The remaining medical works of that famous and renowned physician Dr. Thomas Willis ...: Viz I. Of fermentation, II. Of feavours, III. Of urines, IV. Of the ascension of the bloud, V. Of musculary motion, VI. Of the anatomy of the brain, VII. Of the description and uses of the nerves, VIII. Of convulsive diseases : the first part, though last published, with large alphabetical tables for the whole, and an index ... : with eighteen copper plates / Englished by S.P. esq.

CHAP. XI. Of the motion of Fermentation, as it is to be observed, in the Precipitation of Bodies.

WE have hitherto treated of the Solutions of Bodies; it remains now that we speak of Precipitation, this is performed only in Liquids, which, when as they are stuffed with Heterogeneous Particles, are compelled by a matter Precipitating those Particles, to separate one from another, and to obtain for their substance, divers places and conditions: wherefore, since in this operation, there is an agitation and motion of parts, its consideration ought to be referred to the Doctrine of Fermentation.

Precipitation is performed, either in Natural things, as chiefly in Milk, Blood, Urine, and perhaps in some others; or in Artificial things, which are of a diverse Kind and Nature: but they may be described and ranked in a certain order, according as the Liquor to be Precipitated, or Precipitating, is either Spirituous, Sulphureous, Watery, or Saline: besides, according as the Particles separated from the rest, are ei∣ther Elementary, (viz. either Sulphureous, Earthy, or Saline) or Integral, which participate of the Nature of the whole mixture, and are only very small portions of it very much broken.

There are two common and known ways of Precipitation, whereby is made from Milk, both Cheese, and Butter: As to the first, if any sharp thing be poured into warm Milk, the thicker and Cheesie parts, presently separate from the serous and thinner, and are gathered together into a thick substance. The reason of which consists in this: Milk has a somwhat thick consistence, and its pores and passages are very much be∣set, with the thicker (to wit the Cheesie) contents; wherefore when somthing more subtil and penetrating, (as is Rennet) passes through the Liquor, it easily thrusts forth the more thick Particles, with which the pores were possessed; which then mu∣tually Embrace one another, and are separated a part from the thin, and Wheyie Li∣quor. When Milk is kept long to a sourness, it is Precipitated after the same manner, without Rennet, by warming it over the fire. For in stale Milk its Saline parts get a Flux, then being stirred up by the fire, supply by their own sourness the turn of Rennet, yea it is not improbable that the fluid Salt in the Rennet provokes the Saline Particles of the Milk, into a Flux, and that for this reason chiefly its Coagulation succeeds: for that the Saline parts having gotten of their own accord a Flux, so bind the pores of the Liquor, that the more thick Contents are willingly exterminated from them: wherefore we do say, for that reason, the same thing happens, when a Flux of the same Salt is caused by some thing else put into it. But that the Coagulation of Milk happens not only by reason of the passages and pores being possessed by a strange Body, the sign is; because the Salt of Tartar, tho exceeding Precipitatory, effects nothing of this, and this effect is excited almost only by sour things. Sugar hinders the Pre∣cipitation of Milk, and many other Liquors, because it restrains the Flux of the Ace∣tous Salt, and as it is easily Soluble, and its Particles are soft and blunt, they extrude not the former Contents implanted in the Liquor, but fill all vacuities, that afterwards there is no space whereby another Precipitating Liquor may unfold it self, and break into anothers quarters.

But Country people are wont to make Butter of the Flowers or Cream of Milk, kept for the most part to a sourness, only by shaking or Churning it. The reason of which (as it seems to me) is this: in Cream there is great plenty of Sulphur, with which also a mean portion of Salt and Earth is mixed, as may be conjectured, both by the sourness of the Liquor remaining of the Butter, or the Butter-Milk, and by its thicker consistency. In this mixture, the parts both Saline and Sulphureous are in mo∣tion, and a Flux: but as the Liquor is thicker they cannot presently fly away: where∣fore it remains, that if the bond of the mixture be further loosned, they will separate into parts, and that first the Sulphureous Particles, which exceed the others in power, are Congregated together with a mutual embrace; wherefore these two things, the

Churning of the Cream performs, viz. it brings the Sulphureous parts by their often obvolution together, whereby they do the better intangle themselves, and mutually ensnare one another; besides it breaks their mixture with the rest. For this reason, in the Winter time, (when Cream is thinner, and abounds less with Sulphur) Butter is hardly made. Besides the admixtion of Salt or Sugar wholly hinders its making; be∣cause by the coming between of those little Bodies, the Sulphureous parts are hindred, from a mutual adhesion.

