B. The chlorine used in the separation of arsenic (p. 385) must be _pure_. The best process for making it is to heat _pure_ potass. dichromate with _pure_ hydrochloric acid. The latter may be obtained by heating the “pure” acid of commerce in a retort until a portion of the distillate gives no indication of arsenic by the tests. The remainder in the retort is then arsenic-free. * * * * * ERRATUM. Page 397, line 11, _for_ “Waislow,” _read_, “Winslow.” TRIALS FOR POISONING. CHAPTER I. CHEMICAL INTRODUCTION. Summary of symptoms exhibited by various poisons: (1) Sudden death—(2) Insensibility—(3) Vomiting—(4) Action on the eye—(5) Convulsions—(6) Chronic poisoning. Alkaloids, chemically and physiologically—Processes for their detection—Necessity for keeping the extracts separate—Dragendorff’s process—Dr. Guy’s sublimation process—Effects on animals—Doubtful value of this test—Preparation and effects of reagents: (1) Mayer’s—(2) Potassium tri-iodide—(3) Sonnenschein’s test—(4) Bismuth—(5) Phosphotungstic acid—(6) Picric acid—(7) Animal charcoal—(8) Platinic chloride—(9) Tannin or tannic acid—(10) Phospho-antimonic acid—(11) Silico-tungstic acid—(11) Auric, palladium and mercuric chlorides—Ptomaines or cadaveric alkaloids; difficulties raised by their discovery—Principles to be observed in analysing. BEFORE proceeding to a separate examination of the poisons used in the following trials, it will be advisable to take a general view of poisons, specially noticing those that we have selected as the most important legally. They do not admit, perhaps, of accurate classification, but inasmuch as the manner of death and symptoms are usually the most available indication as to the nature of the poison that has acted, the following arrangement will be serviceable. The heads indicate the most prominent symptom: I. SUDDEN DEATH.—Large quantities of any poison might be rapid in fatal result, but the sudden poisons proper are:—concentrated sulphuric, nitric, and hydrochloric acids; poisonous gases and vapours, such as carbonic acid and sulphuretted hydrogen (_see_ Casper’s Forensic Medicine, Case CCXLI.), carbonic oxide, arseniuretted and antimoniuretted hydrogen, and certain rare organic compounds, as kakodyl, &c.; strychnia sometimes, oxalic acid in large doses, chloroform under certain circumstances. But beyond all others, the quickest of poisons is _hydrocyanic or prussic acid_.