J. P. Cooke—Atomic Weight of Antimony. 385 
greatest confidence in these values to the #1, of a milligram. 
Moreover, it will be noticed that the volumetric method is only 
used to estimate the difference in the atomic weight which has 
been in question, and that if the method were only accurate to 
the =, of the quantity to be measured it would give us the 
value of the atomic weight within ;2, of a unit; while if, as we 
had reason to believe, the process was accurate within one per 
cent, it would fix the atomic weight within +2, of a unit. 
the method just described, the following results were ob- 
tained: The letters a and 6 indicate different preparations. 
Wt. of SbBrs Total wt. of Ag Per cent of Br Corresponding 
taken. used. Ag=108 Br=80. value of Sb. 
a1, 2°5032 2°2528 66°6643 120°01 
@ 2. 2°0567 . 1°8509 66°6620 120°02 
a@ 3. 2°6512 2°3860 66°6644 120°01 
b 4, 3°3053 2°9749 66°6696 119°98 
6 5. 2°7495 2°4745 66°6653 120°01 
Mean value, 66°6651 120°01 
Mean value of fifteen gravimetric de- 
terminations previously published, t piotiniciut 
heory Sb. 120 requires 66°6666 
oe lee 66°2983 
In order still further to control the work, we collected the 
bromide of silver formed in the last two determinations, wash- 
ing the precipitate with the precautions which experience had 
shown to be necessary, and determining its weight, first, after 
drying at 150° C., and, secondly, after heating to incipient 
fusion. In 6 6 there was a loss of fy of a milligram; in 6 7 
a loss of 32, of a milligram only at the second weighing. 
This is an absolute proof that there could be no sensible ocelu- 
Sion of any tartaric acid or any tartrate by these precipitates, 
and, as stated in our original paper, the same test was fre- 
quently applied, although not always, in our previous determi- 
nations. It is also evident that these last experiments give us 
two essentially distinct determinations of the atomic weight, 
although the materials employed were identical with those of 
b4 sel bd. 
Wt. of SbBr; Wt. of Ag Br Per cent af Br Corresponding 
taken. determined. Ag=108 Br=80. value of Sb. 
b 6. 3°3052 5°1782 66°665 120°01 
b 7. 2°7495 4°3076 66667 120-00 
Mean value, 66°666 120°00 
Lastly, it is obvious that these gravimetric determinations, 
taken in connection with the corresponding vo umetric results, 
give us the most conclusive evidence of the purity, both of the 
