Standard Test Method for Vegetable Matter and Other Alkali-Insoluble Impurities in Scoured Wool

Test Method D 1113 is considered satisfactory for acceptance testing of commercial shipments, and the procedure has been used extensively in the trade for this purpose, particularly in connection with the determination of clean wool fiber present by Test Method D 584. The procedure in Test Method D 1113 is used by the U.S. Customs Service for the determination of the vegetable matter in importations of raw wool on which the allowance for loss of wool during commercial cleaning is based in part.

In case of a dispute arising from differences in reported test results when using Test Method D 1113 for acceptance testing of commercial shipments, the purchaser and the supplier should conduct comparative tests to determine if there is a statistical bias between their laboratories. Competent statistical assistance is recommended for the investigation of bias. As a minimum, the two parties should take a group of test specimens that are as homogeneous as possible and that are from a lot of material of the type in question. The test specimens should then be randomly assigned in equal numbers to each laboratory for testing. The average results from the two laboratories should be compared using Students t-test for unpaired data and an acceptable probability level chosen by the two parties before the testing is begun. If a bias is found, either its cause must be found and corrected or the purchaser and the supplier must agree to interpret future test results in light of the known bias.