Information on Arsenic and testing for Arsenic Poisoning
The Encyclopedia of Forensic Science by Brian Lane (Headline Book Publishing Plc 1992)
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The common white oxide of arsenic was traditionally prepared by roasting the metallic ore slowly then putting the product into a vessel and applying even greater heat; the vapours produced condense as a heavy white powder, or a crystalline mass. The vapour smells strongly of garlic and is very poisonous.
Arsenic occurs naturally in many living organisms, particularly fish and crustaceans, and in a number of ores, in coal and in common soil. It is naturally present in the human body, notably n the blood, heart, lungs and liver, and the hair and fingernails, an estimated total of about one ten-millionth of the body's weight.
The symptoms of arsenic poisoning vary a great deal, according to the form and dose which is administered. In a typical case of poisoning by white oxide the patient begins by experiencing an irritation and burning in the throat, faintness, nausea and a feeling of depression accompanied by sickness. These symptoms are followed by vomiting, first of food then of mucus, frequently speckled with blood. Abdominal pain follows, described as like red-hot coals placed on the stomach, which is aggravated by touch. By now the tongue has become covered with white 'fur' and there is a feeling of constriction in the throat. Diarrhoea develops after twelve to eighteen hours, which is more or less violent, and accompanied by pain and tenesmus. At the same time cramp sets in the calves of the legs and the pulse is weak, rapid and irregular. Collapse rapidly comes on, and the patient dies, still conscious. One of the marked external characteristics is cyanosis " blueness of the skin caused by lack of oxygen in the bloodstream. Post-mortem examination reveals the lining of the stomach to be very much inflamed, and in many cases badly ulcerated.
Arsenic can be found in every part of the body of a person poisoned by it, and even after the body has been buried for years it may be found in the bones and hair.
Arsenic can be administered in almost any form but its post-mortem effects are the same. The poison can pass through the skin, and yet the stomach will be inflamed. It can be inhaled as a vapour, and the same symptom will be found.
Of its use to poisoners, one must note that even in comparatively large doses arsenic is virtually tasteless, and the faintly metallic sweetness can easily be masked by administering it in food. Arsenic can also have a cumulative effect, so that the toxin can be built up in the body (particularly the kidneys and the liver) over a period of time until a quite small dose is lethal. The symptoms are so like cholera and dysentery that when those conditions were common in Europe murder could quite easily be attributed to 'natural causes'. Similarly, many cases must have been classed as food poisoning.
The Arsenic Act
So prevalent was arsenic poisoning in England in the 19th Century that in 1851 it was felt necessary to introduce a specific Arsenic Act. The Act forbade the sale of any arsenic compound unless the purchaser was known to the pharmacist. More important, all arsenic compounds were required to be mixed with a colourant " either soot or indigo " in the proportion of one ounce per pound of arsenic. This went a long way to reducing the large number of deaths caused by mistaking arsenic for sugar or other innocuous white powders; and made it considerably more difficult to hide the homicidal presence of arsenic in food and drink.
The Marsh Test
Although the identification of arsenic by analytical means had been pioneered as early as the 1770s, it was not until much later that a test was developed which was held to be reliable enough for its results to be accepted as evidence in a court of law. In October 1836 James Marsh, an Englishman working at the Royal Arsenal in Woolwich, published a paper in the Edinburgh New Philosophical Journal detailing a method for converting arsine gases into arsine gas, which itself was revealed as a metallic 'mirror' on a piece of glass or porcelain. So sensitive was the test that amounts of arsenic as small and one-fiftieth of a milligram could be identified. The principles of the Marsh Test are still used, although improvements and developments to Marsh's Equipment made the later Reinsch & Gutzeit tests more reliable and easier to conduct.
‘Every Contact leaves a trace’ by Dr Zackaria Erzinclioglu (Carlton Books Limited , London, 2000)
Arsenic has the distinction of being the first poison for which a diagnostic test was devised. This is the Marsh Test. This involves the addition of the suspected fluid which may be an extract from tissues mixed with a small quantity of sulphuric acid, to a piece of zinc. The reaction of the zinc and sulphuric acid will produce only hydrogen, but if arsenic is present Arsine will be given off. This gas can be detected by igniting it and then holding a piece of glass above the flame. If arsenic is present it will be deposited on the glass.
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