302 Prof, J. W. Mallet on the Chemical and 
The existence of a distinct protoxide of arsenic, as of antimony 
and bismuth, is doubtful. Arsenious acid is a feeble, volatile, me- 
tallic acid—feebler in its relations as an acid than arsenic acid, 
and volatilizing at a lower temperature than the latter. Arse- 
nious acid, moreover, volatilizes at a temperature below that 
required by metallic arsenic. 
In the antimony column, the oxide SbO® is usually viewed as 
a weak base, but seems also to be capable of uniting as a feeble 
acid to the alkalies, and even of expelling carbonic acid from 
their carbonates (Liebig). The isodimorphism of SbO? and 
AsO? is well established. SbO® is volatile at quite a moderate 
temperature, while metallic antimony requires at least a white 
heat to vaporize it. SbO®* is a body of distinctly acid properties. 
Both SbO® and SbO® are converted by heating in the air into SbO* 
—the so-called antimonious acid, which seems therefore to be 
the most stable oxide when strong bases and acids are not pre- 
sent. It is most probable that, as Fremy maintains, SbO* is not 
itself an acid, but that a so-called alkaline antimonite is, in fact, 
a mere mixture of an antimoniate with the compound of anti- 
monic oxide and alkali (2Sb0*=SbO#-+ SbO*). 
In the bismuth column, the teroxide is homologous as a base 
with teroxide of antimony, but shows little tendency to play the 
part of an acid with even the strongest bases. This oxide and 
the metal itself are volatile at high temperatures. BiO* also 
seems to be devoid of acid properties; but the compound BiO® 
probably exists, and is homologous with SbO®, forming alkaline 
salts of little stability. 
Comparing now ruthenium and osmium with the above recog 
nized members of the arsenic group, we find, first, that both 
metals form protoxides, which are feeble bases, as are probably 
the corresponding compounds of the other members of the group. 
We next meet with the sesquioxides, whose formula is excep- 
tional in the series ; but for neither metal has this grade of oxi- 
dation been obtained in the free state and pure, and in the case 
of osmium its existence may be gravely doubted. Anhydrous 
Ru? O° is supposed by Claus to be formed during the roasting of 
metallic ruthenium in the air ata high temperature ; but only on 
the ground that the absorption of oxygen slackens when about 
enough has been taken up to form this compound, and that the 
proportion necessary for the binoxide is never fully attained. 
Claus, however, describes a sesquichloride with which double 
salts are formed by the chlorides of potassium and ammonium, 
and we must therefore assume a sesquioxide also. Sesquioxide 
of osmium is quite unknown in the separate state; and the belief 
in its existence is founded solely upon the preparation by Ber- 
zelius of a dark brown substance, supposed to consist of the 
