ALKALY, Alkali, or Alkathy, in Chemistry, a Name originally given, by the Arabians, to a Salt extracted from the Ashes of a Plant called Kali; and by us Glass-wort because used in the making of Glass. See KALI, and GRASS.

Afterwards, the Term Alkaly became a common Name for the lixivious Salts of all Plants; that is, for such Salts as are drawn by Lotion from their Ashes. See LIXIVIOUS and ASHES. And hence, again, in regard the original Alkaly was found to ferment with Acids; the Name has since become common to all volatile Salts, and all terrestrial Substances which have that Effect. See ACID.

Alkali, then, in its modern extensive Sense, is any Substance, which being mixed with an Acid, an Ebullition and Effervescence ensues thereon. See EFFERVESCENCE, etc. And hence arises the grand Division of Natural Bodies into the two opposite Classes of Acids and Alkalies. See ACID.

Boerhaave scarce takes this Circumstance to be enough to constitute any determinate Class of Bodies. In effect, Alkalies are not of one similar homogeneous Nature: but there are two several sorts. The first obtained from Vegetable and Animal Substances, by Calcination, Distillation, Putrefaction, etc. such as Spirit of Urine, Spirit of Hartshorn, Salt of Tartar, &c.—The second are of the terrestrial Kind; as Shells, Bole, etc.

The two Species, Boerhaave observes, differ widely from each other; having scarce anything in common, but their being effervescent with Acids. The one is a Class of native, fixed, scentless, insipid, mild, astringent, fossil Bodies: The other a Set of such as are volatile, odorous, sapid, caustic, aperitive, and procured by Art. Hence, adds the same Author, mere Effervescence with Acids, must be allowed to be of itself insufficient to determine the Nature of an Alkaly: and that such a Name, which properly denotes a caustic fiery Substance, should not be affixed to any mild and gentle Body, as Chalk, etc. but other Properties and Considerations are to be taken in, and particularly their Taste, manner of procuring, and the Change of Colour they produce in Bodies.

With regard to this last Circumstance, those Liquors which being poured on Syrup of Violets, change it of a green Colour, are Alkalies; as those which turn it red, Acids. Thus Oil of Tartar turns it of a kindly green; and Oil of Vitriol of a Carmine red: And if to the Syrup thus made red by Oil of Vitriol, Oil of Tartar be poured, it turns that part wherewith it comes in contact, green; leaving the rest red: and the like holds of Oil of Vitriol, poured on Syrup made green by Oil of Tartar.

To the like effect, M. Homberg observes, that a mere heat and bubbling arising upon the Admixture of a Body with an Acid, does not seem an adequate Criterion of the Alkaline Nature; since distilled Oils of all kinds are found to do thus much; and many of them with more vehemence than Alkalies themselves, so as sometimes even to take fire, which Alkalies never do.

To the Definition and Character of an Alkaly therefore, M. Homberg adds this Circumstance; that after the Action, the Mixtures coalesce and shoot into a Salt, or saline Matter.—This excludes the Oils above mentioned; which do not, after Effervescence, unite with the Acids into a saline Substance, but rather compose a resinous one.

All lixivious Salts have these Characters of Alkaly—And not only lixivious, but also all urinous Salts; which are constantly found to imbibe Acids with great eagerness, and after Ebullition, to unite and crystallize with them. See URINOUS SALT.

Hence we have two Kinds of Alkaly Salts, viz. Fixed, or Lixivious Alkalies; and Volatile, or Urinous ones. See SALT; see also FIXED, VOLATILE, etc.

But beside Alkaly Salts, there are an Infinity of other Bodies, not saline; which answer to the Characters of Alkaly, e.g., produce much the same Effects with Acids, as the Alkaly Salts above mentioned. And these alkaline Matters are in other respects of different Natures.

Some, e.g., are merely Earthy; as Quick-lime, Marble, Sealed Earths, etc. Others are Metallic; among which, some have their peculiar and appropriate Acids to act on them, as Gold, Tin, and Antimony, which only dissolve with Aqua Regia; Silver, Lead, and Mercury, with Aqua fortis; and the others with other sorts of Acids, as Iron, Copper, Zinc, Bismuth, etc. There are others of the Animal Class, consisting, 1°, Of stony Matters found in the Viscera of certain Species; as the Calculus humanus, Bezoards, Crab's Eyes, etc. 2°, Testaceous Matters and Shells; as Pearls, Oyster-shells, Cuttle-fish Bones, the Shells of Coats of Lobsters, Crabs, etc.3°, The Parts of Animals, which by length of time, or some other Cause, are become stony, or even earthy; as the fossil Unicorn’s Horn, etc. Lastly, almost all Stone Marine Plants, as Coral, &c. After all, the Alkaline Property does not appear to be native, but rather producible by Art—This Opinion seems to have been first started by Helmont: before him, it was the standing Opinion, that Fixed Alkalies pre-existed in mixed Bodies; and were only separated or extricated from the Parts of the Compound. Helmont advanced, that they did not thus pre-exist in their alkaline Form, but were Productions of the Fire, by whose violent Action, part of the Salt which in the Concrete is all volatile, lays hold of some part of the Sulphur of the same Body; and both melting together, are fixed into an Alkaly: which Fixation he exemplifies, by what happens when Salt-petre and Arsenic, though both volatile, being exposed to the Fire, are fluxed by the Operation thereof, and made to fix each other.

