But to improve the
Experiment, let me add what has not (that I know of) been hitherto
observ'd, and has, when we first shew'd it them, appear'd something
strange, even to those that have been inquisitive into the Nature of
Colours; namely, that if instead of Spirit of Salt, or that of Vinegar, you
drop upon the Syrrup of Violets a little Oyl of Tartar _per Deliquium_, or
the like quantity of Solution of Potashes, and rubb them together with your
finger, you shall find the Blew Colour of the Syrrup turn'd in a moment
into a perfect Green, and the like may be perform'd by divers other
Liquors, as we may have occasion elsewhere to Inform you.
_Annotation upon the twentieth Experiment_.
The use of what we lately deliver'd concerning the way of turning Syrrup of
Violets, Red or Green, may be this; That, though it be a far more common
and procurable Liquor than the Infusion of _Lignum Nephriticum_, it may yet
be easily substituted in its Room, when we have a mind to examine, whether
or no the Salt predominant in a Liquor or other Body, wherein 'tis Loose
and Abundant, belong to the Tribe of _Acid_ Salts or not. For if such a
Body turn the Syrrup of a Red or Reddish Purple Colour, it does for the
most part argue the Body (especially if it be a distill'd Liquor) to abound
with Acid Salt.
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