GEOPHYSICAL LABORATORY. 151 



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

 provided by the continued evaporation, then supersaturation will increase. 

 It is entirely possible under these conditions 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 con- 

 dition was attained experimentally without difficulty in the observations re- 

 corded 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 concentra- 

 tion, 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 Mecklenburg's observations, in which the solution was 

 evaporated to dryness. 



Here six disks of porcelain loaded with weights were all raised a milhmeter 

 or more in the same solution, but Bruhns and Mecklenburg attribute this 

 result to the action of capillarity and adsorption, and deny the competence 

 of the "linear force of growing crystals " to effect such mechanical displace- 

 ments. 



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', 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 occuired 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 can not 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 substance or partly foreign substance) has am^ 

 other effect than to increase solubility and so to raise the concentration 

 necessary for potential supersaturation and growth upon the loaded crystals. 

 This degree of supersaturation is readily attainable through evaporation or 

 otherwise, and when attained the loads are lifted. With this thesis estabhshed 

 there is no conflict between the observations of Bruhns and Mecklenburg and 

 our own, and all the experimental evidence offered is perfectly correlated. 



(18) Bemerkungen iiber die lineare Kraft wachsender Kristalle. George F. Becker und 



Arthur L. Day. Centralbl. f. Min , No. 14-15 (191(3). 



A German translation of "Note on the linear force of growing crystals" 

 (J. Geol., 24, 313-33, 1916). Reviewed under No. 17 above. 



(19) Crystals and crystal forces. Fred E. Wright. J. Wash. Acad. Sci., 6, .326-332 (1916). 



In this paper the general problem of the measurement of crystal forces is 

 stated and an outline is given of the possible modes of attack for its solution. 

 A crystal is a body whose component atoms are arranged in definite space 

 lattices; this arrangement is probably the result of the vectorial action of 

 interatomic forces. These forces are spacially vectorial in character; but 

 little is known of their order of magnitude and of the law of their variation 

 with distance. They find expression in the development of crystal forms, in 

 the rate and character of crystal growth, in the field of atomic forces, in the 

 influence which they exert on other systems of forces, such as light-waves. 

 The effects produced by a crystal on such a system of forces under different 

 conditions of pressure and temperature can be measured and thus the law of 



