ATOMIC ABSORPTION
Samples weighing approximately one gram were placed into solution by the standard sodium carbonate fusion method. The silica was separated, and the filtrate analyzed for the elements present. A Jarrell-Ash model 82-500 atomic absorption apparatus with Westinghouse multi-element hollow cathode lamps was used. Measurements were made with 100 micron entrance and 150 micron exit slits. Aluminum was determined using a nitrous oxide acetylene fuel mixture with a laminar flow burner while all other elements reported in this work were measured using a hydrogen-air fuel mixture with a Hetco total consumption burner.