A spectrophotometric study of the ferric thiocyanate system is reported. The temperature and ionicstrength of the solutions were carefully controlled, and suitable precautions were taken against fading. From the data, values of the equilibrium constant for the formation of FeSCN++ from simple ions, and of the extinction coefficients of FeSCN++ were obtained for different temperatures and ionic strengths, with results that differed somewhat from earlier values. The effect of varying acidity was also investigated. From more concentrated solutions, values for the equilibrium constants for the formation of Fe(SCN)Z+ and Fe(SCN)a were obtained; it was not necessary t o postulate higher complexes.Many investigations have been made of aqueous solutions containing ferric and thiocyanate ions, starting with the original work of Gladstone (9) just over a hundred years ago. However it was only comparatively recently that Moeller (15) and, independently, Bent and French (3) showed t h a t in dilute solution the color was due t o the ion FeSCN++. This put a new interpretation on the measurements made on this system, and as a result considerable further work was carried out (e.g. 6,7,10, 12,18). This work mostly made use of the red color a s a means of investigation, but some work was also done using solvent extractioil (14), or electrochemical methods (15).The present work was begun with the intention of using the red color of FeSCN++ as a method of determining the concentration of free ferric ions in solution, and hence of evaluating the equilibrium constants of the dissociation of other complexes formed by ferric ions with other anions. This type of investigation was made by Lanford and Iciehl (13) for the ferric phosphate system. Although earlier work covered a fair range of conditions, i t became apparent t h a t in order t o have an adequate picture of the system before adding other ions, i t would be desirable t o extend these measurements t o cover systematically a range of temperature, hydrogen ion concentration, and ionic strength. These factors were therefore carefully controlled; temperature control, for instance, was provided by using absorption cells completely immersed in a thermostatted tank. The fading which occurs in these solutions had also t o be talten into account, and it is believed conditions were found such t h a t fading was negligible. I t was also necessary t o talte into account the possible formation of the higher complexes, Fe(SCN)2+ and Fe(SCN)3; and it was in fact possible t o malte a moderately accurate estimate of the extent t o which these species were present, and so t o determine their dissociatioll constants. I n interpreting the experimental data, it is not necessary t o assume t h a t the extiilction coefficients a t various wave lengths were constant over a range of conditions; so that these experiments enable one t o find the effect of temperature and ionic strength on the extinction coefficients. The effect of hydrogen ion concentration was 'ilCa7tuscript received Jzote SO,...

Abstracti \ series of 1-substituted-2-nitramino-2-imidazolin have been prepared and nitrated in mixed-acid and nitric acid -acetic anhydride media. These compounds gave the corresponding 1-substituted-2-nitrimino-3-nitroinlidazolidines which proved to be quite stable. The hydrolysis products of some of these conipounds are described.The nitration studies ( 5 , 8) on 2-nitramino-2-imidazoline have been extended to 1-substituted-2-nitrai11ii10-2-iinidazoIiies. Tlle latter con~pounds on nitration give a new series of compounds, viz., 1-substituted-2-nitrimino-3-nitroimidazolidines.The compounds employed in the present investigation were prepared by the addition of l-ail1ino-3-azabutane, 1-amino-3-azapentane, l-amino-5-hydroxy-3-azapentane, I , 5-diamino-3-azapentane, and 1, 8-diamino-3,6-diazaoctane respectively to N-methyl-N-nitroso-N'-nitroguanidine (4, 6 , 7 ) . In all cases, cyclizations occurred t o give 1-substituted-2-nitramino-2-imidazolines. The reaction of l.-amino-5-hydroxy-3-azapentane with methylnitrosonitroguanidine may be represented as follows:HOCH2CHzNHCH?CI-IzNII? + CH3N(NO)C(NH)NHNO. ---+ NO?NO,

