M. Vauquelin o« the Existence of Iodine in Minerals, 271 



took a yellow tinge, and had the property of giving a blue co- 

 lour with starch on the addition of a few drops of chlorine: 

 it was precipitated blackish-brown by nitrous acid, and red 

 by nitrate of mercury. 



The 4*46 grammes left after the action of the potash, treated 

 with diluted nitric acid, dissolved with effervescence ; but a 

 yellowish substance remained, resembling, except in colour, 

 chloride of silver. Washed and dried, it weighed 80 centi- 

 grammes ; heated, it turned orange, and became of a green- 

 ish-yellow again after cooling. 



We have ascertained this substance to be iodide of silver, 

 which is proved by the alkali's not having decomposed it, 

 although in excess. The quantity of silver dissolved by the 

 nitric acid was 41 J centigrammes. 



Thus the potash having carried off 50 centigrammes from 

 the 5 grammes of ore (which can be nothing but iodine); and 

 as we obtained, besides, 80 centigrannnes of iodide of silver, 

 which contain according to modern chemists 42| of iodine, — 

 it follows that these grammes of ore contain 92*50 of iodine, 

 which, divided by 5, give 18*50 per cent. 



No doubt therefore could remain as to the existence of 

 iodine in the ore in question : however, we were desirous of 

 knowing whether we could obtain the hydriodate of potash in 

 a crystallized state. For this pmpose we saturated with sul- 

 phuric acid the excess of alkali contained in the solution; and 

 after having evaporated it to dryness, we treated it with alcohol 

 of the sp. gr. '867, for the purpose of isolating the sulphate of 

 potash. We then expelled the alcohol; and the mother water 

 left to spontaneous evaporation, produced square prisms which 

 had all the properties of ordinary hydriodate of potash. 



Henceforward iodine may be considered as one of the ele- 

 ments of minerals : and this fact will be a motive for chemists 

 not to neglect to search for it when analysing metalliferous 

 minerals, especially such as contain silver ; for iodine, like 

 chlorine, exerts a great influence on this metal. 



The question now is, with which of the substances contained 

 in the silver-ore it is combined. It will be recollected that we 

 found in it sulphur, silver, lead, and carbonate of lime, which 

 serves as its gangue. The carbonate of lime may be excluded 

 at once ; and the difficulty lies between the sulphur, silver, and 

 lead. It is not very probable that this substance should be 

 combined with the sulphur; this as well as the lead being se- 

 parated by the action of the nitric acid on the ore, even when 

 diluted : it is more probable that the iodine is combined with 

 the lead and part of the silver. On the other hand, if we con- 

 sider that in proportion as the nitric acid dissolves the me- 

 tallic 



