Boltwood — Thorium Minerals and Salts. 425 



buted to the presence of actinium in the compound. In the 

 oxide, No. 6, the greater portion of the actinium had been 

 separated from the thorium in some stage of the chemical 

 treatment. 



It is important to mention a certain fact with regard to the 

 chemical properties of radio-thorium. Particular emphasis 

 has been laid by Ramsay* on the statement that the oxalate of 

 radio-thorium is insoluble in an excess of ammonium oxalate. 

 It has already been pointed out by Mme. Curief that the 

 chemical properties of a radio-active element can not be deter- 

 mined with certainty from experiments conducted on a mix- 

 ture of a small quantity of the active element with very large 

 proportions of a neutral substance. The writer has found this 

 to be particularly the case with actinium, which, when 

 separated from a mineral containing thorium and other rare 

 earths, persistently remains with the thorium through subse- 

 quent chemical operations, including the extraction of the 

 thorium oxalate from a mixture of rare earth oxalates by an 

 ammonium oxalate solution, but which, when separated (as 

 " emanium ") from a mineral containing no thorium, remains 

 just as persistently with the lanthanum, if this element is 

 present in the original mineral or is added to its solution, and 

 remains undissolved if the lanthanum oxalate is treated with 

 boiling ammonium oxalate solution. Similar conditions appear 

 to hold for radio-thorium, and when accompanied by thorium 

 its oxalate is readily soluble in a solution of ammonium oxa- 

 late. The insolubility of the radio-thorium in the thorium- 

 free preparation described by Ramsay can in no sense be con- 

 sidered as indicative of its chemical behavior in an entirely 

 pure condition. In these cases we have probably to do with a 

 peculiar and novel sort of chemical entrainment which is quite 

 distinct from the ordinary processes of solution and precipita- 

 tion. 



It is a very fortunate circumstance that, while the work 

 described in this paper was in progress and before any definite 

 conclusions had been reached, the investigation of the radio- 

 active properties of thorium was quite independently under- 

 taken by Mr. Dadourian, who now presents his results in a 

 paper published in this same number of the Journal. Mr. 

 Dadourian made use of a method which was distinctly dif- 

 ferent from that of the writer, and which depended on the 

 measurement of the activity of the deposit formed on a nega- 

 tively charged plate exposed to the emanations escaping from 

 solutions of thorium salts and minerals. The agreement 



* Journ. de Chem. Phys., iii, 617, 1905. 

 f Compt. rend., cxxxii, 273, 1906. 



Am. Jour. Sci.— Fourth Series, Vol. XXI, No. 126.— June, 1906. 

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