96 



changes. Whatever the testimony of the balance may have been, some 

 of the reactions must have been accompanied by a loss of weight, for it 

 has been proven by chemical means that such reactions are frequently 

 attended by the escape of something through the walls of the glass tubes. 1 

 This loss Is readily explained by the disintegration theory. If one wishes 

 to explain it by assuming the diffusion of ordinary gases through the glass 

 walls of the tube he must explain the fact that, in many cases, it was the 

 heavy and least volatile substances that escaped fastest. 



In the third place the element of time has been overlooked. Matter 

 may be disintegrating, but at such a slow rate that in the limited time 

 over which experiments have been extended the balance has failed to de- 

 tect the change. As far as our experience goes the time of rotation of 

 the earth is constant ; but we know that it cannot be absolutely constant. 

 The moon has slowed down until it takes a month to make one turn. To 

 an ephemeral insect almost everything would appear to be eternal. With 

 due respect for the balance and the wonderful work it has enabled chem- 

 ists to do, it must be admitted that it is, comparatively, a very crude in- 

 strument. Let me prove it. 



Suppose we fix the limit of sensibility of the balance at one one-thousandth 

 of a milligram. Our books on chemistry tell us that lcc of gas, say hydro- 

 gen, at ordinary pressure contains 4X10 19 molecules. The density of II being 

 896X10- 7 . then 1 gm. of H would consist of (4X'10 19 ) -h (896 X ICr 7 ) molecules. 

 Taking 112 as the ratio of the molecular weights of radium and H, then 1 gm. 

 of radium would consist of [(4X 10 19 y h- (896 X 10~ 7 )] -=-112 = 4X 10 22 molecules. 

 Therefore .001 ragm. of radium would consist of 4X10 16 molecules, and this 

 would be the smallest possible number that our most sensitive balance could de- 

 tect. If the gram of radium were disintegrating and its molecules escaping at 

 the rate of a million per second it would require 4X10 10 seconds = 463,000 days 

 = 1270 years for that gram of radium to lose in weight only the one-thousandth 

 part of one milligram, all the while its molecules trooping away at the rate of a 

 million per second. 



The population of the earth is about 1,500 millions. The smallest 

 number of molecules a balance will detect is 4xl0 16 , or about 26,600.000 

 times the population of the earth. We wonder if Mars is inhabited. If 

 a Martian were to come to the earth to make an experiment to determine 

 whether or not the earth is populated and he had no better instrument 



l C. Zenghelis. Zeittchr. Phys. Cheui.65,3, pp. 341-338, Jan. 5, 1909. 



