James Marsh and the Marsh Test
An important test used in early toxicology was developed in 1836 by chemist James Marsh (1794–1846). In 1832 John Bodle had been accused of poisoning his grandfather with arsenic placed in coffee. Marsh was asked by the prosecution to check the stomach contents of the victim. He used a hydrogen sulfide method and was able to produce a yellow solid consistent with the presence of arsenic. Unfortunately, the solid degraded between the time it was prepared and when it was presented to a jury. To Marsh’s dismay Bodle was acquitted.
Marsh went into his lab with one simple goal: develop a reliable and visually convincing method to detect arsenic in messy and complex samples like tissue and stomach contents. First, he turned to Scheele’s procedure in which arsenic was converted to arsine gas. Marsh knew that under the proper conditions compounds containing arsenic, such as arsine, could be manipulated to form arsenic metal. Magnus had demonstrated that conversion centuries earlier. Marsh realized that metallic arsenic is stable, and if he could capture the arsine gas, he could manipulate it so that metallic arsenic would form on a solid surface. This process is sometimes called “plating out.” This simple idea took Marsh four years to perfect, and the method became known as the Marsh test. This famous procedure was the first reliable analytical test for arsenic. For his efforts Marsh received wide acclaim and a gold medal from the Royal Society of Arts.