Some late Chemists, and particularly M. Geoffroy, carry the Point something further, and assert, that all Alkaly Salts whatever, both Fixed and Volatile, are wholly the Effect of Fire; in that before any Action of the Fire, they did not pre-exist in the Mixt wherein they afterwards appear. See FIRE. Notwithstanding all the seeming Opposition and Hostility between Acids and Alkalies, they may be converted into one another; at least, Acids are convertible into Alkalies; as is shown at large by M. Geoffroy in a Discourse express, in the Mem. de l'Acad. An. 1717, where the Nature and Origin of Alkalies is excellently explained. Alkaly Salts, according to this Author, are only Acids concentrated in little Molecules of Earth, and united with certain Particles of Oil, by means of Fire.

When an Acid, which we conceive in general as a small, solid, pointed Spiculum, happens to be absorbed or concentrated in a proper Portion of Earth; the whole becomes denominated a Saline, Compound, Neutral, or Intermediate Salt; by reason the Acid, thus inclosed in a Sheath, cannot excite the same Savour as when disengaged therefrom; and yet excites a saline Taste: and for this reason is compound, &c.

Now, Fire is the only Agent capable of disengaging the Acid, from the Earth it is thus invested withal. Upon this, the Acid being lighter than the Earth, rises, and evaporates; leaving the Earth at the bottom of the Vessel; which for this Reason is called Fixed, in contradistinction to the Acid, which is Volatile. This Earth, thus bereaved of its Acid, is left with its Pores open and empty, which before were filled; and withal, in sustaining the Action of Fire, it necessarily retains some of the Particles thereof, which give it an acrimonious Taste, that mere Earth could never have— From this Taste it is called Salt; and from its Pores being open, and thus disposed to admit and imbibe new Acids, it is called Alkaly Salt. See EARTH, SALT, &c. Now, it is not to be imagined, that an Earth which has once been impregnated with Acids, can ever be perfectly divested thereof; there will still remain some, though much less than before. So that an Alkaly may be conceived as only a too small Quantity of Acid, inclosed in too large a Quantity of Earth.

The visible and sensible Fire is not the only Agent capable of separating Acids from their Earth; Fermentation has the same Effect, in virtue of that pure active Fire produced or concerned therein. Alkalies, therefore, are the Production, either of the one, or the other Fire; and the same may be said of the Acids disengaged therefrom; it being the Disunion of the Parts of the same Salt occasioned by Fire, that yielded both the Acids as well as the Alkalies. All the Difference is, that the Alkaly imbibes and retains certain Corpuscles of the Fire, whereas nothing foreign is superadded to the Acid.

On this Principle every Acid is volatile, and every Alkaly should be fixed, if the Alkaly were only Earth: But, in regard the little Acid still remaining in the Alkaly, may be united with a Portion of Oil, as well as a Portion of Earth; and Oil is known to be volatile; the Compound, that is, the Alkaly, must be volatile, in case the Oil prevail therein. In this Case, the Alkaly is found to have a strong, penetrating, urinous Taste and Smell; and is what we call a Volatile urinous Alkaly Salt. These things well considered; it will be easy to assign what must ensue upon the Separations, or new Unions of the Parts of a Mixt. An Acid, it is evident, may become an Alkaly, in that after having been separated from its Matrix, it may be restored in a small Quantity to another Matrix, either wholly earthy or earthy and oleaginous—In the first Case, it will become a Fixed Alkaly; in the second, it may be, a Volatile Alkaly, if in the supposed Matrix the Proportion of Oil prevail over that of Earth; and in this Case it will be urinous. Again, what before was a fixed Alkaly, may become Volatile and Urinous, by depositing or letting go part of its Earth, and taking Oil in its stead.

