POT 



POT 



having an affinity for oxygen, stronger 

 than any other known substances, they 

 may possibly supersede the application 

 of electricity to some of the undecom- 

 pounded bodies. Further experiments, 

 it is said, have enabled Mr. Davy, since 

 his communication to the Royal Society, 

 from which the above has been partly 

 abridged, to decompose, in the most satis- 

 factory manner, the barytes and stronti- 

 tes, and to show that the other alkaline 

 earths are oxides of highly combustible 

 metals. It cannot now be doubted, that, 

 in the hands of this great chemist, other 

 bodies, hitherto deemed simple, or at 

 least never yet analysed, \Vill speedily 

 yield to the powers either of the highly 

 inflammable metals already discovered, 

 or of a still further increase of the gal- 

 vanic battery. Mr. Davy has decompos- 

 ed carbonic acid by means of those me- 

 tals, and has oxydated them by muriatic 

 acid ; and an excellent writer says, " it is 

 now by no means improbable that char- 

 coal itself, hitherto regarded as the most 

 refractory of all substances, may be de- 

 composed by the new instruments ; and 

 that the means of obtaining it pure, and 

 even crystallized, shall at last be found ; 

 a discovery which would enable art to 

 vie with nature in the fabrication of her 

 most valuable produce." At any rate, to 

 use the words of the Professor himself: 

 " In sciences kindred to chemistry, the 

 knowledge of the nature of the alkalies, 

 and the analogies arising in consequence, 

 will open many new views ; they may 

 lead to the solution of many problems in 

 geology, and show that agents may have 

 operated in the formation of rocks and 

 earths, which have not hitherto been 

 suspected to exist." See Philosophical 

 Transactions of the Royal Society for 

 1808. Parti. 



POT stone, in mineralogy, a species of 

 the Clay genus. The colour of this mi- 

 neral is a greenish grey, of different de- 

 grees of intensity. It occurs massive. 

 The internal lustre is glistening and pear- 

 ly. Fracture, sometimes curved, foliat- 

 ed, sometimes imperfectly slaty. It is 

 soft, feels greasy, and difficultly frangible. 

 ft is found in beds with serpentine, at 

 Como in the Grisons ; in some parts of 

 Saxony, and in Hudson's Bay. It is very 

 nearly allied to indurated talc. It is re- 

 fractory in the fire, and may be used for 

 lining furnaces. It may be turned in 

 a lathe, and made into a variety of ves- 

 sels fit for culinary and other purposes. 



POTATOE, in botany, the English 



name for a species of the tuberose-rooted 

 Solatium. See SOLANUM. 



POTENT, or POTENCE, in heraldry, 

 a term for a kind of cross, whose ends all 

 terminate like the head of a crutch. It 

 is otherwise called the Jerusalem cross. 



POTENTILLA, in botany, cinquefoil, 

 a genus of the Icosandria Polygynia class 

 and order. Natural order of Senticosae. 

 Rosacese, Jussieu. Essential character: 

 calyx ten-cleft; petals five ; seeds round- 

 ish, naked, fastened to a small juiceless 

 receptacle. There are thirty-two species, 

 chiefly natives of the South of Europe. 



POTERIUM, in botany, burnet, a genus 

 of the Monoecia Polyandria class and or- 

 der. Natural order of Miscellanea. Ro- 

 sacese, Jussieu. Essential character : 

 male, calyx four-leaved ; corolla four- 

 parted ; stamina thirty to forty ; female, 

 calyx four-leaved ; corolla wheel-shaped, 

 five-parted; pistils two; berry formed of 

 the hardened tube of the corolla. There 

 are five species. 



POTIIOS, in botany, a genus of the Te- 

 trandria Monogynia class and order. Na- 

 tural order of Piperitx. Aroidese, Jus- 

 sieu. Essential character : spathe ; spa- 

 dix simple, covered ; calyx none ; petals 

 four; stamina four; berries two-seeded. 

 There are thirteen species. 



POTTERY, the manufacture of earth- 

 en ware, or the art of making earthen 

 vessels. The inferior kinds of porcelain, 

 or pottery, are .prepared by the same pro- 

 cess as that which has been described 

 under the word PORCELAIN; less pure, 

 but more fusible materials being employ- 

 eel, and, of course, a less degree of heat 

 being applied. 



The better kinds of English stone-ware 

 are composed of pipe-clay and pounded 

 flints. The yellow stone-ware is made of 

 the same materials, in other proportions. 

 The first is glaied by throwing sea-salt 

 into the furnace in which it is baked, 

 when the heat is strong ; the salt is con- 

 verted into vapour, and this, being applied 

 to the surface of the stone-ware, vitrifies 

 it, and forms an excellent glazing. The 

 yellow stone-ware is glazed by dipping 

 the baked ware in water, in which is sus- 

 pended a mixture ot pounded flint, glass, 

 and oxide of lead. In the glazing of some 

 kinds of stone-ware, oxide of tin enters 

 into the composition with the oxide of 

 lead, and gives a whiter glaxe. All the 

 coarser kinds of pottery are glazed with 

 oxide of lead ; this promoting so much 

 the fusion and vitrification, that the low 



