1815.] On Iodine. ' 105 



decomposed. Hydriodic acid is formed, which remains in solution 

 in water, and the oxide of tin precipitates in white flocks. If the 

 quantity of water be small, the acid being more concentrated, 

 retains a portion of oxide of tin, and forms a silky orange-coloured 

 sah, which may be almost entirely decomposed by water. Iodine 

 and tin act very well on each other in water of the temperature of 

 212°. We may, by employing an excess of tin, obtain pure 

 hydriodic acid, or at least an acid containing only traces of the 

 metal. The tin must be in considerable quantity, because the 

 oxide which precipitates on its surface diminishes much its action on 

 iodine. * 



Antimony presents with iodine the same phenomena as tin ; so 

 that we might employ either for the preparation of hydriodic acid, 

 if we were not acquainted with preferable methods. 



The iodurets of lead, copper, bismuth, silver, and mercury, are 

 insoluble in water, while the iodurets of the very oxidable metals 

 are soluble in that liquid. If we mix a hydriodate with the metallic 

 solutions, all the metals which do not decompose water will give 

 precipitates, while those which decompose that liquid will give 

 none. This at least is the case with the metals of which 1 have 

 spoken : and if this fact, which I consider as general, be not a 

 •ufticient proof of the existence of hydriodates, it at least renders 

 their existence probable. 



There are two iodurets of mercury : the one yellow, the other 

 red ; both are fusible and volatile. The yellow, which corresponds 

 to the protoxide of mercury, contains one-half less iodine than the 

 red, which corresponds to the protoxide. In general there ought to 

 be for each metal as many iodurets as there are degrees of oxidation. 



All the iodurets are decomposed by concentrated sulphuric and 

 nitric acids. The metal is converted into an oxide, and iodine is 

 disengaged. They are likewise decomposed by oxygen at a red heat, 

 if we except 'he iodurets of potassium, sodium, lead, and bismuth. 

 Chlorine likewise separates iodine from all the iodurets ; but iodine, 

 on the other hand, decomposes most of the sulphurcts and phos- 

 phurets. 



(7'o he continued.) 



Article IV. 



Some Ohiervutium on the Sap of the Vine. By Dr. Prout. 



About the middle of April last I was favoured by Mr. Aatley 

 Cooper with some sap which he had collected from a common white 

 vine.* The following are a few of its properties : — 



It was siigluiy opakc, or rather had the whitish appearance of 

 common river water. Taste sweetish; but not rough. No smell. 



• Mr. C. inroniiii nii; thai tlic vinr, rtl(liout;li it hied very profusely, srciiicd t* 

 produce a greater unuibcr vf Ickvct than usual, but noj^mpi'^, ' 