These Transformations are not found equally easy and practicable in the three different Kinds of Mixts, or the three Kingdoms; by reason of the Diversity of Circumstances that must concur thereto. They are much the most rare and difficult in the Mineral Realm; by reason, no doubt, that the Parts of Minerals are more closely tied together, and have, as it were, less play. The only instance Chemistry hath hitherto produced, of a Mineral Acid’s being converted into a Fixed Alkaly, is in the Operation of fixing Salt-petre. The Vegetable Kingdom, it is observed, furnishes a large Quantity of fixed Alkaly Salt; and a little volatile Alkaly: The Animal Kingdom, on the contrary, affords a deal of volatile Alkaly Salt, and but little fixed. The Fossil Kingdom affords a very little native fixed Alkaly Salt, as the Egyptian Natrum, and the Salts procured by Lotion from saline Earth about Smyrna and nine other Places of the East; and the Chemists have also found a Method of converting Nitre into a fixed Alkaly: But nobody hath hitherto produced a volatile alkaly from the Acids of the Mineral Kingdom. And yet, if Acid Salts of the Vegetable Kind be convertible either into fixed or volatile Alkalies, why may not Mineral Acids be susceptible of the same Change? Since Vegetable Acids are originally no other than Mineral ones: For, from whence but the Earth should Plants derive their acid Juice? In effect, M. Geoffroy has at length shown the Operation feasible, by an actual Transformation of the same Acid, Nitre, into a volatile urinous Alkaly. See the Adem. de P Acad. ubi supra. See also Salt-petre, etc.

By the way, it is to be noted, that the Instance of Egyptian Natron or Nitre, furnishes an Objection against the general Assertion of all Alkalies being artificial, or produced by Fire: Mr. Bayle, who had some of this Salt sent him by the English Ambassador at the Porte; found that Vinegar would work briskly on it, even in the Cold. Whence, says he, it appears, that the Egyptian Nitre, acknowledged to be a native Salt, and made only by the Evaporation of the superfluous Water of the Nile, is yet of a lixivious Nature, or at least abounds with Particles that are so, though produced without any precedent Incineration, and the Matter of it exposed to no Violence of the Fire, to make it afford an Alkaly. Producib. of Chym. Princip: He adds, “However, he does not know any other Body in Nature, except this, wherein the Alkaline Properties are not produced.” Ibid.—And proceeds to give Instances of Alkalies being made from Sea Salt, and other Acids; and shows, how the same Body, without the Addition of any other Salt, may by varying the manner of the Fire’s Application, be made either to afford little else than Acids, or a greater or less Quantity of Alkaly. Id. ibid. For the Theory of the Operation of Acids upon Alkalies, See ACIP.

