108 On Iodine. [Fbb. 



cxide of manganese, with red lead, or the brown oxide of lead, 

 iodine is disengaged, and the oxides are brought into a state of 

 solubility in acids. The red oxide of mercury does not regenerate 

 iodine. We may conclude that all the oxides capable of changing 

 muriatic acid into chlorine will convert the new acid into iodine. 

 When the new acid is dissolved in water, and subjected to the 

 action of the galvanic pile, iodine makes its appearance at the 

 positive pole. When this acid has once entered into a combina- 

 tion, it is not easily disengaged again; for example, when sulphuric 

 acid is brought into contact with the combination of the new acid 

 and potash, sulphurous acid is formed and iodine is disengaged. 

 Nitric acid in the same way furnishes nitrous acid. If the phos- 

 phoric or boraeic acid be employed, either dry, or in solution in 

 water, no decomposition takes place. 



It is easy to conceive, from what has been stated, what happens 

 when iodine is placed in contact with other bodies. 



With hydrogen at a low or high temperature the acid is ob- 

 tained : but the acid is usually impure, because it has the pro- 

 perty of dissolving a great quantity of iodine, and of defending it 

 from the contact of the hydrogen. 



Sulphureted hydrogen speedily deprives iodine of its colour, and 

 converts it to an acid, while sulphur is deposited. It produces the 

 same effect, when the new substance is in combination with the 

 alkalies, forming brown and colourless solutions. It is to be ob- 

 served tliat, when a solution of iodine in ether or alcohol is preci- 

 pitated by sulphureted hydrogen, no sulphur is deposited. 



Sulphurous acid speedily converts iodine into an acid, passing 

 itself to the state of sulphuric acid. Phosphorous acid and the 

 sulphureted sulphites likewise produce the same acid. Hence we 

 may conclude that in kelp, which contains a good deal of sul- 

 phureted sulphite, the new substance is in the state of an acid. It 

 does not appear in the mother ley of that substance till the sul{)hu- 

 reted sulj)hites are destroyed. 



Iodine is not altered by charcoal and sulphurous acid, because 

 tliese substances cannot furnish it with hydrogen to convert it into 

 an acid. It does not decompose water at any temperature. It 

 deprives indigo of its colour. It is separated from its combinations 

 by the mineral acids, and even by acetic acid. It conabines with 

 inost of tlie metals without disengaging any gas. When some of 

 these combinations are made to take place under water, as, for 

 example, the combination of iodine and zinc, nothing is disen- 

 gaged. The liquor, at first strongly coloured, becomes by degrees 

 as limpid as water. The alkalies precipitate from it a matter which 

 has all the characters of oxide of zinc, but which retains a little of 

 the new acid. Here the water has been decomposed, and oxide of 

 zinc and the new acid produced. This compound, like all those 

 that contain the new acid, gives out sulphurous acid when treated 

 with sulphuric acid. 18 parts of iodine dissolve about 3-i^ of zinc. 

 Hence w« may conclude that the ratio lu weight pf oxygen ta 



5 



