Page:Cyclopaedia, Chambers - Supplement, Volume 2.djvu/300

 P R I

P R I

by landing lets fall a grey powder, which is true common brimfrone ; a yellow fubftaiice of the like nature adhering likewife to the neck of the retort ; what is left behind being a black, fhining, light, fubllance, difpofed in thin difgregated ftrata or plates, like forhe of the foliaceous talcs, and in thefe iron may be difcovered by the help of the loadftone, 1 hus therefore all thefe bitumens may be artificially produced ; and the mod accurate analyfes of the natural ones, confirm the manner of their formation.

Thus the chemifts have fhewn, that metals are nothing but bituminous fubftances, which have undergone a long digef- tion ; for by depriving them of their fulphur they are firft reduced to afhes, and afterwards to glafs ; this is eafily feen in the imperfect metals; for if any of them be expofed to a long heat, and efpecially if to the rays of the fun collected by a large burning glafs, the fulphureous principle flies off", and only a calx or aihes will be left behind; which in a more vehement degree of fire are prcfently vitrified, and by refloring the fulphur this glafs may be again reduced to metal.

The inflammable fubftances in animals and vegetables, con- fiffc of a different combination of the principle of fulphur and acid fait; for the oil or fulphur in thefe is formed by a fmall portion of earth joined to the elementary fire, water, and acid fait; this oil when joined to an acid fait produces gums ; when joined to a fine acid, and a new acceffion of fiery particles, it produces eflential oils and inflammable fpirits; but if the acids are more grofs, by rcafon of a larger quantity of earth joined to them, it forms refins, as we learn from the artifi- cial compofitions of all thefe fubftances. By mixing fpirit of wine with volatile fpirit of urine, we obtain a mucilagi- nous concretion, or thin gum : oil of olives and fait of tar- tar melted together, make a kind of foap or thick gum ; and if fpirit of wine be digefted for a long time with oil of vitriol, and then dtflilied, an inflammable oil is obtained, refembling in fmell and other qualities the eflential oils of plants, a true rcfin being left behind in the retort.

In animals this fame oleaginous principle forms the fat and other glutinous or gelatinous fubftances ; thefe laft being com- pofed of an acid volatile fait and oil, as appears from their analyfis : but fat is made of the fame oil and acid fait ; for, if oil of olives and fpirit of nitre be mixed together, and digefted, a fubftance will be formed in all particulars refembling the fat of animals.

Sulphureous fubftances found in bodies are either fixed or vo- latile. The fixed fulphurs arc either folid, fuch as, fat, refin, and the bitumens ; or fluid, as oils Volatile fulphurs are fuch as fly oft" with a fmall degree of fire, and have an appearance compounded of that of oil and water Such are inflammable fpirits obtained from the fruits and flowers of plants. Geoff. Trail, p 17.

Tho' fait be in reality a mixed body, yet in the common ana- lyfis of bodies it is obtained intire, and has therefore pafted with many for a true chemical principle : a great deal of pains is ncceflary to decompofe and reduce It to its natural principles, but with accuracy and caution it is reduced to water and earth. It is the fole origin of tafte, fmell, and many other of the mod obvious properties of bodies, and may properly be defined to be a mixed body", formed by the concretion of fire, water, and earth, into a folid, rigid, fubftance, foluble "m water, and fufible by fire. As its particles may be con- ceived to cohere by large furfaces only, fait cannot be friable, like earth; but requires a confiderable force to feparate its parts, which fly ofF from one another with a fenftble noife like thofe of glafs. It becomes the caufe of tafte and fmell, becaufe its particles terminate in ftrong points, which vellicate the nervous membranes of the tongue and nofe. Salt is properly of three diftincl kinds, acid, acrid or alkaline, and neutral, or fa! falfus, compounded of the other two. Geoff. Tract, p. 12.

Acid fait is a congeries of inflexible folid parts, of an oblong figure, pointed at both ends. That its particles are rigid and hard, appears from the force with which it divides and dif- folves folid bodies; and their ftiaipnefs and pungency are evi- dent from the effect they have on the tongue, different from the corrofion of the acrid or alkaline falts. Acid fait is eafily diflblved by water; and after this (olution, its parts are equally fclifperfed through that fluid, and have the fame motion with it. Hence it appears, that the particles of both thefe fubftan- ces have nearly the fame fpecific gravity ; and likewife, that the motion of the aqueous parts is great enough to overcome the cohefion of the parts of the fab.

Concerning the manner in which the particles of acid fait are compounded office, water, and- earth, nothing can with cer- tainty be determined. It may be conjectured, however, that feveral particles of water being collected into one little mats, are'ecmented together by fome particles of fire and earth, lodged in the interfaces left between them ; and that all thefe taken together are difpofed in one oval form, or that of two cones joined by their bafes. This configuration, however, is not the fame in all acid falts ; but the differences may all be reduced to three, the nitrous acid, the muriatic, and the vi- triolic, Gtff. Tract, p. 13.

