PROCEEDINGS OF SECTION B. 361 



cold and boiling solution. The clear filtrate was neutralised by am- 

 monium hydrate (5E solution at first, and E very carefully afterwards) 

 till a slight opalescence showed permanently. Tliis was removed by a 

 few cc of 5EH2SO4. A cold-saturated solution of ammonium oxalate 

 was then added till a heavy precipitate formed permanently : then the 

 precipitation was completed by 50c. c. of cold-saturated solution of oxalic 

 acid. 



Pyrochlore (Tasmania) ) 



Aeschynite (Miask, Ural Mountains) ) 



As these possibly contained both titanium and zirconium, in addition 

 to thorium, they were treated by (e) Delafontaine's method. They were 

 fused with twice their weight of acid potassium fluoride, and the melt 

 treated with water faintly acidulated with HF to remove any titanium or 

 zirconium as the double fluorides with potassium. The residue of fluo- 

 salts was then treated with concentx-aled H2SO4 till the conversion into 

 sulphates was complete. The sulphates were dissolved in ice-cold water 

 and treated as the monazites. The rare eai'th oxalates were converted 

 into nitrates, either directly by concentrated HNO3 or indirectly by con- 

 version into hydroxides (by excess of KOH), which were dissolved in 

 dilute HNO3. The indirect method was found preferable for the richer 

 thoriferous minerals, as nearly pure thorium oxalate requires much time 

 for complete decomposition by concentrated HNO.,. 



For the estimation of the ThOj present, two methods — the NajSjOs 

 method and the m nitrobenzoic acid method — were used to check each 

 other. 



Na,S./)s Method. 



The nitrates obtained as above were evaporated to dr} ness and taken 

 up with water. (Any basic eerie nitrate was redissolved in HNO3 and 

 the evaporation remade more carefully.) The solution of about loOc.c. 

 volume was then precipitated by 15-2oc.c. of a cold-saturated solution of 

 NajSoOa (free from sulphate), boiling: for five (5) minutes after the 

 addition of the Na^^SaOj. The precipitate was very thoroughly washed 

 and dissolved in 5EHC1. It was then evaporated to dryness, taken up 

 in 5U-120c.c. water, according to richness, two or three drops of concen- 

 trated HCl added, and the thorium precipitated by Na^S^Oj. Another 

 similar purification was made and the resulting precipitate reserved. The 

 three united filtrates were precipitated by JNH^OH, the hydroxides 

 filtered, washed, and dissolved in HCl, and the chlorides evaporated. 

 They were precipitated in about 50c. c. solution by NaaS^Os- This preci- 

 pitate was purified once. The two filtrates were united and treated for 

 thorium, and the resulting precipitate added to the other two. All three 

 were filtered through the same filter paper and washed thoroughly. 

 The united precipitates were then dissolved in 5EHC1, evaporated 

 almost dry, and thorium oxalate precipitated by excess of oxalic acid. 

 The precipitate was ignited and weighed as ThOo. 



Throughout the analysis all sulphur residues remaining after dis- 

 solving any thiosulphate precipitates in HCl were ignited and fused with 

 KHSO4, then taken up with water acidulated with HCl and precipitated 

 as hydroxides. These hydroxides were dissolved in HCl and added to the 

 main bulk. The amounts present varied, but were generally very small. 



(e) Delafontaine : Chemical News, 75 (1897), p. 230. 



