2^8 Or Iodine, [April, 



which we wish to convert into iodate. The iodates of barytes, 

 liaie, and strontian. being very little soluble in water, will be 

 obtainecl pure after some washings. The others must be separated 

 from the hydro-chlorates by repeated crystallizations or by alcohol. 



Of the Hydriodaies. 



In general these salts may be prepared by combining hydriodic 

 acid with the bases ; but we may obtain those of potash, soda, 

 barytcs, strontian, and lime, directly by treating iodine with these 

 bases, employing tlie methods above described to separate them 

 from the iodates which are formed at the same time. The hydrio- 

 dates of zinc, iron, and in general of all the metals that decompose 

 water, are obtained l)y dissolving the iodurets of these metals in 

 ivater. We may put together the water, the iodine, and the metal, 

 and by the application of heat the hydriodate is quickly formed. 1 

 do not propose to treat of all the hydriodates in detail, but merely 

 to give their generic characters and their principal properties. 



Sulphurous, hydro-chloric, and hydro-sulphuric acids, produce 

 no change on the hydriodates at the usual temperature of the 

 atmosphere. 



Chlorine, nitric acid, and concentrated sulphuric acid, instantly 

 decompose them, and separate the iodine. 



With solution of silver they give a white precipitate insoluble in 

 ammonia; with the pcrnitrate of mercury, a greenish-yellow pre- 

 ci()itate ; with corrosive sublimate, a precipitate of a fine orange- 

 red, very soluble in an excess of hydriodate; and with nitrate of 

 le;id, a pre(i|)itate of an orange-yellow colour. 



They dissolve iodine, and acquire a deep reddish-brown colour. 



■'I 

 Hydriodate of Potash. 



When a solution of hydriodate of potash is made to crystallize, 

 the oxygen combined with the metal, and the hydrogen with the 

 iodine, unite together, and form water, and we obtain crystals of 

 ioduret of potassium similar to those of chloruret of sodium. This 

 salt easily melts, and sublimes at a red heat. When heated in con- 

 tact of air, it undergoes no alteration. It is more deliquescent than 

 the hydro-chlorate of soda. 100 parts of water, at the temperature 

 of (j'j°, dissolve 1-13 of the salt. We may consider it as a hydrio- 

 date wliile it is in solution in water ; but when melted, or even 

 dried, h is obviously an ioduret of potassium. I find that when 

 ioduret of potassium is dissolved in water, and afterwards dried, its 

 weiglit is not increiised. 



Ioduret of potassium is composed of 



Iodine 100 



Potassium 31*342 



and the hydriodate of 



Hydriodic acid 100 



Potash 37'42() 



