P Y R 



P Y R 



mens from the north-weft coaft. It is now and then met 

 witli ill our more curious gardens, requiring bog earth, with 

 ftiade and nioiiUire, and flowering in June and July. Its 

 ftirubby habit is like the laft, but of more humble growth. 

 Leaves tnore pointed, with (harper tooth-like ferratures ; 

 their upper furface marked, along the rib and veins, with 

 a pale (tripe. 'VsrU-AJJower-Jlalks ufually two, rarely three, 

 drooping. Flowers the lize of the lail, but white. Stamens 

 denfely fringed in their lower part. Anthers witli tubular 

 jagged-mouthed pores. Style very (hort and thick. Stigma 

 hemifpherical, nearly entire, green. Mr. Purfli fays this 

 plant is in high efteem among the natives of North America 

 for its medicinal qualities, and is called Slp-Jtfewa. He 

 witnelTed a fuccefsful cure of fevere hyilcrics by a decoc- 

 tion of this Pyrola. — We can by no means adent to the 

 e(tabli(hment of that able writer's genus Chlmaphila, hinted 

 at by Michaux ; there being furely no diver(ity of habit to 

 fupport it ; nor any charafter, but a difference of length 

 in the ftyle ; which the other fpecies of Pyrola (liew to af- 

 ford admirable fpeciiic, but no generic, diltinftions. 



PYROLAMPIS, in Zoology. See Gl.Q\\-ivonn, and 

 Lampyris. 



PYROLIGNEOUS Acid, or Empyreumatk acid of 

 luood, ill ChemiJIry, a fpecies of empyreumatic Acetous 

 yield (which fee), procured by diililling in a glafs or 

 earthen retort a quantity of fliavings of any kind of wood, 

 fuch as box, guaiacum wood, or beech ; in which cafe an 

 extremely ftrong-fmelhng dark-coloured empyreumatic acid 

 liquor is obtained, nearly one-third of the weight of the 

 wood. This acid is fourer, and alfo much blacker and more 

 empyreumatic, than either the pyroii'Mcous or pyrotartareoiis 

 acid, probably as requiring a ftronger heat for its production. 

 The acid of wood is obtained in a large quantity near London, 

 from the preparation of charcoal for gunpowder, by diftilling 

 wood in caft-iron cylinders. It itains the hands deeply, and 

 wood indelibly. This acid is procured in fuch a quantity as to 

 be an objedl of manufacture. At the bed it is only an in- 

 ferior acetous acid, and the difficulty of purifying it will 

 prevent the profitable ufe of it in many of the arts to which 

 vinegar is applied. However, as the procefs for procuring 

 radical vinegar at the fame time purifies this empyreumatic 

 acid, it may probably be ufed for this purpofe. It may be 

 added, that much of the acid from the diltilled charcoal for 

 gunpowder, near London, is employed by calico-jJrinters 

 in forming the acetated iron, ufed as a mordant, as in this 

 cafe the colour and fmell of the acid are not at all detri- 

 mental. Some time ago Vauquehn announced, as a new 

 difcovery, that pyroligneous acid is identically the fame as 

 the acetous ; but this was known to Glauber near 200 years 

 ago. In the folio edition of his works, p. 188, may be 

 (een direftions for its diftillation, with a copper-plate of the 



apparatus which he employed. He there calls it the vine- 

 gar of wood. Parker's Chem. Catech. p. 195, note. 



PYROMACHUS, a name given by fome to antimony, 

 when reduced to a (tony hardnefs ; and by others to copper, 

 when fufed with fulphur, and thus rendered lefs duftile. 



PYROMANCY, Trpfi-Mtny., a kind of divination, per- 

 formed by means of (ire. 



The ancients imagined they could fortell futurity by iii- 

 fpedting fire and flame : to this end they confidered its di- 

 reftion, or which way it turned. Sometimes they added 

 other matter to the (ire, e. gr. a vefl'el full of urine, with its 

 neck bound about with wool, watching narrowly on which 

 lide it would burll, and thence taking their augury. 



Sometimes they threw pitch on it, and if it took fire im- 

 mediately, they cileemed it a good augury. 



PYROMETER, formed of ■7:v^,Jire, and ^.st^^^, I mea- 

 Jure, in Phyfics, the name of a machine contrived to mea- 

 fure the alteration of the dimenfions of metals, and other 

 folid bodies, arifing from heat. 



Thefe iultruments have been conftrufted of various forms ; 

 but as their objeft is to render the fmall expanfions of 

 folids apparent to the oblerver, they have confilted of a ma- 

 chine adapted to this purpofe, and of an apparatus fit for 

 heating the bodies under examination to a determined degree. 



The mod ufual, and, indeed, the moft: eligible mode of 

 heating the bodies, is to place them in water, in which a 

 thermometer is placed, and to heat the water by means of 

 lamps. Tile (mall expanfions of the heated folids have been 

 rendered vifible, Jirjl, by multiplying-wheels, or by levers, 

 or by fine fcrews, which render a fmall motion communicated 

 to one end of the mechanifm productive of a great move- 

 ment at the other end ; and, fecondly, by magnifying the 

 fmall expanfion through microfcopes ; which feems, upon 

 the whole, to be the method that is both mofl; certain and 

 mod manageable ; for with wheels and pinions, and even 

 with levers or fcrews, there is always fome equivocal mo- 

 tion, arifing from the loofe connection of teeth and pinions, 

 or from the drefs and bending of other parts. 



Mufchenbroek, who was the original inventor of this 

 machine, has given a table of the expanfion of the diflFerent 

 metals, in the fame degree of heat. Having prepared cy- 

 lindric rods of iron, deel, copper, brafs, tin, and lead, he 

 expofed them fird to a pyrometer with one flame in the 

 middle ; then with two flames ; and fucceffively to one with 

 three, four, and five flames. But previous to this trial, he 

 took care to cool them equally, by expofing them fome time 

 upon the fame done, when it began to freeze, and Fahren- 

 heit's thermometer was at thirty-two degrees. The effeCts 

 of which experiment' are digeded in the following table, 

 where the degrees of expanfion are marked in parts equal 

 to the -i-^-n-ijdth part of an inch. 



