TY - RPRT TI - Circular of the Bureau of Standards no. 552 2nd edition: standard samples- a catalog of reference materials issued by the National Bureau of Standards PY - 1957 PB - National Bureau of Standards CY - Gaithersburg, MD SN - NBS CIRC 552e2 DO - 10.6028/NBS.CIRC.552e2 ER -