Soot formation in pyrolysis of carbon-containing gas-phase materials (carbon-particle precursors) is important for many practical applications. The underlying processes have been studied in a number of works. One of the most remarkable results of these studies is the temperature dependence of the yield of final condensed carbon that was determined via extinction measurements. The observed optical densities of the particle-laden mixture show a well-known bell shape when plotted as a function of temperature of shock-heated gas mixtures. However the position of the bells differs for different precursors [1,2]. In [3,4] it was made a conclusion that the actual temperature can differ significantly from the calculated post shock values due to heat consumption and release processes during the decomposition of carbon precursors and the condensed particle formation. Therefore, the temperature dependencies of the optical density and of the particles size in the various mixtures must be reconsidered in view of the actual temperatures of reacting mixtures. For this goal in the present work the purposeful measurements of the actual temperature-time profiles during the carbon particle formation from the different precursors has been carried out.