"Infrared grade " fused quartz ( tradenames " Infrasil ", " Vitreosil IR " and others ), which is electrically fused, has a greater presence of metallic impurities, limiting its UV transmittance wavelength to around 250 nm, but a much lower water content, leading to excellent infrared transmission up to 3.6 ?m wavelength.
12.
The United States Pharmacopeia includes a test for heavy metals that involves precipitating metallic impurities as their coloured sulfides . " In 1997, Stephen Hawkes, a chemistry professor writing in the context of fifty years'experience with the term, said it applied to " metals with insoluble sulfides and hydroxides, whose row 4 or greater, in other words, the transition metals and post-transition metals.
