In a later paper* Berzelius published two analyses of potassium palladiochloride, K,PdCl. The salt was decomposed by ignition in hydrogen, as was the case with the double chlorides of potassium with platinum, osmium, and iridium. Reducing his results to percentages, we get the following composition for the substance in question:

From these percentages, calculating directly, very discordant results are obtained:

Obviously, the only way to get satisfactory figures is to calculate from the ratio between the Pd and 2KCl. Doing this, we get, Pd 105.737; or, if O 16, Pd 105.981.

=

=

This last value varies so slightly from the even number 106 that the latter may be safely used for all purposes of chemical calculation.

The determination made by Quintus Icilius* need be given only for the sake of completeness. He ignited potassium palladichloride in hydrogen, and found the following amounts of residue. His weights are here recalculated into percentages:

64.708

64.965

64.781

Mean, 64.818

=

From this mean, Pd 111.879. Upon looking at the values deduced from Berzelius' figures, it will be seen that

* Poggend. Annal., 13, 454. 1828.

"Die Atomgewichte vom Pd, K, Cl, Ag, C, und H, nach der Methode der kleinsten Quadrate berechnet." Inaug. Diss. Göttingen, 1847. Contains no other original analyses.

the highest, 110.796, is calculated from the chlorine lost upon igniting the palladiochloride. The same kind of error which vitiates that result probably affects also these data drawn from the palladiochloride.

RHODIUM.

Berzelius* determined the atomic weight of this metal by the analysis of sodium and potassium rhodiochlorides, Na, RhCl, and K,RhCl. The latter salt was dried by heating in chlorine. The compounds were analyzed by reduction in hydrogen, after the usual manner. Reduced to percentages the analyses come out as follows:

From the analyses of the sodium salt we get the following

These are discordant figures, and indicate some doubt as to purity of material. The last value is fairly good, however, and is confirmed by results from the potassium compound:

* Poggend. Annal., 13, 435. 1828.

The atomic weight of this metal has been determined only by Claus.* Although he employed several methods, the only results worthy of present notice come from the analysis of potassium rutheniochloride, K,RuCl. The salt was dried by heating to 200° in chlorine gas, but even then retained a trace of water. The percentage results of analysis are as follows:

Reckoning directly from the percentages we get the following discordant values for Ru:

Obviously, the best result is to be obtained from the ratio between Ru and 2KCl. This gives Ru= 104.217; or, if 0 = 16, Ru 104.457. But little weight can be attached to this determination.

=

* Journ. für Prakt. Chem., 34, 435. 1845.

APPENDIX.

ON DUMAS' CORRECTION AND PROUT'S HYPOTHESIS.

In the year 1815 Prout put forth his famous hypothesis that the atomic weights of all the elements were multiples of that of hydrogen. His views were adopted by many chemists, but opposed by others; among them Berzelius and Turner; and down to the present day "Prout's Law" has been the subject of earnest controversy. Of course the fact was early recognized that in its original form the hypothesis could not stand, and accordingly it was modified by Dumas in such manner that half and quarter multiples of the atomic weight of hydrogen were considered as well as the whole numbers.

But of late years Prout's hypothesis, even with its elastic modification, has been in disfavor. Only a few chemists still clung to it as the representative of a veritable law. The researches of Stas were especially directed towards ascertaining its truth or falsity; and his results, as well as those obtained by Marignac, were such as to lead most chemists to the belief that it had been forever overthrown. The atomic weights determined by Stas agreed neither with whole, half, nor quarter multiples of that of hydrogen, and the variations seemed to be wholly outside the range of recognizable experimental errors.

In 1878, however, a probable source of error in some of Stas' researches was pointed out by Dumas.* Many of Stas' ratios had involved the use of pure metallic silver, which had been fused under a cover of borax containing a little

* Ann. Chim. Phys., (5s.,) 14, 289.