Experiments and considerations touching colours first occasionally written, among some other essays to a friend, and now suffer'd to come abroad as the beginning of an experimental history of colours / by the Honourable Robert Boyle ...

Annotation I.

Whereas it is presum'd that the Magi∣stery of Vegetables obtain'd this way con∣sists but of the more. Soluble and Colour'd parts of the Plants that afford it, I must take the liberty to Question the Suppositi∣on. And for my so doing, I shall give you this account.

According to the Notions (such as they were) that I had concerning Salts; Allom, though to sense a Homogeneous Body, ought not to be reckon'd among true Salts, but to be it self look'd upon as a kind of Magistery, in regard that as Na∣tive Vitriol (for such I have had) con∣tains both a Saline substance and a Metall, whether Copper, or Iron, corroded by it, and associated with it; so Allom which may be of so near a kin to Vitriol, that in some places of England (as we are assur'd by good Authority the same stone will

sometimes afford both) seems manifestly to contain a peculiar kind of Acid Spirit, generated in the Bowels of the Earth, and some kind of stony matter dissolv'd by it. And though in making our ordinary Al∣lom, the Workmen use the Ashes of a Sea Weed (vulgarly call'd Kelp) and U∣rine: yet those that should know, inform us, that, here in England, there is besides the factitious Allom, Allom made by Na∣ture without the help of those Addita∣ments. Now (Pyrophilus) when I consi∣der'd this composition of Allom, and that Alcalizate Salts are wont to Praecipitate what acid Salts have dissolv'd, I could not but be prone to suspect that the Curdled Matter, which is call'd the Magistery of Ve∣getables, may have in it no inconsidera∣ble proportion of a stony substance Praeci∣pitated out of the Allom by the Lixivium, wherein the Vegetable had been decoct∣ed, and to shew you, that there is no ne∣cessity, that all the curdl'd substance must belong to the Vegetable, I shall add, that I took a strong Solution of Allom, and having Filtred it, by pouring in a conveni∣ent Quantity of a strong Solution of Pot-ashes, I presently, as I expected, turn'd the mixture into a kind of white Curds; which being put to Filtre, the Paper retain'd a sto∣ny

Calx, copious enough, very White, and which seem'd to be of a Mineral Nature, both by some other signes, and this, that little Bits of it being put upon a live Coal, which was Gently Blown whilst they were on it, they did neither melt nor fly away, and yon n ay keep a Quantity of this White substance for a good while, (nay for ought I can guess for a very long one) in a red hot Crucible without losing or spoiling it; nor did not Water wherein I purposely kept another parcel of such Calx, seem to do any more than wash away the looser adhering Salts from the stony Sub∣stance, which therefore seem'd unlikely to be separable by abiutions (though reitera∣ted) from the Praecipitated parts of the Ve∣getable, whose Lake is intended. And to shew you, that there is likewise in Allom a Body, with which the fix'd Salt of the Al∣calizare Solution will concoaguiare into a Saline Substance differing from either of them, I shall add, that I have taken plea∣sure to recover out of the slowly exhal'd Liquor, that pass'd through the filtre, and left the foremention'd Calx behind, a Body that at least seem'd a Salt very pretty to look on, as being very White, and consisting of an innumerable company of exceeding slender, and shining Particles, which

would in part easily melt at the flame of a Candle, and in part flye away with some little noise. But of this substance, and its odd Qualities more perhaps elsewhere; for now I shall only take notice to you, that I have likewise with Urinous Salts, such as the Spirit of Sal Armoniack, as well as with the Spirit of Urine it self, Nay, (if I much mistake not) ev'n with Stale Urine undi∣stil'd, easily Precipitated such a White Calx, as I was formerly speaking of, out of a Lim∣pid Solution of Allom, so that there is need of Circumspect on in judging of the Na∣tures of Liquors by Precipitations wherein Allom intervenes, else we may sometimes mistakingly imagine that to be Precipitated out of a Liquor by Allom, which is rather Precipitated out of Allom by the Liquor: And this puts me in mind to tell you, that 'tis not unpleasant to behold how quickly the Solution of Allom (or injected lumps of Allom) do's occasion the severing of the colour'd parts of the Decoction from the Liquor that seem'd to have so perfectly imbib'd them.