Iodide

“ Iodine vapour or solution applied to a. silvered plate would cause the formation of silver iodide on those parts not acted upon by light. The removal of the resinous picture would leave an image formed of metallic silver, whilst the black parts of the original would be represented by the darker silver iodide. This was probably the origin of the daguerreotype process. Such observers as Niepce and Daguerre, who had formed a partnership for prosecuting their researches, would not have thus formed silver iodide without noticing that it changed in colour when exposed to the light. ”

“ Great was my surprise on making the experiment to find just the contrary of the fact alleged, and to see that the iodide was not only less sensitive than the chloride, but that it was not sensitive at all to light; indeed that it was absolutely insensible to the strongest sunshine: retaining its original tint (a pale straw colour) for any length of time unaltered in the sun. ”

“ The Double Iodide Solution.—The great difference in the quantity of iodide of potassium ordered by different persons, to dissolve a given weight of iodide of silver in a given volume of water, has induced me to make some experiments on the subject. ”

“ With the aid of this constant and of equation (2) we can obtain, at least, an approximate interpretation of the results of the exposure of hydroiodic acid and of potassium iodide to the influence of atmospheric oxygen.604 We may [p307] calculate, first, what concentration of free iodine would be required to prevent oxidation of hydroiodic acid, in molar solution, by the oxygen of the air, i.e. to establish equilibrium. ”

“ Exposed for some hours to the fumes of a small quantity of iodide under a bell-glass in the cold, pure otto remains white, and continues so when exposed to the air; an adulterated sample, on the contrary, becomes yellow or brown, and afterwards, on exposure to the air, continues to darken in colour, until it becomes of a deep brown, or even perfectly black, according to the quantity of foreign oil present. ”

“ It is thus clear that the conditions for equilibrium between a solution of an iodide and air would be satisfied, in the case of an alkali iodide, by the liberation of a mere trace of iodine, whereas, as was previously shown, in the case of hydrogen iodide, a very large proportion of iodine must be liberated before equilibrium could obtain. ”

“ Freely expose a solution of ferrous iodide to the air; or digest iodine, in excess, on iron, under water, gently evaporate, and sublime. A deliquescent, volatile red compound, soluble in water and alcohol. It is rarely employed in medicine. ”

“ Solarization, and general blueness of all the light parts of the picture, were formerly great obstacles to success, though now scarcely thought of by first-class artists. Beginners in the art, however, are still apt to meet with this difficulty. It is occasioned by dampness in the iodine box, which causes the plate to become coated with a hydro-iodide of silver, instead of the iodide. ”

“ For a white-hot spiral, the absorption of chloroform vapour being 10 per cent., that of iodide of methyl is 16; with the blackened cube as source, the absorption by chloroform is 22 per cent., while that by the iodide of methyl is only 19. This inversion is not the result of temperature merely; for when a platinum wire, heated to the temperature of boiling water, is employed as a source, the iodide continues to be the most powerful absorber. All the experiments hitherto made go to prove that from heated lampblack an emission takes place which synchronises in an especial manner with chloroform. ”

“ Indium is likewise distinguished by a straw-yellow oxide.
57. Iodine Yellow, Or iodide of lead, is one of those compounds whose presence on the palette should never have been allowed. Exceedingly brilliant, it is also utterly fugitive, destroyed by exposure or foul gas, and useless in admixture. We may state here that, whatever its colour, no pigment containing iodine can in the slightest degree be relied upon. One of the most unstable of substances, being slowly volatile even at common temperatures, iodine is or ought to be quite inadmissible as a constituent. ”

“ Likewise the French Pharmacopeia directs that 10 per cent. of potassium iodide and only 2 per cent. of iodine shall be used. Both of these pharmacopeias use water instead of glycerin as the solvent. Loose combinations of iodine and potassium iodide, such as are represented by the compound having the formula KI3, have been described. The quantity of potassium iodide prescribed by the U. S. Pharmacopeia for the preparation of iodine ointment is not sufficient to form such a compound as KI3 with all of the iodine directed to be used. ”

