ON THE COLOUR &C. OP THE METALLIC OXIDES. 25 5 



On the different colours of tlie metallic oxides, xcitli an application 

 of these principles to the Arts. 



I shall now proceed to offer for your further consideration a 

 few remarks on the different colours of the metallic oxides, 

 with an application of these principles to the Arts. — When 

 metals are oxided hy means of heat, " they are converted into 

 earthy-like powders of different colours and properties." The 

 oxigene gas during calcination is absorhed by the metal, and the 

 oxigene and the light, (constituents of oxigene gas) become 

 fixed in the oxide according to the degree of heat employed ; 

 for the oxide assumes the violet coloured ray first, and by in- 

 creasing the temperature, the violet colour is thrown off, in 

 consequence of its being the weakest, or the most refrangible ray: 

 in like manner some oxides assume in rotation the different co- 

 Jours, according to their respective refrangibilities, and they 

 are dissipated m that ratio to the increase of heat: the red ray, 

 the strongest and the most difficult of refrangibility, requires 

 still a higher temperature than the other six constituent colours 

 of light, and from its greater affinity to oxigene than the other 

 rays of light, it is not so easily driven off, hence the red ray 

 becomes iixed in the oxide, which constitutes its led colour, 

 while the heat and the other six constituents of light are set at 

 liberty : even this red ray may be driven off by increasing" the 

 heat, and then the red oxide is converted into white. — Accord- 

 ing to the experiments of Macquer, he oxided gold with a 

 burning glass, more powerful than that of Tschirnhausen, 

 and remarked that the oxide assumed the violet colour. — If it 

 were possible to increase the temperature sufficient to produce 

 the red oxiae of gold, it appears reasonable to infer that all the 

 intermediate coloured oxides of this metal, might be made, 

 provided the heat could be applied in that proportion or degree 

 to the different refrangibilities of the various colours. This 

 doctrine is eminently supported, by the process employed to 

 make vermilion. — If we take four ounces of sublimed sulphur 

 and fuse it in an un glazed earthen pot, and to this add one pound 

 of mercury, and let it be mixed with the sulphur by stiring or 

 agitation. — When these substances have combined to a certain 



