Phosphorous acid, the effects of which have been examined experimentally by Professor Hünefeld of Greifswalde, differs in its operation from phosphoric acid. Twenty-five grains had no effect on a rabbit; but a drachm caused difficult breathing, restlessness, bloody vomiting, slight convulsions, and death in twelve hours; and the stomach was found not much injured. The urine contained phosphoric acid.[[327]]
Of Poisoning with Sulphur.—It does not appear that sulphur, which resembles phosphorus in many particulars, bears any resemblance to it in physiological properties;—which may be ascribed to its not being susceptible of spontaneous acidification. It certainly possesses, however, slight irritating properties. It is often given as a purgative, which is sufficient to prove that it is not altogether inert; and the veterinary school at Lyons found that a pound killed horses by producing violent inflammation, recognizable during life by the symptoms, and after death by the morbid appearances.[[328]]
Of Poisoning with Chlorine.—Chlorine in its gaseous state acts powerfully as an irritant on the windpipe and lungs, and on that account will be noticed under the head of the poisonous gases. But even in solution it retains to a certain degree its poisonous qualities. Orfila says that five ounces of a strong solution of chlorine will kill a dog in twenty-four hours, if it is kept in the stomach by a ligature, and that two ounces diluted with twice its volume of water will prove fatal in four days;—that the symptoms are those of irritation of the stomach;—and that in the former case he found general redness and blackness—in the latter ulceration of its villous coat.[[329]]
Of Poisoning with Iodine.
Iodine is a poison of more consequence than chlorine, both because it is becoming a more common article, and because it is more violent in its effects on the animal economy.
Tests of Iodine.—Iodine when pure is a solid substance easily known by its scaly form, its resemblance in colour and resplendence to polished iron, its peculiar odour, the violet fumes it forms when heated, and the fine blue colour it produces with a solution of starch. It is very sparingly soluble in water, but readily so in rectified spirit and in aqueous solutions of certain salts, more especially the iodide of potassium. Its ordinary forms in the shops are iodine itself, the tincture, and the compound solution, where the solvent is a solution of iodide of potassium in water. It stains the skin brownish-yellow; but the stain is not permanent. Its fumes are intensely irritating to the nostrils, throat, and lungs.
When dissolved in water or in solutions of neutral salts, it communicates to the fluid a yellowish-brown or reddish-brown colour, which is destroyed by sulphuretted hydrogen, because the iodine is converted into hydriodic acid. In the colourless fluid thus formed, if treated with chlorine,—or in the original brown fluid without chlorine,—a solution of starch, obtained by ebullition and subsequently cooled, produces a fine blue colour and precipitate; and these, if the solution be sufficiently diluted, disappear on boiling, reappear on sudden cooling, and are removed permanently by a stream of sulphuretted hydrogen. This is a very delicate and characteristic system of tests. The best mode of using chlorine for decomposing hydriodic acid is to let it descend in the gaseous form from the mouth of a bottle of nitro-hydrochloric acid upon the fluid to be examined; In this way an excess is easily avoided, which bleaches out the blue colour. Sulphuric acid, though often recommended for the purpose, does not act unless it contains nitrous acid,—from which however the sulphuric acid of commerce is seldom quite free.
When mingled with organic substances, the discovery of it is a matter of some nicety; because many substances of this nature, especially in the living body, quickly convert it into hydriodic acid.[[330]] Hence few cases can occur in medico-legal practice, where iodine will be discoverable in its free state. The following method of analysis will meet all possible cases.
Process for Compound Mixtures.—Add water if necessary, and filter. If either the fluid or solid part is little or not at all coloured, test it with cold solution of starch, assisting the action of the test on the solid part by trituration in a mortar. If a blue colour be struck, which disappears under ebullition, and reappears under refrigeration alone, or on subsequently allowing chlorine gas to descend on the surface of the fluid, there can be no doubt of the existence of iodine.—If the colour of the suspected mixture after filtration is so deep that the action of the starch cannot be expected to yield characteristic appearances, then both the solid and fluid parts should be agitated with a third of their volume of ether; and after the ethereal solution has arisen to the surface, it is to be removed and tested with solution of starch. The blue colour will be now perhaps struck, because the ether, in carrying off the iodine from the mixture, leaves many coloured organic principles behind.
Should free iodine not be thus detected, strong presumptive evidence may still be procured of its actual presence, or of its having been at one time present, by continuing the examination with the view to detect hydriodic acid. This is described in p. [159].