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Wednesday, 20 August 2014

Writing – research – Toxicology-01

No self-respecting crime writer would be without their guide to poisons – the so-called coward’s weapon.

The ancient Greeks called the herb monkshood or wolfsbane “stepmother’s poison”. The citizens of Imperial Rome were forbidden to grow it in their gardens. Yet poison usage was so common that the rich employed food tasters.

There are many known natural poisons, mostly of plant origin. Their attraction – besides their efficacy – was that they were undetectable in a dead body.

More recently the mineral arsenious oxide – arsenic – became readily available for poisoning rats and other vermin. It was the most common substance employed for murder, its faintly sweet taste not noticeable in food; the lethal effects were attributed to acute gastric disease.

In 1836 a simple and definite test for the presence of arsenic in a dead body finally became available, but to get to that point took several chemists several decades. In 1775 the Swedish chemist Carl Wilhelm Scheele discovered that when arsenious oxide was treated with nitric acid and zinc  granules, it became a poisonous gas (subsequently named arsine). Later, German chemist Johann Metzger showed that if arsenious oxide were heated with charcoal a mirror-like deposit would condense on a cold plate held over it; the element arsenic. In 1810 in Berlin Dr Valentine Rose extracted the stomach contents of a suspected victim of poisoning, dried the liquid to a white powder, and heated it with charcoal to obtain the characteristic mirror; thus the Metzger test proved sufficient evidence against a domestic servant who had poisoned several of her employers.

Then in 1832 an elderly English farmer, George Bodle, was alleged to have been poisoned by his grandson John. James Marsh, a former assistant to the eminent scientist Michael Faraday, was asked to demonstrate at the trial that Bodle’s coffee had contained arsenic. He did so, but the jury were not convinced so found the grandson not guilty. Frustrated, Marsh went back to Scheele’s initial discovery and developed the Marsh test – treating the suspect matter with sulfuric acid and zinc, he passed the arsine that was evolved through a narrow glass tube, which was heated over a short distance. The arsenic mirror formed further along the tube; any undecomposed gas was burned at the end of the tube and formed a second mirror on a porcelain plate. As little as 0.02 milligrams of arsenic could be detected in this manner, and in 1836 Marsh was awarded the Gold Medal of the Society of Arts for his technique.
The first forensic use of the Marsh test was made by Mathieu Orfila (1787-1853), a Spaniard. In later years, he wrote, ‘The central fact that struck me, that had never been perceived by anyone else … was that toxicology does not yet exist.’

Mateu Josep Bonaventura Orfila - Wikipedia commons

He published his first Treatise of General Toxicology in 1813. In 1819 he was appointed professor of medical jurisprudence at Paris University.
In 1840 Marie Lafarge, a 22-year-old was accused of murdering her husband. Prosecution declared that arsenic was found in the food, but not in the organs of the body. Orfila used the Marsh test and proved conclusively that the previous tests were botched. Furthermore, he stated; ‘I shall prove, first, that there is arsenic in the body of Lafarge, second that this arsenic comes neither from the reagents with which we worked nor from the earth surrounding the coffin, also that the arsenic we found is not the arsenic component that is naturally found in every human body.’ He did and Marie Lafarge was found guilty and sentenced to prison with hard labour.
More to follow in due course.


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