“…A method by Ottemann (193) serves for determining copper, lead, and zinc in copper schist using a rotating pressed wheel electrode. Selenium is determined in the range 0.0015 to 2% in rocks by Waring, Worthing, and Hazel (265). The sensitivity for selenium was extended to 0.0001% by Rockenbauer and Brandenstein (211) using a double arc procedure.…”