AQ FORMATION OF SHELLS OF ANIMALS, ETC., 
mersion of the slides in boiling turpentine, Canada balsam, 
&c., this observation might have been true; but occur- 
ring exactly in the same manner in water, it cannot be so, 
as the crystals must, under such a supposition, have been 
sufficiently soluble in boiling water to have been entirely 
dissolved off the slide, which is contrary to the fact; hence 
some other explanation must be sought for. This sudden 
formation of crystals in one of these compounds, by a 
cause which does not sensibly affect the other, seems to me 
to admit of explanation in different ways, and on different 
hypotheses. It may be supposed, that the separating force 
to which the rectilinear arrangement observable in crystals 
is due, is a form of repulsion, and, that in the compound of 
globular carbonate and triple phosphate, the attractive and 
repulsive forces acting upon their molecules are nearer the 
condition of equilibrium than in the simple globular carbo- 
bonate, so that when these two forces are weakened 
equally in both substances by the temperature of 212°, a 
preponderance of the repulsive over the attractive force, 
indicated by a change of the curvilinear into the rectilinear 
arrangement of the molecules, takes place in the com- 
pound of globular carbonate and triple phosphate, but 
does not sensibly affect the molecular condition of the 
simple globular carbonate, the attraction of tenacity still 
holding them together. Or, if the repulsive force were 
equally augmented in both substances by the same eleva- 
tion of temperature, the effect would be the same upon 
the two compounds as that just mentioned. Hence the 
application of heat in this experiment may have produced 
the effect of sudden crystallization in two ways—either 
by weakening the uniting force without affecting the 
separating one, or by augmenting the separating force with- 
out affecting the uniting one. 
