be due to the presence and dissolution of some metal or metals other than those mentioned, or it may be due to oxidation by the use of excessive aeration, or occasionally to the presence in the pulp of organic substances.

It is only possible here to give an outline of the more common methods of preliminary experiment, and to suggest lines of investigation. Special conditions will call for variation and increase of detail, which each operator will be able to develop according to his needs.

TABLE 20.-MILLING AND CYANIDING COSTS, TONOPAH BELMONT1

TABLE 21.-MILLING AND CYANIDING COSTS, WAIHI GRAND JUNCTION2

1 "Tonopah Belmont Cyanide Plant," by CLAUDE RICE, E. & M. J., July 15, 1911.

2 "Cyaniding of Gold-silver Ores at Waihi Grand Junction," by NOEL CARLESS, I. M. M., Lond., April, 1915.