but on cooling becomes grey. When exposed to the air, it absorbs more oxygen, and becomes potash. There is reason to conclude from some of Mr Davy's recent experiments, that potassium is capable of uniting with a greater proportion of oxygen than exists in potash, and of forming a peroxide, which readily gives out oxygen when heated.

Potassium combines readily with sulphur and phosphorus, and with all the metals hitherto tried. These alloys are destroyed by water or air, the potassium being converted into potash, and the other metal set at liberty. One part of potassium renders 70 parts of mercury solid, and forms with it a soft amalgam, which is speedily decomposed by water, hydrogen gas being evolved, potash formed, and the mercury set free. Potassium is capable of decomposing all the metallic oxides, and likewise all salts hitherto tried. A very copious set of experiments on the subject was made by Thenard and Guy Lussac. Most of the decompositions were accompanied by combustion.

It follows, from Mr Davy's ex.

of 86 potassium,

14 oxygen,

100

or the oxygen in potash amounts to about one seventh of its weight.

4. The properties of sodium are very analogous to those of potas

sium.

It is a white metal like silver, and at the common temperature of the atmosphere is solid, but very malleable, and so soft that two pieces of it may be welded together by simple pressure. It begins to melt at 120°, and is completely fluid at 180°. It does not volatilize at a heat sufficiently strong to melt plate-glass. Its specific gravity is 0.9348.

Its affinity for oxygen is similar to that of potassium. Like potassium, it is converted into soda by simple exposure to the air, and when thrown upon water, decomposes that liquid rapidly, hydrogen gas being evolved. It is not soluble in hydrogen gas. Hence the reason why it does not burn when thrown upon water like potassium. Like potassium, it combines with various doses of oxygen. It combines likewise with phosphorus, sulphur, and the metals, and forms alloys as easily decomposable as the alloys of potassium.

Soda, according to the experiments of Mr Davy, is composed of 78 sodium, 22 oxygen,

100

Thus it has been ascertained, that both the fixed alkalies are metallic oxides a discovery quite unexpected by chemists, which destroys the propriety of the term oxygen, invented by Lavoisier; since that principle is not only the former of acids but of

rather unforeseen shock to the theory of that ingenious philosopher, and points out the impropriety of constructing a language upon the principles of theory alone, as was the case with the chemical nomenclature contrived by the French chemists,— a nomenclature extravagantly praised, but defective and erroneous in some of its most material parts.

5. The striking analogy between the four alkaline carths, barytes, strontian, lime, and magnesia, and the fixed alkalies, rendered it probable that they were similar also in their composition. Indeed it had been long the opinion of certain chemists, that the earths are metallic oxides, and Lavoisier had stated the probability of this opinion in his Elements. It was natural for Mr Davy, after having succeeded in decomposing the fixed alkalies, to apply the same method of analysis to the alkaline earths; but his first attempts were not crowned with success.

He tried to decompose them by the action of the galvanic battery under naphtha, having previously moistened them slightly to make them conductors. In these cases inflammable gas was evolved, and the earths, where in contact with the negative wires, soon became dark-coloured, and small metallic points appeared, which became white when exposed to the air. In these experiments there was reason for believing that the earths had been decomposed; but the quantity of metallic matter evolved was so minute as to elude examination.

An attempt was made to decompose the alkaline earths, by heating them with potassium in glass tubes; but it did not succeed. The earths, indeed, became dark-coloured, but

the glass was always acted on, and no metallic globules were obtained. Mixtures of potash and the earths were fired together, and then exposed to the action of the galvanic battery. By this means metallic globules were obtained less fusible than potassium, and which, when exposed to the air, were converted into potash and a white powder. Hence they must have been alloys of potassium and the basis of the earth employed.

When the earths were mixed with a portion of red oxide of mercury, and exposed to the action of the gal vanic battery, globules were obtain ed, which were alloys of mercury and the earthy basis of the earth employed. But these globules did not in crease after the first application of the galvanic battery, and they were too minute for accurate examination. Mr Davy at last succeeded in obtaining satisfactory results, by employing a method suggested by Professor Berzelius of Stockholm. A portion of the earth to be decomposed was placed upon a disc of platinum connected with the positive extremity of the galvanic battery, a globule of mercury was placed upon the earth, and a wire from the negative extremity of the battery was brought in contact with the mercury. The earth was decomposed, and its metallic basis formed an amalgam with the mercury. To facilitate the process, Mr Davy usually mixed the alkaline earth with a portion of red oxide of mercury. The amalgam thus obtained was put into a glass tube filled with naphtha; the naph. tha was boiled off, and while the tube was filled with the vapour of that fluid, it was hermetically sealed. Heat was then applied to drive off the mercury. It was easy to drive off a portion of the mercury, but dif

ficult to drive off the whole of it, and obtain the metallic basis of the earth in a state of purity.

6. The metallic basis of barytes, obtained in this way, is a white metal like silver, solid at the usual temperature of the atmosphere, but becoming fluid before ignition. When heated it acts violently on the glass vessel in which the experiment is made. It flattened by pressure, but required a considerable force for this effect. When exposed to the air, it rapidly tarnished, and fell into a white powder, which was barytes. When thrown into water it sunk to the bottom; hydrogen gas was evolved, and it was converted into barytes. It is 4 or 5 times heavier than water. When confined with oxygen gas, it absorbs a portion of it, and is converted into barytes. Hence it follows, that barytes is a compound of this metal and oxygen. The metal of barytes has been distinguished by the name of barium.

The metal of strontian possesses nearly the same characters with that of barytes, excepting that, when exposed to the air, or thrown into water, it absorbs oxygen, and is converted into strontian. It has received the name of strontium.

The metal from lime is of a similar nature. When heated it burns with a white light and great brilliancy. It has received the name of calcium.