“ But when potassium iodide is exposed to the air, if iodine is liberated, the solution becomes alkaline605 (HO− is formed according to equation (1) ) and the concentration of HO− consequently grows continuously greater. We will, therefore, formulate the problem as follows: how much iodine606 must be liberated, by oxidation of iodide-ion, in molar potassium iodide solution in order to establish equilibrium? For every two molecules of iodine liberated, four HO− ions are formed (equation (1) ) . ”

“ The presence of iodine artificially added is best detected by agitating the oil with a little rectified spirit, and then testing this last for iodine. Or, a little solution of starch and a few drops of sulphuric or nitric acid may be at once added to the oil, when a blue colour will be developed if iodine, or an iodide, has been mixed with the sample. ”

“ Iodine does not occur in nature in the free state; and iodides are rare, iodargyrite or iodide of silver (AgI) being the only one which ranks as a mineral species. Iodates are found associated with Chili saltpetre, which is an important source of the element.
Iodine and Iodides are largely used in the laboratory, and have already been frequently referred to. It is used as an oxidising agent in a similar manner as permanganate and bichromate of potash, especially in the determinations of copper, arsenic, antimony, and manganese. ”

“ More recently, iodoform has been prepared by the electrolysis of a solution of potassium iodide in the presence of alcohol or acetone, the electrolytic cell being fitted with a diaphragm, in order to prevent the hydrogen which is formed at the same time from reducing the iodoform, or from combining with the iodine to form hydriodic acid. ”

“ As the presence of minute traces of free iodine may be discovered by means of starch paste, with which it forms a very dark blue-coloured substance, a mixture of potassium iodide with starch paste will detect the presence of very small traces of ozone. [8] Ozone is destroyed or converted into ordinary oxygen not only by heat, but also by long keeping, especially in the presence of alkalis, peroxide of manganese, chlorine, &c. ”

“ Economical Way of Iodizing Paper.—The extravagant price of the salt called iodide of potassium has led me to experiments as to whether paper could not be iodized in another form; and having been successful, I offer the process to the readers of "N. & Q." Having verified it three times, I can safely say that it is quite as effectual as using the above salt.
The first solution to be made, is a saturated solution of iodine. Put about sixty grains of iodine (the quantity is not of importance) into an ounce bottle, and add proof spirits of wine ”

“ PROCEDURE.—Weigh out on the rough balances 13 grams of commercial iodine. Place it in a mortar with 18 grams of potassium iodide and triturate with small portions of water until all is dissolved. Dilute the solution to 1000 cc. and transfer to a liter bottle and mix thoroughly (Note 1) . [1]
[Footnote 1: It will be found more economical to have a considerable quantity of the solution prepared by a laboratory attendant, and to have all unused solutions returned to the common stock.] ”

“ Iodine and its compounds are largely used in medicine (as in liniments, antisyphilitics, etc.) , in photography, in the preparation of aniline dyes, and as an indicator in titration.
Iodine green, an artificial green dyestuff, consisting of an iodine derivative of rosaniline; -- called also night green. -- Iodine scarlet, a pigment of an intense scarlet color, consisting of mercuric iodide. -- Iodine yellow, a brilliant yellow pigment, consisting of plumbic iodide. ”

“ Add 25 cc. of iodine solution from a pipette, allowing to drain for a definite time. The excess of iodine should be from 50 per cent to 60 per cent of the amount added, that is, from 100 per cent to 150 per cent of the amount absorbed. Moisten the stopper with a 15 per cent potassium iodide solution to prevent loss of iodine or chlorine but guard against an amount sufficient to run down inside the bottle. Let [Pg 180] the bottle stand in a dark place for 1/2 hr. at a uniform temperature. At the end of that time add 20 cc. of 15 per cent potassium iodide solution and 100 cc. ”

