o Obtruse and Questionable an
Operation, (which yet may be pertinently represented to those that believe
the thing) we may observe, that divers Bodies digested in carefully-clos'd
Vessels, will in tract of time, change their Colour: As I have elsewhere
mention'd my having observ'd ev'n in Rectify'd Spirit of Harts-horn, and as
is evident in the Precipitations of Amalgams of Gold, and Mercury, without
Addition, where by the continuance of a due Heat the Silver-Colour'd
Amalgam is reduc'd into a shining Red Powder. Further Instances of this
Kind you may find here and there in divers places of my other Essays. And
indeed it has been a thing, that has much contributed to deceive many
_Chymists_, that there are more Bodies than one, which by Digestion will be
brought to exhibit that Variety and Succession of Colours, which they
imagine to be Peculiar to what they call the _True matter of the
Philosophers_. But concerning this, I shall referr you to what you may
elsewhere find in the Discourse written touching the passive Deceptions of
_Chymists_, and more about the Production of Colours by Digestion you will
meet with presently. Wherefore I shall now make only this Observation from
what has been deliver'd, That in these Operations there appears not any
cause to attribute the new Colours emergent to the Action of a new
Substantial form, nor to any Increase or Decrement of either the Salt,
Sulphur, or Mercury of the Matter that acquires new Colours: For the
Vessels are clos'd, and these Principles according to the _Chymists_ are
Ingenerable and Incorruptible; so that the Effect seems to proceed from
hence, that the Heat agitating and shuffling the Corpuscles of the Body
expos'd to it, does in process of time so change its Texture, as that the
Transposed parts do Modifie the incident Light otherwise, than they did
when the Matter appear'd of another Colour.

_EXPERIMENT XXXI._

Among the several changes of Colour, which Bodies acquire or disclose by
Digestion, it it very remarkable, that _Chymists_ find a Redness rather
than any other Colour in most of the Tinctures they Draw, and ev'n in the
more Gross Solutions they make of almost all Concretes, that abound either
with Mineral or Vegetable Sulphur, though the _Menstruum_ imploy'd about
these Solutions or Tinctures be never so Limpid or Colourless.

This we have observ'd in I know not how many Tinctures drawn with Spirit of
Wine from _Jalap_, _Guaicum_, and several other Vege