210 On Iodine. [March, 



retort, as well as that which condenses in its neck, is strongly 

 coloured by the iodine which the hydriodic acid holds in solution ; 

 but when it comes to the receiver, where it finds sulphurous acid 

 dissolved in water, it becomes colourless, and sulphuric acid is 

 reproduced. The sulphites, the sulphurated sulphites, the white 

 oxide of arsenic, and the hydro-chlorate of protoxide of tin, when 

 mixed with iodine, produce also a decomposition of water, and 

 hydriodic acid is formed. Several hydrogenated substances, par- 

 ticularly the essential oils, alcohol, and ether, yield, according to 

 MM. Colin and Gaultier de Claubry, a portion of their hydrogen to 

 iodine, and convert it into acid. (See Ann. de Chim. t. xc.) 



Action of Iodine on the Oxides. 



Iodine may be made to act upon the oxides either with or without 

 the presence of water ; and as the phenomena are different in the 

 two cases, I shall explain, in the first place, what happens when 

 iodine in the state of vapour is passed over the oxides in a moderate 

 red heat. 



The oxide of potassium, produced by the combustion of potassium 

 in oxygen gas, is decomposed by iodine. Oxygen is disengaged, and 

 we obtain ioduret of potassium. It may be shown, by collecting all 

 the products, that the potassium does not retain any oxygen, what- 

 ever was its state of oxidation ; but I shall give below an easy means 

 of ascertaining this point. Meanwhile 1 shall state an experiment 

 which shows it in a decisive manner. 



I passed vapour of iodine in a red heat over melted subcarbonate 

 of potash ; and I obtained carbonic acid and oxygen gases in the 

 proportion of two in volume of the first and one of the second, 

 precisely the proportions which exist in the subcarbonate. The 

 oxide of sodium and the subcarbonate of soda are also completely 

 decomposed by iodine. From these experiments it would seem 

 that this substance ought to disengage oxygen from most of the 

 oxides : but this only happens in a small number of cases. The 

 protoxides of lead and bismuth are the only oxides not reducible by 

 heat which presented me with that property. The protoxides of 

 copper and tin, indeed, absorb iodine ; but as the peroxides of 

 these metals do not combine with it, and as no oxygen is disengaged, 

 I conclude that the oxygen of one portion of the protoxide passes 

 into the other portion, and that we obtain a mixture of ioduret and 

 peroxide ; so that it is by the concurrence of the forces that these 

 two protoxides are decomposed by iodine. 



Barytes, strontian, and lime, combine with iodine without 

 giving out oxygen gas. The oxides of zinc and iron undergo no 

 alteration. From these facts we must conclude that tiie decompo- 

 sition of the oxides by iodine depends less upon the condensed state 

 of the oxygen than upon the affinity of the metal for iodine. 



The lodurets of barytes, strontian, and lime, are very alkaline 

 when they are dissolved in water. 1 consider them as subiodurets. 



