tate. In order to obtain this precipitate in a state of purity it must be digested in alcohol, which has the property of dissolving any of the matter of the other crystal with which it may be mixed, but does not affect the pure precipitate itself. This precipitate is a salt of a peculiar nature. When thrown upon burning coals it deflagrates like nitre, but not so strongly. When heated to redness it gives out oxygen, and there remains behind a quantity of iodide of potassium; so that it is quite analogous to the hyperoxymuriate of potash or chlorate of potash. Now Gay-Lussac considers this salt as a compound of potash, and an acid combination of iodine and oxygen, to which he gives the name of iodie acid; so that the salt itself is an iodate of potash. The crystals obtained by evaporating the liquid consist of hydriodate of potash, or of iodide of potassium, if it be supposed that no hydriodate of potash exists. Thus it appears, that the phenomena which take place when iodine is dissolved in solution of potash, are precisely of the same nature as those which occur when chlorine gas is made to pass through the same solution.

Such is the evidence for the existence of iodic acid. It has not yet been obtained in a separate state, but it is considered to exist in the detonating salt obtained by dissolving iodine in potash, and in the whole class of analogous salts which may be procured either by similar solutions, or by double decomposition. Let us, therefore, proceed to describe such of the iodates as have been hitherto examined.

(1.) Iodate of potash. This salt may be obtained in small cubes. It deflagrates on burning coals like nitre; it is not altered by exposure to the air. At the temperature of 60° 100 parts of water dissolve 7.43 of this salt. Iodate of potash has very little taste. By the assistance of heat it may be dissolved in nitric, sulphuric, and phosphoric acids. These solutions when saturated congeal, and form crystalline substances, which have an intensely acid taste. When these solutions are strongly heated the iodate is decomposed, iodine being given out. In phosphorous acid the salt dissolves without decomposition, but on heating the solution the phosphorous acid absorbs oxygen, and is converted into phosphoric acid, and iodine is evolved. When the salt is dissolved in muriatic acid an effervescence takes place, chlorine is disengaged, and chlorionic acid formed. Acetic and oxalic acids dissolve the iodate without decomposition.

When iodate of potash is exposed to a dull red heat its oxygen is driven off, and iodide of potassium remains behind. From the experiments of Gay-Lussac, it appears that 100 parts of iodate of potash, when thus treated, yield

But we have seen already that iodide of potassium is composed of

Iodine...

Potassium.

..100

32

Therefore the 77.41 of iodide of potassium are composed of

The 18.76 of potassium require 3.75 of oxygen to convert them into potash. There remain 22.59 -3.75-18.84 of oxygen, which must have been in combination with the 58.65 of iodine, and have converted it into iodic acid. Therefore iodic acid must be composed of

Or one atom of iodine and 5 atoms of oxygen.

(2.) Iodate of soda. This salt may be prepared by the same process as the preceding. It crystallizes in small prisms usually united in tufts. It has but little taste. 100 parts of water, at the temperature of 60°, dissolve 7.3 of this salt. When thrown upon burning coals it deflagrates like nitre; while, at the same time, some iodine is disengaged. When decomposed by heat 100 parts of it give out 24.432 of oxygen gas; the residuum is iodide of sodium. Hence the salt is composed of

Oxygen.
Iodide of sodium.

.24.432

..75.568

100.000

When the solution of iodine in soda, from which the preceding salt was obtained, is evaporated, beautiful hexahedral prisms are deposited, which have an alkaline taste and convert vegetable blues into green. They deflagrate upon burning coals and therefore contain iodic acid. We must therefore consider them as a subiodate of soda. This salt is very soluble in water, and contains a great deal of water of crystallization.

(3.) Iodate of ammonia. This salt is obtained when ammonia is mixed with a solution of chlorionic acid in water: it crystallizes

in small grains. When thrown upon burning coals it deflagrates with a hissing noise. When heated it is decomposed, and a mixture of oxygen gas and azotic gas is disengaged. It is composed, according to the calculation of Gay-Lussac, of

(4.) Iodate of barytes. This salt is easily obtained by dissolving iodine in barytes water, or by mixing the solution of iodate of potash with a barytes salt. It precipitates in powder which is obtained pure after being several times washed. While drying it concretes into lumps, and becomes mealy. It cannot be freed from its water of crystallization by being dried in the temperature of 212°. It is the least soluble of all the iodates; 100 parts of boiling water dissolve only 0.16 of it, and 100 parts of water at 60° dissolve only 0.03. When heated it gives out water, oxygen gas, and iodine; and barytes remains behind in a state of purity. When thrown on burning coals it does not deflagrate, but gives out now and then a weak light. This must be ascribed, chiefly at least, to the infusibility of the salt. It is composed of

(5.) Iodate of strontian. This salt may be obtained by the same process as the preceding salt. It crystallizes in small octahedrons. 100 parts of water, at 212°, dissolve 0.73 of it, and at 60°, 0.24. When heated it gives out water, oxygen gas, and iodine, while strontian remains behind in a state of purity.

