LEA 



C 142 ] 



L E N 



being fusible at about 600 Fahrenheit. 

 It is the softest of all the durable metals ; 

 it can be scratched by the nail, and is 

 easily cut by a knife. Its elasticity, duc- 

 tility, and tenacity, are comparatively low ; 

 it cannot be drawn into wire thinner than 

 a line in diameter. Lead is very mallea- 

 ble, and can be beaten into thin leaves, 

 but these, from its imperfect tenacity, are 

 easily torn. All the salts of this metal 

 are highly poisonous ; they are, however, 

 most shamefully employed by unprincipled 

 persons to correct or conceal the acidity 

 of cider and wines. The presence of lead 

 in these liquors may be detected by the 

 following means. Dissolve 120 grains of 

 sulphuret of lime and 180 grains of super- 

 tartrate of potash in 16 ounces of distilled 

 water, by repeated shaking the mixture ; 

 when perfectly dissolved, leave the mix- 

 ture to settle, and pour off the clear liquid 

 into clean phials, adding about twenty 

 drops of hydrochloric acid to each. A 

 small quantity of this poured into a wine- 

 glass of the suspected wine, will detect 

 the smallest quantity of lead, if any be 

 present, by producing a black precipi- 

 tate. 



Several instances of the occurrence of 

 native lead have been mentioned, though 

 in few of them does the fact appear to be 

 well established. In the island of Ma- 

 deira, it is found in small masses, in lava, 

 and hai undoubtedly been reduced to its 

 present state by volcanic fire. Next to 

 iron, lead may be considered the most 

 abundantly diffused of all the metals ; it 

 has been known from the earliest ages 

 The lead of our mines is in a state of 

 combination with sulphur, forming a sul- 

 phuret of lead ; this is called galena, or 

 lead-glance. By exposure to a strong 

 heat the sulphur is driven off and pure 

 lead is obtained : the average produce of 

 metal from the Derbyshire ore is about 

 66 per cent. 



LEGU'ME. (legumen, Lat. legume, Fr. le- 

 gume, It.) A species of fruit ; apod; a 

 seed vessel peculiar to leguminous plants, 

 formed of two oblong valves having no 

 longitudinal partition ; the seeds are at- 

 tached to one of its margins only ; the 

 bean, pea, vetch, and all the natural order 

 of leguminosae, furnish examples. 



LEGUMINO'S^E. An order of plants, calyx 

 five-toothed, inferior, the odd segment 

 anterior, or farthest from the axis ; corolla 

 papilionaceous, rarely regular; stamens 

 definite or indefinite, perigynous, either 

 distinct, monadelphous, or diadelphous ; 

 ovarium superior, one-celled, many seed- 

 ed, style and stigma simple ; fruit a le- 

 gume, or, rarely, a drupe ; seeds occa- 

 sionally with an arillus ; embryo, ex albu- 

 minous, cotyledons, either remaining under 



ground, or appearing above, in germina- 

 tion ; leaves oompound, stipulate, alter- 

 nate ; leaflets stipulate ; inflorescence 

 usually axillary, but various. 



One genus of this order, Detarium, has 

 a drupe for its fruit, and Mimosa has a 

 perfectly regular corolla. 



The order Leguminosse is most impor- 

 tant to man both for its beauty and utility. 

 The pea, bean, harico, vetch, liquorice, 

 clover, sainfoin, lucerne, tamarind, indigo, 

 gum arabic, &c. &c., belong to it. Ge- 

 nerally, the order is innocent, if not 

 wholesome ; but some few genera are 

 poisonous. 



LEGU'MINOUS. Belonging to the order 

 Leguminosse ; bearing pods ; having a 

 legume for a pericarp. Linnseus stated 

 that among all the leguminous or papi- 

 lionaceous tribe, no deleterious plant is 

 to be found ; this, however, is not strictly 

 true. 



LE'MMING. The Lapland marmot. The 

 lemming has short ears and a tail, with 

 the toes of its fore-feet peculiarly adapted 

 for digging. Cuvier places the lemming 

 in the order Rodentia, class Mammalia. 

 Bones of the lemming have been found 

 fossil in a breccia at Cette. 



LE'MNIAN EARTH. A mineral found in the 

 island of Lemnos, in the Egean Sea, 

 whence its name. It is also called sphra- 

 gide, from o^payic, sigillum, a seal. It 

 is of a reddish colour and has a soapy 

 feel. 



LENS, (lens, a lentil, Lat. lentille, Fr. 

 lente, It.) So named from its resem- 

 blance to a seed of the lentil. A trans- 

 parent substance having its two surfaces 

 so formed that the rays of light, in passing 

 through it, have their direction changed. 

 Of lenses there are various sorts ; a 

 spherical lens, is a sphere, all the points 

 in its surface being equally distant from 

 the centre. A double convex lens, is a 

 solid formed by two convex spherical 

 surfaces, having their surfaces on opposite 

 sides of the lens. When the radii of its 

 two surfaces are equal, it is said to be 

 equally convex; when the radii are un- 

 equal, it is said to be unequally convex, A 

 plano-convex lens, is a lens having one of 

 its surfaces convex and the other plane. 

 A double concave lens, is a solid, bounded 

 by two concave spherical surfaces, and 

 may be either equally or unequally con- 

 cave. A plano-concave lens, is a lens 

 one of whose surfaces is concave and the 

 other plane. A meniscus, is a lens one of 

 whose surfaces is convex and the other 

 concave, and in which the two surfaces 

 meet if continued. A concavo-convex lens, 

 is a lens one of whose surfaces is concave 

 and the other convex, and in which the 

 two surfaces will not meet if continued. 



