According to Sir H. Davy, chloride of potassium is constituted of 75 potassium + 67 chlorine, proportions which nearly agree with those stated by Gay Lussac, viz. 111.31 potassium + 100 chlorine. Hence it is composed of 1 atom of potassium, = 40, + 1 atom of chlorine = 36, and its equivalent number is 76. One hundred grains, according to Berzelius, when dissolved in water, and decomposed by nitrate of silver, yield 192.4 of fused chloride of silver, formerly called luna cornea.

When chloride of potassium is dissolved in water, a double elective affinity is supposed to operate; water is decomposed; its hydrogen, uniting with the chlorine, composes muriatic acid; and the oxygen of the water, being transferred to the potassium, constitutes potassa. The acid and alkali together form muriate of potassa. By evaporating the solution, crystals are again obtained of chloride of potassium. These crystals are cubical, have a bitter disagreeable taste; undergo little change when exposed to the air; and when suddenly heated to redness decrepitate, with a very trifling loss of weight, arising from the escape of a little water. They are soluble in three times their weight of water at 60° Fahr. and in a rather less proportion of boiling water.

Considered as muriate of potassa (in which state this salt must always exist when in watery solution), it may be regarded as constituted of an atom of muriatic acid 37, and an atom of potassa 48, and its representative number is 85. this view, it is constituted of

Acid....
Potassa

36.57

63.43

100.

Under

Iodide of Potassium.

This compound may be formed, by heating potassium in a tube of green glass with an excess of iodine. At the moment of combination light appears, which, being seen through the vapour of iodine, has a purple hue.

Iodide of potassium enters into fusion, and is volatilized at a heat below redness. It dissolves readily in water, which,

during solution, it decomposes, forming a neutral hydriodate of potassa. It is constituted of 1 atom of potassium = 40, + 1 atom of iodine = 125, and its representative number is 165; 100 of potassium are combined, therefore, with 319 of iodine

Potassium with Simple Acidifiable Bodies.

With hydrogen, it forms two compounds, the one gaseous, the other solid. The first results from the action of potassium on water, the hydrogen of which, while in a nascent state, dissolves a portion of the metal. It may, also, as appears from Sir H. Davy's experiments, be formed, directly, by heating the metal in hydrogen gas. A large portion of potassium is thus dissolved; but the greater part precipitates on cooling.

This gas is spontaneously inflammable in the atmosphere; burns with a very brilliant light, which is purple at the edges; and throws off dense vapours of potassa. It loses its inflammability by keeping; is heavier than hydrogen gas; and is very dilatable by electricity. Besides the gas, which is spontaneously combustible, there is also, according to Sementini, another compound of potassium and hydrogen, which is not possessed of this property, and probably contains a less proportion of the combustible metal.

Gay Lussac and Thenard* have succeeded, also, in forming a solid compound of potassium and hydrogen. The process consists in heating the metal in hydrogen gas; and the only difficulty is to regulate the heat, for a high temperature decomposes the compound. The flame of a spirit lamp, applied to potassium, in a retort filled with hydrogen gas, occasions an absorption of the gas, and the formation of a solid hydruret of potassium.

The colour of this substance is grey; it is destitute of metallic lustre; and is infusible. It is not inflammable, either in air or in oxygen gas at common temperatures, but burns vividly at a high one. When strongly heated in a close vessel, it is totally decomposed; all the hydrogen it contains is liberated in the state of gas; and the potassium remains. When

* Recherches, i. 176.

brought into contact with heated mercury, hydrogen gas is evolved, and an amalgam of potassium and mercury is produced.

Nitrogen gas has not, at any temperature, any action on potassium.

Potassium with Sulphur.-When sulphate of potassa is decomposed by hydrogen gas or by charcoal at a red heat, the residue is a compound of sulphur and potassium. It is difficult to obtain it perfectly pure, for it acts both on glass and on platinum. When prepared in glass, it has a pale cinnabar colour, and a crystalline fracture; fuses at a heat below redness; and then becomes dark and opaque. It attracts moisture from the air, and dissolves into a yellowish fluid, which, when diluted with water, becomes colourless. This appears to be a sulphuret of the first degree of sulphuration.

