RADIUM. 



1^)3 



diffii.sion of the ft ra3^s by the bodies through which they pass. Sharp 

 radiographs are obtained by deflecting' the ft rays with a magnetic 

 lield, so that only the y rays remain; but the y rays are so feeble that 

 several days' exposure must then be employed. 



V. 



Eadium salts continually give off heat." The evolution of heat is 

 so great that it may be shown in a rough experiment made with two 

 ordinary mercury thermometers. Two similar vacuum-jacketed recep- 

 tacles (A and A', Fig. 6) are employed. In one of them, A, let us 

 suppose, is placed a test tube containing 0.7 gram of pure radium 

 bromide, and in the second, A', is a similar tube of inactive substance 

 such as chloride of barium. The temperature of each inclosure is 

 indicated by a thermometer whose bulb is close to the test tube. The 

 top of each vessel is closed by a wad of cotton. In these conditions 

 the thcnnomoter t, which is placed in the same vessel with the radium, 



continually indicates a temperature 

 about 3'-' higher than -that of the other 

 thermometer t'. 



A determination of the amount of 

 licat emitted by the radium may be 

 made with the aid of the ice calorimeter 

 of Bunsen. When a tube of radium is 

 placed in the calorimeter, there is ob- 

 served a continual evolution of heat, 

 which ceases when the radium is with- 

 drawn. Measurements made with a 

 sample of radium which had been pre- 

 pared a long time previously indicated 

 that each gram of radium gives off 

 about 80 small calories per hour. Thus radium gives oft' sufticient 

 heat in an hour to melt its own weight of ice. This evolution of heat 

 produces no change in the appearance of the salt, nor can any ordinary 

 chemical reaction be pointed out as the source of the heat evolved. 



It has been shown that a radium salt when lirst prepared gives oft' 

 comparativel}^ little heat, and that the heating increases steadily toward 

 a maximum amount, which is not fully attained at the end of a month. 

 When a salt of radium is dissolved in water and the solution is 

 placed in a sealed tube, the quantity of heat evolved by the solution is 

 at tirst feeble, but increases and tends toward a constant value, which 

 is attained after about a month. When this constant state is reached, 

 the salt in solution evolves the same amount of heat which it would 

 give if in a solid state. 



The amount of heat given out l)y radium at dift'erent temperatures 

 may be determined l)y causing it to boil a liquefied gas, and measuring 



Fig. C). — Continuous evolution of iK-at by 

 radium. 



o Curie and Laborde, C. R., March 16, 1903. 



