POT 



583 



POU 



as self-evident. It differs from an axiom 

 in being put as a request or petition, 

 whereas an axiom is asserted. 



POT'ASH, Latinixed potassa. The vege- 

 table alkali, so called because it is ob- 

 tained from the lixivium of the ash 

 which remains from the incineration of 

 certain vegetables by evaporation in iron 

 pots. Potash is strictly the protoxide of 

 potassium. In commerce, it is usually met 

 with in the form of black ashes, obtained 

 by evaporating the lixivium and fusing 

 the residue; and pearl-ash, prepared by 

 again lixiviating the black ashes to free 

 them from some of their impurities, and 

 evaporating to dryness. The ashes of 

 commerce rarely contain more than 60 

 per cent, of the alkali. The greater part 

 of the alkali of the black ash is in a caus- 

 tic state (that is, in the state of oxide), 

 but in the pearl-ash it is in the state of 

 carbonate. 



POTAB'SA. The Latinized name of pot- 

 ash, adopted by chemists. 



POTAS'SIDM. The metallic basis of pot- 

 ash. Its sp. gr. being 0'865, it is lighter 

 than water, and when thrown upon it 

 floats, and burns with a beautiful rose- 

 coloured flame, evolving hydrogen, and 

 leaving the water a solution of pure pot- 

 ash. At ordinary temperatures it is solid, 

 soft, and easily moulded by the fingers ; 

 and when cut exhibits a beautiful metal- 

 lic lustre, closely resembling silver, which 

 speedily tarnishes by exposure to the air. 

 It conducts electricity like ordinary me- 

 tals. It must be preserved in pure naphtha. 



POTA'TO. The well-known root of the 

 Solatium tuberosum, a native of North 

 America, where it was called by the na- 

 tive Indians batatas, which Europeans 

 have altered to suit their particular lan- 

 guages. The potato, of which there are 

 now almost innumerable varieties, has 

 generally been regarded as a native of 

 South America ; but this arises from con- 

 founding it with the sweet potato (Con- 

 volvulus batatas), which is a native of the 

 intertropical parts of America, and does 

 not succeed well even in the warmer 

 parts of Europe, and consequently is not 

 attempted to be grown in this country as 

 an article of food. It is often absurdly 

 called the Spanish potato. 



POTEN'TIAL. Having power (potentia] 

 to impress on us the ideas of certain qua- 

 lities, though the qualities are not inhe- 

 rent in the thing, as potential heat. A 

 potential cautery is any caustic application, 

 as nitrate of silver, distinct from an actual 

 cautery, or a red hot iron. The potential 

 mode of a verb is that form used to express 

 the power, possibility, liberty, or neces- 

 sity of an action, indicated by may or can. 



POTENTIL'LA. Cinquefoil. A very exten- 

 sive genus of plants, mostly perennials. 

 Icotandria Pofypynia. Named from poten- 



tia, power, on account of its supposed 

 medicinal virtues. There are 11 indi- 

 genous species, among which are the wild 

 tansy or silver- weed, the common cinque- 

 foil or tive-leaved grass, the barren straw- 

 berry, the white, rock, shrubby, silvery, 

 golden, and spring cinquefoil. 



POTE'RICM. Burnet. A genus of plants. 

 MonaeciaPolyandria. Name from iron}- 

 fiot, a cup, in reference to the shape of 

 its flowers. The burnet-saxifrage, so 

 much used in the beverage called cool- 

 tankard, is the British type. 



POTOROO'. The name given in New 

 Holland to the Kangaroo rat. 



POT'STONE. The Lapis Ollaris of Pliny ; 

 the Toftstein of Werner, the Talc ollaire of 

 Hatty. A variety of steatite, usually of a 

 greenish colour, but of various shades, 

 and often spotted. Sp. gr. 3. 



POT'TERN ORE. An ore, so named by 

 the miners, because it tends to vitrify 

 like the glazing of potters' ware. 



POINTERS' CLAY. A variety of clay 

 usually of a grey colour, but becomes red 

 when highly heated, and so named because 

 it is used in the manufacture of the coarse 

 red earthenware. 



POT'TERY. In reference to chemical 

 constitution there are only two genera of 

 baked stoneware ; the first consists of a 

 fusible earthy mixture, along with an 

 infusible, which when combined are sus- 

 ceptible of becoming semi-vitrified and 

 translucent in the kiln. This constitutes 

 porcelain or china-ware, which is either 

 hard and genuine, or tender and spurious, 

 according to the quality and quantity of 

 the fusible ingredient. The second kind 

 consists of an infusible mixture of earths, 

 which is refractory in the kiln, and con- 

 tinues opaque. This is pottery, properly 

 so called, but it comprehends several sub- 

 species, which graduate into each other 

 by imperceptible shades of difference. To 

 this head belong earthenware, stoneware, 

 flintware, fayence, delfware, iron-stone 

 china, &c. 



PODNCE. 1. Gum-sandarach pulverized 

 to a fine powder, and used to prevent ink 



from spreading on paper. 2. Ground 



charcoal, inclosed in some open stuff, as 

 muslin, to be passed over holes forming 

 the lines of a pattern, to mark the same 

 on the material on which the pattern is to 



be embroidered, &c. 3. In falconry, the 



talons of a bird of prey are called pounces, 

 perhaps from the same root as Sp.punzar, 

 and Ital. punzone. 



POUND, Sax. pund ; a standard weight. 

 1. The imperial troy pound contains 5760 

 troy grains, and the imperial avoirdupois 

 pound contains 7680 avoirdupois grains, 

 or 7000 grains troy ; hence 144 Ibs. avoir- 

 dupois = 175 Ibs. troy. 2. A money of 



account - 80. 



