320 
ME. W. CEOOKES OjST THE ATOMIC WEIGHT OF THALLIUM. 
With N0 6 =G2, 
55-827438 : 183-783921 :: 62 : 204-103. 
The several atomic weights would therefore he 
203-642 
203-738 
203-800 
203-800. 
Accepting the uncorrected weights observed in air, we have, with N-0 3 = 61*889, 
55-8184 : 183-8099 :: 
With N0 6 =62, 
55-8184 : 183-8099 :: 
61-889 
62 
204-007 
204-103 
204-166 
204-166. 
The error of the last deduction, +-524, is sufficiently large to show the necessity of 
neglecting no precaution in chemical manipulation, especially in a determination of 
this character. The largeness of these errors has an immediate bearing upon quantita- 
tive analysis ; for it shows that from data ordinarily given, very varying results may 
be obtained. Chemists have to deal with much smaller quantities than a quarter per 
cent., particularly in organic analysis, where, as I have shown, such a difference from 
the truth may lead to very erroneous reasoning. 
KESULTS. 
Ten results of the most trustworthy weighings (with N0 3 ==6T889) are* : — 
True Weights in vacuo. 
Determi- 
nation. 
Weight of 
thallium 
taken. 
Weight of nitrate 
of thallium + glass. 
Weight of 
glass. 
Calculated atomic 
weight from 
these data. 
grs. 
grs. 
grs. 
grs. 
A. 
497-972995 
1121-851852 
472-557319 
203-666 
B. 
293-193507 
1111-387014 
729-082713 
203-628 
C. 
288-562777 
971-214142 
594-949719 
203-632 
D. 
324-963740 
1142-569408 
718-849078 
203-649 
f E. 
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 
I. 
295-683523 
1153-947672 
768-403621 
203-644 
K. 
299-203036 
1159-870052 
769-734201 
203-638 
* 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 manipulation, is 203-6. 
t Fully illustrated in the preceding text. 
