separated mother liquor is fed back to the triple effect evaporators and the centrifuge cake which consists of sodium carbonate monohydrate crystals and free moisture is conveyed to a dryer 46 to remove free and combined water and yield pure anhydrous sodium carbonate which is soda ash the soda ash thus produced is sized by a vibrating screen 47 and an air classifier 48 the overflow produced by the air classifier is dust and the underflow produced by the classifier is sized sodium carbonate this sized sodium carbonate is conveyed by means of a conveyor 49 to a soda ash product storage 50 the data presented below exemplifies the nature of the size separation achieved by the primary and secondary hydroclones in the manner described ______________________________________primary hydroclone separationinlet solid overflow solid underflow solid 6 14 2 5 3 5 15 25 size distributionfeed overflow underflow______________________________________ 20 42 4 40 1 5 20 43 2 30 4 6 70 6 0 30 9 4 40 4 6 100 9 0 40 9 9 50 6 0 200 24 1 50 7 4 70 5 0 200 59 4 70 5 8 70 39 2 100 6 4 200 8 9 200 8 9______________________________________ ______________________________________secondary hydroclone separationinlet solids overflow solids underflow solids______________________________________ 6 14 2.