and with a cutoff valve 48 and is connected across a viscosity meter 49 to the delivery of an electric pump 50 arranged on the bottom of a storage reservoir 51 for primary cellulose mix downstream of the viscosity meter 49 the pipe 46 is connected to a discharge pipe 52 inside the storage reservoir with interposition of a cutoff valve 53 the storage reservoir 51 also has level detecting probes 54 and a discharge cock 55 on the bottom a water duct 56 and a duct 61 discharge into the storage reservoir 51 said duct 56 is provided with an electric valve 57 driven by the probes 54 for maintaining a preset level within the storage reservoir with a filter 58 with a liter counter 59 and with a cutoff valve 60 and the duct 61 is provided with a filter 62 and a liter counter 63 and is connected to the delivery of an electric pump 64 the intake port of said pump is connected to the inside of a reservoir 65 for the dye or pigment designed to be fed in a controlled manner to the storage reservoir 51 the dye or pigment reservoir 65 is provided with an.