THE LINEAR FORCE OF GROWING CRYSTALS 



321 



potential supersaturation will first be reached. If the rate of 

 evaporation is sufficiently great, the saturation concentration in 

 the liquid layer below the crystal will also be reached, in whole or 

 in part, and growth from below will go on, albeit at an appropriately 

 diminished rate compared with the sides because of the load and 

 the deficiency of circulation. If the upper surface is covered by the 

 load, it will share the limitation of circulation of the bottom surface. 

 If the load upon the crystal is too great, or the rate of evaporation 

 slow, the saturation pressure may not be reached anywhere in the 

 supporting liquid layer, and growth here may be stopped. A still 

 further increase in the load may even 

 cause resolution of the bottom surface, 

 while the side surfaces continue to grow. 

 In support of this analysis, the 

 accompanying photograph (Fig. 2) of 

 a crystal grown under a heavy load 

 and the measurements made upon it 

 (Table III) will be found interesting. 

 A single crystal of potash alum was im- 

 mersed in a solution saturated with Fig. 2.— A crystal grown un- 

 both potash and chrome alum under a derload. Dark portions are new 



, , r „ . , ,.,. growth (under load) . (View 



load of 190 gm. Other conditions were f romaDOve ") 



as heretofore described. The dark areas 



are fresh deposit, colored of course by the chrome alum and thus 



distinguishable from the original crystal. It is plain that there is no 



TABLE III 

 Conditions as Before. Load 190 Gm. 



fresh deposit (colored matter) on the central portions of the original 

 crystal above or below. The accessions of fresh matter are found 

 exclusively on (and beneath) the new lateral faces. Nevertheless, 



