36 A FEW CHEMICAL CHANGES 



small glass tube, containing the radium, was held in the end of 

 a hollow brass rod ; this latter passed through a hole in one end 

 of the leaden cover of the box, so that the radium was over, a'nd 

 about a millimetre distant from, the square of tin in one of the 

 compartments of the box. This box was placed in a large tin 

 box and kept at a temperature of about 0C. for four months. 



At the end of that time, the pieces of tin were taken out and 

 .examined under the microscope, and it was found that there 

 was a formation of grey tin on the surface of each, but that the 

 amount on the piece that had been bombarded by the rays from 

 the radium, was greater than that on the piece which had not 

 been so acted upo'n. This difference, however, was not very 

 great, but the lead box which had contained the pieces of tin, 

 had undergone a. curious change, during the four months. The 

 inside of the compartment into which the tube containing the 

 .radium had penetrated, was completely covered, with the 

 exception of the bottom, with a thin white film, which was 

 .present in some. places, particularly the top of the box, in rela- 

 tively large quantities, while the other compartment did not con- 

 tain the most minute trace of this substance. Around the hole 

 in the top of the box, where the tube containing- the radium 

 entered, the lead was coated with the white substance, much 

 more thickly than anywhere else. Some of this oowder was 

 scraped off and analysis showed that it was lead carbonate. 



The only explanation the author can give of its formation 

 is this. Some of the rays from the radium, after striking the 

 surface of the tin, which was probably not perfectly even, were 

 reflected upward, and bombarded the top of the lead box and 

 ionized it, thus making it more active than it was. The por- 

 tions of the lead which were thus made active, were able to 

 combine with the moist carbon dioxide in the air, with the 

 production of lead carbonate. This seemed to be borne out by 

 the fact that it was the top of the box that was most coated with 

 the carbonate. 



