1. U. S. P. XI Revision Bulletins, Sub-committee No. 6, Assay Bulletin 12, page 28.
2. U. S. P. XI Revision Bulletins, Sub-committee No. 6, Assay Bulletin 16, pages 48–49.
3. U. S. P. XI Revision Bulletins, Sub-committee No. 6, Assay Bulletin 24, pages 86–95.