Article: Continue heating the mixture until it boils. The acid mixture will bubble as you add the water and urea. Add the mixture slowly so that it doesn't cause the acid to bubble out of its container. The water/urea mixture neutralizes the nitric acid but not hydrochloric acid in your solution. In general, you will add 1 ounce of precipitant per ounce of gold that you are refining. Avoid putting your face near the container's opening. The smell is very strong and pungent. The acid will turn a muddy brown color, which is actually caused by the separation of the gold particles. Wait 30 minutes to allow the precipitant solution to work on the gold particles.
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Heat 1 quart of water and add 1 pound of urea to the water. Gradually add the water/urea mixture to the acid. Add a selective gold precipitant to 1 quart of boiling water following the manufacturer's instructions. Add the water/precipitant solution slowly to the acid.