365 



LEAD. 



LEAF. 



368 



lead, remarking that it is the protoxide only which combines with 

 acid. 



Carbonate of Lead: White Lead: Ceruse. It occurs crystallised and 

 massive. Primary form a right rhombic prism ; cleaves parallel to 

 the primary planes. Fracture conchoidal. Hardness 3'0 to 3'5. 

 Brittle. Colour white, yellow, gray, and grayish-black, sometimes 

 tinged green or blue by ores of copper. Lustre on the cleavage planes 

 adamantine, on the fracture surfaces resinous. Translucent, trans- 

 parent, and doubly refractive. Specific gravity 6'3 to 6'6. Phospho- 

 resces when powdered and thrown on hot coals. Soluble in nitric 

 acid with effervescence. By the blow-pipe on charcoal decrepitates", 

 becomes yellow, and is reduced. Massive varieties amorphous; 

 structure columnar, granular, compact. The following is its analysis 

 by Dr. John : 



Carbonic acid 15'5 



Oxide of lead 84'5 



100 



It occurs in most lead-mines and is sometimes used as an ore of 

 lead. The white lead which is used in paint is made artificially. 

 Caledonite is a compound of the carbonates of lead and copper. 



Sulphate of Lead : Anglesite. Occurs crystallised and massive. 

 Primary form a right rhombic prism. Cleaves parallel to the primary 

 planec. Fracture conchoidal. Hardness 2'5 to 3'0. Colourless generally, 

 but has sometimes shades of yellow, green, gray, brown, and black. 

 Lustre nearly adamantine. Transparent, translucent. Specific 

 gravity 6'23 to 6'31. It occurs in Anglesey, Cornwall, the Harz, &c. 

 The following is an analysis by Klaproth ; 



Sulphuric Acid 24-8 



Oxide of Lead ' 71'0 



Water 2'0 



97-8 



Dioxylite is a compound of carbonate and sulphate of lead, BO also 

 Leadhillite. 



Phosphate of Lead : Pyromorphite. The primary form is a rhom- 

 boid. It commonly occurs in hexagonal prisms, and cleaves parallel to 

 its planes, and to the truncations on its terminal edges. Fracture 

 imperfect, conchoidal, uneven. Hardness 3'5 to 4'0. Colour various 

 shades of green, yellow, brown, and gray. Lustre resinous. Trans- 

 parent, translucent. Specific gravity 6-911 to 7"098. It occurs also 

 botryoidal and reniform. It occurs in most lead-mines, especially in 

 those of Saxony and the United States. The following is an analysis 

 by Wbhler. 



Phosphoric Acid 1572 



Oxide of Lead 82-30 



Muriatic Aoid 1-98 



100 



Ifedyphane is an arseno-phosphate of lead and lime. 

 Oxide of Lead also occurs in combination with certain acids whose 

 bases are metallic. 



Argeniate of Lead: Oorlandite. Occurs in crystals and massive. 

 Primary form a rhomboid ; usual form an hexagonal prism, which 

 cleaves parallel to its lateral planes. Hardness 3'5 to 4'0. Colour 

 pale-yellow, yellowish and reddish-brown. Lustre resinous. Trans- 

 parent, translucent. Specific gravity uncertain, stated variously from 

 5-0 to 6-4, and 6'9 to 7'3. It is found in Cornwall and in France. 

 The following is the analysis by Wohler : 



Arsenic Acid 21 '20 



Phosphoric Acid 1-32 



Oxide of Lead 75'59 



Muriatic Acid 1'89 



. _ 100 



It also occurs reniform. Structure compact, opaque. Lustre 

 resinous. Colour brownish-red. Found in Siberia. 



Chromate of Lead : Crocoiiite. Primary form on oblique rhombic 

 prism. Cleavage parallel to the lateral planes of the primary form. 

 Fracture conchoidal. Hardness 2'5. Colour aurora-red. Lustre 

 adamantine. Translucent. Specific gravity 6'004. It occurs also 

 massive : Amorphous. Structure columnar, granular. It is found ill 

 Siberia and Brazil. The following is the analysis by Pfaff : 



Chromic Acid 32 



Oxide of Lead 68 



100 



It is the chrome-yellow of artists, and is made for their purposes 

 artificially. 



Vauquelinite is a chromate of lead and copper, of a dark-green 

 colour. 



Holybdate of Lead : Carinthite. Primary form a square prism. 

 Cleavage parallel to the primary planes. Fracture slightly undulating. 

 Hardnesi 3'0. Colour different shades of yellow, greenish, and red. 

 Lustre resinous. Translucent. Specific gravity 6'69 to 6'76. It 

 rarely occurs massive. It is found chiefly in Carinthia, but also in 

 North America, &o. The following is an analysis by Berzelius : 



Molybdic Acid 39'14 



Oxide of Lead 60'86 



100 



Tunyitate of Lead : Scheelate of Lead, Primary form a square 

 prism. Cleavage parallel to the planes of the primary form. Frac- 



ture conchoidal and shining. Hardness 3'0. Colour yellowish-white 

 and brownish. Lustre resinous. Translucent. Specific gravity 8'0. 

