ig6 PHILOSOPHICAL TRANSACTIONS. [aNNO JGsO. 



sustains the particles of the dissolved solid ; for being so very minute, they are 

 moveable by the least force imaginable, and the action of the particles of the 

 menstruum is sufficient to drive the atoms of the dissolved solid body from one 

 place to another ; and consequently, notwithstanding their gravity, they do not 

 sink in the liquor though lighter than themselves. As a proof of this, he 

 offers a known experiment in chemistry, viz. that a menstruum over a digest- 

 ing fire, will dissolve a greater quantity of a body, than when it is off the fire; and 

 if suffered to cool, a great proportion of that which was dissolved will precipitate. 

 For, says he, the particles of the menstruum acquire a more violent agitation 

 by the fire, and are thereby able to sustain a greater quantity of the dissolved 

 body, or to resist a greater gravity. Against this notion it has been objected, 

 that the common experiment of precipitation, by mixing an alcali with an acid, 

 seems to contradict this ; for thereby the fluidity of the menstruum is not de- 

 stroyed, and consequently the internal agitation of its parts is not diminished, 

 and yet the particles of the dissolved body precipitate all to the bottom. To 

 this he answers, that all mixtures of different liquors introduce in each a differ- 

 ent conformation of pores, and therefore the infusion of a new liquor drives 

 the insensible parts of the dissolved body from their places, and forces them to 

 strike against each other, and cling together, and so becoming larger and 

 heavier than formerly, the internal agitation of the liquor is no longer able to 

 move and sustain them, and consequently they fall to the bottom. 



But I conceive another account may be given of this appearance, and that 

 the aforesaid law of hydrostatics is a little defective. It is true indeed, if we 

 consider only the specific gravity of a liquor, and the specific gravity of a solid 

 particle floating in it, the forementioned rule is exact ; but in sinking there is 

 requisite a separation of the parts of the liquor by the sinking body ; and there 

 being a natural inclination in the parts of all liquors to union, arising from an 

 agreement or congruity of their parts, they resist any thing that endeavours to 

 separate them. Now unless a body have weight sufficient to overcome this 

 congruity or union of parts, such a body will float in a liquor specifically lighter 

 than itself. But that a heavy body, as mercury or iron, may have its parts 

 reduced to that minuteness, as that their gravity or tendency downwards is not 

 strong enough to separate the cohesion or union of the parts of a liquor, will 

 be manifest by considering, that the resistance made by the medium to a falling 

 body, is in proportion to the surface of the body ; but as the body decreases in 

 bulk, its surface does not proportionably decrease; thus a sphere of an inch 

 diameter has not 8 times less surface than a sphere of 2 inches diameter, though 

 it has 8 times less bulk ; and consequently passing through a medium, as sup- 

 pose air or water, the sphere of 1 inch diameter is proportionably to its bulk more 

 resisted than a sphere of 2 inches diameter in proportion to its bulk; and hence 



