t 



i 



r0 



I 



56 



THE BE GmNINGS OF LIFE. 



If, instead of pouring a certain amount of a solution of 

 potassic sulphate into one of baric chloride, we allow 



means of 



1 



the mixture to take place gradually 



dialysis, then crystals of calcic sulphate are formed 



rather than an amorphous precipitate. It has been 





bsta 



iices 



are 



u 



ake 



, it P^' 



roba 



ble 



aecoinP^" 



sil 



ascertained 



M 



It fls, 



-e 



moreo^ c. 



% Robert 



Were f 



If 



had not pr 



fere to 



be obtains 



Fremyi that insoluble compounds 

 generally, which appear in the laboratory as a result 

 of double decomposition in the form of amorphous 

 precipitates, can almost invariably be obtained in a 

 crystalline condition when the chemical reaction is 

 allowed to take place very slowly. This may be 

 brought about by making the saline solutions mix after I ds taken up by 

 osmosis — either through membranes, wooden vessels ciiriflg a long list 



or porous porcelain. By one or other of these i tte wliich had hi 



d galvanic curi 

 KKSsary ingredien 



methods, he obtained many very insoluble salts in the I mitteral veins and ( 

 crystalline condition— such as the sulphates of baryta, | faiiation in the 

 strontia, and lead, the carbonates of baryta and lead, 

 oxalate of lime, chromate of baryta, and several sul- 

 phides 2. These facts are highly interesting because a 



of 



1 ' Compt. Rend.' t. Ixiii. p. 714. 



^ We find in Watts's Dtc/ionary the following statement, which has an 

 explanatory bearing upon M'hat has been above stated :— ' The more slowly 

 the liquified body is brought back to the solid state, and the more the 

 liquid is kept at rest, the smaller the number and the greater the size 

 and regularity of the crystals ; but if the solvent be cooled or separated 

 quickly the crystals are numerous, but small and ill-defined. In the 

 former case, the particles of the solidifying body have time to unite 

 themselves regularly with those which separate first from the fluid and 

 form nuclei of crystallization; if, on the contrary, the crystallization 

 takes place rapidly, a great number of particles solidify at the same time, 

 each forming a nucleus to which other portions attach themselves, and 



any par 



nse to the most 

 f«-' Thus, refe 

 'Dictionar 



statements ;■ 



■'Ma 



^ 



) 



Kent 



ojstallize i 

 system 



S( 



«'c 







^^^_^orp 



