055 vols. of spec. gr. 26.75 = 28.22 and
12.32 " " " " 13.375 = 164.78
------ ------
13.375 " 193
has the spec. gr. 193 / 13.375 = 14.43. The proportion in one vol. of
the undecomposed to the decomposed salt is, therefore, as 1 to 11.68 and
the percentage of volume of the former 0.0789, and that of weight 28.22
/ 193 = 0.146, and not 0.16.
It is not easy to imagine why a small fraction of the heavy molecules
should be volatilized undecomposed, the temperature being sufficient
to decompose the great bulk. Marignac assumes, indeed, partial
decomposition, but the difficulties which he encountered in making the
experiments, on the results of which his opinion rests, were so great
that he himself accords to the numbers obtained by him only the value of
a rough approximation.
The heat absorbed in volatilization will comprise the heat of
combination as well as of aggregation, if decomposition takes place, and
will therefore be the same as that set free at combination. Favre and
Silbermann found this to be 743.5 at ordinary temperature, from which
Marignac concludes that it would be 715 for the temperature 350 deg.; he
found as the heat of volatilization 706, but considers the probable
exact value to be between 617 and 818.[1]
[Footnote 1: See _Comptes Rendus_, t. lxvii., p. 877.]
An uncertainty within so wide a range does not justify the confidence
of Mr.
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