r 44 The Complete Englifh ^Difpenfatory. Part h

SECT. XIV.Of Sublimation.

SXJbltmatton differs very little fromDiflillation, excepting that inDiflillation only the fluid Parts ofBodies are rais'd, but in this the Ib-lid and dry ones ; and that the Mat-ter to be diftill'd may be either folidor fluid : but Sublimation is concern'donly about lblid Subftances.

There is alio another difference,namely, that Rarifaciion, which isof very great ulè in Dißillation, haslardly any room in Sublimation;for the Subftances, which are to befublim'd, being folid, are incapableof Rarifaciion: and fo it is onlyImpulfe, which can raife them. Itbeing therefore Impulfe alone, whichis the caufe of the Aicent of Bodiesnow under notice, the nature ofthis Operation may be clearly de-duc'd from what has been laid con-cerning Impulfe.

However, it may not be impro-per to inquire a little more nicelyinto the reafon of iiich a Diverlïtyin the Elevation of Bodies; whyibme afcend with a gentle Heat,and others are not to be rais'd withthe moll vehement Fire. And fuchan Inquiry will more properly comein here, beciuiè this Head containsall the Bufmefs of Volatility andFixation ■■, concerning which lbmuch has been writ, fo little to thepurpofe.

Fix'il Bodies are fuch as abide theFire i Volatile, liich as not beingable to endure the Fire, are rais'd bythe Force of its Heat. We willtherefore begin with the fhit, andexplain the Manner how in 'volatile

Subßances, which feem to be of théfame Nature, there happens fo greata Variety and Difference in the«?Elevation.

The Cauiè of this Elevation andAfcent in the Particles of Bodies, isto be afcrib'd to the Fire, not onlyon the account of Impulfe, butof another Property the Fire has ;namely, to inlmuate it felf into allthe Interfaces of theiè Bodies, andthereby break the Cohelion of theirParts, ib that they are at laft dividedinto very fmall Particles, if not intothe fmaÜcft, which Art can reducethem into. Particles thus feparatedand divided, lofe much of their Gra-vity, as was taken notice of before.For the Gravity of the fame Parti-cle decreafes in the lame proportion,as the Cube of its Diameter is lef-lèn'd. Suppofè therefore a Body,;whofe Diameter is 12, and its Gra-vity 12: If then its Diameter bemade lels by 1, the Gravity of thatBody will be only 9^, or there-abouts. For 1331, which is theCube of the laft Diameter, bears thefame proportion to 9|, which 1718,the Cube of the firft Diameter, doesto 12, the Gravity of the Body.But if the Diameter be reduc'd to10, the Gravity will but jufl exceed6; and if it is diminifh'd halfi thatis to 6, then the Gravity will beleft than 2. So that very minuteCorpufcles, when their Diameter isleflen'd as much as may be, havefcarce any Gravity at all. There-fore when once they are dividedafter iiich a manner as has beendeícrib'd-í