68 Ashman — Radio- Activity of Thorium. 



sive reagent and the necessity of working in alcoholic solutions. 

 Schlundt and Moore* also found that precipitation with nitro- 

 benzoic acid removed some form of radio-active matter from 

 thorium but they did not identify the products separated. 

 The extensive use of meta-nitrobenzoic acid by McCoy and 

 Rossf in the analysis and purification of thorium minerals sug- 

 gested also the use of this reagent as a substitute for fumaric 

 acid. It was found that the first precipitate of thorium with 

 meta-nitrobenzoic acid lost its activity at a much greater rate 

 than would correspond to the period of thorium- A. The 

 minimum activity was reached in four or five hours, then an 

 increase due to the growth of thorium-X and its products set 

 in. When the precipitate was dissolved and the thorium 

 reprecipitated at the end of two hours the activity was dimin- 

 ished still further ; and it was found that two additional pre- 

 cipitations at intervals of two hours gave finally pure thorium 

 dioxide free from thorium-X and all its subsequent products. 

 The activity of the oxide prepared by this method began 

 immediately to increase. On account of the convenience of 

 working in aqueous solutions and the ease and rapidity with 

 which filtration takes place, the nitrobenzoic acid method 

 offers many advantages over the fumaric acid method, and 

 leaves nothing to be desired concerning purity of the product 

 and completeness of separation. The precipitation with nitro- 

 benzoic acid was carried out in the following manner : The 

 solution of thorium nitrate, containing approximately 2 grams 

 of thoria, was nearly neutralized with dilute ammonia, methyl 

 orange being used as indicator, a slight excess of a saturated 

 solution of nitrobenzoic acid was slowly added, and the mix- 

 ture kept at a temperature of 80° for a short time. The pre- 

 cipitate of thorium nitrobenzoate was filtered from the solution 

 and washed well with water. Two hours later it was dissolved 

 in dilute nitric acid, diluted to about 300 cc , almost neutralized 

 with ammonia and the thorium then reprecipitated by the 

 addition of 400 cc more of the nitrobenzoic acid solution. The 

 fourth thorium precipitate was rapidly filtered from the solu- 

 tion, placed directly in a platinum crucible and ignited first 

 over a Bunsen flame and finally, at the highest attainable tem- 

 perature of the blast lamp for ten minutes. Four lots of 

 thorium oxide were thus prepared ; two from " old " material, 

 two from thorite. Oxide "A" was from sample "A" of 

 thorium nitrate described by McCoy and Ross.J It had been 

 precipitated 100 times with ammonia and was known to be 

 poor in radiothorium. It was repurified by the nitrobenzoic 



*Loc. cit. 



f J. Am. Chem. Soc, xxix, 1709. 1907. 



% J. Am. Chem. Soc, xxix, 1712, 1907. 



