" '- ff£. 



THE BEGINNINGS OF LIFE. 



55 



ii 



into the nature and respective characters of the solid 

 ' ^POntaneol! aggregates, which, under the influence of different con- 



^tJy flow 



:olloid 



molec^. 



6- 



to 



ditions, may be made to emerge from crystallizable 

 and colloidal solutions respectively. 



Although saline materials so frequently aggregate 

 into crystalline shapes when they emerge from the state 

 of solution 1, still, in many cases, the assumption or not 

 of such a form is entirely dependent upon the con- 

 ditions under which the separation takes place, 



Many substances which, in the chemist's laboratory, 

 are only seen in the form of insoluble precipitates 

 existence, as made up of amorphous granules, could have been 

 Dntinual mete procured in a crystalline condition if the same decom- 



pcct to water: position which had given rise , to the amorphous 



to show, the 



m as a class, 



influences 

 .^gcs in its 



ch 



CO: 



3- re-arran«i: 



)nstituent at?: 



ier its usual fe precipitate had been allowed to take place more slowly. 



solution/ 



soluble — some' i The conditions under which crystallization occurs are thus given in 



1, Watts's Dictionary of Chemistry : — ' To enable a body to assume the 



are held in ^^■ 



crystalline state, its particles must possess a certain freedom of motion ; 



e 



force with^' hence the fluid state is for the most part an essential preliminary to 



1 lies art' crystallization. Sometimes, indeed, an amorphous solid—that is to say, 



^^^ ^ ^ one which has no definite structure, either crystaUine or organized— 



her peCUu^^^T passes spontaneously into the crystalline state without previous 



r rirranff''' liquefaction But, generally speaking, it is in the passage of a 



* ^^ fl body from the liquid or gaseous to the solid state that the regular and 



mol^^^ symmetrical arrangement of the molecules takes place which constitutes 



most ^^ crystallization. The vapours of many substances when they come in 



J^ g contact with cold surfaces pass at once to the state of crystalline solids, 



ndergO^^S a e.g. sulphur, iodine, benzoic acid, arsenious acid, camphor, &c. It is, 



Cif^ however, in the transition from the liquid to the solid state that 



crystallization most frequently takes place. If the body has been 

 brought into the liquid state by the action of heat alone, it may be 



, made to crystallize by cooling, e. g. bismuth, sulphur.' 



0^' 



forces 



IS 



a 



little 



