Another important mine is reported at Whitehall, in the same State.
Australia possesses valuable graphite deposits, near Moreton Bay ; at Ballarat, a very pure vein bas been discovered, 5 in. thick at the top of the drive to 18 in. thick at the bottom. In New Zealand, impure graphite occurs in the Carrick Range, Otago, in considerable quantities, sometimes 13 ft. thick. A seam of graphite runs along the eastern shore of Fairfax Harbour, New Guinea.
Rammelsberg gives the following comparative tables of some graphites Loss by ignition.—Ticonderoga (New York), 3.85 per cent.; Ceylon, 2.56; Borrowdale, 3.80-5.08 ; Upper Jellied (Siberia), 2.5;1; Tunguska (Sidorow), 1.77-2.38.
b. Earthy matters.—Ceylon, per cent. ; Borrowdale, 7.00 ; Upper Jenisei, 4•50; Tun guska, C. Combustibility in contact with fused saltpetre : completely combustible—Ceylon, sp. gr. Borrowdale, 2.286 ; Upper Jenisei, ; Upernavik, 2.298 ; Arendal, Incom pletely combustible—Ticonderoga, sp. gr. 2.17 ; Ceylon, ; artificial carbon, 2.30.
The application of graphite to the manufacture of pencils (see Pencils), and of stove polish (see Blacklead), are sufficiently familiar, but it is used for other equally important purposes. It is now much employed as a lubricator for the steam cylinders of engines ; about 120-180 grains of the fine, dry, pulverized mineral being iotroduced twice a day through the usual tallow box. It is found to be much superior to oil or grease. Enormous quantities are consumed in erucible making, and another wide application of the substance has been created by.the electrotype process, it being used to coat the surfaces of wood, plaster of Paris, guttapereha and other non-conducting materials, so as to make them conductors.
Very erroneous impressions are still generally entertained concerning the commercial value of graphite, so much so that it is a cermet' thing for the discoverer of a new deposit to believe himself possessed of an immensely valuable property, whereas the mineral may be all but worthless. The reasons for this may be sought in the high price of the renowned Borrowdale graphite, and the common error of supposing all graphites to be alike. As a matter of fact they differ moot essentially, not only in chemical eompoeition—for crude native graphite is not purely carbon —but also in physical constitution, necessitating the greatest care in purchasing the raw material, that it may be of a character in accordance with its proposed application.
The value of graphite depends largely upon the amount of carbon it contains, which is beet ascertained in the following way. The pulverized graphite is dried at about 182° (360° F.), then
placed in a test-tube 4-5 in. long end in. wide, of hard glass. To this is added about 20 times as much well dried oxide of lead, and the whole is well mixed. The tube and its contents are carefully weighed, and then heated by the blowpipe flame till the mixture is completely fused and no longer evolves any gases. After this operation, lasting about 10 minutes, the tube ie allowed to cool, and the weight is again ascertained. The loss in weight is carbonic acid, the oxygen of which has been taken from the lead oxide, while the carbon ie all that there was in the graphite. For every 20 parts of loss there must have been 12 of carbon. In general it is sufficient to take 1 to 2 grammes of graphite, and 20 to 40 of oxide of lead. Touching other chemical peculiarities, it will be useful to observe that tirgillaceous matters, though they reduce the value of the mineral, are not prejudicial ; but the presence of carbonate of lime, or oxide of iron, is very objectionable in graphite intended for refractory applications. Presently it will be seen how far chemical treatment can be made to overcome these drawbacks ; but first of the physical differences.
On freeing graphite from its ash constituents, by means of grinding it very fine, and subjecting it to trentment with alkali at the point of fusion, aqua regia, and hydrofluorie acid, the so-called graphitic acids are produced. Graphitic acid thus obtained from amorphous graphite is a fine yellow, amorphous powder, which, when decomposed by heat, yields a black mass of great colouring and covering powers, exceeding those of the finest lamp-black. The same acid prepared in the same way from foliaceous graphite appears under the microscope to consist of foliaceous crystals, whose residue does not colour and has no covering property. The division of graphite into amorphous and foliaceous varieties is, therefore, of the greatest practical importance. When a lubricating or covering body is required, as in antifriction compounds, blackleading, electrotyping, &c., amorphous graphite must be chosen ; but for metallurgical and refractory purposes, the foliaceous variety is preferable. Granular or amorphous graphite, which ie often the purest, ie of little for crucibles ; but, with suitable manipulation, produces the finest grades for electrotyping and fine pencils.