Intelligence and Miscellaneous Articles. 239 



Among the products obtained in consequence of slow actions in 

 a vessel hermetically sealed during twenty years, and which have 

 their analogues in nature, I will mention the following : — 



(1) Some crystals of arragonite, formed upon a piece of gypsum 

 shaped like a spearhead, 1 decim. in length and 1 centim. in thick- 

 ness, digested in a solution of bicarbonate of potash contained in a 

 vessel hermetically sealed ; the sulphate of lime almost entirely dis- 

 appeared, and there remained a thick coating of crystals of arragonite. 



(2) Operating with a solution of subcarbonate produced rhombo- 

 hedric crystals of carbonate of lime. 



(3) A similar piece of gypsum, kept during the sam.e time in con- 

 tact with a solution of arseniate of ammonia, gave crystals of arseniate 

 of lime, perhaps as fine as the natural ones. 



(4) With a solution of aluminate of potass and gypsum, I obtained 

 crystallized double sulphate of lime and potass, which is no other 

 than glauberite in which soda has been replaced by potass. 



(5) Pieces of galena, immersed during twenty years in a solution 

 of bicarbonate of potass, gave well-characterized crystals of carbonate 

 of lead belonging to the system of the right prism with rhombic base. 



(6) With pieces of limestone immersed in a solution of plumbate 

 of potass, I obtained hydrated carbonate of lead in crystalline scales 

 with a nacreous aspect. 



(7) Malachite (bibasic carbonate of copper) I had already obtained 

 by the reaction of a solution of nitrate of copper upon limestone to 

 change it into subnitrate, which was then digested with bicarbonate 

 of soda to form a double carbonate, which was decomposed with a 

 fresh solution of nitrate of copper. Working thus I obtained a 

 crust of more or less thickness adhering to the surface of the lime- 

 stone. I studied this formation again, modifying the process. The 

 limestone was in slabs of 1 centim. thickness ; and the operation 

 took place in vacuo, in order that the solutions might penetrate the 

 interior of the slabs and the gases formed there escape. By v/orking 

 with a solution not much concentrated, it was ascertained that the 

 first two transformations sufficed for obtaining a slab of malachite 

 sensibly free from lime and nitric acid, having the same grain as the 

 limestone ; the epigeny, therefore, was complete. The grains are in 

 the crystalline state. Under high pressures the same result may 

 probably be obtained with rather compact limestone. 



The effects of the slow actions we have here considered, and 

 which sometimes produce epigeny (that is, replacement of substances 

 by other substances without changing either the form of the body or 

 those of its constituent parts), I explain as follows : — 



When, for example, porous limestone is digested in a concentrated 

 solution of nitrate of copper, there results from the reaction which 

 takes place a disengagement of carbonic acid gas and a production 

 of nitrate of lime, which remains in solution, and of insoluble sub- 

 nitrate of copper, which takes the place of the grains of limestone 

 thus transformed into subnitrate, as the subnitrate is forced to occupy 

 the place of the grains of limestone by the carbonic acid gas and the 

 solution of nitrate of lime filling the pores. The gas and the solu- 



