"Rich zinc ores are relatively rare now in this country but are still abundant in countries like México, that have not yet developed all their mineral potentialities. In almost all Mexican zinc districts there has been reported sporadic production of oxidized ores, although until now no specially designed plants have been built for the beneficiation of such ores. Generally the zinc carbonate and zinc silicate ores are hand picked and shipped to this country for beneficiation. The Mexican production of zinc ores has never been steady, because of economic factors such as bad transportation systems and lack of market for the product ... During the last few years, particularly after the outbreak of the second World War, there has been in México an increasing demand for zinc oxide to be used in the rubber and paint industries. This product has to meed rigid specifications, similar to those established by the Bureau of Standards of this country"--Introduction, leaves 1-2.