7:51 GRAPHITE 



which contain more than a thousand millions to tho cubic inch. Since tho ]; 

 of fluid-cavities indicates formation by tho wet way, whilst stone-cavities point to 

 fusion, and gas-cavities to sublimation, the co-existence of all these varieties in 

 granite leads Mr. Sorby to believe that this rock has been formed under highly com- 

 plex physical conditions, 'combining at once both igneous fusion, aqueous solution, 

 and gaseous sublimation. The proof of the operation of water is quite as strong as 

 that of heat/ 



GRAXTITITE. A granite, containing oligoclase, orthoclaso, quartz, and a mag- 

 nesian mica. 



GRA3TUXATIOXT is the process by which metals are reduced to minute grains. 

 It is effected by pouring them, in a melted state, through an iron cullender, pierced 

 with small holes, into a body of water ; or directly upon a bundle of twigs immersed 

 in water. In this way copper is granulated into bean-shot, and silver-alloys ;ir<; 

 granulated preparatory to refining. It has recently been proposed to granulate pig- 

 iron before introducing it into Danks's rotatory puddling-furnace. 



CRAPES. The fruit of the grape-vine (Vitis vinifera). They are largely used 

 as fruit, both fresh and dried ; forming, in the latter case, raisins and currants. Tho 

 juice of the grape yields wine, brandy, wine-vinegar, &c. The residue of the expres- 

 sion of the juice is known as marc, and is used in the preparation of verdigris, or 

 acetate of copper. Oil is prepared from the seed of the grape, whilst the lees aro 

 burnt for the sake of the potash they contain. 



CRAPE STJCAR. A sugar so called from its being produced in the grape ; but 

 it also occurs in many other fruits, and it forms the crystalline portion of honey. A 

 great quantity of grape-sugar is now prepared from starch. The formula of grape- 

 sugar is C 12 H 12 12 . 2HO (C 6 H 12 6 . H 2 O). 



GRAPHIC GRANITE. A peculiar form of granite, in which some of the 

 crystalline constituents are so disposed in the matrix as to suggest a resemblance to 

 some forms of oriental characters. 



GRAPHIC TELLURIUM. A name applied to sylvanite, in allusion to the 

 curious forms in which its crystals are generally arranged. See SYLVANITE. 



GRAPHITE, Plumbago, or Black-lead. (Plombagine, Fr. ; Eeissblei, Ger.) A 

 mineral substance of a lead or iron-grey colour, a metallic lustre, soft to the touch, 

 and staining the fingers with a lead-grey hue. H = 1 to 2. Specific gravity, 2'08 

 to 2'45. It is easily scratched or cut, and affords a black streak, displaying the 

 metallic lustre in its interior. B.B. infusible both alone and with reagents ; but 

 burns with great difficulty in the outward flame without flame or smoke, generally 

 leaving a residue of oxide of iron. It consists of carbon in a peculiar state of 

 aggregation, with an extremely minute and apparently accidental impregnation of 

 iron. Graphite occurs in gneiss, mica slate, and their subordinate clay-slates and 

 limestones, in the form of masses, veins, and kidney-shaped disseminated pieces. 

 It has been found also among the coal-strata, as near Cumnock in Ayrshire. This 

 substance is employed for counteracting friction between rubbing surfaces of wood or 

 metal, for making crucibles and portable furnaces, for giving a gloss to the surface 

 of cast iron, &c. 



The following report of the late Von Haidinger and others, of Vienna, on the origin 

 of graphite, contains much that is valuable. 



Iron, after long remaining buried in the earth, at last entirely decomposes, leaving 

 a black, porous, eminently combustible residuum, known as graphite or pure carbon. 

 Haidinger's report on the ferruginous masses of Kokitzau and Gotta, near Dresden, 

 masses of uncertain origin, lends support to this general fact. 



One word on the formation, still so little known, of graphite. Tho presence of 

 graphite in granite, gneiss, and diorite, has renewed tho disputes between tho Nep- 

 runists and Plutonists. Graphite is well known to be nearly pure carbon, for it leaves 

 in burning but a very small quantity of ash. Now, if these primitive crystalline rocks 

 are of igneous formation, it is impossible to explain how graphite could co-exist with 

 silicates of protoxide of iron without having reduced these salts. Judging merely by 

 what takes place in blast-furnaces, carbon reduces all oxides of iron at a high tem- 

 perature. It must, then, be admitted that granite, gneiss, and diorite did not mm a in 

 graphite when the mineral elements of these rocks, such as mica, hornblende, and other 

 ferrous silicates, were in a state of fusion. Graphite, then, must have been subse- 

 quently introduced into these rocks, but when and how? Questions such as these are 

 very difficult to answer satisfactorily. The most plausible hypothesis is that graphite 

 has been introduced by the wet way into the crystalline rocks, and substituted tor 

 one of the mineral components. Tims in the gneiss of Passau (Kavaria) it takes the 

 place of mica. 



(liMphite is frequently to be mot with in granular limestone, a fact particularly 

 interesting to geologists. Is limestone a product of eruption, or is it a sediment 



