richards, McCaffrey, and bisbee. — calcic oxalate. 391 



In the light of all these facts, there can be no question that calcic 

 oxalate is soluble euough to demand further precautions in washing than 

 are usually taken. The obvious means of diminishing this solubility is 

 to wash the precipitate with a dilute solution of amnionic oxalate, instead 

 of with pure water. With the idea of testing the efficacy of this pre- 

 caution, as well as with the purpose of determining the strength of a 

 new solution of calcic chloride, the following series were made. 



In the first place three portions, removed with a very exact 25 c.c. 

 pipette, were individually precipitated by degrees in our usual fashion 

 from a solution having a volume of two hundred cubic centimeters. 

 They were each allowed to remain four hours before filtering. The 

 weights of calcic oxide resulting upon ignition to constant weight at a 

 bright yellow heat were respectively 0.3479, 0.3480, and 0.3480 gram. 

 The last two of these were now dissolved in hydrochloric acid and repre- 

 cipitaied with the utmost care by means of amnionic oxalate. The 

 weights were now, after ignition, 0.3474 and 0.3475 gram respectively — 

 an average loss of 0.00055 gram or 0.16 per cent. If pure water had 

 been used for washing, the loss would have been much greater. This 

 loss may have been due to incomplete precipitation, or to a slight solu- 

 bility in the wash-water in spite of the presence of amnionic oxalate, or 

 to the mechanical passage of exceedingly small particles through the 

 filter. Whatever may be the cause, this deficiency is clearly a quantity 

 which must apply to most if not all of the foregoing work. Its applica- 

 tion does not cause sufficient change in the results to affect the con- 

 clusions which have been drawn ; in many cases of comparison each of 

 the numbers compared is affected equally. 



It became now an interesting question to carry out in the presence of 

 magnesium the operations just described. Except for the degree of 

 dilution, the other conditions were in every respect like those named. 

 In two experiments where the precipitation took place in a volume of 

 300 c.c, the weights of impure calcic oxide were respectively 0.3491 

 and 0.3489 gram, a gain of a milligram, or 0.29 per cent. In two other 

 cases where the volume was GOO c.c, the weights were 0.3486 and 

 0.3483 gram respectively, a gain of 0.13 per cent. 



This last gain is almost exactly equal to the inevitable loss during 

 filtration, so that the occluded magnesia almost exactly replaced the lime 

 which is not collected. 



The slightly impure specimens of lime of the last two experiments, 

 weighing respectively 0.3486 and 0.3483 gram, were now dissolved and 

 reprecipitated as oxalate, which was washed with ammonic oxalate as 



