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GEOLOGY: S. TABER 
is of the same order of magnitude as the ascertained resistance which 
the crystals offered to crushing stresses."^ 
In 1913 Bruhns and Mecklenburg published a paper^ in which they 
claim to have repeated the experiment of Becker and Day with nega- 
tive results. In a reply to this paper Becker and Day explain the dif- 
ferent results obtained by Bruhns and Mecklenburg as due to the fact 
that the original experiment was not duplicated.^ This conclusion 
was reached independently by the present writer.^ By placing an un- 
loaded crystal in the same solution with the loaded one supersaturation 
with respect to the supporting surface of the loaded crystal was prevented. 
Bruhns and Mecklenburg^ (pp. 106-108) describe another experiment 
in which the crystalHzation of chrome alum resulted in raising porcelain 
fragments, loaded with weighted beaker-glasses, but they thought it 
essential that evaporation be carried to completion. The elevation of 
these beakers and similar evidences of pressure phenomena accompany- 
ing crystal growth they attribute to the ' 'forces of adsorption and 
capillarity" and not to a ''force of crystalHzation." Becker and Day 
show that in this experiment the lifting action occurs in spite of capil- 
lary attraction rather than because of it, and that adsorption merely 
diminishes the rate of growth by delaying diffusion.^ 
As a result of their investigations Becker and Day conclude: (1) that 
there is "a linear force, apart from the volume expansion, exerted by 
growing crystals;" (2) that this force enables them to grow in directions 
in which growth is opposed by external force "notwithstanding unre- 
stricted opportunity for growth in other directions; and (3) that the 
linear force thus exerted is of the order of magnitude of the breaking 
strength of the crystal."^ "The crucial experiment [briefly described 
above] offered in support of this conclusion" is not, in the opinion of 
the present writer, decisive. It is significant that no growth occurs on 
the upper face of the crystal although it is subjected to less pressure than 
the lower face, and crystallographically both are the same. The eleva- 
tion of the crystal is due to the fact that it rests directly on a thin layer 
of solution which is supersaturated by diffusion from without; and in 
this experiment the solution at the bottom of the crystallizing dish is 
of higher concentration than elsewhere. Furthermore, the effect of 
expansion in volume is not eliminated in this experiment, for alum 
separates from solution with increase in volume. 
A crystal is enlarged through the addition of layers of material to its 
outer surfaces, and this takes place when these surfaces are in contact 
with a supersaturated solution. A very thin coating of impervious 
material is sufficient to prevent crystal growth. In the Becker and Day 
