130 REPORTS ON THE STATE OF SCIENCE. 



pitchblende have been worked up for it. Half of it changes in 143 days, 

 which is more than a thousand times faster than radium. Hence the 

 activity is of the order of a thousand times greater, but correspondingly 

 the quantity in pitchblende is of the order of a thousand times less than 

 in the case of radium. 



No other cases except those mentioned of two elements always 

 occurring together in constant ratio in nature have as yet been proved, 

 but if this is done it is, as stated, almost sufficient to prove that the rarer 

 element has been formed from the one present in greater abundance, and is 

 itself changing further into some other constituent of the natural mineral. 

 It remains to point out the limitations of this argument. No 

 equilibrium state can be reached if the parent element is not the most 

 stable of the series. If, for example, thorium were being produced from 

 uranium, there could be no constant ratio between the quantities of 

 uranium and thorium, for the I'ate of change of the thorium is five times 

 slower than that of uranium, according to a recent accurate determination 

 of Brigg. This indicates that thorium is not a member of the uranium- 

 radium series, for in this case there would exist no proportionality 

 between the uranium and the radium, although there would be between 

 the thorium and radium. The limitation serves to show that the case 

 is likely to be rare if the instability of the radio-elements, as is commonly 

 supposed, is in some way connected with their heavy atomic weight. 



We are thus led to consider constancy of association in nature apart 

 from a constant ratio of quantity. This, it will be remembered, gave the 

 necessary clue indicating helium as a disintegration product of radium. 



These cases are common enough in chemistry, but little can be at 

 pi'esent deduced from existing knowledge. Tantalum and niobium are two 

 inseparable companions in nature. Donald Murray has recently directed 

 attention to the companionship of silver and lead in this connection, and 

 examples could be multiplied. We are still in darkness as to whether 

 there is any process complementary to disintegration, simultaneously 

 building up the elements of heavier atomic weight and maintaining their 

 quantity, and this constant association in nature could result as well from 

 a simultaneous formation of both elements or from the building up of one 

 from the other. Without other evidence no certain conclusion can yet be 

 drawn in this field. ^ 



A slightly different phase of the same question is seen in an element 

 having an approximate constant rarity in nature after prolonged and 

 extensive search for it. I have drawn attention to the fact that the 

 coinage metals, in particular gold, silver and platinum, of necessity 

 fulfil this condition more or less completely, indicating that these metals 

 are likely subjects for a direct examination for evidence of slow changes. 

 I have referred to the case of coins, where for practical reasons a direct 

 examination is probably more likely to yield fruit than in any other case. 



So far as the economic evidence goes, the scarcity of gold is a matter 

 of concentration, like that of I'adium, for in small quantities it is, like 

 radium, very widely distributed. Seeing that 500 tons of gold were produced 



' In the writer's opinion Mr. Strati's remarkable results, showing that the 

 quantity of radium in the common rocks of the earth's crust is so great that a crust 

 composed of these rocks only a few miles thick would supply the heat lost by the 

 earth and maintain it at constant temperoture, seem to suggest the first experimental 

 indication that there is actually taking place a process of atomic upbuilding with 

 the necessarily enormous absorption of energy. 