The chief Precipitation of the blood, which is performed within a living Body, is made in the Reins; where, not without the strength of a certain Coagulum or Rennet, the serous matter is separated from the rest of the blood; just as Whey from Milk: For which reason Diuretical things are of the same Nature, as those which bring a Coagulation to Milk; and therefore, because they more Precipitate the blood by fusing it, they cause a large profusion of urine. The blood being sent forth of the Vessels, separates into various substances, by its own disposition: whilst it is warm, it is variously Precipitated, by some Liquors poured to it, (in like manner Urine) not without a pleasant Spectacle. If you pour upon warm blood the spirit of Wine, Harts Horn, Soot, Vitriol, or other Liquors, chiefly Spirituous or Saline, a wonder∣ful Ebullition, and heat is stirred up; whence we may conjecture after what manner it grows turgid, in Feavers. But before the rest. the Salt of Tartar, and a Soluti∣on of Alum, procure both in Blood and in Urin, a great perturbation of the Liquor, and falling down of the parts: for these disturb all the Contents in the pores and pas∣sages of the Liquor, and by their astriction, very much lock them up for a long time.

Precipitation in Artificial things is of greater note and use: for this for the most part follows Dissolutions, and succeeds them as it were by a certain right of Order; because this takes out of their Jaws, and as it were lays by, the prey, which all Men∣strua take by dissolving. According to the diversity of the Menstruum, and of the Body dissolved, Precipitation also variously happens: but in some Subjects there are two chief remarkable things, concerning the manner of Precipitation, to wit, the soluted Particles, immersed in the pores and passages of the Menstruum, are wont to fall out of them; either by reason of the narrowness of the conteining space, or else by reason of the Contents being increased in weight and bigness: for in some the pores of the Sol∣vent, being either leisurely bound up, or beset with a strange Body, shut forth from their Cells, the little Bodies of the thing soluted, and send them to the bottom; as may be ob∣served in Sulphureous Solutions, or such as are made of the whole mixture of integral parts, in a thin Liquor; which are disturbed, and lay away their Contents by external cold, simple water, or at least by any Acid infusion. After this manner resinous Tinctures, also of Sulphur, Olibanum, Benzoin, and the infusions and decoctions of Vegetables, also Urin, Milk, and Blood, are wont to be Precipitated: but in several others, besides that the pores, and passages of the Menstruum, are either leisurely drawn together, or pos∣sessed by a new guest, also somthing new grows to the Particles of the thing soluted from the Precipitating matter, whereby being increased in weight and bulk, they can be no longer sustained; but that they are necessitated to sink to the bottom. This is chiefly seen in the Saline Solutions of Minerals, which are only Precipitated by the Salts; whose Particles presently cleave to the little Bodies of the thing soluted, and increase their sub∣stance, that presently they descend to the bottom by their own weight: For in Saline solutions, the little Bodies of the thing soluted, are strictly bound together by the fluid Menstruum, with the Saline Particles; and the Particles run hastily and are heaped to∣gether into the Embraces of the same fluid Salt, from the Precipitating infusion of the fixed Salt: wherefore, when these three, (to wit, the little Bodies of either Salt, and of the soluted matter) do cohere together, they constitute greater grains than can be contained in the narrow spaces of the Menstruum, and therefore being thrust out, they fall down towards the bottom: That this does truly happen after this manner, the great affinity, both of the fluid and fixed Salt, is a sign; that the Particles of both being placed near or mixed together, are presently combined in one: also, because many solutions of Minerals, are presently Precipitated by a fixed Salt, but not by Vitriol or Alum be∣ing put in, which do much more bind, and stop up the pores of the Liquor. Thirdly, it appears clearly even to sense, because that the matter put for a Precipitate, far ex∣ceeds the thing soluted in bulk and weight, and is impregnated by the fixed Salt ad∣hering to it, But these being thus disposed, we will descend to the particular cases of Percipitations, forasmuch as Precipitation is made manifold, to wit, according to the diversity of the Menstruum, of the soluted matter, and the Precipitating infusion.

