_Tests._ 1. Iodine may be readily detected by the blue color it gives to starch. Iodide of potassium gives the same when the iodine is set free by an acid, such as sulphuric acid. 2. It also forms a scarlet precipitate with perchloride of mercury; and 3. It gives a yellow precipitate with acetate of lead. CHAPTER XIV. PHOSPHORUS. This substance is sold in a pure state in small wax-like cylinders, which must be preserved under water. It is soluble in oil, alcohol, ether, and chloroform, and still more so in carbon disulphide; it is luminous in the dark, and it ignites at a very low temperature, giving off a dense white smoke. Phosphorus is much more frequently used as a poison abroad than in England; but since restrictions have been put on the sale of poisons, and rat poisons containing it have been more common, cases of poisoning have more frequently occurred, and are likely to do so even oftener in future. The cases which have occurred show that it is a very powerful irritant, and capable of causing death when taken, even in small doses. One grain has caused death; the shortest period in which it has followed the administration of the poison being four hours. The phosphorous paste sold consists of flour, sugar, and fat, with phosphorous, ordinarily colored with Prussian blue. Coloring matter is also generally present in lucifer-match tops, which contain phosphorus and chlorate of potash, or nitre; hence, the vomited matters after either of these has been swallowed may be variously colored. In the so-called “safety matches” the phosphorus is on the box and not on the match. Phosphorus does not readily lend itself to the purposes of the criminal, its luminosity, its taste, and its garlic odor rendering it difficult of concealment. The _symptoms_ of poisoning by phosphorus are very varied, often insidious. At first there may be merely the ordinary signs of irritant poisoning. The vomited matters are luminous in the dark, sometimes bilious, sometimes bloody. There is very great prostration, and there may be diarrhœa with bloody stools. These symptoms sometimes abate, and everything seems going on well, when suddenly a new train of symptoms, still more serious, develop themselves. These are such as would occur in the worst forms of blood poisoning: harsh, dry, yellow skin, with discharges of blood from the various passages, and the formation of extravasations below the skin. The urine is ordinarily retained or suppressed, what little there is being albuminous or bile-stained. Finally, acute delirium with convulsions sets in; the patient dies comatose a few hours after taking the poison, or it may be as many months.