SCO On Iodine. [Aprii-, 



bydriodic gas cooled to ~ 4° over barytes obtained from tbe recent 

 calcination of tbe subnitrate ; tbe barytes instantly becaoie incan- 

 descent, and water made its appearance in the vessel ; yet this 

 barytes gave no oxygen gas when dissolved in water ; nor did it 

 undergo any alteration when I passed over its surface a current of 

 dry hydrogen gas. I ascertained, likewise, that sulphur disengaged 

 nothing ; hut that hydro-sulphuric gas produced much water when 

 it combined with it.* We cannot, therefore, doubt that at a red 

 beat, and even at a lower temperature, hydriodate of barytes is 

 converted into ioduret of barium. 



, , r , • riodine 100 



Ioduret ot banum < ry ■ c^.'-o- 



(^ Barium 54'/ 3o 



IT , . , , f , , TAcid 100 



Hydriodate of barytes . . ^^-^.^^^^^^ 60-G22 



The hydrlodates of lime and strontian are very soluble, and the 

 first is exceedingly deliquescent. I have neither determined the 

 shape of their crystals, nor the quantity of water necessary to dis- 

 solve them. The hydriodate of strontian melts below a red heat, 

 while the hydriodate of lime requires a higher temperature for its 

 fusion. If they are heated in close vessels they become only 

 slightly alkaline ; but if air or oxygen have access to them while 

 hot, thick vapours of iodine are immediately exhaled. If we con- 

 sider these compounds as iodurets, tbe calcium and strontium are 

 oxydizcd, and abandon a portion of the iodine. If we consider 

 them as hydriodates, tbe hydrogen of the acid must combine with 

 oxvgen, and water be formed. I endeavoured to ascertain whether 

 this was the case by passing dry oxygen gas over hydriodate of lime 



* The action of the hydrosulphuric gas %vas accompanied by a strong heat. 

 The compound which was partly fused, being treated with hydrochloric acid, 

 hydrosulphuric gas -was disengaged, and a little bulpliur precipitated. From this 

 it is probable that a sulphuret with excess of sulphur is formed, and hydrogen 

 disengaged. But as I employed a sulphuret which yielded a gas not totally ab- 

 sorbed by the alkalies, 1 could not ascertain the fact. Yet the abundant produc- 

 tion of water wiiich accompanies the combination of hydrosulphuric gas with 

 barytes, and even with strontian, cannot be explained, except by admitting that 

 thcJe alkalies are reduced by the hydrogen in consequence of the united affinities 

 of the oxygen for hydrogen, and of the metals for sulphur. Rut if this be the 

 case, it is very probable that many metallic precipitates, which have been taken 

 for hydrosulphate^ (tiydrosulphurets) arc only sulphurets. At a red heat, all the 

 oxides which combine with sulphur give out v.ater, and are changed into sul- 

 phurets when hydrosulphuric gas is brought in contact with them. This fact 

 proves nothing against the existence of hydrosulphales at a low temperature. 

 But hitherto there is not a single decisive experiment in proof of their existence; 

 while the insolubility of them all seems to be a fact of an opposite nature. To 

 confirm llicse conjectures, T dissolved a determinate weight of zinc in hydrochloric 

 acid. I supersaturated the solution by ammonia, and precipitated by hydro- 

 sulphuric acid. The precipitate dried in the temperature of between 140^ and 

 ]76^ assumed the appearance of horn. Its weight was too great for a sulphuret, 

 and too small for a hydrosulphurel. When heated to 212° it gave out wafer, and 

 a new quantity was disengaged at a higher temperature. This experiment is not 

 entirely decisive; but from the appearance of the precipitate I think it was .1 

 hyilrate. At all events, this experiment is rather favourable than otherwise to roy 

 conjecture. 



