Richards, McCaffrey, and bisbee. — calcic oxalate. 387 



end of two hours and a half there probably still remained a trace of 

 calcium in the solution. 



While the possibility of separating calcium from magnesium with con- 

 siderable completeness by a single operation had thus been demonstrated, 

 one point still remained to be studied. In the course of the washino- of 

 these precipitates of calcic oxalate, it was noticed that the wash-waters 

 always gave a faint opalescence with neutral argentic nitrate, an opales- 

 cence which dissolved in nitric acid. Unlimited washing seemed not 

 to free the precipitate from this substance, hence the substance must 

 have been calcic oxalate itself. In short, calcic oxalate appeared to be 

 soluble in boiling water to an extent sufficient to affect a precise analysis. 

 Since no account of accurate determinations of the solubility of calcic 

 oxalate in boiling water could be found, the next problem was to deter- 

 mine this solubility. 



The calcic oxalate was precipitated in the usual manner and washed 

 with exceeding thoroughness. A solution, not necessarily saturated, but 

 closely resembling one which might be obtained in the process of wash- 

 ing, was made by stirring the powder for fifteen minutes with water in 

 a platinum dish kept at the desired temperature. Of the three usual 

 methods of analyzing such a solution, — by weighing, titration, and the 

 measurement of electrical conductivity, — volumetric determination 



Solubility of Calcic Oxalate. Series I. 



