﻿968 Mr. J. Kendall on the Solubility of 



bubbling carbonic acid gas through water containing finely- 

 powdered carbonate in suspension, could not be employed. 

 The solution of the crystalline carbonate under these condi- 

 tions is very slow, and it is essential, to ensure that the 

 precipitate to be obtained afterwards shall be naturally 

 deposited, that no trace of solid carbonate should be present 

 in the liquid. 



The solution was therefore prepared as follows. Finely- 

 powdered calcite Was converted into lime by roasting in a 

 platinum crucible, and transferred to a flask of" Jena glass, 

 filled with water t A second flask was half filled with water 

 through which carbon dioxide had been bubbled for about ten 

 minutes. To this the lime water was added in a glow stream by 

 filtration. A hardened filter-paper was used, supported in a 

 funnel with a long stem, drawn out to a fine jet, dipping into 

 the water. As the liquids met a fine^ cloudy precipitate was 

 produced, which immediately dissolved on shaking the flask. 

 The solution could be kept clear only by means of constant 

 agitation ' if the precipitate was once allowed to settle, it 

 assumed a hard, crystalline torni and was hiost difficult to 

 dissolve. The addition of the lime-water Was stopped before 

 the solution became saturated with bicarbonate, as soon as 

 the precipitate began to be slow in disappearing. 



The solution was now added to a large excess of water 

 Contained in one Of the vessels. The water in the silica flask 

 was maintained, during this addition, at the temperature of 

 the subsequent experiment^ and the bicarbonate solution was 

 added slowly, so that ally immediate precipitation of carbonate 

 took place at the required temperature. This was of special 

 importance in the case of solutions at the boiling-point. 

 The experiments were now carried on exactly as previously 

 described; At 25 5 C. and 50 5 0. the silica flask was 

 suspended in a thermostat and air free from carbon dioxide 

 drawn through the solution ; at 100° C. the carbon dioxide 

 was expelled by boiling. Supersaturation was very liable to 

 occur at the loWer teniperatUres, unless the solution was made 

 concentrated enough to give a large excess of calcium 

 carbonate on removal of the carbon dioxide. 



The precipitates obtained were always tested by the micro* 

 scope, and examination showed :-=■==- 



at 2d° Ci rhombic crystals only. 



at 50° C an intimate mixture of rhombic 



and needle-shaped crystals* 

 at 100° 0. needle-shaped crystals* with a 



very few rhombic. 



