Intelligence and Miscellaneous Articles. 297 



SOLUBILITY OF CARBONATE OF LIME IN WATEIl CONTAINING 

 CARBONIC ACID. BY M. LASSAIGNE. 



The solubility of carbonate of lime in water containing carbonic 

 acid has been long known to geologists, mineralogists and chemists ; 

 it is in this state that all waters which contain this calcareous salt 

 convey it for the assimilation of plants and animals. 



The spontaneous precipitation of this salt, by contact of the air, 

 fully explains the cause of the deposits formed by the water, and of 

 the incrustations, frequently so abundant, which occur on the sur- 

 face of bodies exposed to the water for a certain time. 



There are other facts, however, connected with the subject which 

 have not been examined into : such are the degree of solubility of 

 carbonate of lime at common temperatures in water saturated with 

 carbonic acid, and the state of saturation in which the salt exists in 

 this condition. 



The plan on which M. Lassaigne operated was to prepare a solu- 

 tion of pure carbonic acid by agitating at a temperature of 50° F. 

 and a pressure of ■29'7 inches : in this solution chalk reduced to a 

 fine powder was digested for twelve hours. 



The solution obtained was filtered to separate the excess of car- 

 bonate of lime, and was perfectly limpid ; it reddened tincture of 

 litmus slightly, but had no immediate effect on syrup of violets ; but 

 after several hours' contact the solution became gradually green. 

 The solution when treated with a little potash became immediately 

 turbid, and deposited white flocculi of hydrated carbonate of lime, 

 which soon diminished in volume by losing water, and were con- 

 verted into a white powder, which partly adhered to the sides of the 

 vessel ; the same effects were obtained with ammonia. When the 

 solution was heated it became turbid, as the gas was expelled by the 

 action of the heat, and carbonate of lime was precipitated. 



It was found by experiment that the carbonic acid, which effected 

 the solution of the carbonate of lime, was five times greater than 

 that which existed in the carbonate of lime dissolved at 50°. 



This result indicates that the calcareous salt to be dissolved in 

 w^ater by carbonic acid, is directly converted into sexticarbonate of 

 lime, that is to say, into a compourid of one equivalent of lime and 

 six equivalents of carbonic acid, which would give CaO, 6C0'- as the 

 formula of the soluble salt. M. Lassaigne thinks it probable that 

 this is the state in which the combination exists in certain sjiring 

 waters which contain it, unless it be regarded as a bicarbonate of 

 lime, rendered soluble by four equivalents of free carbonic acid. 

 The author is, however, disposed to consider the first hypothesis as 

 more conformable to the theory of the saturation of metallic oxides 

 with oxacids. 



In operating at the temperatures of 50" F. and 32° F., a differ- 

 ence was observed in the solubility of neutral carbonate of lime in 

 the same solution of carbonic acid. At the former temperature, a 

 volume of the saturated water dissolved 000088 of its weight of 



