1. Cornells and Gille, of Liege, give a method of obtaining iodoform by adding to an alcoholic solution of iodide of potassium, heated to 104° C. (40° C.) hypochlorite of calcium in successive portions, stirring after each addition until the liquid no longer assumes a dark-red colour on the addition of a fresh portion of calcium hypochlorite (which is a sign that the process is completed). It is then allowed to cool, when the iodoform and calcium iodate crystallize out; the mass of Crystals are then treated with boiling alcohol of 90 per cent., which dissolves only the iodoform; this is largely deposited on the cooling of the alcohol.
The Following process: - Put 100 parts iodine in a comparatively long-necked flask or mattrass, add 100 parts bicarbonate of potassium, 1200 parts of distilled water, and 250 parts of alcohol; insert a cork through which passes a long glass tube; beat in a water-bath, not too quickly, to about 176° F. (80° C); and add, after decoloration of the liquid, 25 parts of iodine; then add 20 and afterwards 10 pnrts of iodine, waiting with each addition till the liquid has lost its brown colour. If iodine should happen to be a little in excess, add cautiously some solution of potash until decolorized, which shows completion of the process. Now poor the liquid into a porcelain dish, cover, and let stand 24 hours; throw on a filter, and wash the iodoform with cold distilled water. The iodoform which has separated is now spread on folds of bibulous paper and dried in the open air. Hager recommends to then evaporate the filtrate to dryness, calcine with charcoal, and extract the iodide of potassium with diluted alcohol. As this is quite troublesome to do, Wilder recommends to concentrate the filtrate by evaporation, and decompose the iodide and iodate of potassium with nitric acid in excess, whereby iodine is precipitated as a fine black powder, and washed with water.
As to the yield, Hager states the highest obtained by him to be 35 per cent. Wilder did not succeed in getting more than 28 per cent., the regained iodine amounting to 62 per cent., thus leaving 10 per cent, of iodine to be accounted for, which he thinks is partly due to the formation of iodide of ethyl; but he thinks 10 per cent, is too much, and probably to be ascribed to the small quantities he operated upon.
3. Filhol recommends the following process: - Put into a mattrass or flask similar to the one used in Bouchardat's process, a solution of 200 parts crystallized sodium carbonate and 1000 parts of distilled water, and add 100 parts of alcohol; heat in a water-bath at 140° to 160° F. (60° to 71° C), then gradually add 100 parts of iodine, about 10 parts at a time. When the liquid has become colourless, remove the flask from the water-bath, and allow to cool 3 or 4 hours, then pour out on a filter; return the filtrate to the flask, add 200 parts of carbonate of sodium, 100 parts of alcohol, heat to 160° F. (71° C), and pass a slow current of chlorine gas through the mixture as long as iodine is separated, continuing until the brown liquid is again decolorized. A small excess of chlorine is of no consequence (Hager states that for every 100 parts of iodine it requires the chlorine which can be evolved from about 200 parts of hydrochloric acid by means of manganese dioxide). Let the flask stand 24 hours, then throw the contents on a filter, and examine the filtrate with chlorine water to see whether it still contains an appreciable amount of iodine compounds; then if necessary subject the filtrate to a second treatment of chlorine gas, adding previously only 20 parts of carbonate of sodium and 10 parts of alcohol.
Collect the iodoform after 24 hours. The filtrate may be concentrated, and decomposed by excess of nitric acid, according to the method recommended in Bouchardat's process. The collected crystals of iodoform are now well washed with the smallest quantity of cold distilled water, spread out on pieces of bibulous paper, and dried in the open air. Respecting the yield, Hager says that with the utmost accuracy he did not obtain higher than 72 per cent, in two different operations he made. Wilder succeeded in getting 42 per cent, and 53 per cent., the regained iodine amounting to 40 per cent, and 35 per cent., thus leaving 18 per cent, and 12 per cent, unaccounted for. He makes the same remarks in regard to the ioding loss as he did in Bouchardat's process, which was that of working with too small quantities, and thinks that in working with proportionally larger quantities the loss will be less.
Bell tried the following experiments to test the different methods that had been proposed for the manufacture of iodoform: -
Bouchardat's process, as mentioned before. He used a round-bottomed flask, into the neck of which he inserted a cork through which was passed a long glass tube (§ in. in diameter and 3 ft. long) which acted as an inverted condenser. The flask was placed in a water-bath, and supported so that the tube was held in an upright position, thus condensing all the liquid volatilized, and allowing it to run back in the flask again.
He placed in the flask 5 grm. of iodine, 5 grm. of crystallized bicarbonate of potassium, 60 cc. of water, and 12.5 grm. of alcohol (95 per cent.), and heated in a water-bath between 140° and 176° F. (60° and 80° C), till the colour had disappeared, when 1.25 grm. of iodine was added, and the flask heated until the colour had disappeared a second time; then 1 grm. of iodine added, and heated until it was decolorized; then 5 grm. of iodine added, and again heated until decolorized. After the third addition of iodine (or 1 grm. lot), he found the crystallized bicarbonate of potassium used insufficient to decolorize the solution; so he added more of this salt (small portions at a time), until there had been added 3.848 grm., which completely decolorized the mixture.