“ Saccharine iodide of iron, Saccharum ferri iodidi, Ferri iodidum saccharatum, L. Iron (in powder) , 1 dr.; water, 5 dr.; iodine, 4 dr.; obtain a solution of iodide of iron, as above, and add to it of sugar of milk (in powder) , 11⁄4 oz.; evaporate at a temperature not exceeding 122° Fahr., until the mass has a tenacious consistence, then further add of sugar of milk, 1 oz., reduce the mixture to powder, and preserve it in a well-stoppered bottle. Every 6 gr. contains 1 gr. of iodide of iron.
From “syrup of iodide of iron” exposed in a shallow vessel, in a warm place, until it crystallises ”

“ Mastering the few is said to be the key to success, and the writer believes it, for he has seen it proven. An eminent physician from New York was once called in consultation to a western city. His prescription was mercury iodide, potassium iodide, and infus. gentian. He stated (and the other physician said, “I see”) that the only object of the potassium was to dissolve the mercury iodide. But potassium's great affinity for iodide accepted it, at once dropped the free mercury to the bottom, likely to be taken all at the last dose, equal to fifteen or twenty grains of blue pill. ”

“ I have tried several: with some I find that the combination of their starch with the iodide of iron causes a dark precipitate upon the face of the paper; and with those papers prepared with size, there appears to me great difficulty (in his improved process after the paper is moistened with aceto-nitrate of silver) to procure an equal distribution of the iodide over its surface, as it invariably dries or runs off parts of the paper, or is repelled by spots of size on the paper when dipped in the iodide of iron bath.—A reply to the foregoing question would greatly oblige
A Constant Reader. ”

“ Boiling water, hot air, and light, also produce a like effect.
Mercurous Iodide. HgI. Syn. Subiodide Of mercury, Green iodide of mercury, Mercurous iodide; Hydrargyri iodidum viride (B. P.) , Hydrargyri subiodum, H. iodidum (Ph. L.) , H. i. viride (Ph. D.) , L. Prep. 1. (B. P.) Mercury, 1 oz.; iodine, 278 gr.; rectified spirit, a sufficiency. Rub the iodine and mercury in a porcelain mortar, moistening occasionally with a few drops of spirit, and continue the trituration until the mass assumes a uniform green colour, and no metallic globules are visible. ”

“ The ether gradually absorbs oxygen from the atmosphere, being converted into acetic acid; this, by its superior affinities, reacts on the iodide present, converting it into acetate, with liberation of hydriodic acid; while this latter, under the influence of the atmospheric oxygen, is very rapidly converted into water and iodine.
I am satisfied by experiment that this is one of the causes of the separation of iodine, and I think it is the only one, for the following reason; neither bromised nor chlorised collodion undergo the slightest change of colour, however long they may be kept. ”

“ I do not deny that there are rare individuals who, although untainted, can resist the action of iodide, but in ten years' practice in large hospitals, embracing probably some thousands of cases, I have not met with more than one or two instances which I believed to be of such character. ”

“ It liberates iodine from solutions of potassium iodide, the reaction in neutral solution proceeding thus: O3+2KI+H2O=O2+I2+2KHO, whilst in acid solution the decomposition takes the following course: 4O3+10HI= 5I2+H2O2+4H2O+3O2 (A. Ladenburg, Ber. 1901, 34, p. 1184) . ”

“ A simpler method is to dissolve equal parts of lead nitrate and potassium iodide separately, each in 20 parts of hot water, to mix the solutions and cool quickly, when lead iodide separates in very small crystals. When pure lead iodide is melted in the absence of air, and the fused mass powdered, a product of yet finer colour is formed. It is necessary to completely imbed the crucible in which the fusion is performed in the fire. ”

“ Iodide of nitrogen is just as explosive as nitrogen chloride. [78 bis] In the [508] action of iodine on sodium hydroxide no bleaching compound is formed (whilst bromine gives one) , but a direct reaction is always accomplished with the formation of an iodate, 6NaHO + 3I2 = 5NaI + 3H2O + NaIO3 (Gay-Lussac) . Solutions of other alkalis, and even a mixture of water and oxide of mercury, act in the same manner. [79] This direct formation of iodic acid, HIO3 = IO2 (OH) , shows the propensity of iodine to give compounds of the type IX5. ”