408 On Iodine. [June, 



difference proceeds from the water which the iodate contained being 

 retained by it, Iodate of barytes is the least soluble of all the 

 alkaline iodates. 100 parts of water dissolve only 0"16 at 212°, 

 and 0*03 at 64 '5. It is composed of 



Iodic acid LOO 



Barytes 46-340 



It does not deflagrate on burning coals, but only gives out now 

 and then a weak light. The difference in this respect between 

 iodate of potash and iodate of barytes depends on two causes : first, 

 the barytes not being reduced like the potash by iodine, it gives out 

 less oxygen than the iodate of potash ; but the second, and principal 

 cause, is, that the iodate of barytes and the product of its decompo- 

 sition being infusible, only a very small portion of the iodate comes 

 in contact vvitli the coal, and all the rest of the salt is decomposed, 

 without its oxygen serving to the combustion at all. The iodate of 

 potash, on the contrary, being fusible, as likewise the ioduret of 

 potassium, all the parts of the salt come successively in contact 

 with the coals, and support the combustion in a jiowerful manner. 

 Among the sulphates, we shall find several that detonate, if that 

 name is to be given to those which are decomposed by fire and give 

 out oxygen. This is the case with alum, and with sulphate of zinc. 

 They do not support combustion, for the same reasons that iodate 

 of barytes does not. 



Iodate of strontian is obtained like the preceding salt. It is in 

 small crystals, which viewed through a glass appear to be octahe- 

 drons. It gives out water before it is decomposed by heat, and the 

 products which it gives out are perfectly similar to those of iodate of 

 barytes. 100 parts of water dissolve 073 of it at 212°, and 0-24 

 at 59°. 



Iodate of lime is usually pulverulent ; but it may be crystallized 

 in the hydro-chlorate or hydriodate of lime, which augment its 

 solubility. It then assumes the form of small quadrangular prisms. 

 100 parts of water dissolve 0-98 of it at 212^ and 0-22 at 64°. 

 The quantity of water which it holds in combination appears to me 

 to amount to about three per cent. The products of its decomposi- 

 tion by fire are the same as those of the iodates of barytes and 

 strontian. These three salts require a higher temperature for their 

 decomposition than the iodate of potash. 



To obtain the other iodates I employed double decompositions. 

 Nitrate of silver gives with the iodate of potash, and even with 

 iodic acid, a white precipitate, very soluble in ammonia. If we 

 saturate the alkali with sulphurous acid, the precipitate appears 

 again ; but it has lost its solubility in ammonia, because it has been 

 changed into ioduret of silver. This experiment furnishes us with 

 the means of distinguishing in a combination hydro-chloric, 

 hydriodic, and iodic acids, and of separating them from each other. 

 If we treat the precipitates obtained by nitrate of silver with ammo- 

 nia, those containing iodic acid, or hydro-chloric acid, will be dis- 



