1315.] On Iodine. 299 



Hydriodate of Soda. 



I obtained it in pretty large flat rhomboidal prisms. These prisms 

 uniting togetii^r form larger ones, terminated in echelon, and 

 striated longways, like thoae of sulphate of soda. They contain a 

 great deal of water of crystallization, and yet are very deliquescent. 

 Heat drives otf this water, melts the salt, and tiv;'n renders it some- 

 what alkaline. It does not sublime so easily as hydriodate of potash, 

 100 parts of water, at the temperature of about bj°, dissolve I73 

 of the salt. When dried, it must be considered as an ioduret of 

 sodiun). 1 found that 100 parts of iodate of soda give, when de- 

 composed by heat, 24-4.5 of oxygen. From the data given by that 

 analysis, we may conclude the composition of the iodmct of sodium 

 and hydriodate of soda to be as follows: — 



, , ^ r ^• riodine 100 



Ioduret of sodium S c r . . . . iwu 



tbodium 18-53G 



Hydriodate of soda j^'^^^ ^?,^ .. , 



The hydriodates of potash and soda converted into iodurets by 

 desiccation, are the only ones not altered when lieated to redness in 

 contact with the air. The reason is, tiiat iodine decomposes the 

 oxides of potassium and sodium.*' 



Hydriodale of Barytes. 



This salt crystallizes in very fine prisms, very similar in appear- 

 ance to the hydro-chlorate of strontian. After about a montii's 

 e.Kposure to the air. I found it partly decomposed. Water dissolved 

 the hydriodate coloured l)y iodine, and there remained undissolved 

 subcarbonate of barytes. Hence the hydriodic acid is gradually 

 destroyed by e.\{)osure to the air. Its hydrogen has fcrnicd water, 

 and its iodine has been dissipated in the atmosphere, or has re- 

 mained dissolved in the undecomposed hydriodate. The hydriodate 

 of barytes, though very soluble in water, is hut faintly deliqiiescent. 

 When evaporated in a close vessel, and heated to rediuss, it does 

 not melt, nor is its state of neutralization altered. If air, or still 

 better, if oxygen, be made to play on its surface when thus heated, 

 vapours of iodine Amw tliemseKes in abundance, and the salt be- 

 comes alkaline. I did not continue the ex])eriinent till the iodine 

 ceased to he disengaged ; but I presume that the hydriodate would 

 be changed into a subiodurct, as we have seen hefoVe that this was 

 the compound obtained when iodine in vapour was passed over 

 barytes at a red heat. 1 have said tiiat iodine does not disengage 

 oxygen from ijarytes ; yet 1 have nu doubt ihpt a red heat changes 

 hydriodate of barytes into ioduret of barium. 1 have passed 



• A» ioiliiie (li.,ciip,ii};rs oxjc" fiiitii (lie oxides of lead ,iiid bisinutli, ii is evi- 

 «l«nl thai ilic iodurcls of tlicsc mclulj «ill uoi Le dtcouipoiid by Inc air at a red 

 lii-al. 



1 



