of Edinburgh, Session 1884-85, 67 
the nickel they contain, so it is needless at present to mention them 
farther. 
Cobalt is almost entirely consumed in the arts in the state of 
oxide, and there are two fairly well-defined oxides of this metal 
that are so employed, The lirst of these, or what is known as the 
ordinary black oxide of cobalt of commerce, is a sesquioxide (Co 2 0 3 ), 
corresponding to the ferric oxide Fe 2 0 3 ; and the other oxide is 
partly protoxide and partly sesquioxide of cohalt, corresponding to, 
though not so well defined* as the magnetic oxide of iron Fe 3 0 4 . 
This oxide is known in the arts as prepared oxide of cobalt , and is 
made from the black or sesquioxide by heating to whiteness for 
some time, and thus depriving it of a part of its oxygen. 
In physical character the two oxides of cobalt are somewhat un- 
like, the higher oxide being blacker than the lower oxide, and less 
dense , and though the former is apparently much lighter, I was 
surprised to find that the specific gravity of the two oxides are not 
very widely different, as will be seen from the following results : — 
The specific gravity of two different representative samples of black 
oxide being 5 ’82 and 5*82 respectively, while the specific gravity of 
four different samples of prepared oxide were found to be 5*93, 
6*48, 6-38, and 6T2. 
I have here two specimens of the cobalt oxides just described, and 
which have been produced from the cobalt ores of Hew Caledonia. 
The following are the analyses : — 
Black Oxide of Cobalt. 
Sesquioxide of cobalt, 
. 96*15 = 68*3 per cent. Co 
96*91 
Protoxide of nickel, 
. 2*06 
1*12 
Sesquioxide of iron, 
. 0*68 
0*40 
Tetroxide of manganese, 
0*44 
Nil. 
Lime, 
. 0*76 
1*80 
Magnesia, 
Trace 
0*50 
Insoluble, silica, &c. 4 
, Trace 
0*16 
100*09 
100*89 
Analysis of Prepared Oxide of Cobalt. 
Per cent. 
Protoxide of cobalt (CoO), ; . *93*85 94*27 
Protoxide of nickel, , . . • • 1'79 1*17 
* Equal to Sesquioxide of cobalt, Co 2 0 2 , 103*86 
Do. Tetroxide of cobalt, Co 3 0 4 , . 100*52 
Do. Metallic cobalt, Co, . . 73*84 
