Fergusonite, an Endotlicrmic Mineral. 



327 



Density before heating 5' 619 



„ after „ 5*375 



It is thns seen that the mineral loses density on incandescence. 



The amount of heat lost by this curious mineral in parting with 

 its helium was determined. The plan of operation was to burn in 

 oxygen a known weight of hydrogen, ascertained by measuring it, 

 under a small platinum crucible, in a calorimeter. The rise of tem- 

 perature was noted. This operation was repeated several times, so 

 as to standardise the calorimeter. Some grams of mineral were 

 then placed in the crucible, and the operation was repeated ; the heat 

 evolved by the incandescing mineral added itself to that from the 

 burning hydrogen, and the rise of temperature was greater. 

 Knowing the heat of combustion of hydrogen, a simple calculation 

 gave the heat evolved by the exothermic change in the mineral. 

 The actual data are as follows : — 



i. ii. in. iy. 



Rise of temperature per gram of 



hydrogen 14-65° 14-68° 14-47° 14-56° 



Additional rise for 6'059o grams 



mineral 213° = 0-352° per gram 



Additional rise for 4*0830 grams 



mineral 1-38° = 0'338° 



Mean rise per gram hydrogen .... 14-59° 



Mean rise per gram mineral 0*345° 



Heat of combustion of 1 gram hy- 

 drogen 34200 calories. 



Heat of decomposition of 1 gram 



mineral 809 ,, 



In these experiments, a correction was of course introduced for 

 the change of temperature of the calorimeter during the experiment, 

 due to the temperature of the surrounding air being higher or lower 

 than that of the calorimeter. 



The percentage of helium in the mineral, by weight, is 0*0194, 

 evolved on incandescence, and on further heating, 0132 ; the total 

 percentage is 0*0326. 



Dr. Shields was so kind as to determine the specific heat of 

 fergusonite. A Bunsen's calorimeter, in thorough working order, 

 was used. The data are : — 



Weight of mineral. 8*789 grams. 



Temperature before introducing into calorimeter. . 17*3° C. 



Deflection (1 mm. = 0*001053 K) 154*4 mm. 



Mean specific heat between 0° and 17 - 3° 0-1069 



