G L A 



vci-y fliort prifm with rliomboidal bafe. The planes of 

 the baie arc generally fmooth and Ihining ; the lateral planes 

 ilriated parallel to the edges of the bafe. Cleavage double, 

 the one parallel to the bales, the other lefs diftinft and pa- 

 rallel to the edges of the bafe ; in all other direftions the 

 frafture is vitreous. Hence the primitive form is an oblique 

 prifm with rhomboidal bafe, the obtufe angles of which cor- 

 refpond with the obtufc angles of the fecondary prifm. TV.e 

 cryilals arc from topaze yellow to nearly colpurlefs ; they are 

 tranfparent, and, provided they are kept dry, preferve their 

 tranfparency and folidity though cxpofed to the air. . Their 

 hardnefs furpaffes that of fulphat, but is inferior tp' that of 

 carbonnt of lime. 



Expofed to an intenfe heat, the glauberite decrepitates and 

 melts into a white enamel. Immerfed in water, its furface 

 is covered by a milk-white crull, whicli penetrates deeper 

 and deeper, till the whole cryllal is white and opaque 

 throughout : taken out of the water and dried, the white 

 cruit crumbles into dull, leaving the nucleus, if there be 

 any remaining, unaltered and pertcftly tranfparent. Specific 

 gravity about 2.73. 



From M. Brongniart's experiments it appears, that 

 glauberite is effentially compofed of anhydrous fulphat-of 

 lime and of fulphat of foda, equally anhydrous. 2. That 

 thefe two falls exill in this fubllance nearly in the following 

 proportions : 



Anhydrous fulphat of lime .... 0.49 



Anhydrous fulphat of foda .... 0.51 



100 



A trace of water, indicated by the calcination, is not 

 brought into account, as little as the accidental admixture 

 of a fciurcely perceptible quantity of iron, to which the yel- 

 lowifli colour of this fubftance appears to be owing. 



Mr. B. adds the following obfcrvations : the above-men- 

 tioned pieces of fait from Ocana, which contain this fub- 

 ftance, have generally fome clay adhering, which penetrates 

 into the llriac of the furfaces, but feldom into the fubftance 

 of the glauberite. 



The efflorefcence on glauberite, when moiftened, and the 

 property this fait poffeifes of becoming opaque in water, 

 proceed from this, that the water, by diffolving the fulphat 

 of foda, transforms the fulphat of lime into a Ipongy fub- 

 ftance, and thus produces a phenomenon which is the reverfe 

 of that exhibited by the hydrophane. 



The exiftence of native fulphat of foda, or Glauber fait, 

 is well known to mineralogifts, and, indeed, it has been met 

 •with in the neighbourhood of beds of rock-falt ; but this 

 was only as folution in the water of lalt-fprings, or as efflo- 

 refcence near falt-mines : in a folid and cryllallized ftate, en- 

 tirely deftitute of water of cryftallization, and intimately 

 imited with felenite, it had never before been obferved. Even 

 the anhydrous fulphat of foda was almoft entirely imknown, 

 till Berthier proved that it conftitutes nearly the fifth part 

 of thofe hard fcales found at the bottom of the pans in which 

 the fea-falt is obtained by evaporation. 



It reniains to be afcertained, under which ciixumftances 

 the rock-falt occurs which contains the glauberite, and 

 particularly in what relation this latter ftauds to it, and whe- 

 ther it occur in the rent-s or on the furface of the beds. See 

 Journal des Mines for 1808. 



Haiiy places the glauberite feparately at the end of the 

 fuhjlances acicUfcrcs ; and it appears to this mineralogift, that 

 the integrant molecules of the two falts of which it is com- 

 pofed exill together in the glauberite. He refers, for an 

 analogous combination, to Leblanc's experiments, according 



G L A 



to which a folution of fulphat of copper and fvilphat of iron 

 mixed, yielded cryftals compofed of thefe two fubftances, 

 while their primitive form proved to be that of the latter, 

 which had impreftcd on this mixture the character of its par- 

 ticular cryftallization. The qneftion, therefore, is, whe- 

 ther the glauberite be in afimilar cafe. Its form has, indeed, 

 nothing in common with that of the anhydrous fulphat of 

 lime ; but we are totally unacquainted with the cryl"- 

 talline form of the anhydrous fulphat of foda. But 

 even if it (hould be found that in this cafe the two molecules 

 combine in fuch a manner as to produce a third of a different 

 form from either, this circun. tance could, according to 

 Haviy's opinion, not be add'.'.ced as an objeftion againll the 

 th?ory of cryftallization, and muft be confidered as a pro- 

 blem, the folution of which is more interelling to the chemiif 

 than to the mineralogift. 



