410 Ow Iodine. [Jcnk, 



reason why a very weak acid precipitates iodine from a mixture of 

 iodate and hydrlodate; for how weak soever its action should he, it 

 will always decompose a sniall portion of each salt, as Bertliollet has 

 ihown, arid the acids separated producing immediately iodine which 

 precipitates, the decomposition may continue, and make great 

 progress, ivithout, however, becoming comjilete. 



The solution of neutral iodate and hydrlodate, and the solution of 

 iodine in potash, present, however, this remarkable difference, th^t 

 the first always preserves its neutral state, while the second is con- 

 stantly alkaline ; but if the two salts be really formed at the instant 

 iodine is mixed with solution of potash, it would appear that we 

 ought either to obtain a complete saturation of the alkali, or that 

 the mixture of neutral iodate and hydrlodate ought to become alka- 

 line as soon as it is made. The reason why this is not the case is, 

 that we cannot suppose that in a mixture of various bodies each 

 element acts rigorously, as if it were merely mixed, and as if the 

 -mobility of its particles were perfect. We ought rather to admit, 

 that to destroy a compound stronger forces are necessary than those 

 that formed it. On this supposition it Is easy to conceive that the 

 alkalinity of the solution of iodine in potash, and the constant neu- 

 trality of a mixture of neutral iodate and hydrlodate, may take 

 place at the same time ; and of consequence, that the two salts of 

 which we have been speaking may be formed, and exist separately^ 

 in a solution of iodine and potash. 



Hydriodic Elher. 



I have paid but little attention to the action of iodine on animal 

 and vegetable substances ; yet it may produce several new combina- 

 tions. MM. Colin and Gaultier have described that which iodine 

 forms with starch ; and I shall now make known an ether formed 

 by hydriodic acid and alcohol. 



J mixed together two parts in volume of absolute alcohol and 

 coloured hydriodic acid of the specific gravity r700. I then dis- 

 tilled the mixture in a water-bath. I obtained an alcoholic liquid, 

 perfectly neutral, colourless, and limpid, which, when mixed with 

 water, became muddy, and let fall in small globules a liquid Jit first 

 milky, but which gradually became transparent. Tins liquid is 

 hydriodic ether. What remained in the retort was very dark 

 coloured hydriodic acid. Thus In this experiment a portion of the 

 alcohol had united with the hydriodic acid, and formed an ether, 

 which distilled over with the rest of the alcohol, and there remained 

 hydriodic acid very dark coloured, because it held in solution all the 

 iodine which had coloured it at first. It was probably the action of 

 the iodine and the water which prevented the whole hydriodic acid 

 from combining with the alcohol. 



Hydriodic ether, after having been washed two or three times 

 with water, in vi^hich it is but very little soluble, is perfectly neutral. 

 Its odour is strong, and, though peculiar, is analogous to that of the 

 other ethers. After some days it acquires a red colour, whicii doe* 



