| Mirabelle, common yellow. | Greengage. | Black- blue, middle- sized Plums. | Dark black- red Plums. | Mussel Plums. | |||
| Yellow- green, middle size. | Large green, very sweet. | Common. | Italian, very sweet. | ||||
| Soluble matter— | |||||||
| Sugar | 3·584 | 2·960 | 3·405 | 1·996 | 2·252 | 5·793 | 6·730 |
| Free acid, reduced to equivalent in malic acid | 0·582 | 0·960 | 0·870 | 1·270 | 1·331 | 0·952 | 0·841 |
| Albuminous substances | 0·197 | 0·477 | 0·401 | 0·400 | 0·426 | 0·785 | 0·832 |
| Pectous substances, &c. | 5·772 | 10·475 | 11·074 | 2·313 | 5·851 | 3·646 | 4·105 |
| Ash | 0·570 | 0·318 | 0·398 | 0·496 | 0·553 | 0·734 | 0·590 |
| Insoluble matter— | |||||||
| Seeds | 5·780 | 3·250 | 2·852 | 4·190 | 3·329 | 3·540 | 3·124 |
| Skins, &c. | 0·179 | 0·680 | 1·035 | 0·509 | 1·020 | 1·990 | 0·972 |
| Pectose | 1·080 | 0·010 | 0·245 | 0·630 | 1·534 | ||
| [Ash from insoluble matter included on weights given] | [0·082] | [0·039] | [0·037] | [0·041] | [0·063] | [0·094] | [0·066] |
| Water | 82·256 | 80·841 | 79·720 | 88·751 | 85·238 | 81·930 | 81·272 |
| 100·00 | 99·971 | 100·00 | 99·925 | 100·00 | 100·00 | 100·00 | |
PLUMBA′GO. Syn. Graphite, Black-lead. One of the native forms of carbon. It contains from 95 to 100% of pure carbon; has a metallic lustre, and conducts electricity nearly as well as the metals. It was formerly regarded as a carbide of iron, but the iron generally found is now known to be merely in a state of mixture. There are two distinct varieties of graphite—crystallised or foliated graphite, obtained chiefly from Ceylon; and amorphous graphite (the ordinary plumbago or black-lead), largely imported to this country from Germany. The Borrowdale mine in Cumberland, from which the finest black-lead was formerly derived, is now nearly exhausted. The foliated graphite of Ceylon and other parts is the principal material employed for making plumbago crucibles and other fire-resisting goods. The amorphous graphite is used for making black-lead pencils, polishing powder for stoves and grates (‘lustre,’ ‘servants’ friend,’ &c.), and to diminish friction in heavy machinery (anti-friction powder). Its powder is also used to give conducting surfaces to articles on which it is desired to deposit copper by the electrotype. In medicine plumbago has been used with apparent advantage in herpes and several chronic skin diseases—externally, as an ointment made with four times its weight of lard; and internally, made into pills.
Purification. For medical and chemical use graphite may be treated as follows:—
1. (Dumas and Stas.) Heat it to redness with caustic potassa, in a covered crucible, then wash it well with water, boil it in nitric acid and in aqua regia, again wash it with water, dry it, and expose it at a white heat to a stream of dry chlorine gas; lastly, wash it with
water, and again heat it to dull redness. In analysis.
2. (Ph. Bor.) Pure native plumbago, 1 lb., is boiled in water for 1 hour, then drained, and digested for 24 hours in a mixture of water, 8 oz.; nitric acid and hydrochloric acid, of each 2 oz.; it is, lastly, well washed with water, and dried.
3. (Brodie’s patent.) This process is only applicable to the hard varieties of graphite, as that of Ceylon. It consists in introducing coarsely powdered graphite, previously mixed with 1⁄14th of its weight of chlorate of potassa, into 2 parts of concentrated sulphuric acid, which is heated in a water bath until the evolution of acid fumes ceases. The acid is then removed by water, and the graphite dried. Thus prepared, this substance, when heated to a temperature approaching a red heat, swells up to a voluminous mass of finely divided graphite. This powder, which is quite free from grit, may be afterwards consolidated by pressure, and used for making pencils or other purposes.
PLUM′BIC ACID. Binoxide of lead occasionally receives this name on account of its combining with some of the bases to form compounds which have been called plumbates.
PLUM′BUM COR′NEUM. See Lead, Chloride of.
PLUM′OSE AL′UM. The old name of the silky amianthine crystals of the double sulphate of aluminum and iron occasionally found on alum slate. Asbestos has also been so called.