Crystalline anhydrous sodium metasilicate cannot be dissolved in water to much over 35% to 40% dissolved solids, a phenomenon that is not clearly under stood, and it thus is necessary to evaporate the solution in the absence of undissolved crystalline sodium meta
silicate in order to attain a 57.5% sodium metasilicate concentration-that is, a sodium metasilicate pentahy drate liquor.