1814.] Philosophical Transactions, Part I. 1814. 443 



it than British kelp. It is a solid substance, having the appearance 

 of plumbago; but it is very volatile, and gives out a peculiar odour, 

 and it is proper to know that its properties are decidedly poisonous. 

 The properties of iodine stated in this paper are the following : — 



It is a substance analogous to oxygen and chlorine, and could 

 not be decomposed by any methods which the author could devise. 

 It is partially soluble in water, and soluble likewise in alcohol and 

 ether. When its solution is mixed with nitrate of silver, a lemon- 

 yellow precipitate falls, which melts in a low red heat, and becomes 

 red. It is rapidly decomposed by caustic potash, oxide of silver 

 being separated. When iodine is passed over red-hot silver, the 

 same substance is formed. 



When iodine is passed over hot potassium, that metal burns with 

 a pale blue flame, no gas is given out, but a white substance is 

 formed, soluble in water, and fusible in a red heat. It has an acrid 

 taste, and when treated with sulphuric acid yields iodine. 



Iodine absorbs chlorine, and forms a volatile solid substance of a 

 yellow colour, soluble in water, and forming an acid to which the 

 name of chlorionic acid has been given. 



Iodine, when heated in oxygen gas, ot brought in contact with 

 red-hot hvperoxymuriate of potash, undergoes no change. 



It combines readily with metals, without any violent action. 

 With tin it forms a deep orange substance; with iron, a brownish 

 red ; with lead, a bright orange; with mercury, a bright crimson; 

 and with zinc, a white compound. The iode of iron was not de- 

 composed by ammoniacal gas, but combines with it. The iode of 

 tin has the properties of an acid, and is called stanniodic acid. 



Iodine combines very rapidly with phosphorus, producing heat 

 without light. When the iodine is in excess, a red volatile solid is 

 produced ; when the phosphorus is in excess, the compound is 

 more fixed. During this combination an acid gas is evolved, at 

 first taken for muriatic acid, but possessing different properties. It 

 is absorbed by water and by mercury. This acid is called hydrionic 

 mid* Abundance of this acid is exhaled when the iode of phos- 

 phorus is heated in water, and phosphorous acid remains behind. 

 Davy considers this acid as a compound of iodine and hydrogen. 



Iodine combines readily with potash and soda, and forms with 

 each two saline compounds ; the first, composed of oxygen, iodine, 

 and the alkaline base, is analogous to the hvperoxymuriate of potash ; 

 the second is more soluble, and is a compound of iodine and the 

 metallic base of the alkalies. Similar compounds are obtained with 

 barytcs, and probably all the alkaline earths. 



When iodine in vapour is passed over dry red-hot potash, oxygen 

 i- expelled. 



Iodine is expelled from its compounds by chlorine, but in general 



• D»*J calls it hijdroionk arid ; but it ii better to a>oi.l the hiatus of id mnny 

 »owel». 



