Abstract: Methods and apparatus for measuring the concentration of decomposable substances, such as urea, are disclosed. The disclosed methods include adding a gaseous buffer, such as CO2, to the solution containing the decomposable compound, measuring the conductivity of the solution, decomposing the decomposable compound, measuring the conductivity of the thus-decomposed compound solution, and calculating the differential conductivities between the two measured solutions. The apparatus for carrying out these methods are also disclosed.

Abstract: Methods and apparatus for measuring electrical parameters of a test fluid are disclosed. The methods include maintaining the test fluid and a reference fluid at the same temperature and in thermal proximity to each other, equalizing the temperature of the test fluid and the reference fluid prior to the measuring step, measuring the electrical parameter of the test fluid and the reference fluid at substantially the same time, and standardizing the measurement to a predetermined temperature. The apparatus includes a heat exchanger for maintaining the flow of a primary heat exchange fluid in thermal proximity to the test fluid in the reference fluid, and a metal wall having one surface in contact with a measuring cell and another surface in contact with the flow of the primary heat exchange fluid whereby the measuring cell and the heat exchanger are separated thereby.

Abstract: Methods and apparatus for measuring the concentration of decomposable substances, such as urea, are disclosed. The disclosed methods include adding a gaseous buffer, such as CO.sub.2, to the solution containing the decomposable compound, measuring the conductivity of the solution, decomposing the decomposable compound, measuring the conductivity of the thus-decomposed compound solution, and calculating the differential conductivities between the two measured solutions. The apparatus for carrying out these methods are also disclosed.

Abstract: A fiber preform having a web and at least one flange has fibers disposed in the web such that each follows a zig-zag path and is interlocked with the fibers of the flange. A manufacturing method for the preform includes interlocking the web yarns with those of the flange and engaging the web yarns at a plurality of points spaced longitudinally of the prefrom and also spaced from the flange in the direction of the web to define the required web dimension.