Published Weekly. Annual Subscription free sy post £1. Entered at the New York Post Office as Second Class Mail Matter Determination of Hydrogen, Nitrogen, and Methane in Gas by ARTICLES: Criticism of a Recent Contribution to the Theory of Indicators, by A. G. A. Miller Preliminary Note on a New Method for the Direct Determination of Rubber, by L. G. Wesson Potassium Permanganate in the Quantitative Estimation of some A Representation of the Chemical Elements by means of Points in Ordinary Space, by Arnaldo Piutti Electrodeposition of Tin, by E, F Kern... NOTICES OF Books ....... MISCELLANEOUS... The Scientific Week CHEMICAL NOTICES FROM FOREIGN SOURCES TEN POUNDS will be given to the first person who can show that there is something radically wrong with the proof that the valencies of carbon are unequal, as demonstrated by 188 molecules in two books (price is. 3d. each post free) which can be obtained from Messrs. MORTON and BURT, 187, Edgware Road, London, W. 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CRITICISM OF A RECENT CONTRIBUTION TO action, any addition of ammonium salts (ammonium ions) THE THEORY OF INDICATORS. By ARTHUR G. A. MILLER. B.Sc. (Lond.), F.C.S. In a recent contribution to the theory of indicators (Dr. J. Waddell, CHEMICAL News, 1913, cvii., 206), the author states that, according to the ordinary theory of indicators, it is strange that methyl-orange, a strong acid, should act towards weak acids, as phenolphthalein, a weak acid, acts towards weak bases, and that the anomaly is removed if methyl-orange is considered to be a weak base instead of a strong acid. The author appears to have based his conclusion upon purely physico chemical considerations, without having due regard to the question of the chemical constitution of the indicator, which is now generally admitted to play a most important part. Indeed, many chemists are strongly of the opinion that the two views are complementary, and experimental evidence seems to confirm this. Indicators are now regarded, not as a true, but as pseudo acids or bases (so-called by Hantzsch), and that the undissociated molecule is really a mixture of one or more tautomeric forms in equilibrium, only one of which ionises to a considerable extent (see H. T. Lizard, B.A. Reports, 1911, p. 268). Thus, on the old theory, it was considered that phenolphthalein behaved as follows: must diminish the concentration of hydroxyl ions in order to preserve equilibrium, and with corresponding increase of hydrogen ion concentration Configuration I. becomes the Chemical evidence is not lacking in support of the statestable one; that is, the solution becomes colourless. ment that tautomerism exists. In the case of phenolphthalein the red colour is destroyed on the addition of alcohol or acetone, and this is undoubtedly due to ionisation change. On the other hand, the dry salts of the indicator are red, and, further, a coloured quinonoïd carboxylic methyl ester has been isolated; in these cases there can be clearly no question of ionisation. Both explanations are thus accounted for in dealing with the colour change of phenolphthalein. one which has both acidic and basic groupings in the moleComing now to the case of an amphoteric indicator (i.e., cule) such as methyl-orange, its sodium salt, NaSO3C6H4N = NC6H4N(CH3)2, is yellow, while the free acid is violet. It seemed very probable that the strongly acidic sulphonic group was modified by the basic aminic group, and accordingly Hewitt (Analyst, 1908, xxxiii., 85) assigned to the free acid in the solid condition, or in acid solution, the constitution of an internal salt. Thus, -C6H4.NH.N-C6H4= N(CH3)2 Addition of hydrogen ions will diminish the dissociation and produce the internal quinonoïd configuration, while, on the other hand, the addition of even a weak base will remove hydrogen ions, and the yellow colour due to the azoïd ions will appear. There is, again, chemical evidence for the assumption that tautomerism exists in this case. Thus the sodium salt of methyl-orange has the wellknown orange-yellow colour, and it has been shown that the dry silver salt has the same violet colour as the free "acid." Clearly here there is no case of ionic dissociation, and it is naturally concluded that the free acid of methylorange can exist in tautomeric forms. One has now to explain the behaviour of methyl orange to a weak