The sample for chemical analysis shall be composed of sawings or drillings taken from each piece selected to represent the lot in accordance with paragraph F-3a and paragraph F3b. Sawingsor drillings shall be taken so as to represent the average cross section of each piece. The sawings or drillings from all pieces shall be thoroughly mixed, and not less than 6 ounces of the mixture shall be forwarded by the inspector for analysis. Samples from Navy purchases shall be forwarded to a Government laboratory.