I will now describe some typical methods of practicing my invention, whereby lithopone of any desired grade may be produced. One of the known grades of lithopone as prepared and mixed for the trade contains sev- 6o enteen per cent. of zinc sullid. To produce this grade and a by-product of hydrosulfid of sodium, for example, I proceed as follows: The usual precautions, it will be understood, mustbe taken in preparing or for insuring the purity of the several ingredients used; but these preliminaries do not require description here. Separate aqueous solutions of the following ingredients in the proportions named are prepared: zinc sulfate, one x hundred and sixty-one pounds; barium sulfid, three hundred and thirty-eight pounds, and sodium bisulfate one hundred and twenty pounds. These ingredients, it will be recognized, are readily soluble in water. The separate solutions are then mixed and the following chemical reaction at once takes place:
We know that there are a lot of suspended organisms and colloidal impurities in natural water. The forms of suspended solids are different. Some large particles of suspended solids can settle under their own gravity. The other is colloidal particles, which is an important reason for the turbidity of water. Colloidal particles can not be removed by natural settlement, because colloidal particles in water are mainly clay with negative electricity The Brownian motion of colloidal particles and the hydration on the surface of colloidal particles make colloidal particles have dispersion stability. Among them, electrostatic repulsion has the greatest influence. If coagulant is added to water, it can provide a large number of positive ions and accelerate the coagulation and precipitation of colloid. Compressing the diffusion layer of micelles makes the potential change into an unstable factor, which is also conducive to the adsorption and condensation of micelles. The water molecules in the hydrated film have fixed contact with the colloidal particles and have high elastic viscosity. It is necessary to overcome the special resistance to expel these water molecules. This resistance hinders the direct contact of the colloidal particles. The existence of some hydrated films depends on the electric double layer state. If coagulant is added to reduce the zeta potential, the hydration may be weakened. The polymer materials formed after coagulant hydrolysis (the polymer materials directly added into water generally have chain structure) play an adsorption bridging role between the colloidal particles. Even if the zeta potential does not decrease or does not decrease much, the colloidal particles can not contact each other and can be adsorbed through the polymer chain Colloidal particles can also form flocs.