The Treatment of Water by Certain Forms of Silver

Abstract

Bacillus coli in distilled-water suspensions is apparently killed by exposure to silvered porcelain rings, without affecting color, odor or taste of the water. There is a very definite time factor for silvered commercial rings and silvered laboratory rings to affect B. coli, even under opt. conditions. Although definite evidence of revival of organisms exposed to Ag has not been obtained, further investigation is necessary before final conclusions can be made. The amt. of Ag in water exposed to silvered commercial rings, or to Agplated laboratory rings increases with time of exposure, introducing another variable factor. Presence of organic matter markedly increases time of exposure necessary to prevent subsequent growth of B. coli. Temp. of exposure markedly affects rate of action of silvered rings, sterilizing time increasing with lowered temp. Rings which become inactive may be reactivated by treating with dilute HC1. Silvered laboratory rings are more active in darkness than in light. Water containing Ag after exposure to Agplated porcelain has the ability to inactivate B. coli added to it. The effect of light on the action of AgNO3 on B. coli was studied, but it was found that under the most carefully controlled conditions there was no difference. The conc. of Ag in water exposed to silvered rings, which is effective against B. coli, is of a similar order to the effective conc. of Ag in a AgNO3 or AgCl sol. and colloidal Ag. In general, factors affecting the so-called oligodynamic effect of Ag metal also affect the action of the other forms of Ag studied. Although application of the oligodynamic action of metallic Ag to treatment of water has some points of interest, it can not at present be recommended, since temp. and organic and inorganic constituents definitely influence the "oligodynamic" action of Ag toward B. coli to a degree which renders results unsatisfactory for practical application. Furthermore, the definite, rather prolonged time factor, which markedly increases under unfavorable conditions, necessitates constant and careful bacteriological control. Lack of a simple, delicate test of Ag would require water to be stored until a bacteriological analysis could be completed.