52 J. W. Mallet on Osmious Acid. 
Tt does not seem likely that the cork closing the neck of the 
flask used for distillation had anything to do with the poo | 
of osmious acid, if such took place; the cork itself did not show 
any appearance of being acted on, and there was no blackening 
of its surface until some time after the experiment was ended. 
The reduction of osmic acid generally results in the formation 
of the basic oxyds; Berzelius, however, observed that on add- 
ing sulphurous acid to a solution of osmic acid the latter passed 
through various shades of color—yellow, orange-yellow, brown, 
green, and at last blue; he attributed these tints to the succes: 
sive formation of sulphates of the bin-oxyd, sesqui-oxyd, and 
blue oxyd; but may not the first step in the reduction have 
been osmious acid, giving the yellow color? 
Another and altogether different view of the nature of the 
volatile yellow substance above described was suggested as pos 
sible by some remarks of Claus in a recent paper on the tem 
dency to reduction of salts of iridium (Ann. d. Chem. u. Pharm, 
Aug., 1858, S. 129). This author has shown that the platinum 
metals fall naturally into these groups, in each of which are con- 
. tained two metals resembling in general habit and relations each 
other more closely than members of the remaining groups. 
Platinum and palladium constitute the first of these pairs, irid- 
inm and rhodium the second, osmium and ruthenium the third. 
The atomic weight of the first-mentioned member of each pair 
is higher than (nearly double) that of the second. <3 
n the paper quoted Claus remarks that the metal of lower 
atomic weight in each of these groups is much more easily re- 
duced than the other from superior to inferior grades of combi 
nation with chlorine; thus the bichlorid of palladium is reduced 
with much greater ease to proto-chlorid than is the correspond- 
ing compound of platinum; and, for the same season, probably, 
the bi-chlorid of rhodium ig not known, but only the sesqui- 
chlorid, while both salts of iridium can be easily obtained. O2 
this same principle Claus explains the fact that no oxyd of ru 
thenium homologous with osmic acid has been obtained, while 
he gives the following reasons for suspecting the existence ¢ 
such an oxyd: ‘This opinion is based upon the fact, that in 
my preparation of compounds of ruthenium, which can be ° 
tained only by energetic processes of oxydation, the material 
worked upon, notwithstanding all my care and economy, gradu 
all; diminished, and yet I have never succeeded in collecting 4 
volatile product. Once only, when I had fused ruthenium, per: 
fectly free from osmium, with caustic potash and nitre, dissolved 
the mass in water, and decomposed it with nitric acid, I ob 
served a peculiar odor, quite distinct from that of osmic or Di 
trous acid; and afterw having covered the beaker, whic 
was smeared on the edge with tallow, witha plate of glass, I 
