820 EXPERIMENT STATION EECORD. 



autl consequently the solid couipound resultiii;:; wlien lime is added in excess to 

 a sugar solution is one of a series of solid solutions. 



" Cold sugar solutions have a much greater solvent action upon lime than 

 have the same solutions when hot. Heating tends to precipitate one of the 

 solid solutions described above. 



" The ratio of lime to sugar in solution depends on the tem{)erature and on 

 the concentration." 



The results of the studies of the solubility of calcium carbonate lead to the 

 conclusion that — 



" Calcite is the stable form of calcium carbonate at ordinary temperatures. 

 In concentrated salt solutions or at the higher concentrations, aragonite is 

 probably the stable phase. Regarding the formation of natural dolomite, the 

 literature affords no satisfactory explanation. High temperatures and concen- 

 trated solution seem to be necessary for its formation. At the low temperatures 

 calcium carbonate forms a hydrate with five molecules of water of ci'ystalliza- 

 tion. The results upon the solubility of calcium carbonate in water are very 

 discordant, but there is good authority for the generalization that it is more 

 soluble in hot water than in cold. The solubility ... in water containing 

 carbon dioxid increases as the quantity of carbon dioxid in solution increases. 

 [It] is dei)ressed by the addition of caustic soda to the solution. 



"The canstitication of sodium carbonate by lime is more complete in dilute 

 solution. Calcium carbonate forms with sodium carbonate two double com- 

 pounds, whose stability depends on the tempoi'titure and the concentration of the 

 sohition with which they are in contact. 



"The solubility of calcium carbonate is inci'eased by addition of sodium 

 chlorld or of sodium sulphate. When the pressure of carbon dioxid is one 

 atmosphere, the solubility of calcium carbonate passes through a maximum 

 upon increasing the concentration of sodium chlorid in solution, both in the 

 presence and absence of gypsum. When increasing quantities of sodium sul- 

 phate are added, however, the solubility of the carbonate constantly increases. 

 The solubility of calcium carbonate at 25° C. is about six times as great in a 

 saturated solution of sodium sulphate as in a saturated solution of sodium 

 chlorid. When certain solutions containing sodium sulphate and chlorid are 

 saturated with carbon dioxid in the i)resence of calcium carbonate a new solid 

 phase ap|)ears, 2CaS04.3Xa2S04. 



"When the pressure of carbon dioxid is one atmosphere, the solubility of cal- 

 cium carbonate passes through a maximum upon increasing the concentration 

 of potassium chlorid or sulphate in solution. 



" In the presence of sea water the crystalline modification of calcium car- 

 b(niate is more stable than the amorphous form. In general the presence of 

 ammonium salts in solution increases the solubility of calcium carbonate. On 

 Heating, carbon dioxid and ammonia escape." 



Calcium carbonate is soluble in calcium and magnesium salts, in salt solutions 

 which have an acid reaction, and in strong acids whose lime salts are soluble 

 in the strong acid. 



"The various determinations of the solubility of magnesia in water are not 

 In accord. The modern writers, however, agree that this solubility is about 

 10 mg. per liter at 20° C. The solubility of magnesia is augmented by various 

 salts, including magnesium salts, but is depressed by caustic alkalis. Several 

 basic chlorids and bromids of magnesium have been recorded in the literature, 

 and are obtained by adding magnesia to a solution of the chlorid or bromid 

 of magnesium. . . . 



•' Magnesium carbonate forms several hydrates, each of which is stable 

 within limits of concentration and temperature [and] several double compounds 



