oG A I'EW CHEMICAL CHANGES 



small o'lass tiibo, ('ontuiuiiiu- the radiiiiii. was held in the ciul of 

 a hollow brass rod; this hitter jjasscd tlirouuii a Indc in one <'nd 

 of the leaden cover of the h().\, so that tlic railiuni was over, and 

 abont a milliniotre distant from, the s(juare of tin in one of the 

 conipartnients of the box. This l)ox was placed in a hiri>-e tin 

 box and kept at a tenii»crature of ahont 0°(\ for four months. 



At the end of that tini(\ the pii^ces of tin were taken ont and 

 examined nnder the microscope, and it was found that there 

 was a formation of gTev tin on the snrface of each, bnt that the 

 amount on the ])iece that had been bombarded by the rays from 

 the radinm. was iireater than that on the piece which had not 

 been so acted n[)o'a. This ditference, however, was not very 

 _i>reat, but the lead box which had contained the pieces of tin, 

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

 inside of tlu^ compartment into which the tube containing the 

 radium had ])onetrated, was completelv covered, with the 

 excei)tion of the bottom, witli a thin white film, wliich was 

 present in some places, particularly the toj) of the box, in rela- 

 tively hirge cpiantities, while the c>ther 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 nowder Avas 

 scraped off and analysis showed that it was lead carbonate. 



The onlv 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 perfectlv even, were 

 reflected u])ward, and ])ond>ar(kHl the top of the lead box and 

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

 tions (d' the lead which were thus made active, were able to 

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

 ])roduction of lead carlx)nate. This seemed to be borne out by 

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

 the carbonate. 



