Sed. 1 4^

Of Sublimation.

defcrib'd, they are very eailly fub-lim'd.

Nor does only a Decreafe of Gra-vity follow from this Divilion ofthe Particles of Bodies, but there isanother thing too, which is the Re-fult of it, that conduces very muchto haften the Afcent ; and that isthe Variety of their Surfaces : Forthe Surface of a Body decreafes, in avery different manner from its Gra-vity, only as the Square of the Dia-meter is lejfen'd. To look backtherefore upon what has been faidabove, where the Gravity decreafesin fuch a Series, as is exprefs'd bythe Numbers 1718, 1331, iooo,the Diminution of the Surface willobferve this Proportion, viz.. 144.,121, 100. And when upon redu-cing the Diameter to 6, the Gra-vity will be leis than 2, the Surfacewill ilill amount to 36. So thattho' the Gravity of a Particle be foleiîèn'd, as to be reduc'd almoft tonothing, yet there will be Surfaceenough left, which will ferve toraiiè it, This Argument, which isdrawn from the Largenefs of theSurface, and which has been ex-plained by Calculation, may be de-monftrated, as it were to Senfe, bythe following Experiment. If Wa-ter be poured upon the Filings ofIron, and a little Oil of Vitriol dwpdupon it, a Fermentation will pre-fently arife, and the Globules of theAir, in ftriving to di¡engage and ex-tricate themfel ves, will carry up withthem lome of the Particles of Iron tothe Surface of úítWater. This canhappen upon no other account, butthat the Proportion of Gravity inthe Filings of Iron is very fma'.l inrefpect to the Largenefs of theirSurface ; and therefore Iron isforc'dupwards by a Body, which is agreat deal fpecifically lighter thanit ièii. Bat how mach this muft

4J

contribute to a more quick Afcent,has been in general explain'd alrea-dy, and will be much more evidentto the Senfes from the Sublimationof Camphire, Benz.oia, and Arfe-nic; whofe Particles, as they co-here but loofely, are for that reafondiffus'd into a larger Surface; uponwhich account they are the eaiieilto be l'ublim'd of any. Nay, thefefolid Particles, upon account of theirSurface, will looner afcend thanfbme Fluids. So Flower of Sulphurrifes iboner than Oil, not only thatof Vitriol, but any other, tho' everfo light. By this Contrivance ofNature, viz.. that the Gravity ofBodies decreafes in a Triplicate, buttheir Surface in a Duplicate Propor-tion of their Diameters; it comesto pafs that Bodies, which have avery different Gravity, may be rais'dwith the very lame Force. Thus theSalts of Animal Subfiances, as ofHartfhorn, Human Blood, of Vi-pers, &c. being compos'd of very mi-nute Corpufcles, as is found by Ex-perience in diftilling them, do eafilyafcend, becauie the Surface in themis not leiîèn'd fo much as the Gra'vity is. And the Salts of Vegeta-bles, as of Tartar, ¿re. which areof a more clofe Texture, by reaibnof their large Surfaces, are withoutmuch difficulty rais'd. The Cor-pufcles alio of Minerals and Metals,tho' very compact and heavy, doin fome meafure give way to theFire, and are capable of being fub-lim'd. In all theie Inftances theBreadth of the Surface, which ex-pofes the Particles more to the Im-petus of the Fire, is the reaibn whythey are rais'd with as much cafe, asif their Gravity had been leifen'd bydimimfhing their Surface. So thatParticles, tho' ever fe> different inWeight, may be equally rais'd bythe fame Degree of Hçat, if the