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FORMALDEHYDE POLYMERS 73
paraformaldehyde may also have an appreciable effect on the values obtained.
Paraformaldehyde decomposition pressures reported by Nbrdgren
47 for temperatures from 10 to 58°C are reproduced in Table 16. Decomposition
pressures for paraformaldehyde at higher temperatures as
reported by Nielsen and Ebers 42 are also included, but these are admittedly
rough measurements which were made merely for purposes of approximation,
It is of interest to note that the Lacy equation (page 54) for the partial
pressure of formaldehyde over water solutions gives values approximating
Nordgren'e decomposition pressures when values of 90 to 100 are substituted
for W (weight per cent formaldehyde). The extrapolated equation
obtained in this way is shown below:
log i>cH2o - 9.941 ^
This equation does not reproduce the approximate values of Nielsen and
Ebers at higher temperatures, giving instead much lower pressure figures.
Solubility: Paraformaldehyde dissolves slowly in cold water, more rapidly
in hot water, hydrolyzing and depolymerizing as It dissolves. Formaldehyde
solutions obtained in this way are identical with those obtained by
dissolving gaseous formaldehyde in water 7 . According to Auerbach, solutions
containing approximately 28 per cent formaldehyde may be obtained
by agitating paraformaldehyde with water at 1S°C for 5 weeks. At reflux
temperatures almost any desired concentration of formaldehyde can be
obtained in one or two hours.
The effect of temperature and other variables on the solution of paraformaldehyde
and the higher polyoxymethylene glycols in water has been
studied in considerable detail by Lobering and various co-workers 33-3 *.
According to their findings 36 , the temperature coefficient for the rate of
paraformaldehyde solution at 21 to 28°C is 2.53 per, 10°C temperature
rise. This coefficient increases rapidly with rising temperature, e.g., in
the range 32.2 to 37.0°C it has a value of 8.39, The activation heat calculated
for the range 21-28°C is 14.5 kcal per mol CH20, and for the range
32.2-37°Ca 54.2 kcal,
Dilute alkalies and acids markedly accelerate the rate of paraformaldehyde
solution, which varies with pH in the same manner as the solution
reactions studied by Wadano, Trogus, and Hess (pages 34r-36). The rate
of solution as found by Lobering goes through a minimum between the pH
values 2-5, increasing rapidly on either side of these limits, as illustrated
in Figures 13 and 14 33 .
According to Lobering and his co-workers 33j36 ,' measurements of the
rate of solution of paraformaldehyde in water indicate that at low con-