362 Further Experiments and Ohervaiions on Iodine. 



compound of iodine and )jata'=siuin, but depends either upon the 

 subcarbonate not deconijjosed, or upon the alkali fonned during 

 the ignition of the compound ; the pure double compound seems 

 to have no power of action on the acids it does not decompose ; 

 I fused it in cgntact with sulphurous acid gas confined by mercury 

 in a glass tube, the salt gained a slight tint of yellow, but did 

 not absorb its own volume of gas : after this, it slightly reddened 

 litmus, so that the acid must have had little more than a me- 

 chanical adhesion to the salt. 



When poiassame, or iode of potassium, is fused with boracic 

 acid, there is a perfect mixture of the two bodies. In my first 

 researches on this mixture, I conceived that they entered into 

 chemical union, and formed a violet-coloured glass, and that 

 the acid property of the boracic acid was neutralized by the new 

 compound ; but I s-ince find that the violet colour of the glass is 

 owing to the development of iodine, and when the application of 

 heat is long continued, much iodine is disengaged, and the co- 

 lour of the glass chaijgfts to olive, and borate of potassa is 

 formed. When the glass is dissolved in warm water, an olive- 

 coloured power separates, soluble when boiled in the caustic al- 

 kalies, so that there is great reason to suppose that it is boron, 

 and that the boracic acid is decomposed by the attraction of the 

 potassium combined with the iodine for oxygen, assisted by the 

 tendency of iodine to assume the clastic state. 



I fused the neutral compound of iodine vyith silica ; no change 

 was effected when the experiment was made in close vessels, but 

 when tlie mixture was exposed to air, and intensely heated, a lit- 

 tle iodine was evolved, some potassa formed, and some silica dis- 

 solvetl by it. 



3. On other acid Compo^mds of Iodine. 



1. I have made several experiments on the combination of 

 iodine and chlorine, obtained by admitting chlorine in excess to 

 known quantities of iodine in vessels exhausted of air, and re- 

 peatedly heating the sublimate. 



Operating in this way, I find that iodine absorbs less than 

 cne-third of its weight of chlorine. 



The compound of iodine and chlorine is a very volatile sub- 

 stance, and in consequence of its action upon mercury, I have 

 not been able to determine the elastic force of its vapour. 

 Hence the estimations of its composition from experiments on 

 the quantity of chlorine absorbed in close vessels must neces- 

 sarily be liable to error. In one experiment, in which I dis- 

 solved the suldimate, by admitting a small quantity of water into 

 the retort, I found that eight grains of iodine had caused the 

 disappearance of five and a quarter cubical inches of chlorine. 



In 



