1815.] On Iodine. 409- 



solved. If we saturate the solution with sulphurous acid, and treat 

 the precipitate again with ammonia, the chloruret of silver will be 

 alone dissolved. 



On digesting in iodic acid oxide of zinc recently precipitated and 

 well washed, I obtained a pulverulent salt, but little soluble in 

 w.iter, which deflagrates on burning coals, Ijut n)uch more feebly 

 than iodate of potash. We may olatain the same salt by mixing a 

 ■'^lution of sulphate of zinc with that of a soluble iodate. No pre- 

 "■6ipitate appears at first; but after some hours, small crystals are 

 deposited, sometimes in grains perfectly spherical, which are iodate 

 of ziuc. It is necessary for success in this experiment that the 

 sulphate sliould not be very much concentrated, for its viscosity 

 would qppose the motions of the molecules, and of course the for- 

 mation and separation of the iodate of zinc. 



The solutions of lead, of pronitrate of mercury, of pernitrate of 

 iron, of bismuth, and copper, give with the iodate of potash white 

 precipitates soluble in acids. The solutions of peroxide of mercury 

 and of manganese were not altered. 



There do not exist any iodureted iodates ; at least 1 have not been 

 able to form them. Iodates and iodic acid do not dissolve more 

 iodine than water. 



To complete the history of the saline combinations of iodine, it 

 remains to be determined whether, when a base acts upon this sub- 

 stance in water, the two salts which may be obtained exist sepa-' 

 rately in the solution, or if they are formed at the instant that any 

 cause whatever determines their separation. 



If we mix together the neutral solutions of iodate and hydriodate 

 of potash, they do not mutually decompose each other ; but if we 

 add any acid whatever to the mixture, even carbonic acid, which is 

 driven from all its combinations by hydriodic acid and iodic acid, 

 iodine is precipitated, owing to the mutual decomposition of the 

 two salts. 



To render the solution of iodate and hydriodate entirely the 

 same with that which we obtain in making iodine, potash, and 

 water, act upon each other, and which is always alkaline, it is sufli- 

 cient to add to the former the quantity of potash necessary to bring 

 it to the same degree of alkalinity. In that case we can no Ioniser 

 distinguish the one from the other. It would appear, tlic'ii, that the 

 iodate and hydriodate of potash are formed at the instant that the 

 iodine acts on the alkali in water; but that the oxvgen of the iodic 

 acid and the hydrogen of the hydriodic acid preserve a great ten- 

 dency to combine together, and that it is suflicient to favour this 

 tendency in order to cauie it to take elVect. Iodic and hydriodic 

 acids, and in general all acids j)roduced at once by Hie two elements 

 of water, destroy each other when mixed together.* This is the 



• M. Kcrlliiillet li.-m iibtervril tliat hiilphurnuti acid and liydro-sulphuric ncid 

 may exibl logcllMT wficii dJA^iulvcd in a f,Tr.d ilral iif waliT. Tlic- wiiiif (liiii^ holds 

 Milh ihe. iwo arid, of iudnic, wliicli if I'oiit ciitrated givi; a cupioiis preciiiit.itc of 

 iiidiiie asiouii an mixed, but du nul (kficm pose cacti other whrii diliilrd. 



