PROPERTIES OF IODINE. 91 



tities in various parts of the world, for the purpose of manu- 

 facturing soda from their ashes. The crude or impure soda 

 obtained by this means, called Barilla, in Spain, and some 

 other countries, and Kelp in Scotland, also contains the Iodine, 

 which the plants have abstracted from the sea-water ; and by 

 proper means the iodine is obtained from it in a pure state." 



After this statement, IODINE, as a solid supporter of com- 

 bustion, was contrasted with gaseous Chlorine and Oxygen ; 

 and its properties were described. Since iodine, in this state, 

 is several thousand times heavier than the air, being indeed 

 much heavier than water, it would have been inconvenient to 

 have compared its specific gravity with that of the air; and the 

 opportunity was taken of making a few explanatory remarks 

 on the subject of estimating the specific gravity of solid bodies, 

 so far as its use in Chemistry is concerned, by comparing it in 

 each instance with that of water ; the specific gravity of iodine 

 being thus stated to be 4?'94?6, or very nearly five times as 

 great as that of water. The beautiful vapour into which 

 iodine is converted, on gently heating it, was exhibited, 

 and also the effects of that substance in changing vegetable 

 blue colours to yellow ; its solutions in water and in alcohol 

 were also exhibited ; together with the test of its presence in 

 any solution, arising from the property it has of forming a 

 deep blue compound with starch. The results lately obtained 

 by means of this and other tests, as to the detection of iodine in 

 what are called mineral waters, as well as in that of the sea, and 

 also in common spring water, were then explained ; together 

 with the presence and probable efficacy of iodine, in the waters 

 drank for medicinal purposes at Bath, Leamington, Matlock, 

 Buxton, and other places*. The intense spontaneous combus- 

 tion ensuing on bringing iodine and phosphorus into contact, 

 was exhibited, in illustration of the properties of iodine as a 

 supporter of combustion ; and the subject was concluded by 

 noticing the use of this substance in curing certain disorders 

 of the throat, and the alleged fact of its being the cause of the 

 long established, but not understood, efficacy of burnt sponge, 

 in the relief of such complaints ; the sponge being stated to 

 contain iodine, abstracted from the water of the sea in which 

 it has been formed. 



* The statements made on these subjects accorded with the views which 

 have of late been generally entertained by chemists respecting them. 

 From the facts, however, which have been detailed in Dr. Daubeny's 

 " Memoir on the Occurrence of Iodine and Bromine in certain Mineral 

 Waters of South Britain," recently published in the Philosophical Transac- 

 tions, it is probable that these views will require considerable modification. 

 It will be found, perhaps, eventually, that Bromine, instead of Iodine, is 

 the chief medicinal agent in many mineral waters. 



