Page:Cyclopaedia, Chambers - Supplement, Volume 2.djvu/311

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early ripe, wild plum. 26. The wild plum, with large white fruit. 27. The wild plum, with red, harih, and unpleafant fruit, called in England the hedge-plum, or borfe-plum. Town. Init. p. 612. See Plum.

PRUSSIAN blue. In a paper of Dr. "Woodward's, communi- cated to the royal fociety from another hand, there is given a fhort way of making the Prujftan blue, which when tried over again by Mr. Brown the cbemift, was found to anfwer perfeaiy well ; and gave hints and occafions to feveral expe- riments which gave great light into the true nature of the bo- dies ufed in that preparation.

The method was this : four ounces of blood dried, and tour ounces of fait of tartar were calcined together ; two hours after which, a black fpungy fubftance remained in the cru- cible weighing four ounces ; a folution of which being made in rain water, and afterwards filtered, left a remainder which when dried weighed nine drachms. An ounce of Englifh vitriol was diflblved in fix ounces of rain water, and eight ounces of crude alum in two quarts of water. Thefe being mixed hot with the blood, became green ; and on adding two or three ounces of fpirit of fait, they became of a fine blue, which will fubftde, and leave the water clear at top. Mr. Brown found the procefs exactly anfwer, and the product was an ounce of a very fine colour, and perfectly fit for the painter's ufe.

Among the feveral experiments which were made by mixing, in different manners and proportions, the feveral liquors of which this colour was to be prepared, all produced a blue ; but that in different degrees, fome being deeper, and others much paler. In one experiment the alum was wholly left out. and a very pale blue was produced ; in another, the alum and vitriol were ufed in equal quantities, and then the pro duel was an extremely deep blue.

Upon the whole, the prefcription feems given after repeated trials, and appears to be that very combination of the feveral ingredients, which muff give the very fineft colour they are capable of giving.

It would be curious to know what gave the firft hint for the production of fo fine a colour from a combination of fuch materials, efpecially when we come to confider, that the blood has the principal fhare in this furprifing change. Blood of anv kind, or flefh of any kind, would produce the fame effects; but it is probable that flefh would not yield fo ftrong or fine a colour. Beef has been tried, and found to yield a Hue, but not fo fine as the blood. Phil. Tranf. N°. 38 r. p. 17.

The folution of alum, mixed with that of vitriol, produces no change of colour. If to thefe the fpirit of fait is added, there is ftill no change ; but as foon as ever the blood is added, the blue is produced, if inffead of the lixivium with blood, there be added to thefe ingredients, a lixivium with fait of tartar only, there follows a precipitation, indeed, but of no colour ; and when the fpirit of fait is added to this, it clears up, and the precipitation is received again into the liquor. The very fame effect will follow if any volatile alkaline fpirit ■ is made ufe of as a precipitant, or any volatile fait diflblved in water; nor can the blood itfelf be fuppofed to communi- cate this change from any fuch properties, the heat of the fire it undergoes in calcination being fufHcicnt to drive them off. In thecalcination of the dried blood and fait of tartar it was obferved, that there was a lofs of juft one half. It is difficult to determine with certainty, what quantity of either was loft in this operation; but it will eaflly be granted, that a much greater quantity of blood was loft than of the fait : and this is confirmed by experiment ; for the fame quantity of fait of tartar, calcined alone in the fame heat, has been found to lofe only one eighth part ; whereas, whendried blood was calcined by itfelf, it loft more than fix eighths. It appears that the blood In calcination parts with its tinging quality to the fait, or that quality is extracted from it by the fait, and pafles with it in its diflblution with the boiling water.

To prove this, fome dried blood was calcined alone, and a ftrong decoction of it made in water, and afterwards filtered : this when mixed with the former folutions, produced little or no alteration; and on the addition of the fpirit of fait, the whole became of an amber colour, without any precipita- tion. When this, mixed with oleum tartari, was added to the former folutions, it caufed a precipitation, but no colour ; and the fpirit of fait being added to the liquor, made it clear again ; but of no other colour than the amber tinge it had

" before.

The change of colour is not effected in any of the materials,

except

_. ..1 that of the folution of the vitriol ; fo that the alu feems only to be of ufe in fixing the colour, as it is often ufed by dyers to that purpofe : and the fpiritus falis gives it a deeper dye ; for if the lixivium with blood be poured to a folution of alum alone, there will fall a fediment a little inclining to the purple; which on adding fome fpirit of fait, changes to a brown. Much the fame changes will alfo be produced if you pour the fpiritus falis to the lixivium ; but not the leaft ap- pearance of blue: but when the lixivium is poured to a fo- lution of vitriol, there is immediately a deep blue produced, and this is ftill heightened by the fpirit of fait. In all the recipes which have been given for making the Pruf- Supp. Vol. II.

