Boltivood — Radio-activity of Cranium Minerals. 277 



oxalic acid was added and the mixture was allowed to stand 

 for 24 hours. The rare earths present together with a little 

 calcium were precipitated as oxalates. The filtrate from the 

 oxalates was evaporated to dryness and cautiously heated to 

 destroy the oxalic acid present. The residue remaining was 

 dissolved in a small amount of dilute nitric acid and this solu- 

 tion was poured into a cold solution of about 1 gram of ammo- 

 nium carbonate in 20 oc of water. To this mixture a little 

 hydrogen sulphide was added. It was then heated to boiling, 

 allowed to cool and filtered. The filtrate was boiled to remove 

 the ammonium carbonate present, made slightly acid with 

 nitric acid, and added to the residue obtained by the evapora- 

 tion of the ether solution. The uranium solution was then 

 transferred to a standard volumetric flask and diluted to 

 exactly 100 cc . Separate portions of this solution 10 cc in 

 volume were measured out with a standard pipette. The 

 uranium was determined in these portions in the following 

 manner : — The solution was diluted to about 50 oc , and 10 cc of a 

 freshly prepared solution of pure yellow ammonium sulphide 

 was added.* The mixture was heated nearly to boiling for an 

 hour, and the separated uranous oxide was filtered off and 

 washed with hot water. After drying, the filter paper and 

 precipitate were ignited in a porcelain crucible, at first gently 

 in the air and finally at the highest heat of the blast-lamp in 

 an atmosphere of oxygen. After determining the weight of 

 the uranoso-uranic oxide obtained in this manner it was in 

 many cases converted into the uranous oxide by a similar, 

 intense ignition in an atmosphere of hydrogen, f and the 

 weight of the uranium when in the form of the lower oxide 

 determined. Very good agreement was shown by the results 

 obtained in this manner. 



Determination of the Thorium.— The determination of the 

 thorium in the minerals was made by separating the thorium 

 from the precipitate of rare earths thrown down by oxalic acid 

 in the solution of the residue remaining after extracting the 

 dry nitrates with ether. The oxalates were converted into 

 oxides, the oxides dissolved by fusion with sodium bisulphate 

 and subsequent treatment with water, and the thorium 

 removed by making use of the solubility of thorium oxalate in 

 an excess of ammonium oxalate. £ In some cases the determi- 

 nation of the thorium was also carried out by other standard 



*Eemele, Zeitschr. f. anal. Chein.. iv, 379, 1865. 



f In the various works on analytical chemistry which I have consulted 

 sufficient emphasis is not placed on the importance of highly heating both 

 the uranoso-uranic and the uranous oxide. A very high temperature is 

 essential in order to insure the complete conversion of either form of the 

 oxide into the other. 



\ This Journal, xxi, 416, 1906. 



