18 DIAL 



above the step is surrounded by a loose rim, around which a certain qxiantity of lead 

 shot, or other granular matter, is contained in the rim in the box which serves for the 

 step. The top of this box is pierced with an opening, into which, when the machine 

 is at rest, a cord connected with the shaft sinks, controlled by the shaft, and when the 

 drum is raised by the action of the regulator D, this cord quits its place, which allows 

 the shaft to displace the shot a little, and to take a position conformably to the point 

 of the centre of gravity, 



But after all, great attention should be paid to the proper working of the machine. 

 There are many other drying machines used, some of which are described in the 

 articles devoted to special manufactures. 



DETERXVIA. A wood used in Guiana for masts, booms, and planking. It is 

 very durable, insects will not attack it, and it will sqiiaro from 14 to 16 feet. 



DETONATION 1 . For the mode of preparing detonating-powder for the percus- 

 sion-caps of fire-arms, see FULMINATES. 



DETRITUS. (De, from, tero, to rub.) Matter worn off rocks, and re-deposited. 



DEUTOXIDE, literally means the second oxide, but is usually employed to denote 

 a compound containing two atoms of oxygen to one or more of a metal. Thus we say, 

 deutoxide of copper and deutoxide of mercury. Berzelius abbreviated this expression 

 by adopting the principles of the French nomenclature of 1787 ; according to which 

 the higher state of oxidisement is characterised by the termination ic, and the lower 

 by ous. It is now rarely employed. 



DEVIL The name of a spiked mill, used in Yorkshire, for tearing woollen rags 

 into fragments for the manufacture of SHODDY. 



DEVIIiIiINE. A basic sulphate of copper, known also as Lycllite. 



DEVITRIFICATION. A process by which glass loses its characteristic 

 vitreous properties, and becomes opaque. This change may be induced by very slow 

 cooling, or by the prolonged heating of glass. See KEAUMUR'S PORCELAIN. 



DEVONSHIRE BATTS. A porous fine-grained sandstone, from the quarries 

 of Black Down Cliffs, near Collumpton, in repute as a grindstone. 



DEVONSHIRE OIL-STONE. This stone occurs near Huel Friendship Mino, 

 about three miles from Tavistock, in the Devonian slates of that district. It has con- 

 siderable local repute for sharpening all kinds of thin-edged broad instruments ; it 

 has not, however, become an article of commerce. Knight, Trans. Society of Arts. 



DEWEYIiITE. A hydrous silicate of magnesia, occurring in several localities 

 in the United States, and named after Prof. Chester Dowey. 



DEW-RETTING. See FLAX. 



DEXTRIN. Starch gum. There are three modes of obtaining this from starch, 

 viz., by torrefaction, by the action of dilute acids, and by the action of diastase. The 

 imp\ire dextrin obtained by roasting is termed roasted starch or leicommc. British 

 gum is prepared by carefully roasting wheat-starch, at a temperature of 300 Fahr. 

 Another method of preparing dextrin consists in moistening 1,000 parts of potato- 

 starch with 300 parts of water, to which 2 parts of nitric acid have been added. The 

 mixture is allowed to dry spontaneously, and is afterwards heated for two or three 

 hours in a stove, at 212 Fahr. Dextrin in many of its characters resembles ordinary 

 gum, but it is distinguishable from it by its right-handed rotation of a ray of plane 

 polarised light, hence its name dextrin, and by its yielding oxalic acid, but not 

 mucic acid, when heated with nitric acid. 



DEXTROSE, or DEXTRO-GIiUCOSE. Names applied to ordinary filuooso 

 or grape sugar, in consequence of the power which a solution of such sugar y 

 of turning the plane of polarisation of a ray of light towards the right hand. This 

 rotation is often distinguished by the symbol + . See GRAPE-SUGAR. 



DHIIi MASTIC. A mixture of massicot (protoxide of load) and eight or ten 

 times as much brick-dust, made into a paste with linseed-oil. It is used for repairing 

 defects in stone facings. 



DHOONA PITCH. A name for Dammar Pitch. See DAMMAR GUM. 



DIABASE. A fine-grained igneous rock, composed of a crystalline-granular 

 mixture of triclinic felspar, with augite and chlorite. The felspar is gent-rally either 

 oligoclaso or labradorite, and the augitic constituent is frequently hypcrsthono. Tho 

 presence of chlorite gives a green colour to the rock ; hence diabase is often included 

 under the general name of greenstone. 



DIACTINIC XiENS. A name proposed to be given to the best construction of 

 lens for the photographic camera obscura. It should l>f transparent to all the chcniic.il 

 rays, or rather, it should be a lens which unites the chemical and luminous focus in 

 one point. The name has not been generally adopted. 



DIAIt. The compass used in underground surveying is culled a miner's dial, and 

 is essentially the same instrument as the ciremnfcrentor used by the land-surveyor. 

 Improved forms of dial have been brought out by Wilton, Philipps, and others. It i? 



