Feb., 1942
FERRIC ION
&ACTION
WITH ORTHOPHOSPHATE AND
THIOCYANATE
291
TABLE VI1 DIPOLE MOMENTS PER MONOMER UNIT
summary 1. Data a t 40 and 60°, a t 60, 600 and 6000 P c P P cycles are given for polyvinyl chloride plasticized Distyrene 1,2-Diphenylethane with 8 to 30% by weight of the following com19.9 2.17 19.8 2.16 pounds : tetralin, diphenylmethane, diphenyl22.8 2.16 23.2 2.16 25.6 2.16 26.0 2.13 methylmethane, dibenzyl, amylnaphthalene, di2.05 28.6 styrene, di-a-methylstyrene, diphenoxyethane, Diphenylmethane Tetralin dibenzyl ketone, dibenzyl maleate, dibenzyl 19.8 2.17 19.3 2.21 succinate, dibenzyl phthalate, dibenzyl sebacate 22.7 2.16 22.3 2.22 and dioctyl phthalate. 25.8 2.16 25.2 2.20 2. Plasticization is essentially a separation of 28.8 2.15 28.3 2.20 chain molecules by the plasticizer molecules, ac1,I-Diphenylethane Amylnaphthalene companied by a rapid decrease in microscopic 19.9 2.16 23.0 2.13 22.8 2.16 25.9 2.12 and macroscopic coefficients of friction. 25.9 2.13 29.0 2.11 3. A simple empirical relationship connecting 28.8 2.13 loss factor and plasticizer concentration is given. In order to give some information on the influ- Very roughly, the viscosity varies inversely as the ence of plasticizer on polar properties, in the last third or fourth power of the relative concentracolumn of Table VI are given values of the static tion, depending on the temperature. dielectric constants at 60’ for 25% plasticizer. 4. The concentration a t which a given plasThese are values obtained by interpolation on an ticizer produces a given internal viscosity, as 6 0 - p plot, for which the eo values were obtained by measured by a characteristic electrical response, the Cole extrapolation. It will be noted that eo is depends on the size and shape of the plasticizer larger for the polar plasticizers than for the hydro- molecule. A long cylindrical molecule is more carbons, which average to EO = 8.3. Diphenoxy- effective in reducing viscosity than a spherical ethane comes somewhat higher, due to the polarity molecule of the same molecular weight. of the oxygens, and the esters are still higher. Di5. Plasticizers of about the same size and shape benzyl sebacate is low, because the molecule con- are about equally effective as plasticizers, regardtains a lot of non-polar methylenes, and dibenzyl less of their chemical structure. For polyvinyl ketone is highest. A very definite parallelism be- chloride, however, a polar or polarizable group tween the static dielectric constant a t a given tem- must be present in the plasticizer in order for it perature and composition, and the relative dipole to interact with the polymer. content of the plasticizer molecule is thus observed. SCHENECTADY, N. Y. RECEIVED NOVEMBER 8, 1941 [CONTRIBUTION FROM THE
DEPARTMENTS OF CHEMISTRY, NEWYORK UNIVERSITY ]
STATE COLLEGE FOR
TEACHERS, AND
COLUMBIA
A Study of the Reaction of Ferric Ion with Orthophosphate in Acid Solution with Thiocyanate as an Indicator for Ferric Ions BY OSCARE. LANFORD AND SAMUEL J. KIEHL
Introduction It is well known that the addition of orthophosphoric acid to an acid solution of a ferric salt produces an extensive decrease in the activity of the ferric ions. This property probably constitutes the fundamental principle in the effectiveness of the Zimmerman-Reinhardt “Preventive Solution.”’V2 Beyond this, however, little is known
concerning the reaction of ferric ions with phosphate. Therefore, to ascertain its nature and to discover, if possible, the type and formula of the complex formed, the present investigation was undertaken. By the method used we were able not only to establish the reaction
775 (1881); Chcm. Zfg.,
but also to determine the dissociation constant of FeHPOc+, the ferric phosphate complex formed. The method suggested by the recent
( 1 ) Zimmerman and Reinhardt, Be?., 14,
13, 323 (1889). (2) H. A. Fales and F. Kenny, “Inorganic Quantitative Analysis,” The Century Company, New York, N.Y.,1939, p. 426.
Fe+++
+ HPOr‘
FeHPO,+
(1)
vmrli of Bent and French" by means of which this information was obtaincd, is based upon the use oi thiocyanate ion as an indicator for ferric ion. Moreover, these authors have demonstrated that the red color produced on the addition of sodium thiocyanate to a so!utwn of a ferric salt is due to the formation oi tht. iciti FeCSS * 7 . In addition they determined its dissociation constant. Further, the 1;cCXiS t - + iori itself has certain properties uhich make it well suited as an indicator for ferric ion in certain cases: uiz., it is relatively highly dissociated (its dissociation constant IS of about the same magnitude as the first dissociation constant of phosphoric acid) ; and its color is so intense that one may accurately ascertain its cnncentratioii rolorimetrically when relatively small quantities are present. 'l'hus, with a visual spectrophotometer the concentration of Irrric thiocyanate, even if the amount is considcraly less than 5 x IO-*' m./i., may be established :rith an accuracy better than 13,. The Ratio of Iron and Phosphorus in the Complex.---The ratio iit iron phosphorus in the icrric ph,)sphatt; wmiplex r a s determined by the method of contirwous variations, prOpOSCd and publishrd by Job i n !LIBF;,' Accordingly, solutic,iis of ferric nitrate and phosphoric acid were nii.iecl 111 x-arying iatios so that the sum of the 111( *le5 of Et rrrr nit rat c arid phosphoric acid was tistant throughtiiit tlie series r j i solutions. The iirial vdurnt ( d the sdutinns was also constant. 1 lit. lerric m r i COIL(eritration in each of these solutims was deterniinect eulorinietrically by use of iii
