PROCEEDINGS OF SECTION B. 365 



Discussion of Results. 



. " corrected activity " 

 The values for the ratio^ are quite constant. 



rh02 



As the volume of air whose activity was measured was constant, 

 the time it took to reach the testing vessel constant, and the solubility of 

 the emanation in the solutions constant (by the use of standard checks), 

 this " corrected activity " is proportional to the emanation evolved in 

 unit time, and thus to the total emanation activity. This total emanation 

 activity is proportional to the radio-thorium, hence the radio-thorium is 

 jjroportional to the thoria. 



The constancy of the ratio in such widely different localities and 

 occurrences is explicable only on the assumption that radio-thorium is a 

 product of thorium. The absence of any thorium emanation in non- 

 thoriferous minerals confirms this fact. 



Taken in conjunction with the results of Boltwood and McCoy and 

 Ross (cited above), it seems very probable that actinium is a radio- 

 product of either thorium or uranium, probably the latter. 



The properties of radio-thorium are somewhat indefinite, owing, no 

 doubt, to the effect of large masses of other rare earths on its real pro- 

 perties ; but, judging from those described by Hahn floe. cit.J, it would 

 seem to show enough similarity to thorium to differ from it somewhat in 

 atomic weight. If so, several changes would seem necessary. The 

 work of McCoy and Ross on thorium salts will serve to determine whether 

 any or all of these are rayless. 



The experimental work in this paper was carried out in the chemical 

 laboratory of Sydne}' University ; and I would like to express my sincere 

 thanks to Professor Liversidge for his kind assistance and encourage- 

 ment. I also owe my thanks to Mr. G. W. Card, of the New South 

 Wales Geological Survey, for his kindness in procuring me Australian 

 specimens. 



10.— GOLD NUGGETS FROM NEW GUINEA POSSESSING A 

 CONCENTRIC STRUCTURE. 



By Professor A. LIVERSIBGE, M.A., F.R.S. 