Hypothesis of Alkaly and Acid. Tachenius, and Sylvius de la Boe, followed by the Tribe of vulgar Chemists, strenuously assert Sal Alkaly and Acid to be the only universal Principles of all Bodies; and by means hereof, account for the Qualities of Bodies, and the rest of the Phenomena of Nature; particularly those in the Animal Oeconomy. In a word, Alkaly and Acid are substituted in the stead of Matter, and Motion. See PRINCIPLE, ELEMENT, etc. Mr. Boyle attacks this Hypothesis with great force of Argument. In effect, it's at best but precarious to affirm, that Acid and Alkaline Parts are found in all Bodies. When the Chemists see Aqua fortis dissolve Filings of Copper, they conclude, that the acid Spirits of the Menstruum meet in the Metal with an Alkaly, upon which they work; but how unsafe a way of arguing this is, appears hence, that Spirit of Urine, which is allowed a volatile Alkaly, and accordingly makes a great Conflict with Aqua fortis, readily dissolves Filings of Copper, and more genuinely than the acid Liquor. So, when they see the Magistery of Pearl or Coral, prepared by dropping Oil of Tartar into the Solution of those Bodies made with Spirit of Vinegar; they ascribe the Precipitation to the fixed Alkaly of the Tartar, which mortifies the Acidity of the Spirit of Vinegar: whereas, the Precipitation would no less ensue, if, instead of the alkalizate Oil of Tartar, that strong Acid, Oil of Sulphur per Campanam, were used. It may also be doubted, whether it be just to suppose, that when an Acid is discovered in a Body, the Operation of that Body on another, abounding with an Alkaly, must be the Effect of a Conflict between those two Principles. For, an acid Body may do many things, not simply as an Acid, but on account of a Texture or Modification, which endows it with other Qualities as well as Acidity. Thus, when the Chemists see an acid Menstruum, as Aqua fortis, Spirit of Salt, Oil of Vitriol, etc., dissolve Iron, they presently ascribe the Effect to an Acidity in the Liquors; though well dephlegmed urinous Spirits, which they hold to have a great Antipathy to Acids, will readily dissolve crude Iron even in the Cold. Further, the Patrons of this Hypothesis, seem arbitrarily to have assigned Offices to each of their two Principles, as the Chemists do to each of their tria prima; and the Peripatetics to each of their four Elements. But it is not enough to say, that an Acid, for instance, performs these things, and an Alkaly those; and that they divide the Operations and Phenomena of natural Bodies between them. Assertions of such moment ought not to be received, without further Proof. Indeed, the very Distribution of Salts into Acids and Alkalics, has something arbitrary in it; there being not only several things wherein the Acids agree with Alkalies, but also several things wherein each differs from itself—To say nothing of the Diversity of fixed and volatile Alkalies aforementioned; some, as Salt of Tartar, will precipitate the Solution of Sublimate into an Orange-tawny; others, as Spirit of Blood and Hartshorn, precipitate such a Solution into a milky Substance; and Oil of Tartar very slowly operates upon Filings of Copper, which Spirits of Urine and Hartshorn will readily dissolve in the Fire. And among Acids themselves the difference is no less; for some of them will dissolve Bodies that others will not: and this even where the Menstruum that will not dissolve the Body, is reputed much stronger than that which does; as dephlegmated Spirit of Vinegar will dissolve Lead reduced to minute Parts in the cold, which is an Effect that Chemists expect not from Spirit of Salt. Nay, one Acid will precipitate what another has dissolved, and vice versa; as, Spirit of Salt will precipitate Silver out of Spirit of Nitre. Add, the Properties peculiar to some particular Acids, as that Spirit of Nitre or Aqua fortis, dissolves Camphire into an Oil, and coagulates common Oil into a consistent Substance like Tallow; and though it will both corrode Silver, Copper, Lead, and Mercury, and keep them dissolved, it quickly lets fall almost the whole Body of Tin. It's no wonder that the Definitions given of Acid and Alkaly should be inaccurate and superficial; since the Chemists themselves do not seem to have any determinate Notion of sure Marks, whereby to know them distinctly.—For, to infer, that, because a Body dissolves another, which is dissoluble by this or that known Acid, the Solvent must also be Acid; or to conclude, that, if a Body precipitates a dissolved Metal out of a confessedly acid Menstruum, the Precipitant must be an Alkaly, is precarious: since Filings of Spelter will be dissolved by some Alkalies, viz. Spirit of Sal Ammoniack, etc. as well as by Acids; and Bodies may be precipitated out of acid Menstrua, by other Acids, and by Liquors wherein there appears not the least Alkaly. Add, that a Solution of Tin-glass, made in Aqua fortis, would be precipitated both by Spirit of Salt, and by common Water.—Nor does that other Criterion of Acids and Alkalies, viz. the Heat, Commotion, and Bubbles excited upon their being put together, appear more determinate; since almost anything fitted variously and vehemently to agitate the minute Parts of a Body, will produce heat in it—Thus, though Water be neither an Acid nor an Alkaly, it will quickly grow very hot, not only with the highly acid Oil of Vitriol, but with the alkalizate Salt of Tartar. See HEAT. Neither is the Production of Bubbles, though accompanied with a hissing Noise, a certain Sign; such Production not being a necessary Effect of Heat, excited by Conflict, but depending on the peculiar Disposition of the Bodies put together, to extricate, produce, or intercept Particles of Air.—Hence, as Oil of Vitriol, mixed in a due Proportion with fair Water, may be brought to make the Water very hot, without exciting Bubbles: so Mr. Boyle has found, that alkalizate Spirit of Urine, drawn with some kinds of Tin, being mixed with Oil of Vitriol moderately strong, would afford an intense heat, whilst it produced either no manifest Bubbles at all, or scarce any; though the urinous Spirit was strong, and in other Trials operated like an Alkaly: and though with the Spirit of Urine made per se, in the common way, Oil of Vitriol will produce a great hissing, and a multitude of conspicuous Bubbles. On the other side, some acid Spirits, as of Verdigrease, made pure, poured on Salt of Tartar, will frequently make a Conflict, and produce a large froth; though not accompanied with any manifest heat. See EFFERVESCENCE. Many make the Taste the Touchstone whereby to try Acids and Alkalies: But there is a multitude of Bodies, wherein we can so little discern by the Taste which of the Principles is predominant, that one would not suspect there was a Grain of either of them therein: Such are Diamonds, most Gems, and many ignobler Stones; Gold, Silver, Mercury, etc. There are also Bodies abounding with acid or alkalizate Salts; which either have no Taste, or a quite different one from that of the chemical Principles.—Thus, though Venice-glass be in great part composed of a fixed Alkaly, it is insipid on the Palate: And Crystals of Silver and Lead, made with Aqua fortis, and containing numerous acid Particles of the Menstruum, manifest nothing of Acidity in the Mouth; the latter having a saccharine Sweetness, and the former an extreme Bitterness. And even in Vegetable Substances of a manifest Taste, it's not easy to know by that, whether it be the Acid or the Alkaline Principle which predominates in them: As, in the effentigy Oils of Spices, and the gross empyreumatical Oils of Wood.And even in Alcohol of Wine, which some contend to be an Acid, and others, an Alkaly. Lizperfelt.of Chym. Dokt.of Dua