70 DRAGON'S BLOOD 



Dolomite was employed -first by the late Mr. Hugh Lee Pattison, for the manufacture 

 of carbonate of magnesia, and it is still used for that purpose. 



When dolomite is calcined, within certain limits of temperature, it is said to furnish 

 an excellent hydraulic lime. M. H. Sainto-Claire Devi lie has called attention to tho 

 powerful hydraulic properties of caustic magnesia by its union with water to form a 

 definite hydrate. It appears that if dolomite be calcined below a rod heat, tho 

 carbonate of magnesia suffers decomposition, whilst the carbonate of lime remains 

 almost intact; on slaking this calcined dolomite, the magnesia combines wit h water, 

 and this hydrate cements the unaltered particles of carbonate of lime. F.W.K. 



DOIVIEYILITE. An arsenide of copper, occurring in Chili, in Bolivia, and .-it 

 Lake Superior. Mr. D. Forbes found the domeykite of the Corocoro sandstone, in 

 Bolivia, to contain copper 71*13; arsenic 28'41 ; silver 0*46. This has probably been 

 formed in situ by the action of arsenical vapours on metallic copper disseminated 

 through the sandstone. Faraday's Condurrite from Cornwall is closely allied to if 

 not identical with domeykite. 



DONARIUM. Bergmann supposed that he had detected, in a Norwegian 

 mineral, a new metal, to which he gave the name of Donarium, from the Scandinavian 

 god Donar. This metal is now proved to be identical with thorinum. 



DONKEY ENGINE. A very small engine employed to pump water into boilers. 

 If the use of the donkey engine were more usual than it is, we should hear less of 

 steam-boiler explosions. 



DOXSHA. JEschynomone Canndbina. See FIBRES. 



DOOPARA RESIST. A resin obtained in considerable quantities in the East 

 Indies from the Vateria Indica, which is used as a fragrant incense in the temples, 

 makes an excellent varnish, and is sometimes called East Indian Copal, or Gum Pincy. 

 Simmonds. 



DO KNOCK, is a species of figured linen of stout fabric, which derives its name 

 from a town in Scotland, where it was first manufactured for table-cloths. It is the 

 most simple in pattern of all the varieties of the diaper or damask style, and there- 

 fore the goods are usually of coarse quality for common household wear. It receives 

 the figure by reversing the flushing of the warp and woof at certain intervals, so as to 

 form squares, or oblong rectangles upon the cloth. Tho most simple of these is a 

 succession of alternate squares, forming an imitation of a checker board or mosaic 

 work. The coarsest kinds are generally woven as tweels of three leaves, where every 

 thread floats over two, and is intersected by the third in succession. Some of the 

 finer are tweels of four or five leaves, but few of more ; for the six and seven leaf 

 tweels are seldom or never used, and the eight leaf twill is confined almost exclusively 

 to damask. 



DORSETSHIRE CIiAY. Clay shipped from Poole in Dorsetshire. See CLAY. 



DOUX. or DOUKE. Mr. Wallace, in his work on the mines of Alston Moor, 

 expresses his belief that this term is derived from the Saxon deagan, to knead or 

 mix with water. It is a soft substance, often found in veins, especially in crop veins, 

 and where their walls or sides are formed of shale. It is evidently pounded or decom- 

 posed shale, though not unfrequently as compact as the rock from which it is derived, 

 but differs from the latter in exhibiting no traces of bedding. Exposed to the atmosphere, 

 it rapidly decomposes into a blue kind of clay. 



DOWLAS. A coarse kind of linen. 



DOWN. See FKATHKRS. 



DOWSING ROD. See DIVINING EOD. 



DRAGON'S BLOOD (Sang-dragon, Fr. ; DracJimblut, Ger.) is a resinous 

 substance, which comes to us sometimes in small balls of the size of a pigeon's egg, 

 sometimes in rods like the finger, and sometimes in irregular cakes. Its colour, in 

 lump, is dark brown -red ; in powder, bright red ; friable ; of a shining fracture ; specific 

 gravity 1*196. It contains a little benzole acid, is insoluble in water, but dissolves 

 readily in alcohol, ether, and oils. It is brought from tho East Indies, Africa, and 

 South America, as the produce of several trees, tho Draccena draco, the Ftcrocarpus 

 santolinus, Ptcrocarpus draco, and tho Calamus rotang. 



Dragon's blood is used chiefly for tingeing spirit and turpentine varnishes, for 

 preparing gold lacquer, for tooth tinctures and powders, for staining marble, &c. 

 According to Herbengcr, it consists of 9'07 parts of red resin called Dnicniiin, 2 of 

 fixed oil, 3 of benzoic acid, 1'6 of oxalatc, and 3'7 of phosphate of lime. Aivording 

 to Johnstone, the resin of lump dragon's blood, has the formula C lo H 21 O g (C^'H-'O 4 ), 

 that of reed dragon's blood, C 40 H 20 0' J (C"HO). 



Pereira enumerates tho following varieties of this substance found in commerce : 

 . Dragon's blood in the reed; Dragon's blood in sticks (Sanguis Draconis in 



2. Dragon's blood in oval masses; Dragon e blood in drops (Sanguio Draconis in 

 lacHrymilt} 



