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king himself acquainted with that Between each pair of plates there was science. For some years past, che- a cell, these cells were filled with a limistry has become the prominent ob- quid, and the trough was fit for ac, ject of investigation, and has, in tion. Various liquids were used, but some measure, supplanted the other the most efficacious was found to be sciences. It is in chemistry, there. a very weak nitric acid. Very confore, that the greatest number of dis- siderable improvements were gradual. coveries are to be expected : it occu- ly introduced into the trough, both pies the fore-ground of the picture; in the size and shape, and position of we shall therefore commence our his. the plates. The latest

and most aptory with that science.

proved form is this : The trough is 1. The most splendid discoveries made of stone-ware, and is divided inin chemistry which have been made to cells by diaphragms of stone-ware, in modern times, owe their existence about three quarters of an inch disto an apparatus invented by Volta, tant from each other.

The plates an Italian philosopher of great emi- are cut square, having a slip attached nence, and first described by him in to the upper part of each, about an the Philosophical Transactions for inch high, and thicker than the rest.

He found, that when plates These slips only are soldered togeof copper, plates of zinc, and wet ther, so that there is a certain distance cloths were piled above each other in between the two plates at every part, regular order, placing the copper low- except where they are soldered. est, then the zinc, then the wet cloth, Each pair is let down into the trough, then copper again, then zinc, then so that there is a diaphragm of stonethe wet cloth, and always observing ware between the plates. The lithe same order till 40 or 50 pairs of quid is then poured in, and the the plates, with wet cloths between trough is fit for action. them, were raised into a pile, then if Almost all the discoveries in che. the finger of one hand be brought in mistry, which have resulted from the contact with the bottom of the pile, use of the galvanic trough, have and the finger of the other hand with been made in England. Messrs Nithe top of the pile, an electrical shock cholson and Carlisle discovered, that is felt at the instant of contact. If if a wire of platinum or gold be at. a wire be made to pass from the bot- tached to the extremity of the trough tom to the top, so as to complete at which the zinc plate is, (which we the circuit, a current of electricity shall call the zinc end,) and a similar passes through the pile, and conti- wire to the copper end, if these two nues to pass for a considerable time; wires be introduced into a glass of wa. this pile got the name of the Galva- ter, and placed within a small distance nic Pile, because some discoveries of of each other, the water will be decomGalvani gave birth to the investiga- posed, the oxygen gas being separated tions which led to the discoverv of it. from the wire attached to the zinc The galvanic apparatus soon under- end, which is the positive end, and

went considerable improvements. In the hydrogen gas from the wire atLastead of the pile, Mr Cruickshanks tached to the negative or copper end.

substituted a trough of wood, into By the subsequent experiments of which each pair of plates, previous- Cruickshanks, Wollaston, Davy, &c. ly soldered together, was cemented. it was found that other substances

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besides water-for example, nitric a. stant or two, it becomes sufficiently cid, sulphuric acid, ammonia, metale moist on the surface to conduct eleco lic oxides, &c.—were decomposed by tricity. If, in this state, it be placed the same energy, and that the power upon a disc of platinum, connected of decomposing depended upon the with the negative extremity of the size of the trough.

galvanic trough, and a platinum wire But Mr Davy is the person to from the positive extremity of the whom we are indebted for the most trough be made to touch it, gas is important discoveries respecting the evolved, and small metallic globules, action of the galvanic trough. By similar to globules of mercury, make a most ingenious and satisfactory set their appearance. New experiments of experiments, he succeeded in de informed him, that the gas evolved monstrating that galvanism has the was oxygen, and that the potash, by property of decomposing all com- the galvanic energy, had been decompound bodies, provided it be suffi. posed into oxygen and the metallic ciently strong, that oxygen and acids substance. One hundred pair of always separate at the wire in con- plates of 6 inches square form a galtact with the positive end of the vanic battery sufficiently powerful trough, while hydrogen, alkalies, to decompose potash. Soda is likeearths, and metals, accumulate round wise decomposed by the same means, the negative pole. Galvanism then, but it requires a more powerful bat. or electricity, is capable of destroying tery. Thus Mr Davy ascertained chemical affinity, however powerful, that potash and soda are metallic and of producing repulsion and con- oxides. To the metals which consti. sequent separation between particles tute their basis he gave the names of of matter, however intimately com. potassium and sodium. bined. From this curious and unex. These bodies differ exceedingly pected law, Mr Davy drew, as an in- from all the metals with which we ference, that when bodies unite che- were previously acquainted. By the mically, they are in opposite states of galvanic battery, they could only be electricity, the one negative, the obtained in small globules ; but other positive ; and that when they Thenard and Guy Lussac, two are brought to the same state they French chemists, discovered a meno longer remain united, but repeland thod of obtaining them in consider. immediately separate from each other. able quantity. Into a bent gun.

