188 Dr. Herapath on the Chemical Constitution of the 



2r7375 iodine in the 66*6 grs. of crystals at 32'63 per cent. 

 1"0800 iodine in the acid mother-liquids (as crystals). 

 1'9510 iodine in the alcoholic mother-liquids (as crystals). 

 2"6715 iodine in the distilled fluids as free iodine. 



27-4400 

 2'56 grs. iodine lost in drying the crystals by expression 

 between folds of bibulous paper. 



Had a substitution compound been formed, one-half the iodine 

 should have formed hydriodic acid, the other half should have 

 been in the crystalline compound ; therefore it is evident to me 

 that no such substitution base can be the result. 



One other question arises, Does the iodine exist in the com- 

 pound as hydriodic acid ? Some of the crystals were dissolved 

 in diluted alcohol boiling, and starch was added to the hot liquid ; 

 instantly an abundant precipitation of the blue iodide of amidine 

 occurred ; starch was added in excess, and until no further indi- 

 cations of iodine were evident ; the fluid was then separated by 

 decantation, and tested with nitrate of silver ; not the least trace 

 of hydriodic acid or any soluble iodide was apparent ; similar 

 results were obtained when the crystals were dissolved in hot 

 acetic acid and tested with starch ; but if they were dissolved in 

 hot rectified spirit of wine, •838 spec, grav., there was no evi- 

 dence of iodine ; on cooling, the crystals again formed, the rea- 

 son being that the chemical attraction of alcohol for iodine was 

 greater than that of iodine for starch, whereas it was less than 

 that of the iodine in the compound. It has therefore been 

 proved satisfactorily that the iodine cannot exist in the com- 

 pound as a substitution base or even as hydriodic acid. 



The iodine separating in the free state so readily upon dissol- 

 ving the crystals in alcohol or in acetic acid, rendered it a some- 

 what difficult matter to estimate it correctly. Starch was first 

 used as the precipitant ; the resulting iodide of amidine was de- 

 composed by sulphui-etted hydrogen, the hydriodic acid produced 

 neutralized by ammonia, then precipitated by nitrate of silver, 

 and the resulting iodide of silver estimated ; but accuracy was 

 very far from being attained by this method, in consequence of 

 ioduie distilling during the heating of the fluid and solution of 

 the crystals. 



At length it was found, that by passing a current of washed 

 and pure sulphuretted hydrogen through acetic acid, in which 

 a known weight of crystals had been placed, and applying heat 

 to the mixture, as soon as gas commenced being evolved, the 

 iodine was converted into hydriodic acid upon its being liberated 

 from the crystals ; the decomposition being perfect and the ope- 