acid such as acetic acid. Consider an indicator which is a weak acid (methyl orange is relatively weak in comparison with a strong mineral acid), and let its degree of ionisation in solution be a. Appling Ostwald's law of dilution one has Kx concentration of undissociated molecules = concentration of dissociated molecules x concentration of hydrogen ions, NEWS where K is the dissociation constant of the indicator. The | through the solution to saturation. Dr. Waddell points out that the sulphonic group is strongly acidic, but acting against this is the aminic group, conferring a basic character which is accentuated in the sodium compound. There is, however, no doubt that the acidic character of the molecule predominates. At the same time, it is believed that the basic character of the aminic group very largely influences the sensitiveness of the indicator to hydrogen ions. Thus dimethyl-a-naphthylamine is more basic in character than dimethylaniline, and the author of this communication found that an indicator prepared by coupling the former substance with diazotised sulphanilic acid was more sensitive to hydrogen ions than methyl-orange. On the other hand, diphenylamine is almost non-basic in character, and the azo-compound made by coupling it with diazotised sulphanilic acid was found to require a considerable concentration of hydrogen ions to effect a noticeable colour change. Finally, Dr. Waddell stated that he believed if almost dry hydrochloric acid was passed into an alcoholic solution of methyl orange the colour of the solution would still remain yellow. The experiment has been carried out using a solution of methyl-orange in absolute alcohol, but there was an immediate red coloration produced owing to the fact that hydrochloric acid, one of the strongest acids, can exert its power of ionisation even in the presence of absolute alcohol. Thus it seems as if the theory of indicators accepted at the present time is in complete accord with the behaviour of methyl-orange, and that Dr. Waddell's views regarding the yellow sodium salt of methyl-orange as being undissociated in solution, and the red colour produced by the addition of acids is due to the dissociated cation are untenable. PRELIMINARY NOTE ON A NEW METHOD FOR THE chief difficulty that has stood in the way of the direct The procedure, in brief, consists in allowing the acetoneextracted sample to dissolve or swell up in carbon tetrachloride, after which nitrous gases, evolved by dropping HNO3 on As2O3, form the nitrosite of rubber by passing Paper presented at the Annual Meeting of the American Chemical Society, Milwaukee, March, 1913. (Published by permission of the Director of the Bureau of Standards). From journal of Industrial and Engineering Chemistry, v., No. 5. 1913 After standing, the now soluble nitrosite is dissolved in acetone, from which it is obtained in a form ready for combustion by a method of precipitation or evaporation. The details of both of these methods are being studied to eliminate known sources of error and to further simplify the manipulation. The tediousness of the latter has been considerably relieved by the development of a durable electric organic combustion furnace adapted for this work. It consists of a tube of Jena glass 60 cm. long and 2 cm. bore, containing a coil of electrically heated platinum wire, and a boat of lead peroxide and minium heated by an external coil of nichrome wire. Two heavy copper wires, coated with iridium and pushed through the one-holed rubber stopper at the forward end of the tube, solve, in a convenient manner, the problem of making an external contact for the useful directly heated catalyser coil. The leads for the coil simply rest on the hooked ends of these wires, thus permitting an easy removal and replacement of the stopper, the coil, or the lead peroxide boat which rests between the coil and the stopper. It is thought that, with a few modifications, this form of furnace is adapted for general organic combustions, and it will be tested soon with that end in view. The use of the lead peroxide boat which absorbs the sulphur of the nitrosite as lead sulphate, should give a means for the estimation of the sulphur of vulcanisation, if, as Alexander emphatically asserts (Ber., xl., 1077; Zeit. Angew. Chem., xx., 1364; xxiv., 687), the sulphur combined with the rubber is carried quantitatively