XIII. On the atomic weight of graphite
The term Graphite has been indiscriminately applied to many varieties of native carbon of very 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 their structure, and other well-defined properties. In the following paper, the term Graphite is mited to these two varieties, which may be further distinguished as "lamellar” and 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 dates. Specimens of a similar graphite have also been given to me, from Moreton Bay an Australia, in a matrix of quartz, and from Ticonderoga, in the State of New York, associated with olivine and sphene. When cast iron is dissolved in acid, a residue is eft 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 Borrowdale in Cumberland, and is also largely imported into this country from Germany, probably from 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.