A spectrophotometric method has been used to determ in e the di ssociation constants of o-chloroanilinium ion, m-n itroanili ni um ion , and 4-chloro-2,6-din itrophenol in methanolwater solvents at 25°C. The ranges of solvent composition s (in weigh t percent metha nol) were as foll ows: o-ehloroan ilinium ion , 0 to 99.9; ?n-nitroanilinium ion, 0 to 93.7; a nd 4-ehloro-2,6-dinitrophenol, 0 to 33.4. The 1)K of t h e first two ac ids f a lls with addition of methanol and passes through a minimum when the mole fraction of methanol in the solve nt mixture is abo ut 0.7 . The pI( of the substituted phenol, however, rises as the di electric constant of t he solvent is decreased by addition of m ethanol. It is suggested that the total m edium effect for both t y pes of acid can be explain ed by the superposit ion of an electrostatic e ffect and a non electrostatic effect. The latter is a constant for each particu lar s olvent co mposition and probably characterize's the acid-base proper t.v of the m ed ium itself.

Potassium p-phenolsulfonate is a good buffer for the pH range of 8.4 to 9.2 and for spectrophotometric studies of metacresolsulfonphthalein and thymolsulfonphthalein. Its useful pH range lies between those for borates and secondary phosphates and therefore fills an important gap. The purified product is not commercially available and quantitative tests for indicating its purity have not been reported. It was found t hat a pure product may be obtained after only three recrystallizations. A quantitative method of analysis by bromometric titration was developed. Two molecules of bromine react quantitatively with 1 molecule of p-phenolsulfonate in molar hydrochloric acid at 0° C within 5 minutes.Ultraviolet absorption spectra were obtained and showed differences between the primary and the secondary salt. The spectrophotometric data indicate that the sulfonate group is almost completely ionized in dilute solutions. CONTENTSPage

Spectral transmittancy values at room temperatures approximating 25° C were obtained for 1.25 X 10-5 M metacresolsulfonphthalein in water and in 0.001-to 8-M hydrochloric acid. In water the indicator exists in the yellow form (Y), and hydrogen ions (H) from acids convert it into the red form (R). The molar concentrations of each form of the indicator in various concentrations of hydrochloric acid were computed from the spectrophotometric data. The dissociation constant (Kb) for the reaction of the indicator with hydrochloric acid is given by the equation in which M and j, with appropriate subscripts, represent the molarities and activity coefficients, respectively. The value of Kb is 1.98 X 10-2 and that of -log Kb or pK2 is 1.703 ± 0.005. The indicator is useful over the pH range 0 to 3. CONTENTS Page

No abstract

The effect of temperature upon the absorption spectr~ in the ultravio. let an~ part of the visible ranges was determined for several c~mpounds Jl1 aqueo~ls SOlutlOll. 1 e m.p e r~ tures used were 10 0 , 25 0 , and 40 0 C. The 1l1~ten al s used as solu tes JI1cludedbot h morgalllc and organic compounds, namely, potassium I1ltrate, potassIUm dIChromate, d lpl;enylsulfon e, diphenyl phosphate, 4,4'-diaminobenzophenone! and. m-creso]sulfonphthalem. As the temperature ,yas dec reased there was a n IIlcrease 111 l?aXlmU1l1. absorbance of all compol:llds except i n the case of dip henyl phosphate, the behavlOr of .WhlC!"t was anomalous. A slJght s hift of the absorbance curves also occurred. The relatlOns hlp betwee n absorbance and temperature was not linear in the temperature range i~v es tigated. The results showed that temperature shou ld be controlled within ± 2 deg. C If molar .absorbance values are to .be obtained within 0.5 perce nt. T emperature coeffiClents for an llldlvldua.l compound req uIre extensive absorption m easurements of that compound III k~lown medIa, and such coefficients wi ll hold for the sp ecifi ed wavelengths only under speC Ifi ed condItIOns. As a general guide the temperature shou ld be controlled to ± 0.5 d eg C.