404 On Iodine. [June, 



nation and solution depend upon the same force, and that it is diffi- 

 cult to draw a limit between them. But we may distinguish them 

 from each other by defining a solution to be a combination in which 

 there is no saturation of properties. At any rate, there is no incon- 

 venience in adopting the expression iodi/reted hydrioaate to denote 

 the combination of iodine with a hydriodate, provided we entertain 

 an exact idea of that combination. 



Of the lodates. 



When speaking of the action of the alkaline oxides on iodine by 

 means of water, we have shown that there form at the same time 

 a hydriodate and an iodate, and we pointed out the method of sepa- 

 rating them from each other. We may c-tain the iodates of the 

 other oxides either by double decomposition, or by saturating 

 directly iodic acid, or the acid liquid from chloruret of iodine, 

 which we have considered as a mixture of iodic and hydro-chloric 

 acids, and which, at any rate, possesses exactly the properties of 

 such a mixture. 



There are but very few of the iodates that fuse on burning coals ; 

 that of ammonia is fulminating. 



They are all soluble in hydro-chloric acid, with the disengage- 

 ment of chlorine. The solution contains subchloruret of iodine. 



Sulphurous and hydro-sulphuric acids decompose them, and 

 separate the iodine. Chlorine does not decompose them. Sulphuric, 

 nitric, and phosphoric acids, have no action on them at the ordinary 

 temperature, except as far as they seize a portion of their base. 



At a faint red heat all the iodates are decomposed. Some give 

 oxygen only ; others, oxygen and iodine. 



They are all insoluble in alcohol of the sp. gr. 0-82. 



Iodate of Potash. 



I have only obtained it in small crystals, which have nearly the 

 cubic form. It deflagrates on burning coals like nitre. It is not 

 altered by exposure to the air. 100 parts of water at 58° dissolve 

 7*45 of this salt. It is decomposed at a temperature somewhat 

 higher than is required by the chlorates. Oxygen is disengaged, 

 and ioduret of potassium remains, which forms a neutral solution in 

 water. It is easy to see that the residue is ioduret of pota?sium. If 

 the metal were in the state of an oxide, iodate and hydriodate of 

 potash would be formed on dissolving it in water, and sulphurous 

 acid would occasion a precipitate of iodine. If, then, we wish to 

 obtain a pure hydriodate by treating iodine with potash, we must 

 evaporate the solution to dryness, and melt the residue. On rc- 

 dissolving it in water, we are certain to have only hydriodate ; but 

 there will always be an excess of base. 



From various experiments on the decomposition of iodate of 

 potash by heat, I have found it composed of 



