Note:  Do not rely on this information. It is very old.

Marsh's Test

Marsh's Test for arsenic is one very commonly adopted for the examination of liquors, etc, suspected to contain arsenic. The liquor is added to a flask, from which hydrogen is evolved by the action of sulphuric acid and zinc. Arseniuretted hydrogen is so formed, and passes through combustion tubing heated by three or four'bunsen burners, when it decomposes and arsenic becomes deposited as a brown stain in the cool portions of the tube. It is, of course, necessary to take great care to ensure the complete absence of arsenic in all the reagents employed.