Salt alkali has its' name from the Arabian /<//', a plant, from whole afhes a fait proper for glafs -making was obtained ; and from thence it came to be ufed For the fixed falts got from the afhes of all plants, and afterwards for all falts and other fub- ftances whatever, that will ferment with acids. Acrid or alkaline fait feems to be a congeries of fphericaf par- ticles, with rough, prickly furfaces; becaufe of their great dif- pofuion to motion, and their corrofivc burning tafte. The points of their furfaces act on the nervous papilla; of the tono-ue like fo many files; whereas acid fait is only pungent. But then by thefe points a larger furface is expofed to the action of the fire than could otherwife be, and thus the par- ticles of fome alkaline falts are very volatile, or eafily railed by a gentle heat. The origin of this fait is probably from a connection of acid points and terreflrial particles ; becaufe, in many operations in chemiltry, fuch falts arife from the mix- ture of acid falts and earth ; as we fee particularly in the pre- paration of fixed nitre and fermentation of urine. Nitre being diftilled, leaves a compound fixed fait behind, of the fame nature with fea-falt; out of which, by a nicer dif- tillation, an acid liquor may be extracted without any volatile fa t, or at leaft but a very fmall quantity : but if the fame fixed fait be previoufly fermented, and then diftilled, it yields a large quantity of volatile fait, and a very little fixed fait or acid; becaufe by fermentation or calcination, ihe acid and terreftrial particles are intimately mixed, the acid fpicula en- tering the pores of the earth, and fo forming new molecules, which are denfe and clofe toward the center, and prickly on the furface by the acid points flicking out. Such are the par- ticles of volatile alkalies, of which, if a great number be joined together, they muff; cohere very ftrongiy by means of their points, and form malecuke of irregular figures j in the pores of which, watery, fulphureous, earthy, or acid par- ticles may be received and abforbed.

Hence it is, that thefe falts are feldom pure; and as they are very often filled with particles of earth, they refill the molt violent degree of fire, and will fooner melt than be raifed by it. This is the true nature of fixed alkaline fait, fuch as fait of tartar, or the falts got from the afhes of plants, called iixivial falts. If they be impregnated with fulphureous particles, they continue very volatile, and are railed by a fmall degree of fire ; as we fee in fait of urine, hartfhorn, and others got from animals.

Acrid falts eafily melt, when expofed to a moift air, becaufe the particles of water contained in fuch air readily enter their pores: when thus melted, they become properly lixivia, and are commonly termed oils, as oil of tartar per deliqulum. Volatile alkaline faks, diluted with water, arc called volatile urinous fpirits ; fuch as the volatile fpirit of urine, of hartihorn, of blood, and others. Geoff. Tra&. p. 14. Neutral fait is a kind of fait compounded of acid and alka- line moleculre united together, and the figure of its particles is chiefly owing to the kind of acid that enters its compofi- tion. The impreftion thefe particles make on the tongue is more dull and languid than that made by acid or acrid panicles alone ; becaufe the moleculx formed by ihe union of thefe are larger in bulk, and confequently !efs difpofed for motion; and therefore, tho* there is a greater quantity of aculei, or points, in one of thefe moleculre than in one of the former; yet their bulks make them lefs capable of entering the pores of the (kin, and vellicating the nervous papillae, than when they are in a disjoined flare. The tafte of thefe falts is term- ed faline, and varies according to the differences both of the acid and alkaline particles that compofe them, according to the thicknefs of the fpicula, their number, and the other parts that may be mixed with them. That this is the true original of this kind of falts, is evident from the artificial compofition of fuch a fait from acid and acrid particles blend- ed together, and from the refolution of them into the fame. Thus by pouring fpirit of nitre, of fea-falt, or of vitriol, on fait of tartar, new falts are produced exactly of the fame ap- pearance with nitre, fea-falt, and vitriol ; and by analyiing thefe three falts, the eflential falts of plants, fa I armoniac, and others of the neutral falts, an acid and an alkaline fait may be obtained, in fome fixed, in others volatile. Geoff. Tract.

PR1NOS, in botany, the name of a genus of plants, the cha- racters of which are thefe : the perianthium is very fmall and permanent; it is compofed of one leaf, lightly divided into fix fegments. The flower confifts of one petal, and is of the rotated kind ; it has no tube, but its edge is d vided into fix oval fegments. The ftamina are fix erect tubulated filaments, fhorter than the flower. The anthene are oblong and obtufc. The germen of the pifKl is oval, and terminates in a flyle, which is fhorter than the ftamina. The ftigma is obtufe. The fruit is a roundifh berry, containing fix cells, and is much larger than the cup. The feeds are lingle; they arc very hard and obtufe, convex on one fide, and angular on the other. In fome fnecies the ftamina are but five inftead of fix. L'Wm/ Gen. PI. p. 151. P/nhwet, p- 452. Gronav,

PRINTING (Cyd )— The arts and fciences, efpecially ftatuary and fculpture, were arrived at fo great perfection anion.', the Romans, at the time when that empire was in its ^reateft

glory, 3