Rose on the Heteromorphous Conditions of Carbonate of Lime. 517 



G. Rose* has communicated the commencement of a series of 

 experiments on the circumstances under which the different forms 

 of carbonate of lime (calc-spar, Arragonite, and chalk) are formed. 

 When chloride of calcium was added to a fusing mixture of equi- 

 valents of carbonate of potash and carbonate of soda, it dissolved 

 without effervescence ; when a portion of the cooled mass was 

 placed in water it gradually dissolved, leaving a pulverulent 

 residue of carbonate of lime. Viewed under the microscope 

 shortly after treatment with water, it was found to consist of 

 small globules, which after twenty-four hours changed into well- 

 formed individual or aggregated rhombohedra. 



When another piece was thrown into hot water and boiled, it 

 was seen to consist of microscopic prisms with occasional rhom- 

 bohedra. This residue, on standing, gradually changed into 

 aggregations of calc-spar. 



The same results were obtained when calc-spar or oxalate of 

 lime were added to the fusing mixture, except that in the latter 

 case some carbonic oxide was given off. 



As calc-spar had not been directly formed in these experiments, 

 Rose, with Siemen's assistance, repeated Sir James Hair's cele- 

 brated experiment, by which marble is said to be obtained when 

 chalk or compact limestone is heated in a closed vessel under 

 pressure. Fine chalk was pressed in a musket-barrel which was 

 hermetically sealed, and heated in a gas furnace, the temperature 

 of which could be raised so as to melt large masses of platinum. 

 During the experiment the barrel burst. On afterwards exami- 

 ning the contents, the chalk was agglomerated into a compact 

 light-bluish mass, full of cracks. The experiment was repeated 

 with small pieces of calc-spar, but the same result was obtained. 

 It appears thence that these substances are not changed into 

 distinctly crystallized calc-spar by being heated in a closed space. 

 Rose considers that Sir James Hall thought the compacted mass 

 to be crystalline marble. 



When a solution of carbonate of lime in carbonic acid water 

 was allowed to stand, a crust and a sediment gradually formed. 

 The latter consisted of chalk, the former was found to be com- 

 posed of very perfect microscopic rhombohedra. 



When the liquid was placed on a hot stove, a disengagement 

 of gas commenced, which lasted for six or eight hours. In this 

 case the crust which formed consisted chiefly of acicular crystals 

 of Arragonite, while the deposit was nothing but well-shaped 

 rhombohedra. 



When the solution was evaporated, prisms of Arragonite and 

 rhombohedra, laminse and plates of calc-spar were obtained. 



Hence by evaporating a solution of carbonate of lime in car- 

 * Ber. der Berl Akad. I860. 



