B. Further proof that dirtier is not extracted by the vacuum-extraction method was obtained by placing a known amount of purified dimer in a sample tube and vacuum-extracting it for 2 hours at 200°C. and at 1 mm. of mercury pressure. This procedure did not remove any detectable amount of dimer from the sample tube, as determined by weight loss of the sample tube, and no condensed material was found in the cold trap.Because vacuum extraction will not extract dimer from polymer samples, whereas water extraction does, the difference in results obtained by the two procedures on a given sample indicates the amount of dimer, plus any water-soluble, linear molecules present in the sample. PRECISION A statistical study was carried out on 16 analyses on each of two flakes of different monomer and moisture contents. In the higher range, an average of 7.99% monomer and 1.70% moisture was obtained wdth standard deviations of 0.26 and 0.25%, respectively. For a polymer of low monomer and moisture content, an average of 0.53% monomer and 0.47% moisture was found with standard deviations of 0.03 and 0.06%, respectively.

Carminic acid reagent has been used by several authors for the colorimetric determination of boron. Discrepancies among procedures and lack of reproducibility have led to a reevaluation of the factors affecting sensitivity and precision: reagents, concentrations, and their relationship to development time and sensitivity, as well as laboratoryware and procedures for evaporation of aqueous samples prior to colorimetric analysis.The procedure proposed has shown accuracy and precision to ± 0.3 y of boron over the range of 0 to 40 7 of boron.

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