218 PRESENT PROBLEMS OF INORGANIC CHEMISTRY. 



emanation, a most interesting fact was observed, namel}-, that pre- 

 cipitation of the thorium as hydroxide by ammonia left unprecipi- 

 tated a substance, which they termed " thorium-X," and which was 

 itself highly radio-active. Its radio-active life, however, was a short 

 one; and as it decayed, it w^as reproduced from its parent thorium at 

 an equal rate. Here is a case analogous to what was sought for with 

 radium and uranium; but evidently uranium is not the only parent 

 of radium: the operation is not one of pai-thenogenesis. Similar 

 facts have been elicited for uranium by Crookes. 



The a- -rays, caused by the disintegration of radium and of its em- 

 anation, are accompanied by rays of quite a dift'erent character; 

 they are the //-rays, identical with electrons, the mass of which has 

 been measured by J. J. Tliomson and others. These particles are 

 projected with enormous velocity, and are capable of penetrating 

 glass and metal screens. The power of penetration appears to be 

 ])roportional to the amount of matter in the screen, estimated by its 

 density. These electrons are not matter; but, as I shall relate, they 

 are capable of causing profoinid changes in matter. 



For the jjast year a solution of radium bromide has been kept in 

 three glass bulbs, each connected to a Topler pump by means of caj^il- 

 lary tubing. To insure these bun)s against accident each was sur- 

 rounded by a small beaker; it happened that one of these beakers 

 consisted mainly of potash glass; the other two were of soda glass. 

 The potash-glass beaker became brown, while the two soda-glass 

 beakers became i)urple. I think there is every probability that the 

 colors are due to liberation of the metals potassium and sodium in 

 the glass. They are contained in that very viscous li(|uid, glass, in 

 the colorless ionic state; but these ions are discharged by the //-rays 

 or negative electrons, and each metal imparts its own j)eculiar color 

 to the glass, as has been shown by Maxwell Garnett. This phe- 

 nomenon, however interesting, is not the one to which T desire to 

 tlraw special attention. It nnist be remembered that the beakers 

 have been ex])osed only to /i-rays; ^v-rays have never been in contact 

 with them; they have never been bombarded by Avhat is usually 

 called matter, except by tlie molecules of the surrounding air. Now, 

 these colored l)eakers are radio-active, and the radio-active film dis- 

 solv^es in water. After careful washing, the glass was no longer 

 radio-active. The sobitiou contains an emanation, for on l)ubbling 

 air through it, and cooling the issuing air with liquid air, })art of the 

 radio-active nuitter was retained in the cooled tube. This substance 

 can be cai-i-ied into an electr()sco[)e by a current of air, after the liquid 

 air has been withdrawn, and as long as the air current passes, the 

 electroscope is discharged: the period of decay of this emanation, 

 however, is very rapid, and on ceasing the current of air, the leaves of 



