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How to make 4% Picric solution?


Q. I need to use saturated Picral (10 g picric acid + 100 mg methanol + 5 drops of HCl) to etch plain carbon steel for the observation of carbide distribution. Since picric is explosive, what kind of caution should I pay in making these solutions: fume hood, googles? Also the picric is stored in water, how can I weigh 10 g picric acid out?

Rong Yuan
Research Assistant - Berkeley, California, USA


A. Picric acid is not stored in water, it is stored damp. Most metallographic methods will assume that if you are using AR grade picric, that it is damp and thus the percentage includes the dampness. For your storage, you do want to make sure that there are no dry crystals on the top of the bottle or on the threads. Even nitroglycerine can stand some minimal amount of abuse, but you do need to exercise appropriate cautions as the results of excessive abuse can be a disaster. It is a very good etch for some applications.

James Watts
- Navarre, Florida

November 26, 2012

Q. While preparing 50 ml 0.1N picric acid solution using 1.1 g of picric acid and distilled water, the solubility seems to be incomplete. How could I dissolve it completely?

Geethu Joy
- Kerala India

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