The silicone (organosilicon) polymere are a new and remarkable development of the chemical industry, Filling the void between organic and inorganic products, they find a great variety ef uses where their outstanding properties of heat and moisture resistance, general chemical inertness, and high electrical resistance can be applied. They are available as fluid for hydraulic and other uses, lubricants and greases, electrical sealing compounds, resins, and elastomers. Same of the intermediate compounds formed in the manufacture of these final products have also found uses. Organic compounds of silicon have been known and studied for over one hundred years, nearly all of the early study, however, was done on the chemical and physical properties of the monomers and low polymers and until very recently little was accomplished toward the practical application of this type of compound. In the United States, about 1935, impetus was furnished to research on the silicones by the need for a material suitable for binders, varnishes, and adhesives for newly-developed glass fabrics to be used in electrical insulation. The silicones are structurally analogous to glass and therefore seemed a likely starting point for the search. The monomers and low polymers are unsatisfactory and there were finally developed high polymers which proved to have outstanding heat moisture resisting properties, in addition to the desirable qualities for electrical insulation. Since then research on silicones has progressed rapidly. The number of new products developed has created a demand that has far outstripped commercial production, begun in 1943. All efforts are now being directed toward finding better commercial methods of production as present methods are expensive and relatively difficult to control. This seems to be particularly true of the initial step in silicone production, i.e., that of making the intermediate organochlorosilanes. The purpose of this investigation is to develop a process for the production of phenylchlorosilanes by the phenyl substitution of silicon tetrachloride at high temperatures. / Master of Science