The metal of magnesia is similar in appearance to the others. When exposed to the air, or thrown into water, it is converted into magnesia. It is much more easily obtained from sulphate of magnesia than from magnesia; probably in consequence of the insolubility of this last in water. This metal has received the name of magnium.

pure

7. There are five substances which

are considered as possessing the properties of earths in the greatest perfection, and which some chemical writers have, on that account, called earths proper. These are silica, alumina, glucina, yttria, and zirconia. After the decomposition of the alkalies and alkaline earths, it was natural for Mr Davy to turn his attention towards these bodies, in order to as certain whether they are not metallic oxides like the fixed alkalies and alkaline earths. Silica and alumina are the most important of these bodies. Their properties have some resemblance to several of the saline bodies. It was, therefore, necessary to ascertain, in the first place, whe. ther they might not be compounds of an acid with some unknown base. When silica was exposed to the action of the galvanic battery, in a golden vessel filled with pure water, potash was evolved; but it was found to be only mixed with the silica, and to have been derived from the potash employed in the original preparation of the silica. The silica itself was not found to be acted on by the galvanic battery thus applied. Hence there was no reason to consider it as a salt.

None of the earths proper are altered when exposed in a state of purity to a powerful galvanic battery. When melted with potash, and exposed to the action of the battery, while still in a state of fusion, metallic globules separate, swim on the surface, and burn with great brilliancy, and small metallic scales remain attached to the platinum wire employed to complete the circuit. These scales burn spontaneously when exposed to the air, and potash and an earthy matter are formed. The same substances are formed if the scales be thrown into water. When an amal

gam of potassium, in contact with any of the earths proper under naphtha, is exposed to the galvanic energy for some time, if it be thrown into water, not only potash but an earthy matter likewise is formed. From these and several similar experiments made on the earths proper by Mr Davy, it is rendered probable that they likewise are metallic oxides. He proposes to distinguish their metallic bases by the names of silicium, alumium, zirconium, glucium, and yttrium.

8. Ammonia is an alkali, the constituents of which were first pointed out by Scheele, and more accurately determined by the experiments of Berthollet. These philosophers had shewn it to be a compound of hydrogen and azote, and M. Berthollet's experiments were considered as rigid. ly accurate. They had been confirmed by those of Dr Austine. Both of these gentlemen had established that ammonia is composed of nearly four parts by weight of azote, and one part of hydrogen; a determination which was acceded to by all chemists without exception. But after Mr Davy had demonstrated the existence of oxygen in the fixed alkalies, analogy led him to look for it also in ammonia, which is a volatile alkali. He made a set of experiments accordingly, and convinced himself that ammonia is a triple compound of azote, hydrogen, and oxygen. But his experiments were not of that conclusive nature as to produce conviction. But it induced Dr Henry and M. Berthollet, junior, to repeat the analysis of ammoniacal gas with every possible precaution, in order to determine whether oxygen be present in it or not. The method employed originally by Dr Priestley and Berthollet was followed by both these philosophers. Ammoniacal gas, made

as dry as possible, is let up into a glass tube, and exposed to the action of repeated electrical shocks. Its bulk is nearly doubled, and it is converted into a mixture of azote and hydrogen gases. This mixture is fired with oxygen gas, and by that means the proportion of hydrogen present determined, from which it is easy to deduce the proportion of azote. This experiment requires many precautions to secure accuracy. The mercury over which the gas is received ought to be newly boiled, in order to remove all moisture, and the gas itself ought to be well dried by means of pieces of dry potash placed for some time in contact with it.

The result of the experiments of Henry, Berthollet, and the new analysis of Davy, very nearly coincide. By electricity, 100 measures of ammoniacal gas are expanded to 180 measures, and these consist of 74 measures of hydrogen and 26 measures of azote per cent. These experiments do not indicate the presence of any oxygen: azote and hydrogen are the only constituents evolved.

But there is a very extraordinary experiment, first made by Berzelius, and afterwards confirmed and varied by Mr Davy, which it is necessary to consider before we draw any final conclusions respecting the constituents of ammonia. If you take a lump of sal ammoniac, moisten its surface so far as to make it a conductor of electricity, and placing a globule of mercury in a hollow previously made in its surface, bring it in contact with a disc of platinum connected with the positive extremity of a galvanic battery, while a wire proceeding from the negative end of the battery is brought in contact with the globule of mercury, the mercury thus circumstanced gradually swells up to

about five times its usual bulk, loses a good deal of its fluidity, and assumes the consistence of butter. In short, it is converted into an amalgam; of course the mercury has combined with a metallic body. If this amalgam be plunged into water, a portion of hydrogen gas is disengaged, the mercury immediately resumes its original state, and some ammonia is found. dissolved in the water. From these facts it is scarce possible to avoid concluding, that, by the galvanic energy, assisted by the presence of the mercury, the ammonia has been decomposed, that its basis is a metal which amalgamates with the mercury, that when the amalgam is plunged into water, the metallic basis decomposes the water, combines with its oxygen, and is converted into ammonia, while the hydrogen of the water is set at liberty. But, if these conclusions be well founded, it follows that ammonia is a compound of a metallic basis and oxygen; a conclusion very different from that drawn from the decomposition of ammonia by electricity. This metallic substance evolved from ammonia by the galvanic energy has received the name of ammonium. All attempts to procure it, except in the state of an amalgam, have entirely failed. Indeed the quantity of it present in the mercury is so small as to bid defiance to our methods of investigation. A globule of mercury weighing 50 grains combines only with about a grain of ammonium. That so minute a portion of matter added to the mercury should make so great an alteration in its properties, is one of the most extraordinary facts hitherto observed in chemistry.

th part of

In order to reconcile this experiment with the analysis of ammonia by ordinary electricity into hydrogen