Chemistry and Physics. 389 



panion for about twenty-five days, and then both were laid 

 together on a sensitive film for twenty-four hours. On develop- 

 ment, the exposed diamond was found to have impressed a strong 

 image on the film, but only a faint mark could be seen where the 

 other stone had been. A repetition of the experiment confirmed 

 the result. — Ghem. JVeios. xc, 1. h. l. w. 



2. Radio-active Lead, Radio -tellurium, and Polonium. — 

 Debierne has arrived at the conclusion that the radio-active lead 

 of Hofmann and Strauss and the radio-tellurium of Marckwald 

 are identical with M. and, Mdme. Curie's polonium. The radia- 

 tion of polonium is distinct from that of uranium, thorium, radium 

 and actinium, and consists entirely of the almost non-penetrating 

 a-rays, which are only slightly affected by a magnet. The radio- 

 active substances which accompany bismuth, lead, and tellurium 

 are all precipitated from acid solutions by hydrogen sulphide, and 

 they have all been derived from pitchblende. 



Having at his disposal a large amount of the residues from the 

 extraction of radium, Debierne tried to obtain ratio-active lead. 

 The lead nitrate obtained had a radio-activity only about twice 

 that of uranium. Recrystallization of this nitrate was not effec- 

 tive in concentrating the radio-active substance, but when a large 

 excess of hydrochloric acid was added to a concentrated solution 

 of this nitrate, lead chloride crystallized out, leaving nearly all 

 the radio-activity in solution. By repeating this operation several 

 times the non-active lead chloride was eliminated, and the greater 

 part of the activity was concentrated in a small quantity of matter. 

 This portion, consisting chiefly of lead, was purified from small 

 traces of copper and iron, and then transformed into nitrate. 

 Upon adding the concentrated, slightly acid, solution of this 

 nitrate to a large quantity of water, a very slight precipitate of 

 basic bismuth nitrate was formed, which contained nearly all the 

 radio-activity, and corresponded to very active poloniferous bis- 

 muth. The active matter thus obtained also showed all the pro- 

 perties of radio-tellurium; its solution gave an active precipitate 

 with stannous chloride, and an extremely radio-active coating 

 upon a thin piece of metallic bismuth. 



It is thus seen that the same radio-active substance shows suc- 

 cessively properties characteristic of radio-active lead, polonium, 

 and radio-tellurium. The conclusion to be drawn is that there is no 

 distinction between these three bodies, andit is evident from these 

 experiments that a radio-active substance cannot be identified by 

 chemical reactions, since analytical separations merely cause it 

 to be shared among the different fractions. The only certain test 

 is the nature of the radio-activity, and the identity of the radia- 

 tions given by polonium, radio-active lead and tellurium would in 

 itself predict the results that have been reached. 



Circumstances were such that the lead nitrate used in these 

 investigations was kept for three years before the work was com- 

 pleted. During this time it retained all of its feeble activity, 

 although samples of polonium prepared from it gradually lost 



