114 J. P. Cooke—Atomic Werght of Antimony. 
75832 ; and that a corresponding absorption of three-quarters 
of a milligram would reduce the per cent to 75-700, the lowest 
observed. It is not, therefore, surprising tbat we could obtain 
concordant results only with material wbich had been both 
purified by crystallization and also recently sublimed. 
Returning now to discuss again the cause of the disagree- 
ment of the analyses of antimonious chloride with our otherwise 
consistent results in regard to the atomic weight of antimony, 
it was obvious that the strong hygroscopic power of the chloride 
must lead to a replacement precisely similar to that which is 
shyly in the iodide by direct oxidation; for, as we have 
fore said, the crystals of antimonious chloride cannot be 
exposed to the atmosphere for an instant without absorbing a 
perceptible amount of moisture, and every molecule of water 
thus absorbed reacts on a molecule of the chloride, thus:— 
SbCl, + H,O = SbOCI + 2HCL 
And when the antimonious chloride is boiled, the hydrochloric 
acid formed is given off, while the oxichloride remains behind, 
dissolved in the great mass of the liquid. Indeed, it seems 
impossible, with our ordinary appliances, to prepare or purify 
antimonious chloride without its becoming contaminated with 
oxichloride; and our experiments would indicate that when 
once it has been formed, as above described, in the mass of the 
material, it cannot be wholly removed by distillation or crys- 
tallization, however often these processes may , 
aturally, our attention was very early called to this obvious 
source of impurity in the antimonious chloride we prepared: 
and we noticed from the first that, even after the material had 
been many times distilled, there was always left, on repeating 
the process, a very small amount of dark-colored residue. 
had examined the residue, and found that it was a mixture of 
chloride and oxichloride of antimony, colored by a trace of car- 
bonaceous material; and we had made a long series of analyses 
for the purpose of studying the effect produced by the action 
we have described. The result of these analyses is given in 
the following table. We started with material already purified 
by fractional distillation and crystallization, and distilled it ten 
imes in succession ; not, however, carrying the distillation to 
absolute dryness, but leaving, so far as we could judge by the 
eye, about the same amount of residue in the retort each time. 
These residues we analyzed, as we did also the final distillate. 
The material first distilled was the same as that marked ¢ in 
the table on page 47, and we assumed that the average of the 
results there given truly represented its composition. 