(6.) Iodate of lime is usually in the state of powder; but it may be obtained crystallized in small four-sided prisms by dissolving it in hydriodic acid, and evaporating the solution. 100 parts of water, at 212°, dissolve 0.98 of this salt, and at 60°, 0.22. Its water of crystallization, according to Gay-Lussac, amounts to 3 per cent. When heated sufficiently, it is decomposed precisely in the same manner as the iodates of barytes and strontian.

(7.) Few of the other iodates have been examined. The following are all the facts at present known on the subject. When nitrate of silver and iodate of potash are mixed, iodate of silver falls in the state of a white precipitate, which dissolves very readily in ammonia. Oxide of zinc being digested in chlorionic acid, forms a pulverulent salt which deflagrates on burning coals, and is therefore an iodate of zinc. Salts of lead, mercury, iron, bismuth, and copper, when mixed with iodate of potash, furnish precipitates consisting of the iodates of the respective metals.

The solutions of manganese, and of peroxide of mercury, yield no precipitates when thus treated.

VI. Such are the properties of iodine, and such the compounds which it forms with the simple combustibles and the simple supporters of combustion. We have still to notice some curious combinations which it forms with the compound combustibles.

(1.) Hydriodic ether. This curious compound was discovered by Gay-Lussac. He mixed together equal measures of absolute alcohol and hydriodic acid of the specific gravity 1.7, and distilled the mixture in a water-bath. He obtained an alcoholic liquor perfectly neutral, colourless, and limpid, which, when mixed with water, became muddy, and let fall in small globules a liquid at first milky, but which became gradually transparent. This liquid is hydriodic ether. What remained in the retort was hydriodic acid coloured with iodine.

Hydriodic ether, when well washed in water, is perfectly neutral. It has a strong peculiar odour, analogous to that of the other ethers. After some days it acquires a red colour, which does not increase in intensity. Its specific gravity is 1.9206. It boils at the temperature of 148° 5. It is not inflammable; but when poured on burning coals exhales a purple vapour. Potassium may be kept in it without alteration." Neither potash, nitric acid, chlorine, or sulphurous acid, produce any immediate change in it. When passed through a red-hot tube it is decomposed. The products are, an inflammable gas, hydriodic acid, and charcoal. This ether has not been analyzed; but if we consider it as analogous to muriatic ether, it will be a compound of two volumes of hydriodic acid gas, and one volume of vapour of alcohol. On this supposition it is composed, by weight, of

Acid.
Alcohol..

• ....

..100.00
18.55

(2.) Iodide of starch. This compound was first formed by MM. Colin and Gaultier de Claubry, who have published a detailed description of it. If starch and iodine be triturated together in a mortar they speedily combine, and the colour of the compound varies according to the proportion of the ingredients. If the starch exceed, the colour is reddish; if the iodine be in excess, the colour is black; but it is of a beautiful blue when the ingredients are united in the requisite proportions to saturate each other. This blue neutral compound may always be obtained with ease by dissolving the iodide formed by trituration in potash, and precipitating by a vegetable acid. When this compound is boiled for some time in water, a colourless evolution is obtained, part of the iodine being driven off; but if iodine be added to

the solution, or if the water evaporated be poured back again, the blue colour is restored. This iodide is soluble likewise in alkalies, and the solution is colourless; but it is immediately precipitated of its natural blue colour, if an acid be poured into the alkaline solution. The acids dissolve this iodide without destroying the blue colour, unless they be sufficiently concentrated and powerful to decompose the starch. Heat does not alter the iodide of starch, unless it be sufficiently high to decompose the starch. In that case a quantity of hydriodic acid is

formed.

VII. It now only remains to mention the different methods that have been contrived to detect the presence of iodine when present in small quantity in saline solutions. It has the property of corroding metals, and especially of blackening silver more powerfully than any other body at present known. It was this property that led to its original discovery in kelp. Sir Humphry Davy employed its property of blackening silver as a method of detecting it in the solutions of the ashes of different sea-weeds.

When sulphuric acid is poured upon a dry salt containing iodine, a reddish brown liquid is obtained This is a good method of detecting the presence of iodine in salts.

But the most delicate re-agent for iodine, according to Stromeyer, is starch. When this substance is put into a liquid containing jodine in a state of liberty, it detects the presence of so small a quantity as part, by the blue colour which it forms. But he has given us no directions of the method of using this re-agent.

Such is a pretty full detail of the properties of iodine, and of the compounds which it forms with other bodies. If the reader has paid sufficient attention to the properties which we have de scribed, he will be able, without difficulty, not only to appreciate the long details into which some chemists have entered; but even to foretell the action of iodine on those bodies which we have omitted to notice. So that the theory of this curious body may be looked upon as almost complete.

ART. XVII.-The White Doe of Rylstone; or, the Fate of the Norions: a Poem. a Poem. By William Wordsworth. pp. 162. 4to. London, Longman and Co.

IT is usually thought a recommendation of any poem to say, that it is popular. But are the most popular poems always those