GLAUBOTTE, in Geography, a town of Priiftia, in 

 Natangeii ; 14 miles "S.E. of Bartenftein. 



GLAUCEDO, in Surgn-y. See'GLAUCOMA. 



GLAUCHA, in Geografhy, a town of Saxony, in the- 

 lordrnip of Schonburg, on the Mulda, containing about 

 600 houfes ; the inhabitants are employed in the manufac- 

 ture of ftufFs ; 46 miles W. of Drefden. N. lat. 50' 45'. 

 E. long. 12' 25'. 



GLAUCHE, a town of Germany, in the duchy of 

 Magdeburg, adjoining to the town of Halle, but governed 

 by its own magiftrates ; in which are four fcminaries, where 

 the languages, theology, mathematics, mufic, &c. are taught 

 by 120 prt-ceptors. 



GLAUCION, in Orn'ilhology, a fpccies of /Inas, the 

 grey-headed duck. See Duck. 



GLAUCIUM, in Botany, is fo named from its glaucous, 

 or fea-green, colour. Whether the plant intended by Pliny 

 be the Yellow Horned Poppy, according to the opinion ge- 

 nerally received, or any maritime Ipecies oi Euphorbia, leem« 

 a point not eafily determmed. rxau-. lov of Diolcorides appears 

 to be the juice of the firft-mentioned in its wild ftate, though 

 he compares it to his unxiv ze^kIiIi-, (which is evidently the 

 Yellow Horned Poppy itfelf,) faying the plant which yields 

 the 'y^xuxlov, and grows at .Terufalem, has almoft the leaves 

 of the ^rivjjit x^fzlili.;, but thicker, and fprcad on the ground, 

 ftrong fmelling, and more bitter, yielding plenty of faffron- 

 coloured juice. Poffibly this may refer to one of our other 

 fpecies of Glaunnm, if not to the common wild luteum. 

 Moft commentators have taken Argemone me\icana for the 

 plant of Diofcorides ; but that is a tropical produftion, un. 

 known in Europe, as we prefumc, previous to the difcovcry 

 of America, thoHgh now naturalized in the Eaft Indies ; 

 fee EciiTUUS. Neither does the above defcription fuit this 

 plant, for its leaves are much thinner than thole of the 

 Horned Poppy, and their juice pale yellow ; nor are tlicy* 

 fpread on the ground. Matthiolus feems to take the drug 

 Gamboge for •; A-y-v/.m-, but this does not at all help us, as to 

 the botanical quelHon, nor has it any probability in its 

 favour. — Tourn. Inrt. 254. t. 130. Sm. Fl. Brit. 563. 

 Prod. FI. Grxc. v. i. 357. Juif. 236. Girtn. t. 115. 

 (Chelidonium ; Linn. Gen. 262. .Sclireb. 350. Willd. 

 Sp. PI. V. 2. 1 141. Lamarck. Illuftr. t. 450. f. 2. Mart. 

 Mill. Diet. V. 2.) — 'Clafs and order, Polyandria Monogynla. 

 Nat. Ord. Rhicadea, Linn. Papaveracc-a, Juif. 



Gen. Ch Cal. Perianth inferior, of two ovate, concave, 

 bluntilh, deciduous leaves, often tipped with a point near the 

 fummit. Cor. Petals four, large, roundifti, flightly concave, 

 nearly etjual, with a ftiiiiing fpot near the bafe. S/am. Fila- 

 ments numerous, ftiorter than the corolla, flat, incurved, 

 rather dilated upwards ; anthers ereft, roundifti, of tw.> 

 lobes. Pi/?. Germen nearly cylindrical, curved, longer than 



tho 



