A method for treating a mixture in a single-shaft or multi-shaft mixer (M), especially a kneader-mixer, especially for preparing a spinning solution. A solvent or solvent mixture is added to the product over the length of a product chamber in order to reduce a viscosity of the solvent or of the mixture and to increase an evaporative capacity. The viscosity of the solution or of the mixture is determined and/or modified in predetermined locations in the product chamber.

The present invention pertains to an oxygen dissolution device. According to the device, the oxygen and water introduced into the housing are agitated and mixed with each other by eddies and currents formed by the plurality of first smashing blades and the second smashing blades, then converted into oxygen-dissolved water having a large amount of dissolved oxygen. Therefore, an amount of oxygen which is not dissolved in the water to be waste may be decreased so as to reduce purchase costs of oxygen, as well as, when supplying the oxygen-dissolved water having a large amount of dissolved oxygen as described above to a fish farm, the amount of dissolved oxygen of the water in the fish farm may be rapidly adjusted to a level which is suitable for the farmed fish to live in.