Metallic Oxydes and Earths. "gag 
-Inall thefe experiments with the earths, not the 
{malleft particle feemed diffolved, as on the addition 
of any of the acids, they inftantly changed to a 
very dark colour. ‘Thofe oils to which the nitrous 
acid was added, became much darker than thofe in. 
which the metallic oxydes had been digefted, and to 
which the fame addition had been made. 
It is well known, that oils obtain the property of 
drying more quickly by being boiled, either alone 
or in conjunction with metallic oxydes, and argil- 
laceous earths, Oil, according to M. Lavoifier, 
confifts of Hydrogene, or the bafis of Inflammable 
Gas, and Carbone, the bafis of Carbonic Acid, or 
fixed Air. ‘The metallic Calces confift of the Metal 
united to Oxygene, or the bafis of pure air. Accord- 
ing to this fyftem of Chemiftry, the Metal when 
boiled in oil gives up Oxygene to it, while the 
Mucilage-of the Oil unites to the Metal. It feems 
therefore propable, that in high coloured Oils, the 
Carbone is fuperabundant, and that by digefting the 
calces of Metals, in a lower degree of heat, a part of 
the oxygene of the calx may combine with the fuper- 
fluous Carbone, and, forming Carbonic Acid, tend to 
diveft the oil of its colour, while the oxyde, attracting 
the mucilage, may contribute to the fame end. 
How far this theory may apply to the explanation 
of the foregoing experiments, I do not pretend to 
determine. It is remarkable however, that one of 
the earthy fubftances, viz. the alumine, which is 
not known to contain either oxygenous or carbonic 
gas, 
