McCoy and Ross — Thorium Compounds. 



443 



Table XIII. Thorium Dioxide D. 



E 



•2088 57-6 57-2 -00365 

 •1083 35-9 35-7 '00303 

 •0585 21-6 21-5 '00272 



{^) r -00240 



Table XIV. Thorium Dioxide, 



Sample Source ( — ) 



A Th Nitrate -00387 



B Orangite No. 1 -00243 



C Thorite No. 2 -00230 



D Monazite No. 4 -00240 



Mean of B, CandD.. 

 k 



1-1 



(•6) 



(•3) 



fc, 



P 



517 



588 



823 



936 



870 



989 



833 



948 



958 



The mean value of -^ for the last three samples is 958, 



while the value of the corresponding ratio for thorium in min- 

 erals is 953. From this it follows that none of the radio- 

 thorium has been separated from the thorium by the processes 

 of analysis. However, we have been able by certain other 

 processes, many times repeated, to reduce the permanent 

 activity of thorium considerably below that of sample A, pre- 

 sumably by the removal of part of the radio-thorium, but we 

 have not yet obtained thorium which is, or remains, entirely 

 inactive. We shall discuss this problem fully in a later paper. 

 It is possibly still a question whether thorium, entirely freed 

 from radio-thorium, ThX, etc.. will produce rays capable of 

 ionizing gases ;* but that it is undergoing transformation, 

 rayless or otherwise, which gives rise to active products, seems 

 certain from the fact that the portion of the radio-activity due 

 to thorium, of any mineral, is directly proportional to the 

 thorium content of that mineral. We believe our experiments 

 also show clearly that the activity of thorium compounds is 

 not due to bodies accidentally retained by thorium (as radium 

 frequently is by barium sulphate), but that the radio-thorium, 

 ThX, etc., are disintegration products of thorium. 



Kent Chemical Laboratory, 

 University of Chicago, April, 1906. 



* Inactive or slightly active thorium has been reported several times (Hot - 

 man and Zerban, Ber. d. chem. Ges., xxxvi, 3093, 1903; Zerban, ibid., 

 xxxviii, 557, 1905; Baskerville and Zerban, J. Amer. Chem. Soc, xxvi, 

 1642, 1904 ; but in such cases no statement has been made of the minimum 

 intensity of activity that could have been detected. 



