BY MOLECULAR COALESCENCE. 37 
larly oval, and lastly, as before observed, they become per- 
fectly spherical. The transition from the crystalline into 
the globular form takes place according to the increase in 
the quantity of carbonate mixed with the triple phosphate, 
until the quantity of the former is sufficient for perfect 
globules. The incipient stage of this transition is fre- 
quently indicated by a shght molecular change in the 
middle of the crystals, producing a circular nebulous area, 
resembling an obscure nucleus. All these appearances 
can generally be seen on the slides prepared in the man- 
ner before directed (at p. 5 to 7), especially if examimed 
by polarized ight. As I believe no facts of a similar kind 
have ever been noticed, at least in any artificial products, 
though something similar is sufficiently common in natural 
ones (but these have generally been attributed to a vital 
cause), I will give a short explanation of what appears to 
me to be the manner in which they are produced. But 
first I may notice a circumstance connected with this sub- 
ject which may appear singular, namely, that the triple 
phosphate, produced as it 1s in the same solution of gum 
as the carbonate, should not, like it, be globular, that is, 
that the tenacity of the gum should not oppose the recti- 
linear arrangement of the molecules of the triple phosphate, 
as well as the molecules of the carbonate of ime. Proba- 
bly this circumstance admits of no other explanation than 
the one commonly employed in chemical reasoning, and 
which may be inferred from the fact that the carbonate of 
lime, having a tendency to combine with the gum, or an 
affinity for it, which the triple phosphate has not, enters 
into a minute state of combination with it, whilst it does 
not combine in the same way, that is to say chemically, 
with the triple phosphate. A similar difference has been 
before observed with respect to the action of gum on the 
