A method was developed for direct analysis of organic materials in aqueous solutions based on thermal fragmentation followed by gaschromatographic separation and detection of the resulting derivative compositions. Such thermal fragmentation processes were found to be quantitatively linear, i.e., response is proportional to concentration, and independent for each organic compound in a mixture. In addition, the pyrographic pattern produced by a mixture of organic compounds is a simple arithmetic summation of contributing patterns of each compound present. A recorded pattern of pyrolytically produced fragments for a given water sample reflects the total nature of its organic composition, and can be interpreted and differentiated in a number of ways. Using a priori established calibration patterns for individual components to be found in a mixture, the pattern produced by a mixture can be analyzed mathematically. The system can be calibrated in terms of pure organic compounds, classes of organic materials, or any other arbitrarily defined organic mixtures such as those found in industrial waste effluents. The practical hydrochemical methodology, which was developed as a result of this effort, comprises analytical and data processing hardware, mathematical logic, and computer procedures and programs for data analysis and interpretation. The instrumentation was designed and assembles in a unitized package, and required only electrical and telephone lines for its operation. The Mark 1 prototype instrument was tested in a trailer under field conditions of operation for 2 years. An automated Mark 2 instrument was fabricated. The practical utilization of this new hydrochemical tool was studied in three areas : water pollution surveillance, waste treatment processes, and characterization of natural unpolluted water.