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QUANTITATIVE ANALYSIS 273
Dusting Powders. Weinberger 33 recommends determining small quantities
of paraformaldehyde in dusting powders and other mixtures by
treating the sample with sulfuric acid, distilling, and applying Romijn's
potassium cyanide method to the distillate.
Pungicides and Seed-conserving Agents. Fungicides and insecticide*
containing copper sulfate should be treated with potassium ferrocyanide to
remove the copper before the formaldehyde content is determined by the
alkaline peroxide method- 1 . In the case of seed-conserving agents containing
mercury chloride, potassium chloride should be added prior to the
distillation in order to prevent the mercury from distilling over with the
aldehyde and causing erroneous results in alkaline peroxide or sodium sulfite
analysis 5 .
Determination of Combined Formaldehyde in Normals
A good procedure for the approximate determination of combined formaldehyde
in formals was developed hy Clowes 11 *. It is carried out by
heating a weighed sample of the formal plus 5 cc water with a mixture of 15
cc concentrated hydrochloric acid, 15 cc water and a slight excess of phloroglucinol
for two hours at 70 to 80°C, allowing the mixture to stand overnight,
then filtering off the reddish brown phloroglucinol formaldehyde
resin in a Gooch crucible, washing it with 60 cc of water, and drying in an
oven at 100 °C for 4 hours. After cooling in a desiccator, the crucible containing
the precipitate is weighed. The weight of the precipitated resin,
whose empirical formula is approximately C7H503j is divided by 4.6 to
obtain the weight of combined formaldehyde. This procedure can naturally
be employed only with formals whose hydrolysis products are soluble
in water. Formaldehyde and phloroglucinol react in approximately equimolar
proportions.
Determination of Combined Formaldehyde in Formaldehyde-treated
Products
In general, heating with dilute acids followed by distillation makes it
possible to isolate combined formaldehyde quantitatively or almost quantitatively
from paper, textiles, leather and foimaldehyde-protein compositions
. This procedure is widely used in connection with the determination
of combined formaldehyde hi these materials. The following instances
involving protein-formaldehyde compositions are typical.
In the determination of formaldehyde in fur, hair, and wool, the hairs are
treated with dilute acid and the formaldehyde is distilled off in the customary
manner. If the acid distillate gives a positive test for formaldehyde
with Schryver's phenylhydrazine-potassium ferricyanide test (page 247),
Romijn's iodine method of quantitative analysis may be used 43 ,
In the analysis of leather samples, it is recommended that the formalde-