482 Mr. W. Crookes on the Atomic Weight of Thallium. [June 20, 



RESULTS. 



Ten results of the most trustworthy weighings (with N0 3 =6 1*889) 

 are* : — 







True weights in vacuo. 



A. 







;ermina~ 

 tion. 



^_ 



Weight of 

 thallium, 

 taken. 



Weight of nitrate 

 of thallium 4- glass. 



.... — % 



Weight of 

 glass. 



Calculated atomic 

 weight from 

 these data. 





grs. 



grs. ' 



grs. 



grs. 



A. 



497-972995 



1121 -851.852 - 



472-557319 



203*666 



B. 



293 193o07 



1111 OOhA1 A 



1111-387014 



729-082713 



203628 



C. 



288-562777 



971-214142 



594-949719 



203-632 



D. 



324-963740 



1142-569408 



718-849078 



203-649 



tE. 



183-790232 



1005-366796 



766-133831 



203-642 



F. 



190-842532 



997-334615 



748-491271 



203-636 



G. 



195-544324 



. 1022-176679 



767-203451 



203-639 



H. 



201-856345 



1013-480135 



750-332401 



203-650 



L 



295-683523 



1153-947672 



768-403621 



203-644 



K. 



299-203036 



1159-870052 



769-734201 



203-638 



I wish it to be noted that I have made determinations with various 

 weights of thallium. In ordinary analysis chemists are satisfied to take 5 

 or 10 grains of the substance under investigation : here I have gone to the 

 very highest weight that can be entrusted, with safety, to the balance. 

 The lowest weight of thallium taken is 183*790232 grains, the heaviest 

 497*972995 grains, the remaining determinations varying between these 

 limits. It is hardly necessary to say that the purpose has been to eliminate 

 the error arising from manipulation with small quantities, and to produce 

 such variety in the results as renders the chances of coincidence of very 

 small value. 



Let me now tabulate the results of the determinations, with the view to 

 ascertain severally their degree of approximation to the arithmetic mean : — 



A. 



203*666 



4--024 



B. 



203*628 



— '014 



C. 



203-632 



— •010 



D. 



203-649 



4- -007 



E. 



203-642 



4-*000 



F. 



203-636 



— •006 



G. 



203-639 



— '003 



H. 



203*6,50 



4-*008 



I. 



203*644 



+ •002 



K. 



203-638 



— '004 



The arithmetic mean of the ten observations is 



g= 2036-424 = 203 . 642> 

 10 



* It should be noted that the arithmetic mean of all the readings, including the 

 highest as well as the lowest result, in which doubt might arise as to success in manipu- 

 lation, is 203-6. t Fully illustrated in the paper. 



