J. P. Cooke—Atomic Weight of Antimony. 113 
The difference (0°004) between the first mean value and 
theory—corresponding to only about 2; of a milligram in the 
largest amount of argentic iodide weighed—is evidently insig- 
nificant, so that these results confirm the lower value of the 
atomic weight of antimony as closely as did the analyses of the 
bromide. 
As we have already intimated, our analyses of the iodide 
of antimony, as first crystallized from bisulphide of carbon, 
vielded very discordant results. These we give in the table 
below, not, as before, in the exact order in which the analyses 
Ww ade, but in the order of the several values, so as to 
exhibit the distribution of the errors. 
ANALYSES OF CRYSTALLIZED Antrmontous IopIDE, RED VARIETY. 
No. ' % of Iodine. 
Be ee ete ee ae oe. eT 
D tech wht tes big eats i ok Tae 
Beis ce a Eee 75°78 
Be ee ee ee ee 75°80 
Bik ve ae eae ee ee 
| AGN i aca eet ON Ui ong gee Boel 75°85 
ey Etiini 75°87 
Sof ee es ee ee ee 
Vie er Pe ee oe ee eee 
PERO VOlR ce cis ne .-75°83 
Lheory Sbiai09.) 2) <2 eee 75°74 
Theory Sb=-190.. 2 oe ee 
The cause of this discordance we attributed, as we have inti- 
mated, chiefly to the remarkable readiness with which iodide of 
antimony undergoes oxidation in contact with the air, resulting 
A the formation of oxi-iodide of antimony and free iodine, 
us :— 
28bI, + O-O = 2SbOI + 21L-1 
While the free iodine escapes, the oxi-iodide remains as an im- 
purity in the preparation, and the effect is a replacement of a por- 
tion of its iodine by oxygen. Now, since eight parts of oxygen 
replace one hundred and twenty-seven parts of iodine, it can 
readily be seen that an otherwise almost imperceptible amount of 
oxidation would be sufficient to produce all the variation from the 
normal composition which the above results present. A simple 
calculation will show that an absorption of only 7#2,ths of one 
per cent of oxygen, or less than half a milligram by each gram 
of iodide of antimony, would reduce the per cent of iodine from 
the theoretical val ue, 76-047, to the mean of the above results, 
Am. Jour, Sct.—Turp Serres, Vou. XV, No. 86.—Fxs., 1878. 
8 
