A rose is a rose is a rose. Just ask Jean Marsh, known to millions of
Downstairs." Though Marsh has since gone on to other projects, ... it's
with Rose she's forever identified. So much so that she even likes to
joke about having one named after her, a distinction not without its
drawbacks. "I was very flattered when I heard about it, but when I looked
up the official description, it said, `Jean Marsh: pale peach, not very
good in beds; better up against a wall.' I want to tell you that's not
true. I'm very good in beds as well."
The formula PbS corresponds with lead 86.6 and sulphur 13.4%. The mineral nearly always contains a small amount of silver, and sometimes antimony, arsenic, copper, gold, selenium, &c. Argentiferous galena is an important source of silver; this metal is present in amounts rarely exceeding 1%, and often less than 0.03% (equivalent to 10¾ ounces per ton). Since argentite (Ag2S) is isomorphous with galena, it is probable that the silver isomorphously replaces lead, but it is to be noted that native silver has been detected as an enclosure in galena. Entry: GALENA
GALENA, an important ore of lead, consisting of lead sulphide (PbS). The mineral was mentioned by Pliny under this name, and it is sometimes now known as lead-glance (Ger. _Bleiglanz_). It crystallizes in the cubic system, and well-developed crystals are of common occurrence; the usual form is the cube or the cubo-octahedron (fig.). An important character, and one by which the mineral may always be recognized, is the perfect cubical cleavage, on which the lustre is brilliant and metallic. The colour of the mineral and of its streak is lead-grey; it is opaque; the hardness is 2½ and the specific gravity 7.5. Twinned crystals are not common, but the presence of polysynthetic twinning is sometimes shown by fine striations running diagonally or obliquely across the cleavage surfaces. Large masses with a coarse or fine granular structure are of common occurrence; the fractured surfaces of such masses present a spangled appearance owing to the numerous bright cleavages. Entry: GALENA
_Lead sulphide_, PbS, occurs in nature as the mineral galena (q.v.), and constitutes the most valuable ore of lead. It may be artificially prepared by leading sulphur vapour over lead, by fusing litharge with sulphur, or, as a black precipitate, by passing sulphuretted hydrogen into a solution of a lead salt. It dissolves in strong nitric acid with the formation of the nitrate and sulphate, and also in hot concentrated hydrochloric acid. Entry: A
Experimentally this important fact was proved first by Berzelius, who showed that by oxidizing lead sulphide, PbS, to lead sulphate, PbSO4, no excess either of sulphur or lead could be found after oxidation; the same held good with barium sulphite, BaSO3, when converted into barium sulphate, BaSO4. On a much larger scale and with very great accuracy the inverse was proved half a century later by J.S. Stas, who reduced silver chlorate, AgClO3, silver bromate, AgBrO3, and silver iodate, AgIO3, to the corresponding binary compounds, AgCl, AgBr and AgI, and searched in the residue of the reaction for any excess of silver or halogen. As the tests for these substances are among the most sensitive in analytical chemistry, the general law underwent a very severe test indeed. But the result was the same as was found by Berzelius--no excess of one of the elements could be discovered. We may infer, therefore, generally that compounds enter ulterior combinations without change of the ratio of their elements, or that the ratio between different elements in their compounds is the same in binary and ternary (or still more complicated) combinations. Entry: J
_Lead sulphate_, PbSO4, occurs in nature as the mineral anglesite (q.v.), and may be prepared by the addition of sulphuric acid to solutions of lead salts, as a white precipitate almost insoluble in water (1 in 21,739), less soluble still in dilute sulphuric acid (1 in 36,504) and insoluble in alcohol. Ammonium sulphide blackens it, and it is coluble in solution of ammonium acetate, which distinguishes it from barium sulphate. Strong sulphuric acid dissolves it, forming an acid salt, Pb(HSO4)2, which is hydrolysed by adding water, the normal sulphate being precipitated; hence the milkiness exhibited by samples of oil of vitriol on dilution. Entry: A
Anglesite, or lead sulphate, PbSO4, is poor in silver, and is only exceptionally mined by itself; it occurs in quantity in France, Spain, Sardinia and Australia. Of other lead minerals we may mention the basic sulphate lanarkite, PbO<b>·PbSO4; leadhillite, PbSO4·3PbCO3; the basic chlorides matlockite, PbO·PbCl2, and mendipite, PbCl2·2PbO; the chloro-phosphate pyromorphite, PbCl2·3Pb3(PO4)2, the chloro-arsenate mimetesite, PbCl2·3Pb3(AsO4)2; the molybdate wulfenite, PbMoO4; the chromate crocoite or crocoisite, PbCrO4; the tungstate stolzite, PbWO4. Entry: LEAD
The only minerals crystallizing in this class are quartz (q.v.) and cinnabar, both of which rotate the plane of a beam of polarized light transmitted along the triad axis. Other examples are dithionates of lead (PbS2O6.4H2O), calcium and strontium, and of potassium (K2S2O6), benzil, matico-stearoptene. Entry: FIG
In this system the three crystallographic axes are all at right angles, but they are of different lengths and not interchangeable. The parameters, or axial ratios, are a: b: c, these referring to the axes OX, OY and OZ respectively. The choice of a vertical axis, OZ = c, is arbitrary, and it is customary to place the longer of the two horizontal axes from left to right (OY = b) and take it as unity: this is called the "macro-axis" or "macro-diagonal" (from [Greek: makros], long), whilst the shorter horizontal axis (OX = a) is called the "brachy-axis" or "brachy-diagonal" (from [Greek: brachus], short). The axial ratios are constant for crystals of any one substance and are characteristic of it; for example, in barytes (BaSO4), a: b: c = 0.8152 : 1 : 1.3136; in anglesite (PbSO4), a: b: c = 0.7852: 1 : 1.2894; in cerussite (PbCO3), a : b : c = 0.6100 : 1 : 0.7230. Entry: 3
ANGLESITE, a mineral consisting of lead sulphate, PbSO_{4}, crystallizing in the orthorhombic system, and isomorphous with barytes and celestite. It was first recognized as a mineral species by Dr. Withering in 1783, who discovered it in the Parys copper-mine in Anglesey; the name anglesite, from this locality, was given by F.S. Beudant in 1832. The crystals from Anglesey, which were formerly found abundantly on a matrix of dull limonite, are small in size and simple in form, being usually bounded by four faces of a prism and four faces of a dome; they are brownish-yellow in colour owing to a stain of limonite. Crystals from some other localities, notably from Monteponi in Sardinia, are transparent and colourless, possessed of a brilliant adamantine lustre, and usually modified by numerous bright faces. The variety of combinations and habits presented by the crystals is very extensive, nearly two hundred distinct forms being figured by V. von Lang in his monograph of the species; without measurement of the angles the crystals are frequently difficult to decipher. The hardness is 3 and the specific gravity 6.3. There are distinct cleavages parallel to the faces of the prism (110) and the basal plane (001), but these are not so well developed as in the isomorphous minerals barytes and celestite. Entry: ANGLESITE
The galena group includes several other cubic minerals, such as argentite (q.v.). Mention may also be made here of clausthalite (lead selenide, PbSe) and altaite (lead telluride, PbTe), which, with their lead-grey colour and perfect cubic cleavage, closely resemble galena in appearance; these species are named after the localities at which they were originally found, namely, Klausthal in the Harz and the Altai mountains in Asiatic Russia. Altaite is of interest as being one of the tellurides found associated with gold. (L. J. S.) Entry: GALENA