THE PREPARATION OF IODINE AND BROMINE SALTS BY THE EASIEST METHOD E ~ SMACKENZIE T MARSHALL. REDDINO RmoE, BETHEL, CONNECTICUT The recovery of laboratory wastes is a worthwhile problem which should be tackled in its various aspects by every willing pupil. It gives the chance to do some real thinking, to purify a body of material from z impurities; a much more important discipline than the class analysis of mixtures where there are really no impurities. An article in the March issue of the JOURNAL' shows what can be done, but the method on the conversion into iodides can be greatly simplified. If the quantity of iodine to be recovered is very small and there is no chlorine gas set-up, the latter can be dispensed with. Potassium chlorate to liberate the iodine is placed in a suitable flask or bottle, the necessary hydrochloric acid added, and then shaken with water, before adding the solution containing the iodine or the latter may replace the water. Chlorine water, if necessary, made in the same way completes the reaction, giving time for the decomposition of insoluble iodides. Of course this is a crude way, not suitable if there are several gallons of liquor to work, but the method of preparing the chlorine water is a quick one if the small amount of resulting potassium chloride is of no importance. I n fact it has been known to be made this way and sold to chemical laboratories. The recovered iodine after slight washing is placed in a tall earthenware pot or other suitable vessel (a gas jar for small quantities) about twelve times the iodine volume, and desiccated calcipm chloride added to take up water in the paste iodine. A perforated porcelain plate on a glass tripod rests above the iodine. The pot is covered with a sheet of glass, luted t o the pot. Por this class of work, almond or peach kernel meal, made from the cake after the oil is expressed, is mixed with water to a putty. It is particularly useful in making gas-tight apparatus where the joint is too large to be effected with the usual stopper or ring of rubber tube. It sticks wonderfully and is used largely in commercial distilling where the still heads are a loose sliding fit. Set the iodine pot in a tin pan with sand packed around it, but not up to the level of the iodine, and place on a radiator; or if the laboratory extends its bounds t o include the steam boiler of the building, this is the best place. Over the week-end is the time for the sublimation. Cool well before opening. Some crystals will fall down, but the perforated plate will save them for use. Much of "resublimed" iodine bought as pure is the nude product sublimed only once, and too quickly a t that. Hence, as the article in the March issue of the JOURNAL' states, it tests only 95%, although the remaining 5% is chiefly water. ' Bonner and Masaki, "The Recovery of Iodine as Sodium Iodide from Waste Iodide Solutions," 7, 616-7 (Mar., 1930). 1131
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Now what are we going to do with the iodine? Make ferrous iodide. Weigh the iodine and calculate the iron, using 5% in excess of the equation. Commercially pure iron wire, the fine wire found in the laboratory, is used. Place the ironin a suitablevessel, add ten times its weight of water and then add the iodine in small portions, no faster than enough to keep the liquid below 35%; otherwise iodine may be given off. As the solution becomes more concentrated, the reaction may be violent, so add the iodine more carefully. When the free iodine color is discharged, filter the green ferrous iodide and titrate a sample, if several iodides are to be made, otherwise the weight of iodine used gives the equivalent. Any soluble carbonate or hydrate will interact to form the corresponding iodide, with the complete precipitation of the iron. Should one wish to make an insoluble iodide, such as mercuric iodide, it should be done through the sodium iodide. It is not feasible with the iron iodide to precipitate an insoluble iodide which will he free from iron. This whole process is an old and tried one for the commercial manufacture of potassium iodide. The soluble iodide produced by any method should he crystallized and the mother liquor reworked or used to precipitate an insoluble iodide. Sodiunz iodide in the granular powder is best made by melting the large crystals in their water of crystallization in an enameled iron pan, with a handle, heated over a naked ring burner and stirred by a good fat glass rod. Gloves are good to have as the mass may spurt. Stirring faster is the cure. It is not difficult to produce a beautiful product with no iodide adhering to the dish. A bone spatula can be used to keep the dish free as the mass thickens. Do not stop, even for a second, is the only direction necessary to get a good result. Deliquescent iodides, such as calcium iodide, are concentrated until the pellicle shoots across the surface of the hot melt. It is then poured on a warmed plate, broken up, and powdered. These latter iodides (the corresponding bromides may be prepared in the same way) contain an indeterminate percentage of water. Cadmium iodide can he made from the metal by the same method as ferrous iodide. In crystallizing this beautiful iodide great care is required to avoid discoloring the crystals. Try and find out the trick of keeping the crystals pure, and the cause of the unnatural tinting. Ammonium iodide crystals also go off color. There is quite a trick in making these crystals that do not turn yellow. A piece of the sesquicarbonate in the bottle, or a drop of ammonium hydroxide will keep most crystals white. Here is a nice problem for the student to solve. Mercurous iodide is prepared by well triturating mercuric iodide with the equivalent mercury. It is worth trying. The soluble bromides are made through the ferrous salt adding the hro-
