Biomedical Engineering Reference
In-Depth Information
that OCP indeed was known in 1866, let me make another citation
from Ref. [23]: “Octocalcic phosphate can only be produced by the
simultaneous formation of monosodic phosphate:
8CaCl
.” (p. 300).
One can see a balanced chemical equation, fully identical to the
modern ones. It is hard to believe, that it was published in 1866! More
to the point, the hydrated forms of calcium orthophosphates were
known in 1866: “8·73 grs. of the vacuum-dried salt, lost on ignition
12·30 grains, or 26·35 per cent.; the formula Ca
+ 5Na
H
P
O
= Ca
H
P
O
+ 16NaCl + 2Na
H
P
O
2
4
2
2
8
8
2
6
24
2
4
2
8
O,
demands 26·16 per cent. of water.” (p. 299). Needless to explain,
that “Ca
H
P
O
·4H
2
2
2
8
2
O” represents 2 molecules of DCPD (see Table
1.1). Furthermore: “It is interesting to observe that while disodic
phosphate is of an alkaline nature, dicalcic phosphate possesses faint
acid properties.” (p. 300). The form and shape of DCPD crystals were
described as well: “The crystalline form of the dicalcic tetrahydrated
phosphate has been examined by Professor Church. He describes the
crystals as thin rhomboïdal plates, of which the diagonally opposite
acute angles are sometimes truncated, hexagonal forms being thus
produced. This truncation seems to be occasionally hemihedral,
and then may proceed up to the diagonal between obtuse angles;
from this change triangular forms arise. Other modifications are
also met with.” (pp. 300-301). Another interesting conclusion might
be found here: “We may then safely affirm that whenever dicalcic
phosphate, octocalcic triphosphate, or any phosphate of intermediate
composition, is precipitated from solution by ammonia, the salt
obtained will be the octocalcic triphosphate; a tricalcic phosphate
cannot be obtained in this manner. The following is probably a type
of the reaction:
4Ca
H
P
O
·4H
2
2
2
8
2
.” (pp. 301-302).
This seems to be the earliest mentioning on the fact that TCP
cannot be precipitated from the aqueous solutions (currently we
know that ACP or CDHA are precipitated instead). However, the
following citation from the same publication: “It is quite possible that
precipitated tricalcic phosphate may possess somewhat different
solubilities, when prepared by different methods; this difference
can, however, scarcely be great.” (p. 304) means that this fact was
not quite clear in 1866.
The latest available publication by Warington [25] was devoted
to the hydrolysis of a freshly precipitated TCP (
H
P
O
+ 6NH
= Ca
H
P
O
+ 6NH
.P
O
2
2
2
8
3
8
2
6
24
4
2
8
i.e
., either ACP or
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