Heat inn Effect of the 7 Rays from Radium. 6*23 



very well, giving- for the heating effect of the pure radium 

 98*5 gram-calories per hour. (Rd=258.) On surrounding 

 the radium lube with *7 of a millimetre of lead in the same 

 apparatus, no appreciable change in the heating effect was 

 obtained. 



In order to surround the radium bromide with a thickness 

 of lead sufficient to absorb a large proportion of the 7 rays, it 

 was found necessary to use a calorimeter of much larger size. 

 As the increase in the size of the calorimeter caused a corre- 

 sponding increase in the errors involved from the ingress of 

 heat, two exactly similar calorimeters were used. Similar 

 vessels containing mercury were placed respectively on the 

 opposite pans of a balance and supplied equal quantities of 

 mercury to each calorimeter in order to compensate for the 

 increase in the melting of the ice from outside sources. The 

 calorimeters were made with an inner tube 4 centimetres wide, 

 and an outer mantle 8 centimetres wide. Each calorimeter 

 was placed in a stand and surrounded by an air mantle, and 

 each stood in an accumulator vessel. Both vessels were 

 placed >ide by side in a box. Fresh cracked ice was placed 

 in the vessels which were connected by a siphon tube. After 

 waiting from two to three hours for the temperature to 

 become steady, readings were commenced. After ten hours 

 a fresh tilling of ice had to be made. The radium bromide 

 tube was surrounded by a lead cylinder which stood in 

 tnrpentine-oil in the calorimeter. The 7 rays had to pass 

 through a thickness of 1*92 cm. of lead. The balance between 

 the calorimeters in the differential arrangement was kept in 

 general under 5 milligrams per hour without the radium 

 bromide tube. When this tube was inserted in the lead 

 cylinder, the difference in melting amounted in three experi- 

 ment- to 89*6, 905, and 90*3 milligrams per hour. Other 

 results were obtained under less favorable circumstances, 

 which showed wider divergences, but which gave a mean of 

 94 "9 mg. per hour. Taking 90 mg. per hour as the true 

 result, this makes the total heat emission of the 50 mg. radium 

 bromide 5'- s 29 gram-calories per hour, whereas in the previous 

 experiment only 3'04 gram-calories were obtained, leaving a 

 margin of 2'79 gram-calories to be accounted for, apparently, 

 by the 7 ray-. This result was so unexpected, and was of so 

 much importance in considering the nature of the 7 rays, 

 that we decided to verify the experiments if possible by a 

 different method. The difficulty of obtaining steady readings 

 with the ice calorimeter is well known, and it was thought 

 that more rapid and accurate measurements could be made 

 by mean- of the differential air calorimeter which we had 



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