1615.] On Iodine. 211 



In this respect they resemhle the sulphurets of these earths, which 

 have Hkewise an excess of base. 



Having ascertained that the oxides of potassium and sodium are 

 decomposed by iodine, 1 wished to know if this would happen when 

 they were combined with acids. Sulphate of potash was not altered 

 by iodine ; but, what may appear astonishing, I obtained oxygen 

 with the fluate of potash, and the glass tube in which the operation 

 was conducted was corroded. On examining the circumstances of 

 thi? experiment I ascertained that the fluate became alkaline when 

 melted in a platinum crucible. This happened to the fluate over 

 which I passed iodine. It appear.^, then, tiiat the iodine acts upon 

 the excess of alkali, and decomposes it. The heat produced dis- 

 engages a new portion of fluoric acid or of its radicle, which cor- 

 rodes the glass ; and tiius by degrees the fluate is entirely decom- 

 posed. 



The experiments, which I have stated, show that chlorine has more 

 energy than iodine ; for M. Thenard and 1 have shown that chlorine 

 gives out oxygen with barytes, strontian, lime, and even magnesia. 

 I find the same thing happens when it is made to act upon the 

 sulphates of these bases ; but what is remarkable, we obtain no 

 oxygen when chlorine is made to act upon the peroxide of iron, 

 because a chloruret of that oxide is formed. 



The same experiments furnisli a new proof tliat sulphur has less 

 energy than iodine. In fact, if we ol)tain metallic sulphurets with 

 most oxides, while we do not obtain iodurels, this depends upon the 

 great affinity of sulphur for oxygen, and upon the gaseous state of 

 sulphurous acid. If iodine formed a gaseous acid with oxygen not 

 decomposable by a high temperature, there can be no doubt that 

 we should be able to form a greater number of metallic iodurets 

 than sulphurets. The decomposition of potash, soda, litharge, and 

 oxide of bismuth, and the formation of iodurets with the protoxides 

 of copper and tin, show this to be the case. 



It may be wortli wliile to remark that iodine, like sulphur, has 

 little affinity for oxides ; and that, except barytes, strontian, and 

 lime, no oxide can remain in combination with iodine at a red 

 heat. 



Very different results take place when iodine and oxides are made 

 to act upon each other in contact with water. The water is then 

 decomposed. Its hydrogen unites vvith iodine, and forms hydriodic 

 acid ; while its oxygen forms with iodine a peculiar acid, to which I 

 have given the name of iodic acid. All the oxides, however, do 

 not give the same results. VVc obtain them only with potash, soda, 

 barytes, strontian, lime, and nuignosia. The oxide of zinc preci- 

 pitated by ammonia from its solution in sulphuric acid, and well 

 washed, gives no trace of iodate and hydri(jdale. 



Let us examine more particularly wliat happens when iodine is 

 made to act upon a conccntiated solution of potash, in proportion 



o '2 



