Negative Corpuscles hy the Alkali Metals. 587 



from a hot platinum wire has been observed by Dr. H. 

 A. Wilson ; the increase in this case is very much greater 

 than that with cold alkali metals. 



In a previous paper (Proc. Camb. Phil. Soc. xiii. p. 49) I 

 showed that the radioactive substances radium and polonium 

 emit when cold slowly-moving negatively electrified cor- 

 puscles. The experiments just described show that this 

 property is also possessed to an appreciable extent by 

 substances not usually regarded as radioactive. With more 

 delicate apparatus than that used in these experiments it is 

 probable that this property might be detected in all sub- 

 stances : — I tried in my apparatus, in addition to the alkali 

 metals, lead, silver, and mercury, but could get no indication 

 of the emission o£ corpuscles by these metals. 



The alkali metals give out corpuscles when in the gaseous 

 as well as in the solid state ; this was proved in the following 

 way. If the gaseous atoms of sodium give out negative 

 corpuscles, the atoms themselves will be positively charged 

 and so will be attracted by negatively electrified bodies : 

 this was found to be the case. Sodium was heated in a 

 highly exhausted flask, the cooler part of which contained 

 two glass tubes down which ran wires. The wire in one 

 tube was connected to the positive pole of a battery of small 

 storage-cells giving a potential-difference of 600 volts, the 

 wire down the other tube was connected with the negative 

 pole of the same battery. When the bottom of the flask was 

 heated, the sodium evaporated and condensed on the two 

 tubes. When the wires down these tubes were disconnected 

 from the battery, the deposit of sodium was pretty equally 

 distributed between the tubes. When, however, the wires 

 were connected with the battery, there was very little deposit 

 on the tube connected with the positive pole, while the 

 deposit on that connected with the negative pole was very 

 dense. If the connexions with the battery were reversed, 

 the sodium began to deposit on the tube which had previously 

 been clean, while hardly any increase took place in the 

 deposit on the other tube ; showing that the effect was due to 

 the electrical charges on the tubes, and not to any want of 

 symmetry, In these experiments the tubes were not ab- 

 solutely dark. This deposit of sodium on a negatively 

 electrified surface may be compared with the flow of radium 

 emanation to a negatively electrified wire. 



The result at which we have arrived from the preceding 

 experiments, that some substances emit many corpuscles, 

 while others at the same temperature only emit few, if any, 



