Experiment XXII
Our next Experiment (Pyrophilus) will perhaps ſeem to be of a contrary Nature to the two former, made upon Syrrup of Violets, and Juice of Blew-bottles. For as in them by the Affuſion of Oyl of Tartar, a Blewiſh Liquor is made Green, ſo in this, by the ſole Mixture of the ſame Oyl, a Greeniſh Liquor becomes Blew. The hint of this Experiment was given us by the practice of ſome Italian Painters, who being wont to Counterfeit Ultra-marine Azure (as they call it) by Grinding Verdigreaſe with Sal-Armoniack, and ſome other Saline Ingredients, and letting them Rot (as they imagine) for a good while together in a Dunghill, we ſuppos’d, that the change of Colour wrought in the Verdigreaſe by this way of Preparation, muſt proceed from the Action of certain Volatile and Alcalizate Salts, abounding in ſome of the mingled Concretes, and brought to make a further Diſſolution of the Copper abounding in the Verdigreaſe, and therefore we Conjectur’d, that if both the Verdigreaſe, and ſuch Salts were diſſolv’d in fair Water, the ſmall Parts of both being therein more ſubdivided, and ſet at liberty, would have better acceſs to each other, and thereby Incorporate much the more ſuddenly; And accordingly we found, that if upon a ſtrong Solution of good French Verdigreaſe (for ’tis that we are wont to imploy, as the beſt) you pour a juſt quantity of Oyl of Tartar, and ſhake them well together, you ſhall immediately ſee a notable Change of Colour, and the Mixture will grow thick, and not tranſparent, but if you ſtay a while, till the Groſſer part be Precipitated to, and ſetled in the Bottom, you may obtain a clear Liquor of a very lovely Colour, and exceeding delightfull to the Eye. 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 Cæruleous 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.