Duane — Heat Generated by Radio-active Substances. 257 



Aet. XXV. — On the Heat Generated by Radio- active Sub- 

 stances i by William Duane. 



Since the discovery of radio-activity questions relating to 

 the source and the transformations of the energy involved in 

 the processes have been considered of prime importance. 

 Early in the history of the subject Curie and Laborde* dis- 

 covered that radium generates heat continually, and also that 

 the heat effect increases as the emanation accumulates. A 

 little later Rutherford and Barnesf found that the emanation 

 and the first few products of radium that form its induced 

 activity produce their shares of heat, and more recently still 

 Pegram and Webb X have succeeded in detecting a small heat 

 effect in a large mass (about four kilograms) of thorium oxide. 



The ordinary methods of measuring heat (an ice calorimeter 

 for instance) are sufficiently sensitive to detect and measure 

 the heat generated by the quantities of radium, its emanation 

 and its induced activity now at our disposal. I have made 

 recently a number of experiments on the heat effects of other 

 radio-active substances, and in these I have had to use special 

 methods. At first I employed a modification of the differen- 

 tial air calorimeter devised by Rutherford and Barnes (1. c), 

 but this was not sensitive enough and I then constructed a 

 new instrument which is considerably more sensitive than the 

 differential air calorimeter. The method is based on the rapid 

 increase in the vapor tension of a very volatile liquid when 

 the temperature rises. A and A' (fig. 1) represent two glass 

 vessels, which are joined by the capillary tube B. The vessels 

 are half filled with the volatile liquid, and almost all the air 

 is pumped out by means of a water aspirator through the tube 

 C, which is then sealed off. A small bubble formed out of 

 the residual air left in the vessels is inserted in the tube B, 

 and the displacement of this bubble is observed by means of 

 a reading telescope or by projection with a lamp, lens and 

 scale. I usually employ the latter method, and the displace- 

 ment of the image on the scale is about eight times that of the 

 bubble in the tube. 



It is not difficult to place a bubble of any desired length 

 in the tube B. It is sufficient to turn the apparatus upside 

 down, and let the liquid run out of the tube. Then 

 on replacing the apparatus right side up one finds the 

 tube more or less completely filled with air. The bubble is 



* Comptes rendus, cxxxvi, p. 673, 1903. 

 ■(•Nature, Oct. 29, 1903; Phil. Mag., Feb., 1904. 

 X Science, 1904; Le Radium, 1908. 