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mine carefully over periods of time, and with only a single filtration and evaporation to the process. In the case of ammonizw bronzide, bromine is added directly to concentrated ammonium hydroxide, drop by drop from a separatory funnel in a stopper in the neck of the flask containing the ammonia. Keep the bottle cool; as the ammonium bromide crystallizes out i t will encase the drops of bromine, and unless the bottle is shaken continually until the free bromine is combined, the heat generated may burst the crystalline "cyst" and, liberating the bromine, cause a bump to break the bottle, unless held in the hand or supported on some soft pad. As hydrobrwnic acid is easy to make without the preparation of hydrogen sulfide or sulfur dioxide, many bromides are made directly from the acid. For example, weigh out equivalents of bromine and sulfur. Place the bromine in a stoppered bottle with 10% more water than the quantity to make the concentrated 48% HBr solution. Add 5% of the sulfur and shake. The reaction is slow a t first, owing to the slight solubility of the bromine in the water, but as the HBr increases in strength the liquid becomes darker and all the bromine will dissolve. At this point put aside a few cc. When all the sulfur is added the reaction is controlled by the shaking. The quiet surface of the Br2S2with the excess sulfur in solution becomes a coating of sulfur and stops the reaction; therefore a flask is not suitable, as the sulfur hardens in a short time if not shaken to keep up the action, and may have to be broken up with a glass rod. The action is complex, Br& is formed by the bromine water, and by the bromine liquid dissolving the sulfur in itself and reacting with the water, ends in a bromine-free liquid containing HBr, HZS04,free S, and a trace of HzS03. The acid is poured through glass wool into a distilling flask in a sand bath. No sulfur may enter the flask, otherwise it will distil over in the free state and as SO2 throughout the distillation, spoiling the result. When poured into the flask the acid may be cloudy from free sulfur. To remove these last traces, add some of the brown liquid reserved for this purpose, just enough to tint the acid with free bromine when it starts to boil. The first runnings should be used to f o m the basis of the next batch. The 48% acid distils a t 126OC., and may be redistilled for greater purity. This method is used commercially. The same method may be used to prepare HI, but using a greater volume of water to prevent the reverse action. When the free iodine color is completely discharged and the sulfur settled below the clear solution decant the clear, measure and titrate for H2S04. Prepare a solution of barium hydroxide, titrate, and add sufficient of it to precipitate the BaSOr. Distil in the same way as for HBr. A trace of Ba(OH)%in excess is advisable; also it is well to stop the distillation before completion. In the case of the HBr, the residual HzS04 in the flask protects the glass, but as all the H I may distil, toward the end it requires constant watching as a
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drop of acid may drop off the outlet tube and crack the flask. HI in hot sand is not so good. The writer has found that when a process is minutely written up, with the equations and theoretical considerations, the student is inclined to take the whole thing for granted and feel he has actually done the thing practically. For this reason, only the method is given here to prepare the various salts of iodine and bromine. It is advisable for the student to work out his own equations, but if a bookworm, he can look them all up in the literature.
The Teaching of Qualitative Analysis. When I studied qualitative analysis we used the translation of a book by one Remigius Fresenius, who became famous for his goad work in analysis. He directed that the material to be analyzed be first submitted to a preliminary examination. Shortly afterward, a teacher, I was blessed with a student called Porter W. Shimer, who soon distinguished himself in the same and other ways. When his course in qualitative analysis was a t an end, in advance of the other members of his class, I determined t o see how well he could work. To test him, I mixed some beer, sawdust, street sweepings, and several other like conglomerates, added a trace of arsenic and some other metals and handed them over. Some two days later he made a report showing that while he had identified all the anions and cations present, he had also detected the beer, the sawdust, and several other ingredients. It was a notable report for so young a man. I wonder how many students of this generation would do as well, and I wonder how many modern tents or teachers bother with prelidinary examinations. Is i t true that our modern teaching is degenerating and that our boys are losing everything- by losing that intimacy with their teachers which was so common then and so much less common now? We now have a JOURNAL OP CHEMICAI. EDUCATION and laboratories and lecture rooms such as were not then dreamed of, but are we any better or as well off as in the days when Mark Hopkins or Thomas M. Drown on one end of a bench and me on the other represented perfection? Methodism in teaching seems t o me like the heating of d r u m s s o u n d , 'but little sense. The good teacher has always been a good and kind man or woman who made friends with the youngsters. There was perfect equality and strenuous work-together. What generous soul can resist such a combination? And how impossible t o do without it. Prof. H. E. Armstrong's wonderfd paper in the Dec. 13th issue of Chem. & Ind. does not place too much emphasis upon the necessity of moral quality and real attainment in the teacher-and nothing else much matters. The old students who come back t o a lovable teacher, like the late Edgar F. Smith, know that nothing they can possibly give him is an adequate return for the benefits they have received. The impression seems to prevail in many quarters that research qualifications are all that matter much. I was surprised, therefore, to hear Prof. Bradley Stoughton, whose wonderful paper appears in the same issue, say that he thought - - . the most i m ~ o r t a n t occupation of a teacher was teaching. Boys and girls are easily led, but they must lave and resped their teacher before they can be led a t all.-Letter by Edward Hart i n Cormspondence of Chem. & Ind. ~
