63 
Proceedings of the Royal Society 
Sesquioxide of iron, 
1-04 
1-08 
Sesquioxide of manganese, 
0-16 
0-14 
Lime, ...... 
0-32 
0-60 
Magnesia, . . . 
0-25 
0-40 
Silica, ...... 
0-32 
0-44 
Oxygen by difference, 
2-27 
1-90 
ioo-oo ioo-oo 
Jt will be seen from the analysis of the prepared oxide of cobalt 
that it is not a well-defined oxide, but is rather a combination of 
protoxide with sesquioxide. 
The principal use of black oxide of cobalt is in the manufacture 
of pottery ware, where it is employed to counteract the yellow colour 
the ware would otherwise possess after the process of firing, — the 
cobalt here playing the part of the blue of the laundry. So intense 
is the colouring power of cobalt that about 6 oz. to the ton of china 
clay is sufficient, and if more than about 1 lb. to the ton of clay be 
used, the ware has a distinct blue colour. I have received from a 
large pottery two specimens of china ware, one of which has had the 
usual admixture of cobalt, while another one has had no cobalt 
added to the clay from which the dish was made. In daylight a 
very decided yellow tint is visible in the latter. 
The other uses of black oxide of cobalt are in colouring glass, and 
in the manufacture of cobalt ultramarine. 
The principal use of prepared oxide of cobalt is as a pigment, 
especially in painting china (I have here a familiar specimen of a 
plate painted wdth this pigment), cobalt being the only blue colour 
that will stand the high temperature required in this case. 
Up to the present time I have not heard of cobalt being found 
in any well-defined veins in New Caledonia — in this matter cobalt 
differs from the ores of nickel, which are found also in the island. 
The nickel ores of New Caledonia contain no cobalt, but the 
cobalt ores, as we have seen from the analyses, contain a consider- 
able percentage of nickel compared with the cobalt present. 
It is rather troublesome to separate all the nickel from the oxide 
of cobalt in the process of refining, and in no sample that I have ex- 
amined is the nickel entirely absent in the finished oxide of cobalt. 
Nickel exists in the ores of New Caledonia as a silicate, — possibly 
a double silicate of nickel and magnesia, — and this ore is probably 
