Oooch and Kobayashi — Determination of Thorium. 227 



Art. XVI. — The Oxidimetric Determination of Thorium 

 precipitated as the Oxalate; by F. A. Gooch and Mat- 

 susuke Kobayashi. 



[Contributions from the Kent Chemical Laboratory of Yale Univ. — ccxcix.] 



There appears to be in the literature no account of an 

 oxidimetric method for the determination of thorium, 

 based upon the precipitation of that element as the oxa- 

 late, by procedure similar to that which is applicable in 

 the case of many oxalates of definitely known constitu- 

 tion. In the well-known gravimetric method in which 

 thorium is precipitated as oxalate and weighed as thorium 

 dioxide the exact constitution of the precipitated oxalate 

 is not a matter of moment since the final product will be 

 definite whatever the form of the precipitated oxalate 

 may be. It is necessary, however, that definiteness in the 

 constitution of the precipitate shall be assured in order 

 that the determination may be made to depend upon the 

 oxidimetric measurement of the oxalate. The following 

 account gives the results of a study made to fix the con- 

 ditions under which an accurate determination of thorium 

 may be made by estimating either the oxalate radical 

 combined in thorium oxalate or the excess of oxalic acid 

 remaining from a known amount of oxalic acid used to 

 effect the precipitation of the thorium. 



In the experiments to be described a solution of tho- 

 rium nitrate was made by dissolving 10 grm. of that salt 

 (hydrous) in a liter of cold water acidified with 1 cm 3 of 

 concentrated sulphuric acid and this solution was stand- 

 ardized accurately by the gravimetric method in which 

 thorium oxalate is precipitated by oxalic acid and ignited 

 and the residue weighed as thorium dioxide, Th0 2 . 



Potassium permanganate, made up in approximately 

 N/10 solution, and standardized against pure sodium 

 oxalate, was used as the oxidizing reagent and the solu- 

 tion of oxalic acid employed as the precipitant was stand- 

 ardized against the permanganate. In making use of 

 these solutions, the burette readings were corrected for 

 any change of temperature from that prevailing at the 

 time of standardization. 



In all the experiments the precipitation was brought 

 about by the reaction of measured amounts of the stand- 

 ard oxalic acid with measured amounts of the solution 



