The Engineer's and Mechanics Encyclopædia: Plumbago.

The Engineer's and Mechanics Encyclopædia,
comprehending practical illustrations of the machinery and processes employed in every description of manufacture of the British Empire.
With nearly Two Thousand Engravings.
By Luke Hebert, civil engineer, edifor of the History and Progress of the Steam Engines, Register of Arts and Journal of Patent Inventions, etc.
In two volumes.
VOL. II.
London: Thomas Kelly, 17, Paternoster Row.
MDCCCXXXVI (1836).
Graphite, or black lead, is an ore obtained from the mines of Keswick and Borradaile, in Cumberland, from Ayr in Scotland and other places. It occurs in beds of various thickness, and constitutes an important article in commerce. The finer kinds are boiled in oil, and afterwards sawn into the required pieces to make pencils. A considerable quantity is used for blacking and polishing the fronts of stoves and numerous other purposes. It has been very common to apply it, in its impure state, to reduce friction in machinery and rubbing surfaces; and, very recently, Mr. Lewis Hebert, of Chelsea, has applied it, in a very refined state, as a substitute for oil, in diminishing the friction of the rubbing parts of clocks. He applied it to a sidereal time-piece, in January, 1816, between which period and 1827 the time-piece was cleaned three times without renovating the plumbago; the friction places being only wiped with a fine muslin rag. In a communication to the Society of Arts, in 1827, eleven years after the plumbago had been applied only once, he states, that the time-piece was going as well as ever. He found a great difficulty in applying it to the jewelled pallats of the escapement, but obviated it by applying it to the friction plane of the teeth of the swing wheel; and he adds, "so ever since the clock has gone without oil."

The process of applying the plumbago is thus: — Take about a quarter of a pound of the purest black lead, the brighter the better; reduce it to a very fine powder in a metal mortar, and, to judge if it is fine enough, take a small pinch of it between your fingers; after rubbing it a few seconds, if it does not feel lumpy or gritty, but smooth and oily, it is good, and beaten enough; have a glassful of filtered water, take some of the powdered plumbago with the clean blade of a knife, spread it on the water, and stir it well; cover the glass, and let it stand for two or three hours; at the top of the water will be a kind of cream, skim it off with a card, and lay it upon a sheet of paper; when dry, put it in a box, to exclude the dust from it; put the sediment aside, repeat the process with some other water and plumbago, until you have acquired a sufficient quantity of fine powder for your purpose; when the whole of the powder is dry, pound it again in the mortar, or bruise it with the bowl of a silver spoon, upon a clean sheet of paper, and repeat the same process two or three times; if the lead is pure, no more sediment will go down; if some does, wash and dry it once or twice more: as soon as no sediment remains, you may be sure that the plumbago dust is pure, and cannot cause any mischief to the pivots and holes; pour some alcohol (the strongest spirits of wine,) into a small glass; having wiped the pivots of the wheels and the holes of the plates very clean, immerse them into the spirits, and immediately into the plumbago powder, they will be covered with it; take a small pencil brush, such as is generally used by miniature pain ters, dip it into the spirits, and fill the pivot holes with it; introduce some powder into them with your finger, by rubbing the plates over the holes till the powder is even with their surfaces; put in the wheel and make it revolve in the frame for five or six minutes; do the same to every wheel, and also repeat it two or three times; then the holes and pivots will be charged with a thm crust of plumbago, smoother than any polish you can give them; the piece will go twice as long without cleaning as with oil, and truly; if its movement is entirely secluded from dust, there will be no necessity of cleaning it for twelve years, which will be about the time for renovating the plumbago.