378 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



which form a complex ion or uiidissociated substance in solution involving 

 eitlier magnesium or oxalic acid. 



One of the most effective causes diminishing the concentration of the 

 magnesic oxalate, and therefore the occlusion, should be the hydrogen 

 ion, for this tends to remove the oxalic ion, and hence to cause the 

 ionization of undissociated magnesic oxalate. 



Another effective cause should be an increase in the concentration 

 of amnionic salts present, which not only exert the effect of any other 

 partially dissociated salts, but have also the well-known property of 

 forming complex compounds with magnesium. This formation naturally 

 removes magnesic ions and hence magnesic oxalate from the solution. 



A third obvious means of diminishinjj the concentration of the majr- 

 nesic oxalate is by diluting the solution. By this process, the actual 

 amount of undissociated oxalate is diminished, and the concentration of 

 the undissociated part is thus diminished even more rapidly than in the 

 ratio of the changing volumes. All of these tendencies except the sec- 

 ond apply to the calcium as well as to the magnesium, although to a less 

 extent, for calcic oxalate is far less soluble than magnesic oxalate. Cal- 

 cium has not so great a tendency to form complexes with ammonic salts 

 as magnesium. 



These relations are partially expressed by the following scheme, in 

 which no attempt is made to express the exact nature or the ionization 

 of the magnes-ammonium complex : — 



MgCL tz 



+ 



X NH4CI 



Mg(NH,).Cl.,^,(?) 



2 CI- + Mg++ 



+ + 



211+ + C20,= ±=^ H2C2O4 



2HC1 MgCaOi in solution 



MgC„04 + CaCoO^ 



Precipitate 



Reviewing the older work upon this subject, one finds that most of 

 the known tacts support the hypothesis. Fresenius, in the few exi)eri- 

 ments which are recorded in the end of the second volume of his 

 "Quantitative Analysis,"* showed that the weight of the calcic pre- 

 cipitate obtained was less when the dilution was greater ; that it was 



* Fresenius, Quantitative Analyse, 2, 821 (1877-1887). 



