P Y R 



l.tr property to its being a combination of earth or alkali 

 with phlogifton ; the vitriolic acid, when prefcnt, only occa- 

 fionally increafing or diminifhing thecfTcdt, according to cir- 

 cumftances. In theproccis of calcination, the earth or alkaline 

 principle is not merely mixed, but aftually, though loofely, 

 combined with the phlogillic principle of the coal ; fo that 

 the pyrophorus, confidering it in its moft fimplc Hate, is 

 only a perfectly dry phlogifticated alkali or earth. On thefe 

 data, the phenomena may be explained in the two following 

 methods ; with refpefl particularly to the influence of moif- 

 ture and heat upon the pyrophorHS. Suppofing either the 

 alkaline or earthy principles to have a greater affinity to water 

 than to the phlogillon with which either of them is united, 

 they may, on being expofed to a moift atmofphere, attraft 



t* Y R 



and the conftituent parts, according to Hdinjrer and Ber- 



zel 



lus, are 



Alumine 



Silex 



Lime 



Oxyd of iron 



Volatile matter 

 Lofs 



53-5 

 32-88 

 .88 

 .88 



•75 

 11.26 



The fubftance loft during the procefs is fufpefted to be 

 fluoric acid. Hauy claffes this mineral with the topaz. See 

 Toi'Az. B. 



PYROPCECILOS, in tbe Nalural Hi/lory of the An. 



the humidity, and therefore fet the phlogillic principle at li- cients, the name by which they call the granite of Arabia' 



'''■■ " -'—- — ^ -•' '--—■-J'--- commonly known to this day under the name of the Oriental 



granite. 



Tlie name is derived from the Greek, ^i/^, fre, or fre-co- 



loured, and miu-Ko:, f potted ; and the ancients having ufcd the 

 epithet fiery to yellow, as well as red, fomehave imagined the 

 granite muft be a yellow ftone ; but it is evident that red is 

 the colour meant by it here. 



PYROSCOPE, an inftrument invented by profefibr Ledie 

 for meafuring the intenfity of fire. This is merely the differen. 

 //^/Thermometer (which fee), with one of its balls covered 

 with filver leaf, while the other is naked. The fire heats 

 the naked ball, but not the filvered ball. Hence the liquid 

 m the tube rifes or falls, according to the intenfity of the 

 fire, and of courfe marks that intenfity. 



PYROSCOPIA, formed of ^.p, fire, and ™^s. 



berty ; which may, in its turn, attraft and be ignited by, 



the fuppofed aerial acid, its ftrong affinity to which is well 



knovrn : — or, if this hypothcfis be rejected, the inflammable 



matter may be kindled, merely in confequence of the heat 



produced by the combination of the alkali, &c. with 



moiilure. This reafoning, however, fuppofes the exiftence 



of phlogilton, which modern chemifts have generally exploded. 

 The chemical changes that take place during the formation 



and decompofition of pyrophorus, as they are ftated by Aikin, 



appear to be the following : i. By being heated below red- 



nefs in the open air, the ingredients enter into fufion, and 



thus mix accurately with each other ; then the water of 



cryftaUization is driven off from the alum, and of the fugar 



or flour, little elfe than the charcoal efcapes volatilization. 



2. The red heat to which it is expofed in the phial caufes the 



fulphuric acid of the alum and charcoal of the fugar to Jider, among the Greeks, a kind of divinat 



re-a£t on each other, by which part of the charcoal is driven fame with pyromancy and ignifpicium. 



off in the form of carbonic acid, and part of the fulphuric TTcrr.^ox,, 



acid efcapes as fulphureous acid. The blue flame that cha- 



rafterizes the latter part of thi;; procefs is probably caufed 



by the volatilization and combuflion of a portion of fulphur, 



more than is requiiite to faturate the potafh of the alum. 

 Thus the pyrophorus, when prepared, confifls of alumine, 

 charcoal, and fulphuret of potafh in intimate mixture. 

