332 GEORGE F. BECKER AND ARTHUR L. DAY 



of the unloaded crystal is insufficient to take up all of the excess 

 concentration provided by the continued evaporation, then super- 

 saturation will increase. It is entirely possible under these condi- 

 tions that the potential supersaturation necessary for the growth 

 of the loaded crystal may then be attained or even exceeded, and 

 that the loaded crystal will also grow and lift its load. This condi- 

 tion was attained experimentally without difficulty in the observa- 

 tions recorded in this paper. If concentration increases still more 

 rapidly, and exceeds the ability of both unloaded and loaded crystals 

 to take up, through their continued growth, all the matter in excess 

 of the saturation concentration, then additional nuclei may form 

 upon which excess matter may be deposited. This appears to have 

 been the condition attained in the last series of Bruhns and Meck- 

 lenburg's observations in which the solution was evaporated to dry- 

 ness. 



Here six disks of porcelain loaded with weights were all raised 

 a millimeter or more in the same solution, but Bruhns and Mecklen- 

 burg attribute this result to the action of capillarity and adsorp- 

 tion, and deny the competence of the ''linear force of growing 

 crystals" to effect such mechanical displacements. 



A simple analysis suffices to show that capillarity in a solution 

 evaporating to dryness can have no other effect than to press the 

 crystal down upon its base with a force equal to 2TV/d 2 , where T 

 is the surface tension, V the volume of the drop of liquid between 

 the crystal and its base, and d the distance separating the two, and 

 that the lifting action observed by Bruhns and Mecklenburg has 

 occurred in spite of this opposing force and not because of it. 

 Adsorption delays diffusion and diminishes the rate of growth, but 

 does nothing to promote it. These forces therefore cannot be 

 appealed to in explanation of the lifting observed by Bruhns and 

 Mecklenburg and by us. 



We therefore return to the original thesis that the growth of 

 crystals in saturated solution develops a linear force in the direction 

 of the load, and that neither the magnitude of the load (up to the 

 breaking load) nor its character (whether exclusively crystal sub- 

 stance or partly foreign substance) has any other effect than to 



