1815.] On Iodine. o^'j 



characterized by the precipitation of iodine when an alkali is added, 

 whereas the chloruret gives no such precipitate. 



We obtain but little chloruret in a solid state, as I have already 

 remarked ; but it may be obtained with facility, and in great quan- 

 tity, on solution in water. For that purpose nothing more is re- 

 quisite than to saturate with chlorine a somewhat diluted solution of 

 subchloruret. It is then exposed for some time to the sun till it 

 loses its colour, or it may be put into a large bottle in which the air 

 is continually renewed. By this means we obtain a very acid 

 colourless liquid, having only a slight smell of chlorine, which 

 destroys the colour of solution of indigo in sulphuric acid, though 

 slowly, and gives an abundant precipitate of iodine wiien ammonia 

 is poured into it. VVe cannot employ heat to drive off the excess 

 of chlorine unless it he very moderate ; for 1 have just observed that 

 it converts the liquid into a subchloruret. When we wish to 

 saturate a solution of subchloruret with chlorine, the liquid ought 

 to be dilute ; because, when concentrated, the process does net 

 succeed. The subchloruret presents itself frequently, and possesses 

 stability, while the other (to make use of the exprtssion) has only 

 an ephemeral existence. 



When we pour hydro-chlorate of potash or barytes into a solution 

 of the chloruret or subchloruret, it gives up its base to a portion of 

 iodic acid which we may conceive to be present ; but tlie hydro- 

 chloric acid becoming predominant, prevents a complete decompo- 

 sition. 



We have seen that the solution of chloruret is changed into 

 iodate and hydro-chlorate, when saturated with an alkali. From 

 this fact, and from the characters of the solution, we may suppose 

 it to be a mixture of iodic and hydro-'-hloric acid. On the other 

 side, as it deprives indigo of its colour, it would seem that the 

 chlorine and iodine in it still preserve their properties enllre. We 

 may conceive it likewise to be a peculiar acid, which is decomposed 

 when we saturate it with a base. I adopt the firsf supposition, 

 because I compose exactly the solution of the ciiloruret when I mix 

 Iodic and hydro-chloric acids together. But I consider their 

 elements as very mobile, and capable of taking a new arrangement 

 according to circumstances. On this suf'position the water is 

 dccomputed when the ciilonuct is dissolved in it. Its oxygen 

 combines with the iodine, and its hydrogen with the dilorlne. 

 'i'ht inverse distribution could not take |)lace, for the iodic and 

 hydro-chloric acids are nruch more stalile than tiie ciiloric and 

 liydriodic acids; and it is a general law that, every thing else 

 being crjual, the strong compounds are always formed in j)reference 

 to the weak. 



If we take a given quantify of iodine, and act upon by an alkali, 

 It will hi- divided into two very unequal p.irts. The smallcit [K)ition 

 forms iodate; the greatest, hydriodate. if wc wi^-hrd to convert it 

 cniirely into iodate, we must begin by making it a chlormet ; and 

 after huxiiig dissolved it in water, we saturate it with the alkali 