 3. When this powder is expofed to the air, a rapid decom- 

 pofition of the air itfelf, and of the moiilure which it contains, 

 takes place, the oxygen of each being abforbed by the ful- 

 phuret, while a fufficient quantity of heat is difengaged, to 

 bring the charcoal and remainder of the fulphur to a Hate of 

 aftual inflammation. See on the fubjeft of this article, 



Macquer's Chemical Dift. art. Pyrophorus ; and Prieflley's gellion, and might have been arranged as one of the fymp- 

 Obf. on Air, vol. iii. Appendix, p. 386, &c. vol. iv. toms of dyfpepfia. 



Appendix, p. 479, &c. Aikin's Diftionary. The fits of pyrofis ufually come on in the morning and 



PYROPHYLACIA, a term ufed by Kircher and fome forenoon, when the flomach is empty. The firfl fymptom 



I coti- 

 being the 



^ ^ uaiicy ana igniipicium. 



PYROSIS, in Medicine, called in Scotland the -water- 

 brajh, IS a diforder of the flomach, which is charaifterized 

 by a fudden and violent attack of pain in that organ, follow, 

 ed by a copious difcharge of a colourlefs, infipid, "and gene- 

 rally cold fluid, refembling faliva, from the cefophagus, 

 mouth, and throat. 



The firll defcription of this difeafe was given by Linnjeus, 

 as a common aff"eaion of the Laplanders, under the appro- 

 priate appellation of Cardialglafputatoria ; whence Sauvages 

 gave it the denomination of pyrofis Suecica. (Nofol. Meth. 

 clafs vii. gen. 18.) Dr. CuUen adopted the generic term 

 pyrofis, and deems it an idiopathic difeafe. It feems to 

 occur, however, in conjundlion with other forms of indi- 



others, to exprefs thofe magazines of fire which are placed 

 in the cavities of mountains and other hollows of the earth, 

 and ferve to fupply the feveral volcanoes in the different 

 parts of the world. See Volcano. 



PYROPHYSALITE, in Mineralogy, is fo called from 

 w^,Jire, and •lv-:x.>.i:, a bubble, becaufe this mineral emits 

 bubbles when expofed to the flame of the blowpipe. It is 

 found at Finbo, near Fahlun, in Sweden, imbedded in a 

 granitic rock. The colour of pyrophyfalite is white, in- 

 cHning to green, and occafionally fmall fpots of blue fluor 

 fpar are feen on its furface. It commonly occurs in oblong 

 pieces, fome of which approach to an irregular rhomboid. 

 It differs from felfpar, to which it has the moll refcmblance. 



is a pain at the pit of the flomach, with a fenfe of conitric- 

 tion, as if the itomach were drawn towards the back : the 

 pain is increafed by raifing the body into an eredt polture, 

 and therefore the patient bends himfelf forward. This pain 

 is often extremely levere, with a fenfe of burning ; and after 

 continuing for fome time, it brings on an eruftation of a 

 thin watery fluid in confiderable quantity. This fluid has 

 fometimes an acid tafle ; but moft; commonly it is defcribed 

 as being abfolutely infipid. It continues to be brouo-ht up 

 for fome time, and does not immediately give relief to the 

 pain which preceded it ; but at length it terminates the pain, 

 and the fit ceafes. 



Thefe paroxyfmscome on without any evident caufe, nor 



in having but one determinate direftion in which it can be is the origin of the difeafe always to be imputed to any par. 



fplit ; its fpecific gravity is alfo greater, and it fufes more 

 eafily. The fragments fcratch glafs, but are lefs hard than 

 quartz. The powder of the fineft fragments emit a phof- 

 phorefcent light when heated. Its fpecific gravity is 3.45, 



ticular fort of diet. It feldom,' if ever, attacks thofe peo- 

 ple who ufe frefli animal food daily ; but appears to be mofl 

 common among thofe who live almofl entirely upon tea, 

 milk, potatoes, and farinaceous fubftances. It is much more 

 M 2 common 



