Determination of Residual Ammonia in Phenol-Formaldehyde Molded Materials

Abstract

Conway's microdiffusion analysis has been applied to the determination of the residual ammonia in phenol-formaldehyde molded materials. This method was found to be more accurate than the method of A. S. T. M. D-834-49. It requires only a 0. 5 g sample while the latter uses 10 g sample. The reagents used for Conway's microdiffusion analysis are as follows : (a) a mixed indicator composed of an alcoholic solution containing 0. 033 % bromcresol green and 0. 066 % methyl red; (b) boric acid reagent composed of 10 g. of pure boric acid introduced into a liter measuring flask to which are added 200 ml alcohol and about 700 ml distilled water, and then 10 ml of the mixed indicator (the solution showing a faint red color with the addition of a little alkali or hydrochloric acid, and being made up to the mark with water) ; (c) standard N/50 HCl solution; and (d) 40 % NaOH solution. Preparation of sample: samples are filed and ground to pass through a 150-mesh sieve, and these are kept in tightly stoppered flasks before analyses. Procedure: one ml of the boric acid reagent withindicator is placed in an inner chamber, and 0. 5 g. sample is carefully put into an outer chamber. The lid with ground glass joint is fixed in position with grease and 2 ml 40 % sodium hydroxide solution is introduced into the outer chamber, allowed to stand for 24 hours. The green colored solution in the inner chamber is titrated with N/50 HCl through a horizontal microburette until it gives red coloration. Calculation: percent of NH₃ = SD/C×100, where S=ml of N/50 HCl used; D=weight of NH₃ equivalent to 1 ml N/50 HCl; C=weight of sample.