Acid-insoluble fossils may be freed from a carbonate matrix by placing the sample containing them in a 400-800 ml pyrex beaker, covering the sample with 2-3 N hydrochloric acid, and placing the beaker in a vacuum dessicator. The latter is connected via a length of rubber hose to a 1000-ml laboratory metric narrow mouth bottle, fitted in the manner of a wash bottle. In this way, degree of etching is controlled, use of weak acid permits preservation of delicate structures, and corrosive acid fumes are all trapped in the water bottle.

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