 It is found in Bohemia and Cariuthia. The following is the analysis 

 by Lampadius : 



Tungstic Acid 51-72 



Oxide of Lead 41-28 



100 



Vanadiate of Lead : Johnstonite : Vanadurite, Occurs crystallised 

 and in small globular concretions. Primary form a rhomboid. Frac- 

 ture conchoidal. Brittle. Colour straw-yellow to reddish-brown. 

 Dull, opaque. Specific gravity 6'99 to 7'23. It is found at Tampico 

 in Mexico, and Wanlockhead iu Scotland. The following is the analysis 

 by Berzelius : 



Vanadiate of Lead 74-00 



Chloride of Lead 25-33 



Oxide of Iron 0-63 



99-96 



Chloride of Lead: Cerasite. Has a white, yellowish, or reddish 

 colour, nearly opaque. A pearly lustre. Its specific gravity is 7 to 7 1 . 

 Cotunnite is another chloride of lead. It occurs at Vesuvius iu white 

 acicular crystals. 



Corneous Lead is a chloro-carbonate of lead occurring in whitish 

 adamantine crystals, and found in Derbyshire and Germany. 



Plumbo-Jtesinite is a protoxide of lead, alumina, and water. It is 

 found at Huelgot in Brittany, and in a lead-mine in Beaujeu, also in 

 the mines of Missouri. 



LEAD, BLACK. [GRAPHITE.] 



LEAD, RED. [CHROMIUM.] 



LEAD, WHITE. [LEAD.] 



LEADHILLITE. [LEAD.] 



LEAF. Amongst the higher plants, the whole of their parts can 

 be traced to modifications of the Leaf or Axis. What ia not axis is 

 leaf, and what is not leaf is axis. In the lower plants no such 

 distinctions exist, as the tissues are not formed into leaves and their 

 homologues. Although so common an organ, the leaf is not easily 

 defined, and those who are inclined to enter on the subject would do 

 well to consult Schleiden in his ' Principles of Scientific Botany.' We 

 shall here follow Schleiden in our description of the structure of this 

 most important organ. 



Leaves (Folia) may be divided into Annual (Folia Annua) and 

 Perennial (Folia Perennia) ; the former again into Deciduous (Folia 

 Decidua), which live only in the early part of the period of vege- 

 tation ; Yearling Leaves (Folia Annua sensu stricto), which live through 

 the whole period ; and Late Leaves (Folia Serotina), which are not 

 perfected till toward the close of the period. With few exceptions 

 every plant has temporal^ leaves, namely, the cotyledons and 

 frequently those next following them. The Orchidacece, some species 

 of Ciucuta, and some Cactacece ai-e the only plants at present known 

 with certainty to be destitute of cotyledons. Others, for instance the 

 Ithizanthea;, have not yet been sufficiently investigated. Many plants 

 are wholly destitute of leaves between the cotyledons and the 

 peduncles of the flowers, as, for instance, all the Cactacece, excepting 

 Peireakia, and some species of Ojmntia ; in others these are annual, 

 as in Alma, or perennial, as in Pinus. The floral parts, the leaves 

 last perfected, exist in all Phanerogamous Plants. 



When the leaf emerges from the axis it is a little conical body, 

 the base of which gradually comes to occupy the entire circum- 

 ference of the axis, a stem-embracing or Amplexicaul Leaf (Folium 

 Amplexicaule) ; or it shares the circumference of the axis with one 

 or more other leaves, which have originated with it on the axis in 

 the same plane, Whorled Leaves (Folia Verticillata) ; or, lastly, it 

 is confined to a small portion of the circumference, without any other 

 leaves arising from the axis in the same plane, Scattered Leaves 

 (Folia Sparsa). These three positions of the leaves upon the axis 

 are, most undoubtedly, the primary ones occurring in the plant. We 

 find the first in the cotyledon of the Monocotyledons ; the second iu 

 the cotyledons of the Dicotyledons. But if we disregard, in the 

 Monocotyledons, the character of embracing the stem, only looking 

 to the fact that one leaf alone is formed at one level on the stem 

 if we trace the further development of the leaves of Monoco- 

 tyledons, and of those of most Dicotyledons, since in the latter it is 

 only in a few groups that the later leaves are formed in whorls we 

 find that the great majority of plants have scattered lenves. If every 

 vegetable axis be regarded as a cylinder, the bases of the leaves must 

 admit of being connected by a spiral line. More minute investigation, 

 then, shows that the distances of the bases of the leaves on this 

 spiral are not without law ; but a certain regularity may be observed, 

 and, in fact, the angle (angle of divergence) made by two planes, 

 passing through the middle of the axis and the bases of two adjacent 

 leaves, which angle therefore is the measure of the distance of these 

 leaves from each other, is on an average 137 30' 28", consequently a 

 number bearing no ratio to the circumference of the stem (360) ; so 

 that no two leaves ever can be exactly in the same vertical line. In 

 the course of the entire axis the distances of the turns of the spiral 

 alter, but always regularly, sometimes even on account of accidental 

 influences ; and thus from the simplest fundamental condition 

 proceeds an infinite multiplicity of modes of manifestation, even 



