298 Prof. J. W. Mallet on the Chemical and 
ever to be capable of crystallizing in all proportions with the 
platino- and osmio-chlorides. 
The interesting fact has been discovered by Claus, that osmio- 
cyanide and ruthenio-cyanide of potassium are strictly isomor- 
phous with the well-known ferrocyanide, crystallizing with it in 
all proportions, and even giving very similar precipitates with 
various metallic solutions ; so that, in these double cyanides, os- 
mium and ruthenium are capable of taking the place of ron. 
' In the greater number of its relations, however, osmium pre- 
sents itself as a member of the arsenic group of elements. This 
has been noticed by some recent authors, as by Prof. Dana in 
the arrangement of the elements adopted in his ‘System of Mi- 
neralogy,’ and by Prof. Miller, who says in his lately published 
‘Elements of Chemistry,’ that “it presents more analogy with 
arsenic and antimony than with the noble metals.” Fremy, too, 
compares osmium in platinum ore to arsenic in the native arse- 
niurets. 
Nitrogen, phosphorus, arsenic, antimony, and bismuth are 
generally recognized as forming a distinct and natural group of 
elements ; and into this group it seems from many considerations 
that osmium, and probably ruthenium, ought to be introduced. 
They have some analogies with other natural families, just as 
arsenic is allied to sulphur in native sulph-arseniurets, and nitro- 
gen and chlorine exhibit some resemblance in the nitrates and 
chlorates ; but here appear to be their closest relations. It may 
be interesting to notice some of the principal points of resem- 
blance to or difference from this group. 
Iridosmine occurs in crystals closely related in form to those 
of arsenic, antimony, and bismuth in the metallic state. The 
analyses of iridosmine are not yet sufficiently numerous or ac- 
curate to enable us to decide upon its normal composition ; but 
it seems probable that the two metals occur in variable propor- 
tions, and are in this mineral isomorphous, thus establishing, as 
noticed by Dana, a connexion between the arsenic group and 
that of the distinctly basic metals, as the arsenic and sulphur 
groups are united through homceomorphous bismuth, tetrady- 
mite and tellurium. Dana places iridium in the same section 
with iron, among the metals whose most stable grades of oxida- 
dation are the protoxide and sesquioxide; but the statement of 
Claus, that the binoxide of iridium is the most stable and easily 
prepared compound with oxygen, would remove this metal, as 
also perhaps platinum and palladium, from the iron section to 
that containing tin and titanium; and the propriety of this 
transfer may be supported by the relationship of Fremy’s ery- 
stallized oxide of ruthenium (doubtless the binoxide) examined 
by Senarmont: this was found to be homeomorphous with 
