Abstract: An optical fiber apparatus measures an external parameter, such as temperature, at any of a number of different locations using time-domain reflectometry techniques. Sensor devices, each comprising a chip or plate of ruby glass, are interconnected by optical fibers. A laser launches along the fiber string short pulses of light at a first wavelength on the absorption edge of the ruby glass and a second wavelength in the transmission region away from the edge. A timer controls sampling circuits to measure backscattered energy at each wavelength at spaced times corresponding to spaced points along the fiber on opposite sides of a selected sensor device. A processor calculates the absorption loss in the sensor device at each wavelength by comparing the backscattered energy from the two points on opposite sides of the device, and calculates the differential absorption loss by comparing the losses at the two wavelengths. Embodiments employing a wedge shaped absorber are used to measure displacement.

Abstract: Oxide deposits containing chromium are dissolved by contacting the deposits sequentially with(i) a permanganate salt in acid solution to remove chromium therefrom as hexavalent chromium;(ii) a reducing agent in acid solution to destroy excess permanganate ions and manganese dioxide formed by reduction of the permanganate; and(iii) a mixture of a reducing agent and complexing acid to dissolve the residual chromium depleted oxide.

Abstract: A method for the quantitative determination of a chemical species capable of promoting the disproportionation of Hg.sub.2.sup.2+ to Hg.sup.2+ and Hg.degree. in solution which method comprises causing the species to react with a solution comprising Hg.sub.2.sup.2+ to thereby produce a measurable concentration of Hg.degree. in a gaseous phase above the solution, and determining the Hg.degree. present in the said gaseous phase.The method is particularly applicable to the determination of low concentrations (e.g. as low as 0.1 p.p.b.) of SO.sub.2 in gas mixtures, such as air.