Density data for dimethyldichlorosilane (DDS) and for methyltrichlorosilane (MTS), which were used severd years ago to lay the foundation for a successful routine method to aid in controlling chlorosilane distillation, are given below. There appear to be no comparable earlier published data. Pure Compounds.-As a by-product of painstaking distillation work done in 1943, the details of whic: h are to be published later, the following densities (g./ml. ...