into its nitrosite. The following figures have been obtained by the use of either the precipitation or evaporation methods:A washed and dried fine para, precipitated once from chloroform, dried to constant weight in hydrogen at 92o, and analysed as 99.1 per cent carbon plus hydrogen, gave 99'5, 98.7, 97.8, 980, 971, and 96.6 per cent C10H16. A washed and dried fine para gave 95'7, 94'7, 948, 95°2, and 95.5 per cent C10H16. A rubber compound containing litharge, whiting, barytes, zinc oxide, sulphur, and 48 per cent para, or 45 4 per cent rubber, gave 45'3, 46'4, 48'7, 47°2, and 45.6 per cent C10H16. Another containing the same ingredients with the addition of paraffin, with 28.6 per cent fine para or 27.8 per cent rubber, gave 27'5, 27'4, 27'7, 267, 27°1, and 26.9 per cent C10H16. These results, however, represent only those that have been obtained under the best conditions, and are not subject to the numerous sources of error that have continually appeared. They seem to be of sufficient value to justify putting on record at this time. Further work should give a greater reliability and accuracy, in which case full details of the method and apparatus will be published. POTASSIUM PERMANGANATE IN By C. M. PENCE. POTASSIUM permanganate has been most generally used in the volumetric estimation of iron. Some uncertainties formerly existed since it was impossible to obtain a chemically pure article, and insufficient data were at hand as to proper methods of preparation and standardisation of its solutions. At present these objections have been largely overcome, and almost all of our text-books on quantitative analysis contain an extended treatise on proper means of preparation and standardisation of volumetric permanganate solutions. Read before the Indiana Section of the American Chemical Society. From the Journal of Industrial and Engineering Chemistry, v., No. 3. CHEMICAL NEWS, Potassium Permanganate in Estimation of Organic Compounds. One of the most commonly known organic compounds that is quantitatively determined by the use of volumetric permanganate is oxalic acid. Now oxalic acid and iron are determined in acid solution, but the procedure most applicable for the oxidation of all types of aromatic compounds as well as carbohydrates and hydrocarbons is with alkaline permanganate. Oxidations in acid solution are less energetic than those with alkaline KMnO4, and in the latter case the final product of a completed decomposition of the organic compound is oxalic acid instead of CO2 and H2O. Among the substances mentioned in the literature (see Note) as being oxidised to oxalic acid are propylene, isobutylene, amylene, acetone, fatty acids; butyric, lactic, succinic, and tartaric acids; dextrose, sucrose, glycerol, and phenol. Now when an organic compound is oxidised to oxalic acid, a further oxidation to CO2 and H2O readily follows upon acidifying and warming the solution. Such a procedure forms the nucleus of a method for the determination of the compounds previously enumerated. Tocher | made use of this method, and found that phenol could be determined. His method was substantially as follows:Dissolve 1 grm. phenol in 1000 cc. distilled water, and take 10 cc. for titration. Add 3 to 4_grms. NaHCO3 together with a little distilled water. Then add 50 cc. KMnO4, and boil for five minutes. Set aside to cool, and gradually add dilute H2SO4 to decided excess; warm to 60° C., and titrate the excess of N/10 KMnO4 with N/10 Oxalic acid. (NOTE. "Oxidation of organic Compounds with Alkaline Permanganate," Eduard Donath and Hugo Ditz, Journ. Prakt. Chem., 1899, [2], lx., 566; through Fourn. Chem. Soc., 1900, [1], lxxviii., 197; "Contribution to the Knowledge and Determination of the Carbohydrates," J. Konig, W. Greifenhagen, and A. Scholl, Zeit. Nahr. Genussm., xxii., 705; through Abstr. Journ. Am. Chem. Soc., 1912, vi., 901; "Volumetric Determination of Phenol," Jas. F. Tocher, Pharm. Journ., lxvi., 360). : This method was found to be open to the following objection :-That the manganese dioxide formed as a result of the action of N/10 KMnO4 upon the phenol did not reduce readily enough with consequent solution upon direct titration with N/10 oxalic acid. Thus the solution was full of oxide which not only obscured but rendered the endpoint of little value, in that the oxide was not completely reduced before the permanganate