Precipitated as Thorium Fluoride. 373 



0-04 grm. and 04 grm., in a volume of 30 cm 3 , or that the 

 concentrations of the solution in respect to free acetic 

 acid may be between the* limits of about 02 N and 0-2 N 

 acid. In the work to be further described these condi- 

 tions of acidity were preserved. 



In putting this general procedure to the test, portions 

 of the fluoride solution were measured exactly from a 

 burette and in some cases the portions were further 

 diluted with water. Enough acetic acid was added to 

 make the acidity of the solution in respect to that acid 

 lie between the limits of about 0-02 N and 0-2 N — 

 amounting to a content of about 0-12 grm. and 1-2 grm. of 

 free acetic acid in 100 cm 3 of solution. The thorium 

 nitrate solution was run in slowly in amounts about 25 fo 

 in excess of that theoretically required in the reaction, 

 with constant stirring. The mixture was allowed to 

 stand for a few hours and the precipitate after several 

 washings by decantation with cold water containing a 

 drop of glacial acetic acid in 25 cm 3 , was filtered off upon 

 ashless paper supported by a perforated platinum cone 

 so that suction might be applied at the end of this wash- 

 ing, washed, and ignited in platinum. The weight of 

 thorium oxide, Th0 2 , remaining was taken as the gravi- 

 metric measure of fluorine precipitated as thorium 

 fluoride, ThF 4 .4H 2 0. 



The filtrate containing the excess remaining from the 

 known amount of thorium nitrate taken was poured into 

 a measured amount of a solution of oxalic acid containing 

 a few drops of concentrated sulphuric acid and allowed 

 to stand on the steam bath for a period of from fifteen to 

 twenty minutes. The precipitated thorium oxalate was 

 filtered off on asbestos in a perforated crucible, washed 

 with cold water containing one drop of concentrated 

 sulphuric acid in every 25 cm 3 , and oxidized by stand- 

 ard permanganate according to the method previously 

 described 4 for the volumetric determination of thorium 

 precipitated as the oxalate. The difference between the 

 amount of thorium originally present and that found in 

 the filtrate was taken as the measure of fluorine by the 

 volumetric process. 



It was found that the addition of an emulsion of asbes- 

 tos to the liquid containing thorium fluoride in suspen- 

 sion obviates the necessity of several decantations and 



4 Gooeh and Kobayashi; this Journal, 45, 227. 



