﻿Radium Content of Secondary Rocks, 



287 



With regard to the radioactivity of the disintegrated 

 surface materials themselves, several experiments were made 

 upon soils from both the country around Dublin and from 

 the centre of the city. 



The following procedure was adopted. The soil was 

 dried over a water-bath, then gently broken and dis- 

 integrated with the fingers, and finally sifted, and the ratio 

 of the finer particles to the bulk determined. The coarser 

 fragments, quartz pebbles, organic matter, &c. were rejected 

 and only the finer materi;il examined. In both cases, and 

 particularly in the case of the city soil, much trouble may be 

 caused by the presence of organic and carbonaceous matter, 

 which should be first ignited, otherwise volumes of gases 

 incomparable with the capacity of an ordinary electroscope 

 will be evolved. The results given below express the radium 

 content of the fine particles in one gram of the original soil 

 as found in situ. 



Surface Materials. 





Kadiuin per gram 



of fine soil 



particles passing 



a "50" sieve. 



Equivalent radioactivity 

 of soil as found 



in situ. 



Soil from near Milltown, Co. Dublin... 

 Soil from College Park, Dublin 



5-2x10-12 gram. 

 2-8x10-12 gram. 



2-9x10-12 gr. per gr. 

 1-3x10-12 gr. per gr. 





The actual radioactivity of the soil inclusive of its coarser 

 fragments will therefore slightly exceed this figure, though 

 the radium content of the larger particles may be pre- 

 supposed low. The subsoil in the case of the Milltown soil 

 is fine yellow clay, and under the College park consists of 

 gravel and sand. 



Orrell Coal 



Carbonaceous Rocks. 



No "Radium detected in 10 scrams. 



In dealing with carbonaceous specimens by the furnace 

 method, it is necessary, on account of the formation of a 

 volume of carbon monoxide out of proportion to the volume 

 of the electroscopes, to ignite the specimen first in the open, 

 the residue being then put by for a full period of three weeks 

 be-fore actual examination. In the case, however, of the 



