THE BEGINNINGS OF LIFE. 55 



into the nature and respective characters of the solid 

 aggregates, which, under the influence of different con- 

 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 

 made up of amorphous granules, could have been 

 procured in a crystalline condition if the same decom- 

 position which had given rise to the amorphous 

 precipitate had been allowed to take place more slowly. 



^ The conditions under which crystallization occurs are thus given in 

 V/atts's Dictionary of Chemistry : — ' To enable a body to assume the 

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

 hence the fluid state is for the most part an essential preliminary to 

 crystallization. Sometimes, indeed, an amorphous solid — that is to say, 

 one which has no definite structure, either crystalline or organized — 

 passes spontaneously into the crystalline state without previous 



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



body from the liquid cm gaseous to the solid state that the regular and 

 symmetrical arrangement of the molecules takes place which constitutes 

 crystallization. The vapours of many substances when they come in 

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

 e.g. sulphur, iodine, benzoic acid, arsenious acid, camphor, &c. It is, 

 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.' 