2. It had long been the opinion of barrel, previously coated on the out. chemists, that the fixed alkalies are side with clay, a quantity of iron compounds, but all attempts to de- turnings are introduced ; the guncompose them had entirely failed. It barrel is then placed in a furnace in occurred to Mr Davy, that the gal- 'such a manner that the iron turnings vanic battery, which he had found so can be raised to a very high temperapowerful an instrument of decompo- ture. To one end of the gun-barrel sition, might be successfully used to a bent glass tube is luted, containing separate the constituents of these bo- some mercury, in order effectually to dies from each other. Various un- exclude the air. To the other exsuccessful trials were made ; at last tremity an iron stopper is ground, he found that, when a piece of potash containing about two ounces of potis left exposed to the air for an in- ash, previously exposed to a red

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heat. When the iron turnings are water, with which alcohol, ether, and raised to a white heat, the potash is other similar fluids are always contamelted by means of a chauffer, and minated. The liquid, in which it suffered to pass slowly through the can be preserved for the greatest turvings. It is decomposed; hy- length of time unaltered, is newlydrogen gas rushes out of the glass distilled naphtha : Oil of turpentine tube in abundance, and after the pro- likewise answers pretty well. Hydrocess is at an end, the potassium is gen gas dissolves it in considerable found towards the extremity of the quantity when assisted by heat, and gun-barrel to which the glass tube forms a compound gas, to which Davy is luted. This process has not hi- has given the name of pot-assureted therto succeeded in furnishing sodi- hydrogen.

It combines with various doses of 3. Potassium possesses the follow- oxygen, and of course forms different ing properties, as ascertained by Mr oxides. The peroxide is readily Davy. Its colour is white like that formed by fusing together potassium of mercury. At the temperature of and potash. It has a brown colour 100° Fahrenheit, it is as Auid as when hot, but on cooling becomes mercury; at 50° it is a soft and grey. When exposed to the air, it malleable solid ; while at 32° it is absorbs more oxygen, and becomes hard, brittle, and crystallized in fa- potash. There is reason to conclude cets.

It is much lighter than any from some of Mr Davy's recent ex. other metallic body known, swim- periments, that potassiumis capable of ming in all liquids, even the lightest uniting with a greater proportion of oils. Mr Davy estimated its specific oxygen than exists in potash, and of gravity at 0.770. Its affinity for forming a peroxide, which readily oxygen is so great, that it cannot be gives out oxygen when heated. left exposed to the atmosphere with- Potassium combines readily with out instantly changing its state. sulphur and phosphorus, and with The surface is immediately covered all the metals hitherto tried. These with a coat of potash, which absorbs alloys are destroyed by water or air, water ; this water is decomposed, the potassium being converted into new potash formed, and in a very potash, and the other metal set at lishort time the whole mass is convert- berty. One part of potassium rened into liquid potash. When thrown ders 70 parts of mercury solid, and upon water, it decomposes that lic forms with it a soft amalgam, which quid with great rapidity, hydrogen is speedily decomposed by water, gas is evolved, which holds a little of hydrogen gas being evolved, potash the potassium in solution, and, in con- formed, and the mercury set free. sequence takes fire as soon as it comes Potassium is capable of decomposing in contact with the air. This combus. all the metallic oxides, and likewise tion kindles the potassium, which in. all salts hitherto tried. A very costantly burns with a kind of explo- pious set of experiments on the subsion. One grain of potassium, when ject was made by Thenard and Guy thrown into water, evolves 1.0625 Lussac. Most of the decompositions cubic inches of hydrogen gas. Potas- were accompanied by combustion. sium, in like manner, decomposes the It follows, from Mr Davy's ex.

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periments, that potash is composed alkalies likewise. This is a rude and of 86 potassium,

rather unforeseen shock to the theory 14 oxygen,

of that ingenious philosopher, and

points out the impropriety of con100

structing a language upon the prinor the oxygen in potash amounts to ciples of theory alone, as was the about one-seventh of its weight. case with the chemical nomenclature

4. The properties of sodium are contrived by the French chemists, very analogous to those of potas- a nomenclature extravagantly praisium.

sed, but defective and erroneous in It is a white metal like silver, and some of its most material parts. at the common temperature of the 5. The striking analogy between atmosphere is solid, but very mallea- the four alkaline earths, barytes, ble, and so soft that two pieces of it strontian, lime, and magnesia, and the may be welded together by simple fixed alkalies, rendered it probable pressure. It begins to melt at 120°, that they were similar also in their and is completely fluid at 180°. It composition. Indeed it had been does not volatilize at a heat sufficiently long the opinion of certain chemists, strong to melt plate-glass. Its spe. that the earths are metallic oxides, cific gravity is 0.9348.

