P YR 



G02 



I' YR 



more or less rapidity (when the requisites 

 are present), according as they contain 

 more or less nitrogen. 



PUT'TY, Sp. potea. 1. A cement com- 

 posed of whiting and linseed oil, beaten 

 or kneaded to the consistency of dough ; 

 used to fasten glass in sashes, stop cre- 

 vices, &c. 2. A white powder formed 



by calcining an alloy composed of equal 

 parts of tin and lead. It forms the base 

 of most enamels, and is also used in po 

 lishing metals, stones, and glass. 



PYC'NODONTS. Thick - toothed fishes : 

 wxvot;, compact, and c'Sowj , a tooth, their 

 leading character consisting in a peculiar 

 armature of all parts of the mouth, with 

 a pavement of thick, round, and flat 

 teeth, the remains of which, under the 

 name of bufonites, occur most abundantly 

 throughout the oolite formation. The 

 pycnodonts are now extinct : five genera 

 have been recognised. 



PYC'NOSTYLE, from trvxvo<;, close, and 

 ffrvKvi, a column. A method of inter- 

 columniation which has only a diameter 

 and a half between each pair of columns. 

 Exemplified in the ruins of Palmyra. 



PY.LO'RUS, from TvXj, an entrance, and 

 aiflai, to guard. The inferior aperture of 

 the stomach which opens into the intes- 

 tines. 



PYRA'CIDS. There are several vegetable 

 acids which, when distilled, undergo de- 

 composition, and new acids are generated 

 by the process: these new acids are dis- 

 tinguished by the name of pyracids from 

 JTVJ, fire, and acid. Thus, tartaric acid 

 yields pyrotartaric add; mucic acid yields 

 pyromucic acid ; gallic acid yields pyrogallic 

 acid, &c. 



PYR'AMID, m>(x/M<;. 1. A geometrical 

 solid, having one of its sides, called the 

 base, a plane figure, and the other sides 

 triangles, their points joining in one point 

 at the top, called the vertex. The edge of 

 the base and the vertex are called the 

 two directrices, and the straight line ex- 

 tending between them is called the geti- 

 eratrix. Pyramids are termed triangular, 

 square, &c., according to the number of 

 their sides. 2. A building of a pyra- 

 midal form. Those of Egypt are the 

 most celebrated structures of this sort, 

 and many attempts have been made to 

 ascertain their use. Some have supposed 

 them to have been erected for astronomi- 

 cal purposes ; others have taken them for 

 religious edifices ; but it seems to be now 

 generally agreed that their principal, if 

 not their sole use, was to serve as sepul- 

 chres for the kings and other great nv;n 

 of the land. There are a considerable 

 number of these pyramids between Cairo 

 and Meidan, on the west side of the Nile, 

 but the three of Memphis have attracted 

 particular attention from their size. These 



have from time immemorial been regarded 

 as the most stupendous wonders of th 

 world. The dimensions of the largest 

 has been variously given as follows, in 

 French feet. 



Width of one 

 Height 6fit..ide. 



Le Bruyn, 618 704 



Prosper Alpinus, 625 750 



Thevenot, 520 682 



Niebuhr, 440 710 



Greaves, 444 648 



This pyramid, according to the least of 



these dimensions, covers upwards of H 



acres (English), and may be ascended on 



the outside by 208 steps. 



PYRAM'IDAL NUMBERS are formed by the 

 successive sums of polygonal numbers, in 

 the same manner as polygonal numbers 

 are formed from arithmetical progres- 

 sions, thus: Arithmetical Progression, 1, 2, 

 3, 4, 5, &c. ; Polygonal Numbers, 1,3,6, 10, 

 15, &c. ; Pyramidal Numbers, 1,4,10,20, 

 35,&-c. 



PYRAM'IDOID, ) Parabolic spindle. A 



PTR'AMOID. j solid formed by the re- 

 volution of a parabola about its base or 

 greatest ordinate. 



PYRE'THRUM. Feverfew. An extensive 

 genus of plants. Syngenesia ; Poly, super- 

 flua. Name from rrvfirof, fever, being 

 regarded as a specific for some fevers. 

 Most of the species are hardy, many are 

 perennial, some shrubby, and a few an- 

 nual. The common, sea, and scentless 

 feverfew are British species. 



PYRETOL'OOT, from jrveirof, fever, and 

 Xcyos> discourse. The doctrine of fevers. 



PYREX'IA. Fever: from jrug, fire. Fe- 

 brile disease, under the systematic name 

 Pyrcriee, constitute the first class in Cul- 

 len's Nosology. Epithet, Pyrerial, febrile. 



PYRI'TES, ffv^ifrf, fire-stone. A name 

 first given to the native sulphuret of iron, 

 because it emits sparks of fire when 

 struck against steel, and because, when 

 heated red hot, the sulphur which it con- 

 tains burns with a lambent blue flame. 

 The name is now used to designate three 

 native sulphurets, the ferruginous, the 

 cupreous, and the arsenical. The first is 

 bisulphuret of iron, the second of copper, 

 and the third of arsenic ; and they have 

 all a general similarity in external ap- 

 pearance. Their colour varies from yel- 

 lowish-white to golden-yellow, with a 

 high degree of metallic lustre. 



PV'RO-ACET'IC SPIRIT, \ Acetone. Py- 



PY'RO-ACET'IC ETHER. ) roxilic spirit. 

 A colourless limpid liquid, of a peculiar 

 penetrating odour, so called because it is 

 obtained along with acetic acid by the 

 dry distillation of the acetates. It i 

 highly inflammable, and is therefore often 

 used in lamps, instead of spirit of wine. 

 Boiling point 132 Q F., sp. gr. 0'792. 