end-point was obtained. The following modification of Tocher's method was found to give good results : Dissolve o'4 grm. phenol in 1000 cc. distilled water. Place 50 cc. N/Io KMnO4 and 3 to 4 grms. NaHCO3 in a 500 cc. glass-stoppered Erlenmeyer flask. Add 25 cc. of the phenol solution with gentle rotation. Boil five to ten minutes (with stopper removed). Cool flask to about Acidify with dilute H2SO4, let stand about two minutes; cool to room temperature. Dilute with distilled 60° C. water, add 5 cc. 20 per cent KI, and titrate the liberated iodine with N/10 thiosulphate solution, using starch as indicator. The number of cc. of N/10 thiosulphate sub tracted from the number of cc. KMnO4 originally added No. cc. of KMnO4 consumed by the phenol. I cc. N/10 KMnO4 = 0·000336 grm. phenol. If a glass-stoppered Erlenmeyer flask is not available an ordinary Erlenmeyer may be used, and its contents transferred to a glass-stoppered bottle before acidifying. oxide adhering to the Erlenmeyer is easily removed by the addition of a little distilled water acidified with H2SO4, and containing a few drops of 20 per cent KI. Any In considering the nature of the oxidation with KMnO4 in acid and alkaline solutions it is observed that each molecule of KMnO4 in acid solution liberates 2.5 atoms of oxygen according to the following equation : 75 Now in alkaline solutions the two molecules of MnO are immediately oxidised to 2MnO2 at the expense of 2 atoms of oxygen, so that we actually have 2KMnO4 = K20 2MnO2 +30. Hence, for each molecule of KMnO4 used, only 1 atoms of oxygen are available for our oxidation process. This fact must be recognised in providing sufficient KMnO4 to readily complete the oxida tion process, and it would necessarily enter into a calculation of the value of N/10 KMnO4 in terms of phenol if the MnO2, or rather its hydrated form, were filtered from the solution before acidifying and adding the KI. But since the procedure is not lengthened by a filtration the MnO2 is reduced to its manganous form with the liberation of free iodine, and we must calculate our factor by considering that reaction proceeds as in acid solution with 2.5 atoms of oxygen available per molecule of KMnO4, although such is not literally the truth. To completely oxidise phenol, 14 atoms of oxygen are required, according to the following equation:C6H5OH + 140 = 6CO2+3H2O. Since only 2.5 atoms of oxygen are available per molecule of KMnO4 then 5.6 molecules of KMnO4 would be required for every molecule of phenol, and the factor for N/10 KMnO4 in terms of phenol becomes :Mol. wt. phenol 2.5 X 2 X 10 X 5.6 x 1000 Experiments with a phenol solution containing 0.0005 grm. of phenol per cc., as determined by the Koppeschaar bromine method, resulted as follows: Ex. No. I. 2. 3. 4. 5. 6. Grm. phenol taken. Per cent phenol found. 0.0050 0.0050 0'0075 0'0076 Ο ΟΙΟΟ Ο ΟΙΟΟ Now, when the cresols were run in the same manner as phenol it was found that they were oxidised and that they varied slightly as to the rate with not completely which oxidation proceeded; hence, any permanganate method for their accurate determination must depend upon definitely fixed conditions. Likewise, it was obvious that commercial creosote and guaiacol could not be determined by this procedure, since they are mixtures of several more or less related phenols that are not present in like proportion in different specimens. However, with single solutions of several common phenols and closely related compounds, fairly gratifying results were obtained. Pyrogallol, pyrocatechin, resorcinol, and hydroquinone, from all of which the CH3 group is absent, were readily and completely oxidised. Benzoic acid was very slightly attacked, while under similar conditions salicylic acid and salol were completely oxidised. Thus it would seem that the phenolic OH group predisposes towards a complete oxidation, and that many uninvestigated phenols and closely related compounds would give analogous reactions. In making up solutions of the several phenols, sufficient N/2 NaOH was added when necessary, to ensure ready solution. The following table is self-explanatory :: The alkaline permanganate method is especially applicable for the quantitative estimation of the above compounds when they occur individually in very small amounts in single solutions, or in conjunction with substances not readily oxidised, |