Silver iodide

“ This is found to be a general rule. It was verified very exactly by Stas’s experiments, in which he removed the oxygen from the ternary compound silver iodate and found that the whole of the silver and the iodine remained in combination with each other as silver iodide; his results prove, to one part in ten millions, that the combining ratio of the silver and the iodine is unaltered by the removal of the oxygen. ”

“ Wellington.
[The resultant iodide from fifteen grains of nitrate of silver, precipitated by means of the iodide of potassium, will give the requisite quantity of iodide for every ounce of water; or about twenty-seven grains of the dried iodide will produce the same effect. It is however far preferable, and more economical, to convert all waste into chloride of silver, from which the pure metal may be again so readily obtained. Iodide of silver, collected in the manner described by our correspondent, is very likely to lead to disappointment.] ”

“ 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. ”

“ These rings must be regarded as films of the ioduret of silver, varying, not only in thickness, but in the more or less perfect states of combination in which the iodine and metal are. The exterior circle is an ioduret in a very loose state of chemical agregation; the attractive forces increase as we proceed towards the centre, where a well formed ioduret, or probably a true iodide of silver, is formed, which is acted upon by sunlight with difficulty. The exterior and most sensitive film constitutes the surface of Daguerreotype plates. ”

“ 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. ”

“ A great many experiments which I tried last autumn, for the express purpose of clearing up this point, have convinced me that, cæteris paribus, the addition of free iodine to the iodizing solution, tends to diminish the sensitiveness of the subsequently formed iodide of silver. On paper, this diminution of sensitiveness is attended with some advantages, so that at present I hardly know whether to introduce the free iodine or not; but in collodion, as far as my experience goes, I see no reason for retaining it; on the contrary, everything seems to be in favour of its removal. ”

“ A slight difference in the strength of a solution of iodide of potassium makes a great difference with respect to the quantity of iodide of silver it is capable of dissolving. Thus, if you remove a small proportion of the water from a solution of the double iodide of silver by evaporation, the slight increase of strength which the solution will thereby acquire, will enable it to take up a much larger proportion of iodide of silver than it already contains ”

“ With iodide of silver, bromide of silver, ammonio-nitrate of silver, and other salts of this metal, the result will be much the same.
Some bodies, which under the influence of light, undergo chemical changes, have the power of restoring themselves to their original condition in the dark. This is more remarkably displayed in the iodide of platinum, which readily recieves a photogenic image by darkening over the exposed surfaces, but speedily loses it by bleaching in the dark. ”

“ Operators should endeavor to secure the larger crystals. It melts at 224.6 deg., forming a brown or nearly black liquid. It boils at about 356 deg., and emits a very deep violet colored vapor. It gives off a very appreciable vapor, sufficient for all purposes of forming the iodide of silver on the daguerreotype plate, at a temperature of 45 deg. or even lower. Iodine crystallizes readily. Every operator has found upon the side of the jar in his coating-box, perfectly regular crystals, deposited there by sublimation. ”

“ After the silver solution has taken up all it can dissolve or assimilate, the surplus is held in suspension and is called free iodide, which deposits itself on the surfaces of the plates, and when in quantity causes the plate when taken from the bath to appear as if fine sand had been sprinkled over it. These small crystals prevent the action of the light on the parts they cover, and when the plate has been developed and fixed, every crystal has produced a small transparent spot or pinhole, as it is termed, and many a lovely negative has been ruined by pinholes. ”

“ Then they either put some iodine into this same box or they had an iodine box. After the plate was in there a few minutes, they took it out and put it in there and gave it a dose of bromine. It was found, and by whom I am not sure, that the addition of a little iodine or a small proportion of iodide of silver with iodine of silver gave better effects. So it was then taken out and it was sensitive to light. Now, Daguerre discovered all that. This was then put in the plate holder and exposed in the camera and he got a picture. ”

“ The silver surface is first thoroughly cleaned and freed from all organic matter, then exposed to vapor of iodine, producing an iodide of silver. The plate upon which is this salt, is again exposed to the vapor of bromine, forming a bromo-iodide of silver, a salt also.
As most of the various accelerators are compounds of bromine, with either chlorine or fluorine combination, they partake somewhat of the nature of these latter, giving results which can be detected by the experienced operator. ”

“ I am not quite certain as to whether, theoretically, this position is right; but I find in iodide of potash, and in the above formula, that the iodine is absorbed in greater quantities by the silver, than the alkaline potash by the nitric acid. Thus, by using a solution for some time, it will at last contain but very little iodine at all, and not enough for the purpose of the photographer; hence it requires renewing. And I have lately observed that paper is much more effective, in every way, if it is floated on free iodine twice before it is used in the camera, viz. ”

“ When the picture is fully out, wash, &c. as usual; the iodide of silver is rapidly removed by a saturated solution of hyposulphite of soda, which acts much less on the weaker blacks than it does if diluted. ”

“ 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. ”

“ 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. ”

“ 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. ”

“ 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. ”

“ 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. ”

“ Tincture of iodine also affords a means of identifying lead in certain alloys by the formation of a yellow iodide of lead, while the vapour of iodine has in certain cases been used to tint the constituents. Thin coloured films may often be produced by the oxidation of the specimen when heated in air. ”

“ 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. ”