WRIGHT AND HOSTETTER: CRYSTAL GROWTH 407 



a system, and those stresses applied equally to both a solid and 

 its liquid. That he regarded the process as completely reversi- 

 ble is clearly shown in the following quotation from his work: 



. . . . The following line of reasoning to show that stresses ap- 

 plied to a crystal will cause a resistance to the deposition of additions 

 to it from the liquid, or, in other words, a resistance to its growth, will, 

 I think, prove to be correct. When a costal grows, the additions, it 

 seems to me, must lay themselves dow r n in a state of molecular fitting, 

 or regular interlocking with the parts' on which they apply themselves; 

 or, in other words, they must lay themselves down so as to form one 

 continuous crystalline structure with the parts already crystallized. It 

 thus seems to me that, if a crystal grows when under a stress, the new 

 crystalline matter must deposit itself in the same state of stress as the 

 part is on w r hich it lays itself. If, then, we consider a spiculum of ice 

 growing in water, and if we apply any stress, a pull for instance, to it 

 w T hile it is thin, and then fix it in its distended state, and if then by 

 the transference to the water beside it of cold taken from any other 

 ice at the freezing point we cause it to grow, which it may do if there 

 be no other crystal of ice beside it more free than it to receive acces- 

 sions, then the additional matter will, I think, lay itself down in the 

 same state of tensile stress as the original spiculum w y as put into by the 

 applied pull. The contractile force of the crystal will thus be increased 

 in proportion to the increase of its cross sectional area. If it now be al- 

 lowed to contract and relax itself, it will give out, in doing so, more me- 

 chanical work than was applied to the original spiculum during disten- 

 tion. Hence there would be a gain of mechanical w T ork without any 

 corresponding expenditure; or, we could theoretically have a means of 

 perpetually obtaining mechanical work out of nothing, unless it were 

 the case that greater cold is required to freeze water into ice on the 

 stressed crystal than on a crystal free from stress. Hence we must sup- 

 pose that a greater degree of cold will be required to cause the stressed 

 crystal to grow 



In 1878 Gibbs developed in detail the relations defining the 

 conditions of equilibrium for solids in contact with fluids, having 

 regard to all possible states of strain of the solids. 3 He intro- 

 duced no direct evidence as to the reversibility of the process 

 under consideration but from certain of his statements w T e may 

 infer that he considered the process reversible. He made a dis- 

 tinction between the effects on equilibrium caused by strain in 

 "isotropic" and "crystallized" bodies; this is stated specifically 



3 Gibbs, J. Willard. The Scientific Papers of, p. 184. 



