OH CRYSTALLOGRAPHY. 



nor other liquids, which, notwithstanding, are capable of assuming 

 a crystalline form. This is the case with the metals, with glass, 

 and some other bodies. The method employed to crystallize them 

 is fusion, which is a solution by means of caloric. By this method 

 the particles are separated from one another ; and if the cooling 

 goes on gradually, they are at liberty to arrange themselves in re- 

 gular crystals. 



3. To obtain large artificial crystals of a regular shape, requires 

 considerable address and much patient attention. This curious 

 branch of practical chemistry has been improved by Mr. Leblanc ; 

 who has not only succeeded in obtaining regular crystals of almost 

 any size at pleasure, but has made many interesting observations 

 on crystallization in general*. His method is as follows : The 

 salt to be crystallized is to be dissolved in water, and evaporated 

 to such a consistency that it shall crystallize on cooling. Set it by, 

 and when quite cold pour the liquid part off the mass of crystals 

 at the bottom, and put it into a flat-bottomed vessel. Solitary crys- 

 tals form at some distance from each other, and these may be ob. 

 served gradually increasing. Pick out the most regular of these, 

 and put them into a flat-bottomed vessel at some distance from each 

 other, and pour over them a quantity of liquid obtained in the 

 same way, by evaporating a solution of the salt, till it crystallizes 

 on cooling. Alter the position of every crystal once at least every 

 day with a glass rod, that all the faces may be alternately exposed 

 to the action of the liquid ; for the face on which the crystal rests 

 never receives any increment. By this process the crystals gradu. 

 ally increase in size. When they have acquired such a magnitude 

 that their form can easily be distinguished, the most regular are to 

 be chosen, or those having the exact shape which we wish 

 to obtain ; and each of them is to be put separately in a vessel filled 

 with a portion of the same liquid, and turned in the same manner 

 several times a- day. By this treatment they may be obtained of 

 almost any size we think proper. After the crystal has continued 

 in the liquid for a certain time, the quantity of salt held in solution 

 becomes so much diminished, that the liquid begins to act upon the 

 crystal and redissolve it. This action is first perceptible on the 

 angles and edges of the crystal. They become blunted, and gra- 

 dually lose their shape altogether. Whenever this begins to be 



Jour, de Phys. lv. 300. 



