or PAINTS, are furnished by both the mineral and vegetable kingdoms. The former are the most durable, and are generally prepared from the Oxids of metals (see Chemistry Index in this Suppl. and Colour-Making, Encycl.); but Fourcroy thinks that chemistry furnishes a method of fixing vegetable colours completely. From a number of experiments, which we need not detail, as they will be noticed in the article Vegetable Substances, he draws the following conclusions:

1. That oxygen, when combined with vegetable substances, changes their colour. 2. That different proportions of this principle produce different shades in coloured vegetable matter. 3. That these shades pass, by a sort of degradation, from the darkest colours to the lightest; and that the extreme point of the latter may be considered as a complete deprivation of colour. 4. That in many vegetable substances this degradation does not take place, as M. Berthollet has observed. 5. That many red, violet, purple, chestnut, and blue vegetable colours, are produced by different proportions of oxygen; but that none of these are completely saturated with this principle. 6. That the complete saturation here spoken of generally produces yellow colours, which are the least changeable of all. 7. That vegetable substances coloured by oxygen, not only change their colour according to the proportion of oxygen they have imbibed, but that they also change their nature in the same proportion, and approach more to a resinous state as they become nearer to a yellow colour.

Lastly, that the cause of the changeability of the red, brown, and violet colours, procured from vegetables, is such as has been stated above; that there exists a method of fixing them, or rendering them permanent, by impregnating them with a certain quantity of oxygen, by means of the oxygenated muriatic acid; imitating, by this process, the method purified by nature, who never forms fixed and permanent colours, except in substances which have been long exposed to the open air.