38 



ADVENTURES IN RADIOISOTOPE RESEARCH 



Table 2. — Line Distance of the (422) Interference of Platinum 



Black 



Heating to still higher temperatures resulted in a considerable evapor- 

 ation of lead, as shown in Table 3. With regard to the values in Table 2, 

 it should be mentioned that it was not possible to assess the line distance 

 in the case of platinum grey (lead-free platinum deposit) with sufficient 

 accuracy. The number 124.3 in the second column thus refers to platinum 

 wire whereas the corresponding value in the third column was indeed 

 obtained from platinum grey. After heating, the platinum grey did of 

 course yield lines of adequate sharpness. The exposures for the Debye- 

 Scherrer diagrams were obtained with the aid of the precision camera 

 described by Sachs and Weerts^ ; platinum wires 4 mm thick and 

 coated with platinum black were used for the exposures. A Metalix 

 tube with a copper a/?ti-cathode was used as the source of radiation and 

 was operated for as long as 13 hr at45kV and 20 mA. The lead content 

 present as a solid solution was calculated by means of Vegard's law, 

 according to which the lattice constant of the solid solution is 



a = (3.905^1 -f 4.93ro)/100 



where a is the length of the side of the unit cell of the alloy, q is the 

 number of atoms per cent of platinum and Co, for lead. The calculation 

 showed that, of a total of 1.5 per cent lead, only 0.2 per cent was present 

 in solid solution after heating (Table 2) and of the 7.1 per cent lead in 

 another sample only 0.3 per cent was similarly in solid solution. 



It is hoped to study in more detail, by means of radiographs of platinum 

 black containing thorium-B, the distribution of lead in platinum. 



THE EFFECT OF HEATING ON THE LEAD CONTENT OF PLATINUM 



BLACK 



It has already l)een mentioned that considerable amounts of lead 

 (Ma])orated when platinum black was heated at higher temperatures. 

 in a more detailed study of this point the alphaactivity of platinum black. 



iSack^ and \Vep:rts. Z. I'hy-s. 60, 481 (1930). 