Jian blue, the liquors are ordered to be mixed together boiling hot, except the fpirit of fait ; and experience (hews, that the colour is moffreadily and beautifully made that way : but in, experiments made with all the liquors cold, the colours have been very well produced, only in lefs beauty ; and they have required waffling feveral times in frefli water, to bring them to their beauty.

If after the lixivium has precipitated the blue colour, on mix- ing with the folutions of alum and vitriol, a little more of the blood lixivium be added afterwards, the whole lofes its blue, and becomes brown ; but on adding fome more fpirit of fait, the matter becomes of a fine blue again.

As it appears from fome of the before mentioned experiments, that the folution of vitriol is the only thing which makes the colour with the blood; and as this vitriol is no other than iron diflblved by a liquor running from the pyrites when long expofed to the weather, it fhould feem that the iron was the only fubftance that really produced the colour : and experi- ments confirm this to be the cafe, Phil. Tranf, N°. 381. p. 20. See the article Blood. PRY FANITIDES, in antiquity, a name given to thofe widows who at Athens, and throughout all Greece, had the facred fire of Veffa committed to their care. The cuftom of the Greeks, in this refpect, differed very much from that of the Romans ; who allowed none but virgins to tend this facred fire, whence they were called vejlah. See Vestals, Cycl. They had the appellation of prytaniticles from Uftneamt, a name common to all places facred to Veffa. Hoffm. Lex. univ. in voc. PSALMIST, in the church of Rome, one of the leffer eccle- fiaftical order, the fame with what among us is called clerk, precentor, or finger. Hoffm. Lex. in voc. PSEGMA, a name given by fome of the antients to the flos Eeris,

or flowers of brafs. PSELAPHIA, a word ufed by the antient medical writers to exprefs friction with the hands, in cafes where the diftempered parts required it. This was always efteemed a part of the bufinefs of a phyfician, and was done with his own hand. PSEN, rr.v, the name given by naturalifts to the fig-gnat, a finall fpecies of gnat bred in figs while growing on the tree, and always remaining on the leaves of the fame tree, and feed- ing on its juices. See Caprification. PSEPHISMA, ¥ji<pwp,a, among the Athenians, a decree of the

fenate ; the fame with probuleuma. See Probuleuma. PSEPHOMANTIA, Tupe^owW, in antiquity, a fpecies of divi- nation, the fame with cleromancy. SccCleromancy, Cycl. PSEPHOPHORIA, in antiquity, the art of ufing the pfepbl, Tij^ct, or counters. This was the firft arithmetic taught chil- dren of every condition. Capitolinus, in his life of Pertinax, fays, Puer Uteris elementarily & calculo imbutus. Thofe who taught this art were called calculones y if flaves, or lately made free; but thofe of better condition were called calculators and numerarii. Every family, anywife confiderable, had one of thefe mafters, the title of whofe charge was a calcuHs, a rationibus. See the next article. PSEPHOS, Yupos, in antiquity, a name given to feveral things, as fmall ftones, fhells, and beans "fed among the Greeks in giving their fuffrages, and in their computations. Their ori- gin is, by Mr. Mahudel, afcribed to the fons of Noah, who ufed this kind of calculation to affift their memory in num- bering their flocks. Jofephus affures us, that the Egyptians borrowed this method of counting from Abraham ; and He- rodotus relates, that thefe fmall ftones were ufed both by the Egyptians and Greeks, only with this difference, that the lat- ter placed them and cyphers from left to right, and the former from the right to the left. The art of ufing them in calcu- lations was called pfepbopboria. See Psephophoria. Pfepbi were in ufe too among the Romans, who called them calculi. Whatever materials they confiftcd of, they were all of the fame colour when ufed in calculations; whereas thofe ufed in giving fuffrages were partly black and partly white. Lucky days were denoted by white, and unlucky by black ones. In paffing of laws, there were characters engraved on them, as V. R. i. e. uti rogas; and A. i. e. antique. Thofe marked with V. R. approved, and thofe with A. rejected the law in queftion. Judges made ufe of calculi marked with the letter A. i. e. abfolvo, when they abfolved the accufed perfon ; but if they were for condemning him, they ufed fuch as were marked with the letter C. i. e. condemns : and if the evidence for and againft the accufed perfon was equal, fo that they could neither condemn nor abfolve him, they made u(e of calculi marked with N. L. i. e. non liquet. There was ano- ther kind of calculi ufed at public games, which were marked with figures : thus, if there were twenty athletse ready to engage, they threw into a filver urn twenty calculi, every two of which were marked with the fame figures, from 1 to 10. Then upon drawing, thofe who got the fame numbers were obliged to engage together ; on which account they were called calculi atbletici.

The Greeks and antient Romans made ufe of very fimple ma- terials for their calculi, fuch as fmall ftones, fhells, and beans; and even in the time of the firft Roman emperors, it was thought a piece of luxury to ufe any of ivory. It is queftioned whether the Romans ever ufed any of filver or gold ; becaufe 3 E e the