These sulphides have rarely been used for criminal purposes. Orpiment was employed by Mary Ann Burdock, 1833.[136] Being insoluble, they would only be absorbed after oxidation into As2 O3. Ossikovszky (J. Pract. Chem. 2, xxii., 323) finds that this change happens rapidly in contact with organic bodies. But the opposite change, by putrefaction and development of sulphuretted hydrogen, of As2 O3 into As2 S3, is far more likely and frequent.
ARSENIC ACID
is obtained by oxidizing As2 O3 by nitric acid. It is a white deliquescent solid, inodorous, very soluble in water to a syrupy solution, which is corrosive, strongly acid and metallic in taste. By heat it first gives the pentoxide, As2 O5, then it breaks up into As2 O3 and oxygen, finally completely volatilizing. It is said to be less poisonous than As2 O3. (Wöhler and Frehrichs, Ann. Chem. Pharm., lxv., 335.)
The arsenates are very like the phosphates. Like them they give with acid molybdate solution a yellow, with magnesium sulphate a white crystalline, precipitate. But with sulphuretted hydrogen, after acidifying, they give slowly a yellow precipitate of sulphide of arsenic and sulphur; and with silver nitrate a liver brown precipitate of silver arsenate.[137] Sulphurous acid reduces arsenic acid to arsenious.
Sodium arsenate is in the British Pharmacopœia, and is employed in calico printing. A brominated solution of potassium arsenate (strength = 1 per cent. As2 O3) is used in Russia for epilepsy. “Pearson’s solution” is 1 grain sodium arsenate to 1 oz. water. “Macquir’s neutral arsenical salt” is a binarsenate of soda. “Papier Moure” consists of paper soaked in solution of potassium arsenate (Tidy).
Fischer (Ber. deutsch. Chem. Gesellschaft, xiii., p. 1778) proposes ferrous chloride as better than sulphurous acid for reducing arsenic acid to arsenious (see process for separation, post).
Arsenic Trichloride, As Cl3, is a volatile, colourless liquid, very pungent, and fuming in air. It has been discarded from medical use on account of its dangerous properties. A case of poisoning by it is mentioned in Taylor (Med. Juris. 1, p. 278). It is obtained in the process for separation from the organs. Arsenic Triiodide, a dull red crystalline solid, is used in ointments.
Arseniuretted hydrogen, As H3, is a colourless gas of a garlic odour, almost insoluble in water. It burns with a livid bluish-grey flame, forming water and a white cloud of As2 O3. By heating to redness it is decomposed into hydrogen and a deposit of arsenicum (the “mirror”). It is formed whenever hydrogen is evolved in contact with arsenic compounds, hence has caused accidents in making hydrogen from impure zinc. It is probably the most deadly compound of As, and proved fatal to its investigator, Gehlen, and in several other cases.
EXTRACTION AND TESTS.
If arsenic has been given in the solid form, the greater part will remain insoluble, and will be found either in lumps or powder in the stomach, or as a white powder adhering to its lining. Any substance so found should be washed with water and tested for arsenic. It is absurd to say, as Dr. Letheby did in Ann Merritt’s case (ante, p. 366), that the quantity was too small for examination: if a white powder can be seen, it can be tested. In the contents, or in any fluid food, the heaviness of powdered arsenic will cause it to readily separate as a sediment. Soot or indigo, the legal admixtures, should also be sought.