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face or on the bottom or fides of the veflels that contain it, for 

 the particles in the middle of the folution being confufedly mixed 

 with each other, and exerting their repulfive as freely as their at- 

 traftive powers, the one conftantly counterading the other, no 

 fenfible accretion of a regular kind could take place, whereas the 

 repulfive power of the uppermofl particles, or of thofe that reft 

 on the fides or bottom of the vefiTel, is reftrained and impeded. 



8. The repulfive power of cryftalizing fubftances alfo appears 

 in many other inftances (of the attradive no doubt has ever been 

 formed.) Thus if faturate folutions of nitre, common fait, and 

 tartar vitriolate be mixed and fet to cryftalize, each will cryftalize 

 a part, which could not happen if the particles of each of thefc 

 falts did not only attrad their fimilar homogeneous, but alfo repel 

 thofe of a different fpecics, other wife the mere cafual circumftance 

 of greater proximity to one than to the other would impel them to 

 unite indifcriminately. Again, if a faturate folution of allum be 

 mixed with a turbid mixture of clay, and abandoned to infenfible 

 evaporation, after fome time the clay will fubfide and form a dry 

 mafs, but in the interior of this mafs large regular cryftals of 

 allum will be found, whofe component particles muft, to reunite, 

 have difplaced and repelled the particles of clay Vi^ith which they 

 were furrounded. 



9. If to a faturate folution of a fait that difficultly cryftalizes, 

 a cryftal of a fait of the fame fpecies be inferted, the whole fo- 

 lution will foon be brought to cryftalize, as the cryftal inferted 



Z 2. attrads- 



