Iodine and iodide of potassium in medicinal doses have been supposed by Dr. Lawrie to be capable of exciting in certain constitutions an affection resembling cynanche laryngea in its symptoms, consisting of inflammation of the salivary glands, glottis, and other adjacent parts, and proving sometimes fatal.[[355]] This property is doubtful; but several instances have been published of profuse salivation and soreness of the mouth during a course of iodine; it is apt to cause chronic irritation of the Schneiderian membrane; and some think that it may affect in like manner the bronchial membrane in the lungs.[[356]]
Morbid Appearances from Iodine.—The only account I have seen of the appearances left in the body after death from slow poisoning with iodine is contained in the essay of Dr. Zink. In a second fatal case which came under his notice he found enlarged abdomen from distension of the intestines with gases, enlargement of the other viscera and serous effusion into the peritonæum; adhesion of the viscera to one another; redness of the intestines, in some places approaching to gangrenous discoloration; redness and excoriation of the peritonæal coat of the stomach, and also of its villous coat; enlargement and pale rose-red coloration of the liver. In the chest serum was found in the sac of the pleura. The gullet was contracted in diameter, and red internally.
On Poisoning with Iodide of Potassium.
To these remarks on iodine a few observations may be added on the iodide of potassium, one of its compounds, which is now generally substituted in medicine for the simple substance. The tests and actions of this poison have been examined by M. Devergie; and more lately its medico-legal chemistry has been investigated by Dr. O’Shaughnessey and Professor Orfila.
It is sold in the shops of various degrees of purity. Pure iodide of potassium is in white crystals, tending to the cubical form, permanent in the air, possessing a faint peculiar odour, and easily soluble in both water and rectified spirit. Another variety has the same form, but possesses an odour of iodine, is often yellowish in colour, and deliquesces slightly in moist air. This contains an excess of iodine, but may be otherwise pure. A third variety is impure. It presents less tendency to assume a crystalline form, is more or less deliquescent, dissolves but partially in alcohol, and when dissolved effervesces with acids. The principal ingredient in this article is carbonate of potass; and sometimes the proportion of iodide is inconsiderable. In one specimen I procured 74·5 per cent. of carbonate of potass, 16 of water, and only 9·5 of iodide of potassium.
In the solid state the iodide of potassium may be known by the effect of strong sulphuric or nitric acid, which turns it brown with effervescence, and when aided by heat disengages violet fumes of iodine.
In solution many tests will detect it, such as chlorine, nitric acid, corrosive sublimate, acetate of lead, protonitrate of mercury, muriate of platinum, and starch with chlorine or nitric acid. Chlorine or nitric acid forms a brown or orange-coloured solution by disengaging iodine. Corrosive sublimate forms a fine carmine-red precipitate, the biniodide of mercury; acetate of lead a fine yellow precipitate, the iodide of lead; protonitrate of mercury a yellow protiodide of mercury, which gradually fades into a dirty brown. Solution of starch, followed by chlorine in solution or in vapour, strikes a deep blue colour, which, if the fluid is sufficiently diluted, disappears on boiling, reappears on sudden cooling, and is permanently removed by a stream of sulphuretted hydrogen gases. Of these tests the most characteristic is starch with chlorine; and it is also extremely delicate. Too much chlorine however bleaches the blue colour away.
In compound mixtures most and sometimes all of these tests are useless. If the mixture is deeply coloured, none will act characteristically. If carbonate of potass be present in such proportion as is often met with in the shops, the tests cannot be trusted to.
Process for Compound Mixtures.—The following method of analysis is applicable to all mixtures, organic and inorganic. Add water, if necessary, and filter; and if the fluid which passes through is tolerably free from colour, test a little of it with solution of starch and chlorine. If the colour is too deep to admit of this trial, or the test on trial does not act, unite the fluid and solid parts and transmit sulphuretted hydrogen to convert any free iodine into hydriodic acid. Drive off the excess of gas, supersaturate with a considerable excess of potass, filter, and evaporate to dryness. Char the residue at a low red heat in a covered crucible; pulverize the charcoaly mass, and exhaust with water. This solution will probably act characteristically with starch and chlorine; but on the whole it is better in the first instance to remove some of the salts by evaporating to dryness, and exhausting the residuum with alcohol. The alcoholic solution contains the hydriodate of potass, with some other salts; and on being evaporated to dryness, a residuum is left, on which, when dissolved in water, the starch and chlorine will act characteristically. No other test is necessary; and frequently no other test will act, on account of co-existing salts.
I have found that a grain of iodide of potassium may thus be easily detected in six ounces of urine, which must be considered a very complicated fluid. In the solution ultimately procured nitrous acid struck a pale brown tint, and on the addition of solution of starch a dark-blue precipitate was formed; which, after being sufficiently diluted, disappeared under ebullition, leaving a colourless fluid. On cooling, no change took place; but on the subsequent addition of a drop of sulphuric acid, the blue colour and precipitation were immediately restored. No other reagent acted characteristically, although there was a sufficient quantity of solution to try the starch test ten times at least.