Simple water, though it do not well sustain the Particles of the mixture which it re∣ceives into it self by infusion, or Cohesion, yet hardly sends them away by Precipita∣tion. For the pores of this Menstruum are too open and loose, wherefore the Preci∣pitating matter, doth not easily strike the little Bodies of the thing soluted: in the mean time, by reason of the more loose frame of the Menstruum, some parts of the soluted Body sink down; others of their own accord evaporate, from whence that Liquor doth not long keep the Virtues or Tincture, with which they are impregnated by another. As some more thick parts and Terrestrial may be thrust down to the bot∣tom, or otherways separated, we put in the Juice of Limons, or some acid thing, or boil in it the whites of Eggs, to wit, that whatsoever is thick might cleave to their viscous substance.

Spirituous and Sulphureous Menstrua, being impregnated with the Sulphureous Particles of the thing soluted, easily lay by their burthen; for they are Precipitated by common, or any Distilled water; as is seen in Sulphureous and Resinous Tinctures of Sulphur, Scammony, Benzoin, Frankincense, and others of that kind prepared by the Spirit of Wine, or Oyl of Turpentine, which presently grow Milky, by Water or Phlegm being infused. For in these sort of solutions, the pores are wholly posses∣sed, that they admit nothing besides the thing soluted, and besides, both the Liquor, and soluted Matter are so thin, that they easily give place to any thing else being in∣fused.

When Menstruas of this kind are filled with Saline Particles, as we may observe in the Tinctures of the Salt of Corrals, of Tartar and such like, Precipitation does not presently succeed from common water, but from an Acid Liquor, as the Spirit of Vi∣triol, Salt, &c.

Saline Menstruas impregnated by the solutions of Stones or Metals, are most easily Precipitated by Saline Particles, and scarce by others. The chief Precipitatory Li∣quor, is the Salt of Tartar, or of Herbs burnt to Ashes, deliquated or melted; for this strikes back the Particles of every soluted thing whatsoever, and sends them head∣long to the bottom; to wit, forasmuch, as it passes through every where, the little spaces of the solvent, and sticking to the Contents, increases them in bulk, that they more easily fall out of the pores of the Menstruum, bound also together with their own weight.

What fluid Salt (as Vinegar, Stygian waters, &c.) dissolves, the same a fixed Salt precipitates; and on the contrary: because Salt of Tartar being melted, most excel∣lently penetrates common Sulphur, and receives the Tincture; which then is preci∣pitated by a fluid Salt, viz. by the Spirit of Vitriol, and the like: which indeed does not happen, by reason of the disagreeing Particles of the Salts, and mutually opposing one another; but for that the same are greatly of kin, and rush into mutual Embra∣ces: for from hence, the little grains of the thing soluted, by reason of the cohering of both the Salts together, being increased in bulk and weight, are more readily thrust out of the little spaces of the Menstruum, and descend to the bottom. We will in this place, more sparingly insist upon instances of this nature, because the more full hand∣ling of them belongs to the Chymical Work.

Precipitation is not only observed in the separation of a more thick matter, from a serous latex, and in the settling of the disturbed parts towards the bottom; but som∣times the Particles shut up within the pores and passages of the Liquor, are so small and subtil, that being Precipitated, they are not discerned by the sight, neither do they quickly descend to the bottom; but from their situation and position, being va∣riously changed, the colour, and consistency of the Liquor, are diversly altered. I was wont in times past, to sport with the solutions of Vegetables and Minerals, which be∣ing made by themselves, were clear like Spring water, and appeared bright, being commixed, shewed now a Black colour, now a Milky, Red, Green, Blue, or some other kind. The solution of Saturn, (or Lead) being made with distilled Vinegar, appears bright like common water, if you add to this Oil of Tartar, like clear water, the mixture straight grows White like Milk. If Antimony calcined with Nitre, be boiled in Spring water, the straining seems clear, and almost without smell, which yet being dashed by any Acid thing, presently acquires a deep yellow colour, with a most wicked stink. Common water being imbued by an infusion of Mercury Sublimate, is presently tinged with yellowness, by Oyl of Tartar dropped into it. Quicksilver and Sal Armoniack, being beaten together, and Sublimated in a Matrace by the heat of Sand, go into a white powder, this being soluted by melting shows like to clear Spring