and Lavoisier had stated the probabiIts affinity for oxygen is similar to lity of this opinion in his Elements. that of potassium. Like potassium, It was natural for Mr Davy, after it is converted into soda by simple having succeeded in decomposing the exposure to the air, and when thrown fixed alkalies, to apply the same meupon water, decomposes that liquid thod of analysis to the alkaline earths; rapidly, hydrogen gas being evolved. but his first attempts were not crown. It is not soluble in hydrogen gas. ed with success. Hence the reason why it does not He tried to decompose them by burn when thrown upon water like the action of the galvanic battery potassium. Like potassium, it com. under naphtha, having previously bines with various doses of oxygen. moistened them slightly to make It combines likewise with phospho- them conductors. In these cases inrus, sulphur, and the metals, and flammable gas was evolved, and the forms alloys as easily decomposable earths, where in contact with the neas the alloys of potassium.

gative wires, soon became dark-coSoda, according to the experi- loured, and small metallic points apments of Mr Davy, is composed peared, which became white when ex. of 78 sodium,

posed to the air. In these experi. 22 oxygen,

ments there was reason for believing

that the earths had been decompo100

sed; but the quantity of metallic matThusit has been ascertained, that both ter evolved was so minute as to elude the fixed alkalies are metallic oxi. examination. des: a discovery quite unexpected An attempt was made to decomby chemists, which destroys the pro- pose the alkaline earths, by heating priety of the term oxygen, invented them with potassium in glass tubes ; by Lavoisier ; since that principle is but it did not succeed. The earths, , not only the former of acids but of indeed, became dark-coloured, but the glass was always acted on, and no ficult to drive off the whole of it, and metallic globules were obtained. Mix- obtain the metallic basis of the earth tures of potash and the earths were in a state of purity. fired together, and then exposed to 6. The metallic basis of barytes, the action of the galvanic battery. obtained in this way, is a white meBy this means metallic globules were tal like silver, solid at the usual temobtained less fusible than potassium, perature of the atmosphere, but be. and which, when exposed to the air, coming fluid before ignition. When were converted into potash and a heated it acts violently on the glass white powder. Hence they must vessel in which the experiment is have been alloys of potassium and made. It flattened by pressure, but the basis of the earth employed. required a considerable force for this

When the earths were mixed with effect. When exposed to the air, it a portion of red oxide of mercury, rapidly tarnished, and fell into a white and exposed to the action of the gal. powder, which was barytes. When vanic battery, globules were obtain. thrown into water it sunk to the bot. ed, which were alloys of mercury and tom ; hydrogen gas was evolved, and the earthy basis of the earth employ- it was converted into barytes. It is ed. But these globules did not in- 4 or 5 times heavier than water. crease after the first application of When confined with oxygen gas, it the galvanic battery, and they were absorbs a portion of it, and is contoo minute for accurate examination. verted into barytes. Hence it folMr Davy at last succeeded in ob- lows, that barytes is a compound of taining satisfactory results, by em. this metal and oxygen. The metal ploying a method suggested by Pro- of barytes has been distinguished by fessor Berzelius of Stockholm. A the name of barium. portion of the earth to be decompo- The metal of strontian possesses sed was placed upon a disc of plati- nearly the same characters with that num connected with the positive ex- of barytes, excepting that, when ex. tremity of the galvanic battery, a posed to the air, or thrown into wa. globule of mercury was placed upon ter, it absorbs oxygen, and is convert. the earth, and a wire from the nega. ed into strontian. It has received tive extremity of the battery was the name of strontium. brought in contact with the mercu. The metal from lime is of a similar ry. The earth was decomposed, and nature. When heated it burns with its metallic basis formed an amalgam a white light and great brilliancy. It with the mercury. To facilitate the has received the name of calcium. process, Mr Davy usually mixed the The metal of magnesia is similar alkaline earth with a portion of red in appearance to the others. When oxide of mercury. The amalgam exposed to the air, or thrown into thus obtained was put into a glass water, it is converted into magnesia. tube filled with naphtha; the naph. It is much more easily obtained from tha was boiled off, and while the sulphate of magnesia than from pure tube was filled with the vapour of magnesia ; probably in consequence that fluid, it was hermetically sealed. of the insolubility of this last in waHeat was then applied to drive off ter. This metal has received thethe mercury. It was easy to drive name of magnium. off a portion of the mercury, but dif- 7. There are five substances which

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