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Chapter 4
Commercial Formaldehyde Solutions
Formaldehyde is normally marketed in the form of an aqueous solution
containing 37 per cent by weight dissolved formaldehyde plus sufficient
methanol to prevent precipitation of solid polymer under ordinary conditions
of shipping and storage. In Europe, this solution was first known
under the trade names, "Formalin" and "Formol" 23 , and was generally
described as 40 per cent formaldehyde, since it contained approximately
40 grams of formaldehyde per 100 cc. This volume per cent measure of
formaldehyde concentration has now been generally abandoned both in
Great Britain and the United States for the more accurate weight per cent
measure. Volume per cent figures are unsatisfactory, as concentrations
measured in this way vary with temperature and are also influenced by
the presence of methanol or other solution stabilizers. Unless otherwise
specified, all formaldehyde concentration figures in this book are reported
in weight per cent. The United States Pharmacopeia 25 describes U. S. P.
Formaldehyde (Liquor Formaldehydi) as an aqueous solution containing
not less than 37 per cent CH20 with variable percentages of methanol to
prevent polymerization.
In addition to the usual 37 per cent methanol-stabilised formaldehyde,
solutions which contain less than 1 per cent methanol are also encountered
in some instances. Products of this type containing 30 and 37 per cent
formaldehyde, respectively, may be cited as specific examples of special
commercial solutions 12 .
Specifications and Purity
In general, commercial formaldehyde is a uniform solution of high purity
capable of meeting stringent product requirements. The following figures
are representative of typical product specifications.
Strength: 37.0 to 37.3% CH20 by weight
Methanol content: Normally varies from 6,0 to 15 per cent by weight according
to trade requirements.
Acidity: Usually about 0.02% calculated as formic acid (0.1 cc N KOH per
20 cc}
Iron: Less then 0.5 ppm
Copper: Less than 0.5 ppm
Aluminum: About 3 ppm
Heavy metals: Trace
Organic and inorganic impurities other than those listed above are substantially
absent. However, solutions stored for prolonged periods may
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