Chemical Science, 207 



The substance, therefore, was kermes, and was thus obtained for 

 the first time in a crystalline form. 



By similar processes, cubical crystals of sulphuret of tin were 

 obtained, having a brilliant white and metallic appearance. With 

 the additional circumstance of excluding the air from the tube 6, 

 and substituting the proper substances, sulphuret of iron in bril- 

 liant yellow cubical crystals was obtained. 



According to these results, M. Becquerel thinks it may be 

 permitted us to believe that nature may have followed a similar 

 course in the production of such sulphurets as are found in me- 

 tallic veins. Thus, sulphuret of silver is found combined with the 

 sulphuret of antimony, arsenic, or lead ; and these combinations, 

 unaffected by air, have remained in the state they assumed at 

 their first formation ; but the case is not the same with the double 

 sulphuret of silver with potassium or sodium, which no doub twas 

 formed at the time of the consolidation of the great terrestrial 

 masses : for then the alkali now existing in vegetables probably 

 existed in numerous compounds containing also sulphur. A slow 

 decomposition commenced, and a crystallized sulphuret of silver 

 has been the consequence The planes and appearances of the 

 metallic sulphurets actually formed as above described are so like 

 those of the natural compound, in form, grouping of the crystals, 

 colour, and general characters, as to give the stronges treason 

 for supposing this has been an active natural power. 



From these facts it would also appear, that to obtain an insoluble 

 substance in a crystallized state, it is only necessary to make it 

 enter into combination with another which is soluble, and then to 

 decompose the compound very slowly. In proof of this opinion 

 comes the following experiment : — Finely divided clay being moist- 

 ened with a solution of arseniate of potash was put into a glass 

 tube, and a solution of nitrate of copper poured upon it. After 

 some time there were seen, in certain hollow parts of the clay, 

 crystals exactly resembling those of arseniate of copper. Perhaps 

 many crystals which line mineral cavities may have a similar kind 

 of origin. 



Upon extending the experiments to insoluble iodides, substitut- 

 ing hydriodate of potassa for the hydro-sulphuret of potassa, and 

 using a connecting plate of metallic lead, a double iodide of lead 

 and potassium is first formed, which is gradually resolved into regu- 

 lar octoiidral crystals of iodide of lead, of a golden yellow colour 

 and brilliant aspect. This substance, which is insoluble, is the 

 iodide of lead, and this is the first time that it has been obtained 

 crystallized*. 



By following up this train of reasoning and experiment, it is 

 very probable that other metals could be formed into crystallized 

 iodides, &c.> and that the bromides and seleniurets might likewise be 



♦ This is a mistake. The iodide of lead is not insoluble, aUhough it is but 

 slightly soluble. It may be obtained crystallized at pleasure, by allowing a satu- 

 rated hot solution to cool slowly. — Ed, 



