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Silver Nitrate Test

It is often desired to determine if cargo or another surface has been wetted by fresh or by brackish/salt water. In order to establish this, the field test used is the “silver nitrate test”. The test is carried out by a mixture of 2% silver nitrate (AgNO3) and 98% distilled water (H2O). (Contact your pharmacist for compounding the mixture.) This solution has the aspect of water as it is clear and colorless. Silver nitrate has the property of reacting with Chlorides in the form of a white emulsion.

The reaction obtained will depend on the percentage of silver nitrate in the solution. Even a solution of 3% will give a noticeable difference in reaction compared to a 2% solution, and 5% will tend to react with almost anything.

Cases have occurred where test results have been manipulated by parties involved making use of solutions with more than 2% or with almost no silver nitrate at all, depending on the advantage for the party they represented. It is consequently imperative that a surveyor always carry his own exact solution.

Due to the fact that chlorine is added to tap water, this test should never be carried out with tap water.

On some materials, like galvanized steel for instance, the zinc surface will turn black immediately when contacted with the solution. For this and other difficult surfaces, the wetted surface (wetted by distilled water if necessary) can be wiped with a clean cotton pad. The cotton pad is then submerged in distilled water and later tested.

Laboratory analysis performed on samples will carry more weight compared to the silver nitrate test on site. However, the silver nitrate test is widely accepted as being sufficient evidence of wetting by salt water.

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