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XV. On the Rate of Evolution of Heat by Orangite. 

 By Horace H. Poole *. 



Outline of Method. 



THE method employed is somewhat similar to that used 

 for determining the heat evolution of pitchblende (Phil. 

 Mag. Feb. 1910 & Jan. 1911) but differs from it considerably 

 in detail, and resembles in principle that used by Pegram 

 and Webb. The orangite in the form of lumps from 2 cm. 

 diameter downwards is placed in a thick- walled airtight 

 copper vessel which is then exhausted. The copper vessel is 

 placed inside two Dewar vessels and the whole buried in ice. 

 The difference of temperature between the copper vessel and 

 the ice is measured by means of a multiple thermocouple. 

 In the centre of the copper vessel is a coil of wire through 

 which a small current can be passed, thus generating a 

 known amount of heat inside the copper vessel, which, being 

 a very good conductor, is sensibly at the same temperature 

 throughout. Assuming that the difference of temperature 

 between the copper vessel and the ice is proportional to the 

 heat liberated in the former we can readily calculate the rate of 

 generation of heat by the orangite by observing the ratio of the 

 temperature differences with and without the electric heater. 



Apparatus. 



The general arrangement of the calorimeter is shown in 

 the sketch (p. 184). A is the copper vessel whose walls are 

 about 1*5 mm. thick, the joints being brazed. In the top is 

 a circular hole about 2 cm. diameter through which the 

 orangite was inserted. This hole was then closed by 

 soldering on a brass cover plate in which is a valve con- 

 sisting of a conical steel plunger which can be screwed 

 down into a brass seating, thus closing a small hole leading 

 to the interior of the copper vessel. This air-valve is the 

 identical pattern employed by Dr. Joly in the gas globes 

 used in his steam calorimeter, and was always found 

 absolutely reliable. Down the centre of the vessel is a tube 

 open at the top but closed at the bottom, in which the 

 heating-coil is inserted. 



B and C are cup-shaped Dewar vessels, D is a circular 

 wooden base soaked in molten paraffin wax and E a cork 

 ring, also soaked in wax, which supports B. The annular 

 groove in the base was filled with hot vaseline and C pressed 

 down into it making a perfectly water-tight joint. 



The thermocouple consists of 16 pairs of silk-insulated 

 * Communicated bv the Author. 