A spectrophotometric study of solutions containing ferric and sulphate ions, and also ferric, sulphate, and thiocyanate ions, is reported. T h e ineasurements were made a t constant temperature and ionic strength; the effect of varying acidity was also investigated. The data were interpreted with the help of the results of the first paper of this series. I t is believed that the data show t h a t FeS04+ and FeHS04++ ions are formed. Values are obtained for the equilibrium constants for their formation from simple ions, and for their extinction coefficients. A t higher sulphate concentrations there is evidence for the appearance of Fe(S04)2-and FeS04.HS04, and estimates are made of their equilibrium constants. When thiocyanate is also present, the data can best be interpreted by assuming that the complex FeSO4.SCN is formed, and a t higher sulphate probably also Fe(SO&SCN--. Values are obtained for the equilibrium constants for the formation of these species, and the results would indicate that mixed complexes of this type are formed as readily as 'simple' ones such a s Fe(SOi)?-. INTRODUCTIONOne of the possible methods for investigating the complexes of ferric ions is t o use thiocyanate as an indicator ion. I t is generally observed t h a t the red color of a ferric thiocyanate solutioil fades as another ion is added which also forms a complex with ferric ions; and by suitable colorimetric measurements it should be possible t o determine the equilibrium constant of the formation of this other complex. This method has been employed in a few investigations, e.g. by Lanford and Kiehl (6) using phosphate ions; and it was also used in effect by Bent and French (I) for chloride ions in their early paper on ferric thiocyanate. I n the latter case the equilibrium constant of the reaction Fe++++Cl-$ FeCl++, as obtained with the help of thiocyanate, differs from the result obtained directly without thiocyanate. This matter has been investigated b y the present authors, and will be reported in another paper. T h e present paper reports work on the application of this method t o ferric sulphate complexes. Investigations of the sulphate complexes have been described in two papers appearing since the present work was started, though in neither case was the thiocyanate ion used as indicator. The first paper by Sykes (9) reported measurements on the effect of sulphate ions on the kinetics of the reaction between ferric and iodide ions: Sykes concluded t h a t the equilibrium constant for FeS04+, had a value of 15,000 a t zero ionic strength. He did not investigate the ion FeHS04++. Whiteker and Davidson (10) in the second paper decided that FeHS04++ did not occur in significant amounts because of the rather small differences produced in the absorption spectra of ferric sulphate systems by alteration of the hydrogen ion concentration. On this basis they evaluated lManz~script received J u n e SO, 1966. Contribt~tio+t fro+lt the

A spectrophotometric study of solutions containing ferric and bromide ions; ferric, bromide, and thiocyanate ions; and ferric, chloride, and thiocyanate ions is reported. The measurements were made a t constant temperature and ionic strength. The data were interpreted with the help of the results from the first paper of this series. The data sho~v that FeBr++ and FeBrz+ are formed, and values are obtained for the equilibrium constants for their formation from simple ions, and for theextinction coefficients of FeBr++. When thiocyanate is also present, the data can best be interpreted by assuming that FeSCNBr+ or FeSCNCl+ is formed. A t high chloride concentrations it seems necessary t o postulate also FeC12+ and FeSCN.CI2. Estimates are made for the equilibrium constants for the formati011 of all these species from simple ions. As with the corresponding sulphate complexes, there seems to be no particular reluctance t o form mixed complexes such as FeSCNCI+, as compared with the 'simple' complexes such as FeC12+.In the second paper of this series ( 3 b ) , results were reported which showed that the color of ferric thiocyanate could only be used as a means of investigating complexes of ferric and sulphate ions, if allowance were made for the presence of species containing ferric, sulphate, and thiocyanate, such as FeS04 .SCN. The present work deals with a similar investigation of solutions containing chloride or bromide ions, instead of sulphate. The intention was t o make a critical examination of this method of investigating ferric complexes, and in particular t o discover t o what extent ternary complexes, such as FeSCN.Cl+ or FeSCN.Br+, were important. Rabinowitch and Stoclcmayer have already investigated solutions containing ferric and chloride or bromide ions, but not thiocyanate as well (6). They suggested that the discrepancy between their result for the equilibrium constant for the formation of FeCl++, and the earlier results of Bent and French (I), who examined solutions made from ferric chloride and potassium thiocyanate, was due t o the ion FeSCN.Cl+. The present work attempts a more quantitative estimate of the formation of this ion, and of the analogous FeSCN.Br+. I t is believed that the results demonstrate the existence of these ions, and values for the equilibrium coilstants of their formation from simple ions have been obtained. APPARATUS A N D MATERIALSAll optical measurements were made with a Beclcmann Model DU spectrophotometer, modified so t h a t the temperature of the solutions could be controlled, as described in the first paper of this series (3a).T h e reagents used were the same as described in this same paper, with the following additions.Hydrochloric acid.-The concentrated reagent grade acid was diluted t o give a stock solution of about 1 M concentration. This was standardized volumetrically against borax.'Manuscript