On the atomic weight of graphite

Abstract

THE tel'm Graphite has been indiscriminately applied to many varieties of native carbon of veI'y different properties.The graphite of New Brunswick differs but little in appearance from anthracite coaL The graphite of Greenland is not very dissimilar, but possesses rather more metallic lustre.However, among these varieties of carbon, two may be especially distinguished,-by a superior degree of metallic lustre, by theiI' structure, and other well-defined properties.In the follovving papeI', the term Graphite is limited to these two varieties, which may be further distinguished as "lamellar" ancl " amorphous."The lamellar graphite is found in great abundance in Ceylon, whence large quantities are annually imported into this country.It appears in commerce in masses, sometimes of the weight of many pounds, of a brilliant metallic lustre, and possessing a distinct fibrous structure.It is very difficult by mechanical processes to bring this graphite to a fine state of division; however, by a prolonged grinding in water, it may be reduced to minute flat plates.This graphite is associated with quartz.A deposit of the same variety of graphite has recently been discovered at Travancore.The graphite from Travancore has no fibrous structure, but is in the form of slightly coherent, minute plates.Specimens of a similar graphite have also been given to me, from Moreton Bay in Australia, in a matrix of quartz, and from Ticonderoga, in the State of N ew York, associated with olivine and sphene.vVhen cast iron is dissolved in acid, a residue is left of about 4 per cent. of carbon in the form of graphite.This graphite also consists of minute brilliant plates, and is perfectly similar in its appearance and properties to the lamellar variety of native carbon, Amorphous graphite is found in BOlTowdale in Cumberland, and is also largely imported into this country from Germany, probably f:rom Griesbach near Passau, but I am unable to speak with certainty as to the locality whence it comes.It appears as a powder of a silvery grey colour, soft to the touch, and which rubbed on paper gives a brilliant metallic streak.This graphite is much softer than the other variety, and therefore better adapted for the manufacture of pencils.The graphite used in my experiments was in all cases carefully purified by boiling with acids, and by fusion with hydrate of potash in a silver crucible; unless otherwise mentioned, it is to be understood to be the variety from Oeylon.The graphite thus prepared leaves an almost inappreciable residue, and gave to analysis 99'96 of carbon.Its specific gravity was ascertained in two determinations as 2'25 and 2'26.The following investigation was undertaken yvith the view of asc81taining the weight ' * DEVILLE obtained from 100 parts, 205'3 of silica.Calculated from these numbers, the atomic weight of silicon would be 22'7, approximating to the former atomic weight of BERZELJUS, 22'5, The subject requires fmthcl' investigation.