Red made the Glass so Opacous, (though the Pigment were laid on but upon
two Sides of the Glass, no more being absolutely necessary) that unless I
look'd upon an Inlightned Window, or the Flame of a Candle, or some other
Luminous or very Vivid object, I could scarce discern any Colours at all,
especially when the Glass was cover'd with Red. But when I did look on such
Objects, it appear'd (as I expected) that the Colour of the Pigment had
Vitiated or Drown'd some of those which the Prism would according to its
wont have exhibited, and mingling with others, Alter'd them: as I remember,
that both to my Eyes, and others to whom I show'd it, when the Prism was
cover'd with Yellow, it made those Parts of bright Objects, where the Blew
would else have been Conspicuous, appear of a light Green. But,
_Pyrophilus_, both the Nature of the Colours, and the Degree of
Transparency, or of Darkness in the Pigment, besides divers other
Circumstances, did so vary the _Phænomena_ of these Tryals, that till I can
procure small Colour'd Prisms, or Hollow ones that may be filled with
Tincted Liquor, or obtain Some better Pigments than those I was reduc'd to
imploy, I shall forbear to Build any thing upon what has been delivered,
and shall make no other use of it, than to invite you to prosecute the
Inquiry further.

_EXPERIMENT XVI._

And here, _Pyrophilus_, since we are treating of Emphatical Colours, we
shall add what we think not unworthy your Observation, and not unfit to
afford some Exercise to the Speculative. For there are some Liquors, which
though Colourless themselves, when they come to be Elevated, and Dispers'd
into Exhalations, exhibit a conspicuous Colour, which they lose again, when
they come to be Reconjoyn'd into a Liquor, as good Spirit of _Nitre_; or
upon its account strong _Aqua-fortis_, though devoid of all appearance of
Redness whilst they continue in the form of a Liquor, if a little Heat