By fusing sub-carbonate of potassa with double its weight of sulphur, out of the contact of air, a sulphuret of potassium is formed in which 100 of the metal are united with 207.7 of sulphur, which is equivalent to 10 atoms. Varying the proportions, Berzelius, to whom we owe these facts, obtained sulphurets which he regards as compounds of 1 atom of potassium with 2, 4, 6, 7, 8, 9, and 10 atoms of sulphur.*

When potassium is fused with sulphur, in a vessel filled with the vapour of naphtha, a rapid combination ensues, accompanied with heat and light, and a disengagement of sulphureted hydrogen. The result is a grey sulphuret of potassium not unlike artificial sulphuret of iron. Its formation and properties have been investigated by Vauquelin.†

The phosphuret of potassium may be formed by fusing potassium with phosphorus under naphtha. It requires for its fusion a stronger heat than either of its constituents. It is of the colour of lead; and, when spread out, has a lustre similar to polished lead. By exposure to the air, or by rapid combustion, it forms phosphate of potassa. Besides this, there is, also, a chocolate coloured compound of potassium and phos

* Annals of Phil. N.S. iv. 284.

Ann. de Chim. et Phys. vi. 22.

phorus; so that it is probable these two bodies unite in different proportions, the lead coloured compound consisting of 2 atoms of metal + 1 of phosphorus; and the chocolate of 1 atom of metal + 1 of phosphorus.

Compounds of Potassium with Metals.

With mercury, potassium gives some extraordinary and beautiful results. The combination is very rapid, and is effected by merely bringing the two metals into contact at the temperature of the atmosphere. The amalgam, in which the potassium is in least proportion, seems to consist of about 1 part in weight of basis and 70 of mercury. It is very soft and malleable; but by increasing the proportion of potassium we augment, in a proportional degree, the solidity and brittleness of the compound.

The compound of mercury and potassium may be obtained by an easy and simple process, first pointed out by Berzelius. Mercury, to the depth of a line, is put into a glass capsule, two inches in diameter, with a flat bottom. On this a solution of pure potassa is poured; an iron wire connects the mercury with the negative pole of a galvanic arrangement, which needs not contain more than 20 pairs of plates; and a spiral platina wire, from the positive pole, is immersed in the solution, and kept within about a line from the surface of the mercury. In six hours, the effect is observable, and in 24 is very distinct; for, in that time, more than 1200 grains of mercury will be rendered solid by combination with potassium. Unfortunately, this combination cannot be so decomposed, as to obtain the potassium in a sepa

rate state.

In this state of division, potassium appears to have its affinity for oxygen considerably increased. By a few minutes" exposure to the air, potassa is formed which deliquiates, and the mercury is left pure and unaltered. When a globule is thrown into water, it produces a rapid decomposition and a hissing noise; potassa is regenerated; pure hydrogen disengaged; and the mercury remains free.

The fluid amalgam of potassium and mercury dissolves all

the metals; and in this state of union, mercury even acquires the power of acting on platina.

Potassium unites, also, with gold, silver, and copper; and, when the compounds are thrown into water, this fluid is decomposed, potassa is formed, and the metals are separated unaltered. When the reduction of an ore has been accomplished by the use of fluxes containing potassa, M. Vauquelin has shown that the revived metal contains a greater or less proportion of potassium, which modifies its properties. By exposure to the air, or by the action of water, this impurity may be removed.*

Potassium reduces all the metallic oxides when heated with them, even of those metals which most powerfully attract oxygen, such as oxides of iron. In consequence of this property, it decomposes and corrodes flint and green glass by a very gentle heat; potassa is generated with the oxygen taken from the metal, which dissolves the glass, and exposes a new surface. At a red heat even the purest glass, formed merely of potassa and silex, is acted upon. The alkali in the glass seems to give up a part of its oxygen to the potassium, and an oxide of potassium results, with a less proportion of oxygen than is necessary to constitute potassa. The silica, also, it is probable, is partly de-oxidized.

Salts of Polassa.

Chlorate (Hyper-oxy-muriate) of Potassa.

This salt was discovered by Berthollet. It may be formed either by the direct mixture of liquid chloric acid with solution of potassa or carbonate of potassa;-or by passing -chlorine gas, as it proceeds from the mixture of muriate of soda, sulphuric acid, and manganese, through a solution o caustic potassa. This may be done by means of Woulfe's apparatus, using only one three-necked bottle in addition to the balloon. The tube, which is immersed in the alkaline solution, should be at least half an inch in diameter, to prevent its being choked up by any crystals that may form. The solution, when saturated with the gas, may be gently evaporated, * Aun. de Chim. et Phys. vii. 32.