employed.
516.
Generally, however, these appearances of colour are of so mutable a nature that chemists look upon them as deceptive tests, at least in the nicer gradations. For ourselves, as we can only treat of these matters in a general way, we merely observe that the appearances of colour in metals may be classed according to their origin, manifold appearance, and cessation, as various results of oxydation, hyper-oxydation, ab-oxydation, and de-oxydation.43
XXXVIII.
AUGMENTATION OF COLOUR.
517.
The augmentation of colour exhibits itself as a condensation, a fulness, a darkening of the hue. We have before seen, in treating of colourless mediums, that by increasing the degree of opacity in the medium, we can deepen a bright object from the lightest yellow to the intensest ruby-red. Blue, on the other hand,