Proof of Poison

"Proof of Poison" by Jurgen Thorwald: A Review
 
This book tells the story of toxicology, and explains, by detailed historical examples, how the study of poisons was used to bring the great poisoners to justice.
 
It is surprising to relate that the earliest breakthroughs in toxicology took place as late as the nineteenth century. Some of the chemical methods necessary as preliminaries in this field were developed in the late eighteenth century, with the work of Scheele and Metzger providing the means of chemically isolating arsenic. However, the first real application of this knowledge in criminology came in 1806, when Valentin Rose, of the faculty of medicine at Berlin, "conceived of a method of detecting the presence of arsenic in human organs, especially in the intestines and in the walls of the stomach."
 
After this point, the study of poison finally began to catch up with the poisons and, in particular, with the most commonly used of all poisons, arsenic. Arsenic was popularly known as "inheritance powder" because of its frequent use by members of a family in aiding the departure of an inconvenient relative, and so hastening the time of inheritance. But the method conceived by Rose was, in its final stages of chemical analysis, rather clumsy; it was still possible to cut up a cadaver and be unable to detect arsenic even though it contained quantities of arsenic sufficient to kill.
 
The extraordinary breakthrough in finding the solution to this problem came in 1833, with the invention made by James Marsh. Marsh "had a U-shaped glass tube made, with one end open, the other terminating in a pointed nozzle. In the nozzle, he suspended a piece of zinc; in the open end of the U-tube, he placed the fluid to be examined, to which he had previously added acid.
 
When the fluid reached the zinc, even the tiniest traces of arsenic would produce arsenic which escaped through the nozzle." The escaping gas was ignited and Marsh precipitated it on a cold porcelain bowl in the form of "a black deposit". This apparatus was extremely sensitive, and could measure "a thousandth of a milligram of arsenic added to the test fluid."
 
It might have been though that this would have solved the problem of detecting death by arsenic poisoning. But this was not to be the case: in a manner that was typical of so many advances in toxicology it created new problems. For a start, using Marsh's sensitive apparatus, it was found that "arsenic is an extremely common element"; consequently, some traces of arsenic are to be found in almost everyone. But, in the investigation of poisoning, with exhumation of bodies required, what proved a real stumbling block was that "Marsh's apparatus showed that the ground contained arsenic in many places, especially in certain Paris cemeteries." If this was so, how could one be sure that the arsenic found in a decaying corpse (taken from a rotting coffin) had not been washed in by rain from the surrounding soil?
 
How these problems were eventually overcome, and the setbacks and triumphs on the way, are related later in the book. It also deals with vegetable poisons, and concludes with a summary of the latest developments such as spectrography. It is an interesting story, showing how a science advances, solving problems with both luck and logic.