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LXXXI. On a neio Method of preparing lodous Acid. By 

 Lewis Thompson, Esq., Member of the Royal College oj 

 Surgeons. 



To the Editors of the Philosophical Magazine and Journal. 

 Gentlemen, 

 -[- SEND you a new method of preparing iodic acid ; it is 

 X cheaper and safer than the process of Sir Humphry Davy, 

 and affords a purer acid than the plan pursued by Gay-Lussac. 

 I say purer, because from some experiments which I have 

 lately made, and intend to repeat more carefully, 1 am led to 

 conclude with Sir Humphry Davy, that the acid of Gay- 

 Lussac is sulpho-ipdic acid. 



Process for preparing Iodic Acid. 



Put one atom or 126 grains of iodine into a proper bottle 

 with 24 ounces of water, and pass chlorine, previously washed 

 in cold water, through the mixture until it shall have become 

 colourless ; set the solution aside for an hour ; then heat it to 

 212° Fahr., to disengage the uncombined chlorine, and add 

 2y atoms or 295 grains of recently precipitated oxide of silver ; 

 boil the whole for ten minutes, filter, and evaporate carefully 

 to dryness : the product is pure anhydrous iodic acid. 



It will be at once perceived by the above process that there 

 is no such acid as the chloriodic, the acid so called being in 

 fact merely a chloride of iodine, which when dissolved in 

 water is converted into muriatic and iodic acids, with a vari- 

 able quantity of iodine. How this mistake can have passed 

 so long unnoticed is to me a matter of surprise ; at the same 

 time I must observe that I have not been able to unite chlo- 

 rine and iodine in the proportions necessary to form these 

 acids without the intervention of water; there is always an ex- 

 cess of iodine: but I have no doubt that this may be effected 

 in a sufficiently reduced temperature. In the last experiment 

 which I made on this subject 50 grains of iodine combined 

 with 41*5 cubic inches or about 30 grains of chlorine: the 

 substance thus formed when put into a large quantity of 

 water, and exposed for some days to the sunshine, deposited 

 8 grains of iodine and became of a pale yellow colour. 



That the muriatic and iodic acids exist ready formed in the 

 solution I am confident, not only from the taste and smell, 

 but because I have obtained free muriatic acid from it by 

 distillation, although when this is continued until the solution 

 becomes a good deal concentrated, these acids react upon 

 each other and produce chlorine and iodine. 



