Ionization from Certain Hot Salts. 233 



First signs of emission from the salt occurred at 400°, but 

 soon died out. A fairly permanent emission appeared at 

 470°. The following mean values were obtained : — 



V. H. M. T. e/m. m/H. 



530° 

 112 2030 B & S to 264-3 36-5 



1130° 



460° 

 202 2030 B & S to 254-4 379 



490° fresh salt 



The balance and slit methods were in good agreement. 



(b) The same PbBr 2 was used for this determination. A 

 different Pt strip was employed on which AIF 3 had been 

 heated. The emission from the strip was not comparable 

 with that from the salt up to 1150°. The salt was put on 

 with distilled water and the emission watched for very 

 carefully. 



Emission so very slight as almost to 'escape attention 

 started at 100°, reaching a maximum at 400°, and then 

 dropping to zero. Permanent definite emission set in at 

 560° and reached a measurable value at 660°. The strip was 

 mounted by method (b) and the values were therefore much 

 more consistent, agreeing within 1 per cent, almost all the 

 time : 



V. 



H. 



M. 



T. 



690° 



e/m. 



m/H. 



204 



2460 



B&S 



to 

 1075° 



278 



34-7 



Conclusion. — The values of m/H for PbCl 2 and PbBr 2 

 are fairly consistent. There is no evidence of an emission 

 characteristic of the Pb, for which it might be expected 

 m/H = 103-5. 



The values seem quite evidently to be due to K as an 

 impurity, although at times they are rather low. 



It is possible that a characteristic emission of Pb was 

 obtained in the last experiment with PbBr 2 , namely, the 

 very slight emission detected from 100° to 400°. It was, 

 however, far too slight for measurement. 



4. Aluminium Fluoride. 



Only one experiment was made with this salt, the specimen 

 used being made by Kahlbaum. The melting point of A1F 3 

 is probably about 150°. 



The salt was moistened with distilled water and placed on 

 a new strip from which the emission had been driven out 

 below 900°. The mounting was by method (b). 



