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DAO ( 361 )

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DAOURITE. See Schorl.

DECOCTION. Abkocben-Abficdcn, Germ.

Is the extraction of the foluble part of anyfubftance by means of boiling, generally withplain water. Decoftion is one of the fimpleftand moft efficacious methods employed in theanalyfis of vegetable and animal matters. It isalfo largely ufed in pharmacy.

DECOMPOSITION. Zerfetzung , Germ.Moft of the procefies in chemiftry are attendedwith the difunion of fubftances already joinedtogether, or decompofition, and the confequentformation of new compounds. In the Appen-dix will be given moft of the known decom-politions produced by the mixture of the com-mon chemical fubftances.

DECREPIT ATION. Decrepitiren-Abkniflcrn,Germ.

When hard cryftals of any faline fubftancecontaining but little water of cryftallization areheated fuddenly, they do not liquefy as thewatery falts do, but crack and fly in pieces withvehemence, owing to the efcape of the water,which is called decrepitation. Common fait af-fords a familiar example of this, and for con-venience when ufed as a flux in the reductionof minerals it fhould be previoufly decrepitated.

DEFLAGRATION . This term expreflesa gradual fparkling combuftion of any fubftancewithout violent explofion. It is particularlyapplied to many inftances of combuftion pro-duced by nitre.

DELIQUESCENCE. Zerfiieffen , Germ.

Is the fpontaneous liquefaction of any fait byfimple expofure to air. Potafh is an exampleof the kind. As the deliquefcent falts abforbmoifture from the air they are of ufe in render-ing air dry, which is often required for niceexperiments.

DEMANTSPATH. See Corunbum.

DEPHLEGMATION. Enfwajfem, Germ.

Is the depriving any liquid of part of thefuperfluous water which it may contain, andthus it has the effect of concentration. Thusfulphuric acid is dephlegmated by boiling for atime, which expels at firft little elfe than merewater. Vinegar is dephlegmated by partialfreezing, the ice that firft forms being only thewatery portion containing none of the acid.

DEPHLOGISTICATED AIR. See Oxy-gen.

* Hat»y, R, de Ufle,

DEPHLOGISTICATED MARINE ACID.See Oxymuriatic Acid.

DEPHLOGISTICATED NITROUS AIR.See Nitrous Oxyd.

DERBYSHIRE SPAR. See Fluor Spar.

DESICCATION is the compleat drying ofany fubftance.

DETONATION. Verpuffen, Germ.

Is explofion accompanied with loud noife.A fudden evolution of light attends moft in-ftances of detonation. Fulmination has a fimilarmeaning.

DIAMOND . 1 Demant Werner; DiamaniHauy and Broch.

The diamond is either colourlefs, or of alight yellow, or fmoak-grey paffing into bluifh,or pearl grey, or clear wine colour, on onehand deepening into clove brown, and paflingon the other into yellowifh green: it alfo occursof a deep almoft black brown, pruffian blue orrofe red. The colourlefs varieties are the moftefteemed, and are perhaps the moft frequent;next to thefe in value are the black, blue, and.red, they are alfo by far the rareft, the lightcoloured are in the leaft eftimation.

It is found cryftallized in the regular ofto-hedron (which is its primitive form) compofedof two four-fided pyramids applied bafe to bafe.Sometimes each triangular facet of the primi-tive odtohedron is replaced by fix fecondarytriangles bounded by curvilinear lines, in whichcafe the whole cryftal has forty-eight facets, andis of a fpheroidal figure. Other fpheroidalvarieties of this mineral are the dodecahedron, afolid of 24 facets, and a comprefled fpheroidrefembling a very fhort fix-flded prifm, termi-nated by very fhort curvilinear pyramids. Some-times the pyramids of the odlohedron, infteadof ending in a point terminate in a line, whencerefults a rhomboidal quadrangular prifm withdihedral fummits.

The furface of the regular o&ohedrons isgenerally fmooth and fhining, that of the othervarieties is fomewhat dull and rough; but in-ternally, efpecially when cut and polifhed, theyare all of extreme brilliancy, far furpaffing bothin luftre and lively play of prifmatic coloursevery other fubftance. Rough diamonds areufually covered with a very thin cruft, whichrenders them femi - transparent, but whenthis is removed they are tranfparent, thoughBtocliant, Jaraefon.

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