water, which yet being smeared upon Brass or Copper, appears like Silver; and be∣ing lightly rubbed on brasen Vessels, renders them as if they were perfectly silvered. A solution of Calcined Tin, being put to melted Salt of Tartar becomes bluish. A clear infusion of Galls, being mixt with a solution of Vitriol, makes Ink; if you add to this Spirit of Vitriol, or Stygian water, the black Liquor is by and by made clear like Spring water; and this Oil of Tartar reduces again to Ink. And what is more wonderful, if you write on Paper with the clear infusion of Vitriol, and frame any Letters; what you so write presently vanishes, nor is there any marks of the Chara∣cters left: but if you smear over the Paper with an infusion of Galls, presently the Letters may be read, as if wrote with Ink; which yet, with a Pen run over, dipt in Spirit of Vitriol, you may put quite out at once wetting, and then again render them, with wetting them with another Liquor of Tartar. The Sky-colour Tincture of Vio∣lets, being dashed with Oil of Vitriol, becomes of a Purple colour: to which, if you add some drops of the Spirit of Harts Horn, that Purple colour is changed into Green. Brasil Wood, being infused in common water, leaves a very pleasant Tin∣cture, like to Claret Wine; if you pour to this a little distilled Vinegar, the Liquor appears clear like White Wine: a few drops of Oil of Tartar reduces it to a deep Purple colour: then if the Spirit of Vitriol be poured in, it becomes of a pale yellow, like to Sack; if you add the Salt of Lead, being soluted by deliquation, the mixture grows presently Milky: by this means you may imitate that famous Water-drinker, who having swallowed down a great deal of Spring water, was wont to vomit forth into Glasses placed before him, diversly coloured Liquors, resembling the ideas of di∣vers kinds of Wines: for Glasses being medicated with the aforesaid Tinctures, (so lightly that they may not be perceived by the standers by) will not only cause the wa∣ter poured into them, to imitate every Wine, but will exhibit the very Proteus him∣self of the Poets, changed into waters, and from thence putting on all colours, and infinite forms.

If a Reason of these kind of appearances be asked, it ought to be fought in the minute Particles, contained within the pores of every Liquor; which as to their site and posi∣tion, being diversly altered, by another Liquor infused, transmit variously the Rays of Light, many ways break or reflect them, and so make divers appearances of co∣lours. For when the Rays of Light pass through almost in right Lines, they make a clear colour like Spring water; but it in their passage, they be a little broken, the Li∣quor grows yellowish; but being more refracted, they cause a red colour; if they are bowed back, so as to be drained, or that they cannot shew themselves, a dark or black colour arises; but if they are again reflected, to the outmost Superficies of the Liquor, they create the image of Whiteness: after this manner we might variously Philosophise about other colours, and their appearances, the diversity of which, and sudden alterations in Liquids, depend chiefly on Precipitation: because, as the Par∣ticles conteined in the Liquor, are driven somtimes more near by another infusion that they clasp themselves together; somtimes are ordered into other series of positions, the diverse representation of colours is made. For Liquor being impregnated with lit∣tle Bodies or Atoms, or this Nature, most minutely broken, seems as an Army of Soldiers placed in their Ranks, who now draw into close Order, now open their Files and Ranks, now turn to the left, now to the right hand, as is diversly shown in the exercising of Tacticks, or the Art Military. When two clear Liquors being mixed together shall make Ink, it is because the Particles conteined in either, approach near one another, and as it were placed in their close Orders hinder the passage of the beams of light: when afterwards, this Ink is made clear by another Liquor poured in, it is because the new Bodies of the thing put in, disperse abroad the former close joyned Particles, and drive them as it were into their open Orders.