Physical Relations of Osmium. 295 
In order to ascertain, if possible, which of the above changes 
had taken place, the tube was opened two or three months after 
it had been sealed, and the contents were examined. The fused 
stick of acid was found to be black and partially friable; on 
heating in another glass vessel, most of it sublimed, leaving a 
little black powder behind, and condensed in needles, still 
slightly yellowish, but differing little in appearance from com- 
mon osmic acid. The inner surface of the original tube was 
found coated with a thin, filmy, adherent crust, of a black colour 
and considerable lustre. This was scraped off, and a portion of 
it gently heated in a stream of dry carbonic acid gas until all 
traces of adherent osmic acid were driven off. After cooling, 
the carbonic acid was replaced by dry hydrogen, and heat was 
again applied. Water condensed on the tube beyond the heated 
part, thus proving that an oxide of osmium, not the metal, was 
under examination. Replacimg again the hydrogen by oxygen, 
osmic acid was produced and carried off with the stream of gas. 
The black powder scraped off from the original tube was heated 
with hydrochloric acid, and seemed to be but’ slowly acted on; 
the acid, however, assumed a green colour, and hence it is pro- 
bable that the osmium existed as protoxide. 
It is not easy to see, without further investigation, how os- 
mious acid could have replaced in part osmic acid in the attempt 
to prepare the latter as above described. Is there a particular 
stage of the decomposition of nitre by heat at which osmium 
may replace nitrogen in nitrite of potash (KO, NO*)? From 
the relations of the two elements, to be noticed presently, this 
would seem probable, and in fact Fremy has noticed the crystal- 
lization of osmite of potash from a solution in hot water of the 
fused cake of nitre and iridosmium. A reason for osmic acid 
(OsO*) being usually obtained from the latter, instead of osmious 
(OsO*), might perhaps be found in the fact that the chemists 
who of late years have worked upon osmium recommend the 
use of nitric or nitro-muriatic acid to neutralize the potash ; sul- 
phuric acid, to which Wollaston had recourse in his early ex- 
periments, is now seldom employed. Thomson, in his ‘ Che- 
mistry of Inorganic Bodies,’ published many years ago, observes 
that osmic acid has sometimes a tint of yellow. 
It does not seem likely that the cork closing the neck of the 
flask used for distillation had anything to do with the production 
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 oxides; Berzelius, however, observed that on adding 
sulphurous acid to a solution of osmic acid, the latter passed 
X 2 
