OBSERVATIONS ON BASALT, &C. 125 



But this cryftal'ization will not comprehend the whole of its 

 molecules ; for, after a certain quantity of them are arranged, 

 the proportions of the remaining fluid are ahered; that ingre- 

 dient which was before (he lead, may now be equal, or even 

 greateh 1 , and it will exercife its attraction. As the firft crys- 

 tallization, by fubtraciinga large portion of the fluid particles, 

 mutt have obliged the molecules of the lefs abundant fubftance 

 to approach each other very clofely, they may be able to col- 

 led themfelves entirely in their firft attempt to cryftallize, or 

 they may form alternate cryflallizations with the remaining 

 unarranged molecules of the more abundant fubftance. How- Diverfities. 

 ever various the fpecies of molecules may be, they will be 

 regulated by analogous aws, and only ferve to diverfify the 

 generated fubftances. 



It by no means follows, that the cryftals afterwards found The moftinfu- 

 to be moil inrufible would be firft generated. Theh formation rible "y ftals 



b would not ne- 



does not altogether depend on their greater or lefs fufibility, cefiarily be 



but on the relative ftrength of the attraction which unites them formed fid! < 

 to the matter they are immerfed in, and of the polarity which 

 invites then) to cryftallize. In all cryftallization from com- 

 pound fluids, the order in which the feveral bodies cryftallize 

 mull be determined by their relative quantities and attractions. 

 It is perfectly obvious, that no molecules can form a cryftal 

 in a heat fufficient for its fufion ; but it by no means enfues, 

 that it will be formed as foon as the molecules are cooled to 

 the point where the cryftalline polarity overcomes the difmte- 

 grating power of heat; for they may remain fufpended in a 

 fluid formed by more fufible bodies, provided this fluid be 

 fufficiently abundant to keep them from conlacl with each 

 other, for the cryftalline polarity appears to exert itfelf only 

 at extremely fmall diftances. In a mafs compofed of fub- 

 ftances in a ftate of fluidity, with refradory molecules fuf- 

 pended among them, it is pretty clear, from the preceding 

 paragraph, that the mod abundant ingredient will be the firft 

 to cryftallize. But the removal of a portion of the fu (pending 

 fluid muft bring the refractory molecules nearer together, and 

 perhaps fo near that the cryftalline polarity may overcome 

 the attraction of the fluid for them ; they will therefore cryftal- 

 lize next, and will be followed by the remaining ingredients, 

 in the order their attractions dilate. 



As 



