assay

1. Qualitative or quantitative evaluation of a substance. See also bioassay.

2. Chemical test of a precious metal (such as gold or silver) to verify its purity. A gold bar of 100 troy ounces, for example, must have a fineness of at least 995 (on a scale of 1000) to be traded on a commodities exchange. Assays are carried out usually by government officials. See also assay ton.