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Fergusonite, an Endothermic Mineral. 



Various questions are raised by the behaviour of this interesting 

 mineral. Its evolution, of heat, accompanying its parting with 

 helium, suggest the idea that it is a true endothermic compound of 

 helium. Had its density, as is the ca.se with alumina, and with other 

 oxides which rise spontaneously in temperature when heated, in- 

 creased instead of decreasing, the evolution of heat might justly have 

 been ascribed to polymerisation. But an evolution of heat, accom- 

 panied by a fall in density, leads to the conjecture that the loss of 

 energy is the result of the loss of helium ; and that, conversely, the 

 formation of the compound must have been concurrent with a gain 

 of energy. That the helium is actually in combination, and not 

 retained in pores in the mineral, is evinced by there being no pores 

 in which the helium might be imprisoned. Surface-absorption is 

 equally out of the question, for the mineral is compact. The only 

 remaining possibility is that the helium is in chemical combination. 

 And if this is true, then the compound must be an endothermic one. 



The question next arises, with what constituent of the mineral is 

 the helium in combination ? This question cannot at present be 

 answered. All that can be said is that the amount of helium does 

 not appear to depend on the total percentage of uranium, although 

 minerals containing uranium usually (probably always) contain this 

 element. Even in English pitchblende there was found a trace of 

 helium. And in malacone, a mineral containing no uranium, a trace 

 of helium was found ; also in a specimen of meteoric iron. The 

 presence of niobic and tantalic anhydrides, and of the yttrium group 

 of elements, is also favourable to its presence. But the proportion 

 between the weight of the helium and that of the other elements 

 present makes any calculation of the atomic relations between the 

 helium and the other elements out of the question. 



There is one other substance at least which decreases in density 

 while it evolves heat ; that substance is water, in changing into ice. 

 The effect of compressing ice is to lower its melting point, and at the 

 same time to reduce its heat of fusion. At a sufficiently high pressure 

 there would be a continuous transition from ice to water, no heat 

 change taking place during the transition. Matters would be in a 

 similar condition to those which accompany the change of a liquid 

 into gas at the critical temperature ; the smallest alteration of tem- 

 perature would be enough to bring about the change. In speculating 

 on the origin of such a remarkable compound, is it not allowable to 

 guess that it represents a condition of our earth realised only before 

 solidification had set in ? That these minerals, containing the rare 

 elements, represent a portion of the interior of our planet ; and that 

 under the enormous pressure obtaining at the centre, combination 

 with helium was an exothermic event ; and that such compounds, 

 having by some unexplained accident come to the surface of the 



