The thermal decomposition of acetylene to hydrogen and acetylene soot was studied, and the results of this study are presented. The experiments on acetylene decomposition were performed in a modified internal combustion engine (ICE) and in a flow-type reactor with external heat supply at a constant temperature (1000 +/- 10 degrees C). The experiments were performed without any oxidant additions. In the experiments with ICE, the engine work on acetylene was shown to be possible, and the composition of the gaseous reaction products was determined. In the experiments with a flow-type reactor, the effects of pressure in the reactor, acetylene flow rate, and the presence of a tungsten gauze in the working zone of the reactor on the degree of acetylene decomposition and the composition of gaseous reaction products was determined. Some properties of soot were analyzed: specific surface area, average particle size, bulk density, and combustion heat.