IODINE. 385 



bath, which is heated by a small fire below. The retort has a 

 large opening, to which a capital b c, resembling the head of an 

 alembic, is adapted, and luted with pipe-clay. In the capital 

 itself there are two openings, a larger and a smaller, at b and 

 c, closed by leaden stoppers. A series of bottles d, having each 

 two openings, connected together as represented in the figure, 

 and with their joinings luted, are used as condensers. The 

 prepared ley being heated to about 140 in the retort, the man- 

 ganese is then introduced, and b c luted to a. Iodine immediately 

 begins to come off, and proceeds on to the condensers, in which 

 it is collected ; the progress of its evolution is watched by 

 occasionally removing the stopper at c ; and additions of sul- 

 phuric acid or manganese are made by 6, if deemed necessary. 

 The success of the experiment depends much upon its being 

 slowly conducted, and upon the proper management of the 

 temperature, which is more easily regulated when the quantities of 

 materials are considerable, than when the experiment is attempted 

 with small quantities in glass flasks. In the latter circumstances, 

 chlorine is often evolved with the iodine, which escapes in acrid 

 fumes, as the chloride of iodine, and is lost; but this accident 

 can be avoided in the manufacturing process. A little cyanide 

 of iodine often accompanies the iodine, which being more vola- 

 tile, condenses in the form of white, flexible, prismatic crystals, 

 in the bottle most distant from the leaden retort. 



In this operation, the peroxide of manganese will be in con- 

 tact at once with hydriodic, hydrochloric and sulphuric acids ; 

 and the iodine of the hydriodic acid may be liberated, from the 

 union with its hydrogen of the oxygen of the manganese, and 

 the formation of water ; or hydrochloric acid may be first de- 

 composed by the manganese, and chlorine decompose the 

 hydriodic acid and liberate iodine. If a considerable excess of 

 sulphuric acid be employed, iodine is obtained without the use 

 of the peroxide of manganese, the oxygen required by the 

 hydrogen of the hydriodic acid being supplied by the sulphuric 

 acid, a part of which is converted into sulphurous acid. The 

 presence of iodine in the prepared ley may be observed by sud- 

 denly mixing it with an equal volume of oil of vitriol, when 

 violet fumes of iodine appear. But the quantity of iodine may 

 be more accurately estimated by means of a solution consisting 

 of 1 part of crystallized sulphate of copper and ^j cr. proto- 



c c 



