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Further Experiments and Olservafions on lod'me, 357 



acid should be very frequently distilled from it, and a part al- 

 ways re;niains unaltered ; \vli<;u mixtures ol" the triple and double 

 compounds are exposed to the action of muriatic acid, potas- 

 sane (muriate of potiii<;a) is instantly formed ; and if the pro- 

 per proportions are adopted, none of the double or triple com- 

 pounds remain, and the rchults are potassane only and the oxy- 

 chloric acid. 



Mixtures of the trijjle and double compounds produce abun- 

 dance of iodine when acted on by glacial h\droj)hosphoric acid 

 gas; but the pure double compound affords only hydroionic acid 

 gas, and this decomposition offers the best method which has 

 yet occurred to me of procuring pure hvdroiouic acid. When 

 the two substances are gently heated together, the hydroionic 

 acid gas, which comes over in considerable quantities, forms a 

 colourless solution wlven absorbed by Avater. 



I have endeavoured to ascertain the composition of the triple 

 compound of potassium. Seven graiiis that had been driecj 

 at the temperature of boiling water heated to redness in a smaU 

 crucible of platinum lost 2*2 grains. Seven grains heated to 

 dull redness in a small tube of glass lost Iv grain; a minute 

 portion of iodine conden^ed in the middle part of the tube,- but 

 no violet vapour was observed in the up'por part of it, and there 

 was a very slight appearance only of moisture, so that the loss 

 of weight in this last experiment must be principally ascribed 

 to the expulsion of ox-.-gcn. 



On a comparison of the results of tliese two analyses, it ap- 

 pears very probable that this irijjle conjpound is comjjosed o'f 

 one proportion of iodine about 165, one of potassium 7'"), and 

 six of oxygen iJO; which is a composition exactly analogous to 

 that of the hyper-oxymuriate of potassa. The quantities that I 

 ■used in my experiments were too small to render these results 

 more than approximations, yet the similarity of them to those 

 presented by the hyper- oxyinuriates ought perhaps to render 

 •them more worthy of confidence. 



' I have attem;ited to obtain pure triple compounds from solu- 

 tions of baryta and lime,-^ and from magnesia diffused through 

 water, by dissolving iodine in them by heat, and by evaporating 

 the clear liquor until it began to deposit crystals.' In this way 

 1 have procured substances which, when well washed in distilled 

 water, afforded no iodine to nitric acid, wliicli yielded chlorine 

 and chlorionic acid vvhen acted upon bv muriatic acid, and wiiich 

 ■i^tilled afforded mucli oxygen and some iodine, and left 



^ iJC8fi^tl«»fljfcapM;ared to be .mixtures of tlie earths with 

 compni.ijfjUs -thar i\J^i\{A'^\\\\c to sulphuric acid, producing a 

 smell of siulphuroi^Kafcrrfgas, and which probably consisted of the 

 metals of the eaJlwuiiited to iodi^ie... . . 



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