IS15.] On Iodine. 403 



according to the same principles, to find a greater number which 

 are solul)le than of the sulphurets and ioduiets, because chlorine 

 has a much stronger affinity for hydrogen than sulphur or iodine. 

 This accordingly is the case. All the chlorurets of the metals which 

 form soluble iodurets are likewise soluble, and besides them tljose 

 of lead, bismuth, gold, platinum, the deutochlorurets of copper 

 and mercury possess tlie same property.* We see, then, by the 

 comparison whicii we have just made, that it is the most oxidable 

 metals, and tiie radicles that have the greatest affinity for hydrogen, 

 which liave tlie irreatest tendency to form combinations soluble in 

 water, and which probably decompose it. 



I have attempted to decompose several hydriodates by acids in 

 wliich the oxygen is very much condensed ; but I have not obtained 

 any satisfactory result. The hj'driodate of strontian, aiul that of 

 potash, treated by concentrated phosphoric acid, gave me very deep 

 coloured hydriodic acid. Boracic acid produces no sensible decom- 

 position, because it is too weak as long as there is any water mixed 

 with it, and when there is none tiie hydriodate is clianged into 

 ioduret. Liquid hydro-chloric acid does not decompose the hydrio- 

 dates, because it is move volatile than hydriodic acid ; but in the 

 gaseous state it decomposes the iodurets in an elevated temperature. 

 I passed slowly through a glass tulie containing ioduret of potash 

 that had been melted, a current of hydro-chloric gas. There was 

 no decomposition while cold. When titc temj)erature was raised 

 nearly to a red heat, I obtained hydriodic gas containing but 

 very little hydro-chloric gas. With the iodurets of strontium and 

 calcium, the decomposition takes place much better. This method 

 may be employed with advantage in order to procure hydriodic 

 gas. 



Totlurelcd Hydriodates. 



All the hydriodiitcs have the property of dissolving abundance of 

 iodine, and by this they acquire a deep reddisii-brown colour. They 

 kecj) it in solution by a very weak force : for they let it go when 

 boiled, or when exposed to the air after being dried. The iodine 

 doe;! not ciiange the neutral state of the hydriodates ; and the 

 reddish-brown colour of the solutions, similar to the other solutions 

 of iudine, is a new proof of tlie weakness of the combination. We 

 cannot compare these compounds to the eulphureted sulphites, in 

 which the sul|)liur appears to act the part of an acid. They have 

 rather the characters of a simple sohitiuii. I am aware that combi- 



• Tho prorhlorurcis of roppec and mercury arc insoluble, ^^hilc Ibe deutochlo- 

 riir«Ms arc vrry soluble. 'I'liougli we may cxpljin (his <11fleri-iice on the hypothptis 

 lliat c'liUirnrcd do ixit di-^olvi* in ualcr hut in at, inia'h as Ihey dceoinpriBe it, thetc 

 facts srcid lo inr more favourable to tlie otiier hypolbe^is, tliat the cl'lorurrls ii»ay 

 ilivtolvc III water niiliout deiuiiipu^iiu; it. I have called Che first cumbinati'tn of 

 eiippcr and ui>-i( ury miIIi ctUorine prochloruret, l)e,'au9c it correspoi:d» with ibfir 

 |iraioxide> ; and (lie kri mid deitloc/ilorurel, because it ci'Tresjioiids vttlb the (CKOnd 

 di'|;iee of lUeir oxidutioo. 



•> <• 2 '. 



