Quantity of Radium in Rocks and Minerals, 8fc, 139 



water which is condensed over from the contents of the 

 crucible. They then traverse two U-tubes rilled with soda- 

 lime, and finally, so far as not absorbed, enter a strong rubber 

 bag. The thin rubber bags used for toy balloons will not do 

 for this purpose as they soon develop dangerous leaks. The 

 kind used for footballs is very suitable. The bag has to 

 hold, without generating appreciable back pressure, about 

 600 c.c. 



An experiment is carried out as follows : — The rock is 

 ground so as to pass a sieve of 60 mesh to the inch and 

 mixed with about four times its weight of the mixed carbo- 

 nates of sodium and potassium. The mixture is introduced 

 into the crucible and well shaken down. The crucible is 

 then fitted into its mould in the magnesia powder, the cover 

 placed in position, and finally the silica shade placed over all. 

 The current may then be turned on and very gradually in- 

 creased in intensity till a red heat is attained. At this stage 

 time must be given for nearly complete evolution of the C0 2 

 or there will be risk of boiling over. When the violent 

 ebullition has subsided the temperature is still further in- 

 creased till the interior of the crucible is at a bright yellow- 

 orange or even pale yellow-white. The gases contained in 

 the bag are then admitted into the exhausted electroscope, 

 and when the bag is empty the tube t is opened and the 

 pressure in the electroscope brought up to that of the atmo- 

 sphere by air which has passed through the furnace and the 

 absorption-tubes, washing out any residual emanation. 



By inserting a platinum-palladium couple in the crucible 

 I found that, in a tvpical experiment, the temperatures and 

 durations of the same were as follows: — 



Time from 



Current 







start. 



(amps.). 



Temperature, 





20 mins. 



19 



830° 



Garbs, melting. 



30 „ 



20 



860° 



Boiling. 



50 „ 



21 



900° 



Boiliug violently. 



60 „ 



29 



1150° 



Yellow-white ; efferves- 

 cence over. 



The substance being dealt with in this experiment was a 

 granite. It is evident that the greater part of the decompo- 

 sition is effected at a temperature between 860° and 900° — a 

 full red heat. 



The effervescence in the case of a basic rock is not so 

 intense nor so prolonged as when dealing with an acid rock. 

 The addition of a couple of grammes of boracic acid (I owe 



