The consecutive reactions of acid involved siloxane formation are firstly measured in bulk and analysed by Raman spectroscopy. Influencing factors, which can be identified as the chemical properties of the silanes, the silylium cations, and miscibility are pointed out by using a special technique. The procedure is based on a modified Raman sample cell, which allows a single-phase system with controlled water content to be systematically quantitatively monitored. Additional to the novel opportunity to analyse the acid “catalysed” condensation during the formation of polysiloxanes, this publication contains an alternated theoretical mechanism for sol–gel synthesis considering a restricted water content. A major aspect of this introducing study is a detailed analysis and identification of the relevant Raman vibrational bands and their origin on the hand of ten different organyltrialkoxysilanes (methoxy and ethoxy). The ability to determine the kinetics of the acid catalysed formation is demonstrated on homologous series of alkyltrimethoxysilanes.