Physical Relations of Osmium, 301 
minent only in the case of chromium itself, and indicates the 
relation of this metal with iron. 
In the arsenic series the known oxides are the following :— 
P?0 ‘ 
mo PO Bao AsO (?) OsO SbO (?) Bid (?) 
Ru? O3 (?) Os? 03 (?) 
NO? RuO? OsO? 
NO? PO? RuO® As0* OsO? = SbO? Bid? 
mi FO) OsO* ~=SbO* BiO* 
NO® PO® AsO® OsO®  SbO® BiO® (?) 
The prominent compounds in the Table are the acids MO? and 
MO?®; with respect to the separate columns, the following facts 
are noticeable. 
The oxides of nitrogen are well known; the regularity obser- 
vable in this column causes it to be frequently used as an 
illustration of the ‘law of multiples.” NO and NO? are usually 
said to be neutral ; but the latter plays the part of a base in con- 
tact with sulphuric acid, as in the crystals of the oil of vitriol 
chambers, and possibly the former may do so, too, in the nitro- 
sulphates (KO, NO, SO? and NH*0O, NO, SO??) obtained by 
Davy by bringing nitric oxide in contact with an alkaline sul- 
phite. NO? and NO® are well-known acids. It is doubtful 
whether hyponitric acid (NO*) is capable of combining with 
bases and forming salts; in contact with the alkalies it yields a 
mixture of nitrites and nitrates, yet, when out of contact of bases, 
it seems to be a body of more stability than either NO® or NO? (an- 
hydrous). 
In the column of the oxides of phosphorus, we have first the 
very anomalous suboxide (P?O), which is probably the only 
marked exception to the homology running through the whole 
table. Before the discovery of red (amorphous) phosphorus by 
Schrotter, this substance was, no doubt, to some extent con- 
founded with phosphoric oxide, and may even now throw some . 
doubt upon the cases in which the latter seems to have been ob- 
tained pure and to have yielded a formula supported by trust- 
worthy analyses. PO, unlike the other protoxides of the series, 
is usually considered an acid; but as it has not been obtained in 
the separate state, and all the hypophosphites contain water, it 
may be reasonably assumed that the formula of the acid should 
include hydrogen. PO* is doubtful: this may, perhaps, be the 
composition of Pelletier’s phosphorous acid, produced by the 
slow combustion of phosphorus, a body which undergoes no 
further oxidation by prolonged exposure to the air, and which, 
in contact with bases, yields mixed phosphites and phosphates. 
The last term in the column, phosphoric acid, is well known. 
