Rex J. Robinson

Thermogravimetric analysis: temperature limits and rate of heating

Abstract In the case of the decomposition of carbonates and hydrates, the Polanyi-Wigner equation often applies. A mathematical expression relating the temperature at a given stage of the reaction to the rate of decomposition, fraction of reactant left, initial weight and area of the compound and finally the rate of heating has been derived from the above equation. For a given thermobalance the minimum detectable rate of decomposition and fraction of reactant left are fixed so that the observed final decomposition temperature is a function of the rate of heating for a constant weight and area of material. Using this equation, values for the final decomposition temperatures have been calculated and compared with data found in the literature for the decomposition of calcium carbonate and for the dehydration of potassium chrome alum and orthoboric acid. The equation also has been applied to the dehydration of 5-nitrobarbituric acid trihydrate as determined by us.

THERMOGRAVIMETRIC DETERMINATION OF MAGNESIUM, POTASSIUM AND LEAD BY PRECIPITATION WITH DILITURIC ACID

Abstract The thermolysis curves of magnesium, potassium, and lead diliturate have established that either the hydrated or anhydrous forms of these precipitates are stable enough for their gravimetric use to be possible. Magnesium and lead were determined by precipitation with dilituric acid while potassium was precipitated with trimethylamine diliturate.

A polarographic study of some complexes of molybdenum

Abstract The catalytic current due to the reduction of perchlorate by Mo (IV) or of nitrate by Mo(III) can be decreased by complexing these molybdenum species. When only one complex forms, the instability constant and the ratio of complexing agent to molybdenum can be evaluated. When the catalytic waves are completely suppressed, only the normal polarographic waves appear. The latter can be used to determine molybdenum quantitatively without the necessity of a calibration curve.

Thermogravimetric characteristics of barbituric acid and some of its derivatives

Abstract The thermolysis curves of barbituric acid and some of its derivatives have been determined. Barbituric acid, violuric acid and dilituric acid form hydrates while 1,3-dimethylvioluric acid and barbital are anhydrous. Barbital and 1,3-dimethylvioluric acid sublime before decomposition. The differential thermal analysis for dilituric acid showed a sharp exotherm at 190° indicating a violent explosion.

Thermogravimetric investigation of the alkali metal diliturates

Abstract Thermolysis curves for lithium, sodium and cesium diliturates have been obtained. Lithium and sodium diliturates form monohydrates from aqueous solutions while potassium, rubidium, and cesium, diliturates are anhydrous. The cesium and rubidium diliturates form rapidly, are quite dense, and easily handled. Both diliturates are thermally stable to about 300°. Methods for the thermogravimetric determination of rubidium and, cesium have been developed and found to be quite accurate.

Thermogravimetric determination of ethylenediamine and quinine with dilituric acid: Solubilities of some polymethylenediamine diliturates

Abstract The thermolysis curves of ethylenediamine, trimethylenediamine, tetramethylenediamine pentamethylenediamine, trimethylamine and quinine diliturates were determined. These curves established that (either the hydrated or the anhydrous form of ethylenediamine and quinine diliturate is stable enough for their gravimetric use to be possible. Both ethylenediamine and quinine were determined by precipitation with alcoholic dilituric acid .solution. In addition the solubilities of some polymethylenediamine diliturates were determined.

The spectrophotometric determination of the ionisation constants of some derivatives of barbituric acid

Abstract The ionisation constants of dilituric acid (5-nitrobarbituric acid), violuric acid (5-isonitrosobarbituric acid) and 1,3-dimethylvioluric acid (1,3-dimethyl-5-isonitrosobarbituric acid) have been determined by measuring the variation of absorbance with pH. The spectrophotometric method offers a practical means of determining the dissociation constants of substances that ionise with a detectable change in their absorption spectra with change in pH.

Thermogravimetric investigation of the alkaline earth diliturates

Abstract Thermolysis curves for calcium, strontium and barium diliturates were obtained. Calcium dilituratc forms an octahydrate from aqueous solution while strontium, dilituratc forms a. heptahydrate and barium diliturate forms a tetrahydrate. Methods for the thermogravimetrie determination of strontium and barium were developed and found to be quite accurate; calcium can only be determined semi-qnartitatively by precipitation as the diliturate salt.

Thermogravimetric and magnetic characteristics of some inorganic salts of dilituric acid

Abstract The thermolysis curves of the transition metal diliturates as well as those of copper, zinc, cadmium, ammonium and rubidium have been determined. These diliturates with the exception of ammonium and rubidium diliturates form hydrates. The oxides of the corresponding metals are obtained at relatively low temperatures. Magnetic susceptibility measurements show that these compounds are “essentially ionic” salts.

A spectrophotometric study of the iron(iii)-phenol reaction

Abstract Iron(III) reacts with phenol to form a weakly associated complex in the ratio of 1:1. The weak association of iron(III) with phenol necessitates a correction for significant interference by dimerization of iron (III) due to hydrolysis, particularly at pH 1.4 and 2.0. It seems probable that a slower secondary reaction between iron(III) and phenol proceeds with the formation of iron(II) and a phenolic oxidation.