Abstract: Nitrates, such as alkali metal nitrates and ammonium nitrate, are electrolytically reduced to the corresponding nitrites by a process wherein an aqueous solution containing a nitrate is supplied into a cathode chamber of an electrolytic cell including cathode and anode chambers separated by a cation exchange membrane and an electric current is applied to the electrolytic cell, while maintaining the pH of the aqueous solution at a value of at least about 4. This process can be advantageously applied not only to the manufacture of nitrites but, also, to the treatment of waste nitrates. In the treatment of waste ammonium nitrate, the ammonium nitrite so formed is conveniently further treated by subjecting the electrolytically reduced catholyte to thermal decomposition outside the electrolytic cell, and removing the so formed nitrogen and water from the reaction system.

Abstract: A method of producing an electrode by applying onto a core material a solution of at least one metal salt and subjecting the resultant core material to a heat treatment in a heating zone, characterized in that said heat treatment comprises continuously elevating the temperature of the resultant core material to a temperature of about 400.degree. to 700.degree. C. over a period of about 5 minutes to 2 hours, while blowing air into the heating zone to obtain a coated electrode. The coated electrode produced according to the method of the present invention is excellent in adherence of the coating to the core material and has long life due to low losses of the coating during use.

Abstract: A liquid level detector for detecting whether a boundary surface between a liquid and a medium rises beyond a prescribed level comprises a rectangular prismatic refractor body formed of a material which only allows the transmission of a light having particular wavelengths and absorbs light having other wavelengths. The refractor body have first and second inclined flat surfaces and a base. The base of the refractor body is provided with a light-emitting element for projecting a beam of light having the particular wavelength and a photoelectric conversion element for converting the light to an electric signal. Each of these element is equidistantly spaced from the center of the base, and the optical axis of each of these elements defines an angle of 45.degree. with each of the inclined surfaces of the refractor body.

Abstract: A sodium chloride feed solution containing an iron cyanide complex is subjected to purification to reduce the content of iron cyanide complex to not more than 0.5 ppm before it is fed as anolyte into an ion-exchange membrane electrolytic cell. The iron cyanide complex is preferably converted by oxidative decomposition to iron ions for removal. By use of such a purified sodium chloride as starting material, electrolysis of sodium chloride using an ion-exchange membrane can be performed for a long term at a constant electrolysis voltage.

Abstract: A packing for use in a steel-pipe hydraulic testing apparatus, consisting of: an annular body having an annular cut in its inner peripheral portion; a plurality of backing pieces fastened to the wall of the annular cut at a given circumferential spacing and directed in the radial direction; and a plurality of adapter pieces embedded in the inner peripheral walls of the annular body of the packing at a given circumferential spacing and exposed to the annular cut, so that the aforesaid plurality of backing pieces may be each slidable on the surfaces of a pair of adjoining adapter pieces. This packing is contracted due to a hydraulic pressure being applied to the outer periphery of the body of the packing, and as a result the respective adapter pieces will slide on the surfaces of the adapter pieces in the circumferential direction of the packing.

Abstract: A packing for use in a steel-pipe hydraulic testing apparatus, consisting of: an annular body having an annular cut in its inner peripheral portion; a plurality of backing pieces fastened to the wall of the annular cut at a given circumferential spacing and directed in the radial direction; and a plurality of adapter pieces embedded in the inner peripheral walls of the annular body of the packing at a given circumferential spacing and exposed to the annular cut, so that the aforesaid plurality of backing pieces may be each slidable on the surfaces of a pair of adjoining adapter pieces. This packing is contracted due to a hydraulic pressure being applied to the outer periphery of the body of the packing, and as a result the respective adapter pieces will slide on the surfaces of the adapter pieces in the circumferential direction of the packing.

Abstract: A solid solution of a noble metal oxide, titanium oxide and zirconium oxide, containing 1 to 50 mol % of titanium oxide and zirconium oxide as the total content, is coated on an anti-corrosive substrate, e.g. titanium metal to give an electrode which is excellent in low oxygen content in chlorine gas, low electrode consumption and low chlorine overvoltage when it is used as anode for electrolysis of an aqueous sodium chloride solution.