But, you must have a care to drop in a competent Quantity of Oyl
of Tartar, for else the Colour will not be so Deep, and Rich; and if
instead of this Oyl you imploy a clear _Lixivium_ of Pot-ashes, you may
have an Azure somewhat Lighter or Paler than, and therefore differing from,
the former. And if instead of either of these Liquors, you make use of
Spirit of Urine, or of Harts-horn, you may according to the Quantity and
Quality of the Spirit you pour in, obtain some further Variety (though
scarce considerable) of Caeruleous Liquors. And yet lately by the help of
this Urinous Spirit we made a Blew Liquor, which not a few Ingenious
Persons, and among them, some, whose Profession makes them very Conversant
with Colours, have looked upon with some wonder. But these Azure Colour'd
Liquors should be freed from the Subsiding matter, which the Salts of
Tartar or Urine precipitate out of them, rather by being Decanted, than by
Filtration. For by the latter of these ways we have sometimes found, the
Colour of them very much Impair'd, and little Superiour to that of the
grosser Substance, that it left in the Filtre.
_EXPERIMENT XXIII._
That Roses held over the Fume of Sulphur, may quickly by it be depriv'd of
their Colour, and have as much of their Leaves, as the Fume works upon,
burn'd pale, is an Experiment, that divers others have tried, as well as I.
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