J. P. Cooke—Atomic Weight of Antimony. 119 
boracie acid by the vapor of water, and similar phenomena, the 
result, as it is has always appeared to us, of a feeble kind of 
chemical union which has been usually designated by the term 
“molecular combination.” Such a theory would account for 
the remarkable constancy which we have found in the chlorine 
determinations of the various preparations of antimonious chlo- 
ride purified by distillation. But, on account of the very great 
difficulty of removing all possible disturbing causes, we found 
it impossible to obtain a rigid experimental demonstration of 
our theory without much more time and labor than we could 
then command. We hope to return to the subject hereafter. 
Meanwhile, however, it was evident that we could place no reli- 
ance whatever on the results just obtained. Nevertheless, the 
determinations were of value on account of the contrast 
tween these results and those of a similar series of experiments 
on the residues from antimonious bromide which we collect in 
‘the following table :— 
y Residue chiefly 
No. Wt. of SbBrs. Sb,0,Bro. % of residue. 
if 2°8342 “ 0°035 
2, 2°0220 0°0006 0°030 
3. 4°6730 0°0010 0°021 
As will be seen, this residue is less than one-tenth of that 
obtained from the chloride, and is practically insignificant. 
_ Evidently, then, in the determination of the atomic weight of 
antimony more accurate results may be expected from the anal- 
ysis of the bromide than from the analysis of either the chlo- 
ride or the iodide of thiselement. The intermediate position of 
the bromide renders it, ina very remarkable way, the most 
Stable of the three compounds. It absorbs moisture far less 
eagerly than the chloride, and it absorbs oxygen far less read- 
ily than the iodide, and is thus in great measure protected 
against each of these two sources of the same impurity. 
_ We come finally to the new analyses of antimonious chlo- 
ride we had undertaken. Fortunately, some of the old prepara- 
tion that had been distilled so often had been preserved. It 
been boiled for along time since the last analyses were 
