144 Prof. J. Joly on a Method oj Investigating the 





Result by 

 Solution. 



Result by 

 Fusion. 



Bedded basalt, Ghats 



2-7X10- 12 

 8-2 „ 

 4-9 ., 

 3-8 „ 

 2-4 „ 

 36 ., 

 4-3 „ 



2-2x10-12 

 3-2 „ 

 2-3 ., 

 2-3 „ 

 1-5 „ 

 1-6 „ 

 2-2 „ 



„ ,, Pavagad Hill ... 

 Basalt dyke, Palasi 



Bedded basalt, Palasdari 



„ Keloli 



,, ,, Kaaara 



Means 





1 regard these last results as rather telling against the 

 earlier values than against the method by fusion ; although I 

 am unable to assign any cause for excess in the original 

 determinations *. 



Some time after the completion of the foregoing expe- 

 riments I obtained one of the tube-furnaces of the firm of 

 Herseus. This furnace consists of a porcelain tube 5 cm. 

 internal diameter and 30 cm. long, upon which is wound a 

 ribbon of platinum, the whole being protected by a very 

 .effective lagging. It had originally been intended to carry 

 out the fusions in an inner tube of porcelain or silica. It was 

 found, however, that the first material allowed gas to diffuse 

 in at high temperatures, and the second was attacked by the 

 volatilized alkaline carbonates. Finally a platinum inner 

 tube, prolonged by silver ends where the temperature was 

 lower, had to be provided. The cost of this is a serious 

 drawback to the use of these furnaces. The projecting ends 

 being kept cool by a water-dropping arrangement and ex- 

 tending 10 centimetres beyond the heated part of the tube, 

 may be closed with rubber stoppers. To protect these from 

 i-adiated heat loose plugs of fireclay are inserted at each end 

 before placing the stoppers in position. The rock charge is 

 carried in a platinum boat half circular in section, with 

 rounded ends ; it is 3 cm. in diameter, and 20 cm. in length. 

 With proper precautions in raising the temperature 7 grams 

 of rock and 28 grams of the carbonates may be dealt with in 

 .this boat, or even larger charges. 



The end stoppers are fitted with tubes to lead off or admit 

 gases. At one end the tube entering the stopper is a centi- 

 metre in diameter, and closed with a plate of glass so that a 



* Unless a rather improbable spurious leak due to the action of light 

 ..on the sulphur insulation (an effect not known at the time) be responsible. 



