Takayoshi Yoshimori

Preparation of sulphamic acid single crystals and their assay by precise coulometric titration

Abstract Single crystals or sulphamic acid were grown from aqueous solution. The occluded and adsorbed water of the crystals prepared was measured, and the purities of the single crystals were determined by precise coulometric titration. Large single crystals more than 10 g in weight were readily prepared. The adsorbed water on the surface amounted to ca . 0.0004%. The purities of the small and the medium crystals were not satisfactory for primary standard use. However, the purity of the pieces obtained by dividing a large crystal and polishing the surfaces, was about 99.98%, with a standard deviation of about 0.015%. These large single crystals of sulphamic acid are recommended as a primary standard.

Drying and weighing of standard reference materials for titrimetric analysis, and the status of the faraday constant as an international standard.

A review is given of the methods of drying standard reference materials, and handling them after drying. The status of the Faraday as an international reference standard for titrimetric analysis is also discussed.

Coulometric determination of microamounts of hydrogen in metal

Hydrogen in metal was extracted into a carrier gas (argon) by heating at about 1100 degrees , and oxidized to water with copper(II) oxide. The water was converted into ammonia with sodium amide at 80 degrees . The ammonia was then titrated with electrolytically generated hypobromite ion. The blank value of single determination could be reduced to less than 1 mug of water. Hydrogen in stainless steels, tantalum metal and pure tin metal could be determined satisfactorily, and some results were compared with those obtained by the ordinary vacuum extraction method.

Investigation of manganese(III) fluoride for coulometric titration.

A study has been made of the use of electrogenerated manganese(III), in an electrolyte containing fluoride, for coulometric titration. The addition of fluoride prevented the deposition of manganese dioxide on the anode, and was responsible for increase of the current efficiency and for extension of the feasible range of current density, owing to complex formation between manganese(III) and fluoride. The bonding ratio, the apparent stability constant and the redox potential of the complex were also estimated from the Nernst equation and the current-potential curves.

Investigation on the drying and decomposition of sodium oxalate.

The drying of sodium oxalate at various temperatures was investigated by the micro-determination of the residual water in the heated sample and of the carbon monoxide produced by thermal decomposition. Sodium oxalate heated for 2hr above 200 degrees and cooled contains less than 20 ppm of water, and may be used as a standard for titrimetry. The decomposition of sodium oxalate into sodium carbonate and carbon monoxide was investigated by non-aqueous titrimetric micro-determination of carbon monoxide. The decomposition begins at 290 degrees and heating between 200 degrees and 250 degrees is recommended for the dehydration of sodium oxalate. The decomposition is complete between 750 degrees and 800 degrees within 20 min and the sodium carbonate obtained begins to decompose at above 810 degrees .

Coulometric investigation on the use of single crystals of sodium chloride as a primary standard

Abstract The use of single crystals of sodium chloride as a primary standard substance for argentimetry is described. The water on the surface and the purity of the crystal are measured by coulometric titration methods. The adsorbed water amounts to 0.48 μg cm −2 when the sample is dried in a desiccator containing magnesium perchlorate at room temperature for about 3 h. The loss in weight of the crystal is negligible when it is heated at about 600°. The purities of three crystals, by precise coulometric titrations, are 99,988,99.993 and 99.995%, with standard deviations of 0.0143, 0.0138 and 0.0124%, respectively. It can be concluded that the crystal is useful as a primary standard.

Purification of potassium dichromate and its assay by precise coulometric titration

Abstract Potassium dichromate was purified and crystallized by a zone-melting technique, and the purity of the crystal obtained was determined by precise coulometric titration. The dichromate obtained by zone melting was not a single crystal but lumpy material (aggregate of small crystals). The purity of the dichromate obtained by six zone passages in the upward or downward direction was 99.990 (s=0.015%). The water adsorbed on the surfaces of the lumpy crystals which were stored in a desiccator for 3.5 h was about 0.002%. The zone-melting technique is satisfactory for the purification of potassium dichromate and the purified crystals are suitable for use as a primary standard in titrimetric analysis.

Annotation: Drying conditions for potassium dichromate.

The optimum conditions for drying primary-standard or SRM grade potassium dichromate have been further examined, and it has been established that if organic impurities are present in the material the drying temperature should not exceed 200. At higher temperatures the organic matter is decomposed oxidatively by the dichromate, with a resultant error when the dichromate is used for standardization purposes.

Coulometric investigation of the conditions for drying bauxites for chemical analysis.

In order to dry a bauxite sample to constant weight for the determination of alumina content, the following procedure is recommended. The sample should be placed in a small flat weighing bottle and heated at 105-110 degrees for 5 hr in a dried atmosphere, then cooled in a desiccator containing magnesium perchlorate. After weighing, it should be reheated at 105-110 degrees for 40-60 min then cooled and weighed under the same conditions to ensure it has attained constant weight.

Coulometric investigation of the drying conditions of high-grade iron ores for chemical analysis.

Drying conditions for several iron ores have been investigated by the coulometric microdetermination of water. Samples, which were heated in an atmosphere of dry argon at 110 degrees for 3-4 hr and cooled, usually evolved less than 0.015% of water during a further 1 hr of heating. Therefore the difference in water content of the sample thus treated did not significantly influence the analytical results for total iron. Some magnetites and sintered pellet could be dried readily by heating for 2 hr in dry argon. Heating of samples of high water content for too long is not advisable as they may evolve some combined water.