SILVER Nature's Purifier. The value of silver in medicine, and as a purifier has been acknowledged for centuries. Egyptians implantes silver plates into skulls, with surgery. In ancient Greece and Rome, people used silver containers to keep liquids fresh. When settlers moved across the American West, they would purify a container of water by putting a silver dollar in it overnight, and silver dollars were used to keep milk from spoiling. Toward the end of the 19th Century, other medical uses for silver were developed, including the use of silver and mer- cury in the filling of cavities, and dropping a silver nit- rate solution into the eyes of new-born babies to prevent blindness due to infection. Scores of independent tests by many methods in 6 countries have shown that silver promptly kills bacteria in water and maintains water purity over long periods of time. Russian scient- ists, working on water recycling and purification problems for the Soviet space program have decided on silver as the best long-term sanitizing agent. Researching the problems of water storage over periods of several months, as well as purification for immediate use, they determined that ionized silver provides the safest and longest lasting method of transforming polluted waste into potable water. After testing 23 methods of purifying water, NASA has chosen silver as the purifying agent on the Space Shuttle Program. Silver will be used in two functions that will provide Shuttle crews with pure water for drinking, air condition- ing, food preparation and other operations. Water wastes will be recycled in Shuttle flights and silver's first job will be to treat hydrogen-saturated water coming from the Shuttle fuel cells: this water will pass through a tubular device of palladium and silver alloy. From the silver- palladium tubes water will flow to a purifying unit where silver will eliminate bacteria, including Pseudomonas A and type IIIA bacteria, NASA scientists report. By establ- ishing 100 parts of silver in a billion parts of water as hygenic for drinking in the Shuttle, NASA eliminates the need for 1,000 to 1,500 parts per billion of chlorine generally used for purification. The unit will provide Shuttle crews with 32 gallons of pure water daily for all uses within the Shuttle, and for backpacks when the Astronauts work outside the veh- icle in Space. Compared to earlier prototypes, the new unit weighs 90% less, needs only one third the space, doubles the production of water and simplifies the proc- ess: it eliminates the need for mixing, metering and test- ing water while in flight and eliminates the risk of cor- rosion. The most dramatic purification tests occured in 1976 in a 20,000 gallon swimming pool in Nebraska. There was no dis- infectant of any kind in the water. Fifty gallons of mun- icipal sewage plant effluent was put in the pool. That produced a dangerous concentration of 7,000 E. Coli bac- teria cells per 100 milliliters (half a cup) of water. Contents of the pool were pumped through a tank con- taining alternating anodic and cathodic silver electrodes for disinfection. Within three hours the pool was entirely free of E. Coli bacteria and the water contained only 3.2 parts of silver per billion parts of water. The Allegeny County Health Department in Pennsylvania conducted tests in a 152,000 gallon pool which previously has been disinfected by a 50 pounds-per-day chlorinator. The system was replaced by a silver system for the swim- ming seasons of 1974 and 1975. Pool water circulated thr- ough a filter of activated carbon impregnated with metal- lic silver. The county Health Department took up to 50 daily samples and found that silver ions remained in the pool at a low, steady rate of 20 parts per billion with water free of coliform, pseudomonas and staphylococcus bacteria through-out the two seasons. In contrast, 65 water samples from 30 other pools having a mean concen- tration of 700 parts per billion of available chlorine for disinfecting, showed a mean of 1.3 pseudomonas and 7.3 staph. cells per milliliter of water. "This data", the Health Department reported, "indicates that silver is equal to chlorine in maintaining essentially coliform free pool water, and is somewhat better than chlorine in destroying pseudomonas and staph. aureus org- anisms ....." It should be noted that there were no visible growths of algae during the tests.