Acid, stannic charge

Zinn-bromwasserstoffsaure, /. bromostannic acid, -butter, /. (Old Chem.) butter of tin (stannic chloride), -charge, /. (Textiles) tin weighting, -chlorammonium, n. ammonium chlorostannate, (Dyeing) pink salt, -chlorid, n. tin chloride, specif, stannic chloride, tin (IV) chloride, -chloriir, n. stannous chloride, tin(II) chloride. 

Electrical charges on the particles operate in such a manner that many hydrosols behave during electrolysis precisely as electrolytes with large complex ions. Colloidal stannic acid, the purple of Cassius and many others may be cited as examples. The reactions of hydrosols are often determined by the electrical charge and are generally characteristic of the sign. They are dependent upon the nature of the disperse phase just as in the case of crystalloidal solutions. The particles of reversible and also the irreversible hydrosols behave similarly to molecules and ions in that they are adsorbed by various substances. 

If alkali is added to a gel of stannic acid without doubt a small portion of each unite to form a stannate. It is equally certain that a part of the stannate will be adsorbed by the stannic acid. If now the mixture is diluted with water the dissociation of the stannate occurs, and one has but to assume that the stannate ion is more adsorbed by the ultramicrons than the potassium ion in order to explain the peptisation. The stannate ion imparts the negative charge to the particles and the subdivision goes on in a manner very similar to that. of diffusion. The potassium ion diffuses to portions of the liquid where the concentration is not so great taking in its wake the stannate ion with its attendant ultramicrons, just as in the case of hydrochloric acid the hydrogen ion leads the way to places of lower concentration and the chloride ion follows. The reaction may be expressed by means of the following equation ... 

I SnOaH2 represents a stannic acid molecule on the surface of an ultramicron. As there is no means of deciding between these assumptions and they all lead to the same result, viz the charging of the ultramicrons and the subdivision of the material, it seems easier to abide by assumption one that is the adsorption of the ions by the colloidal particles. The fact that this assumption is the more general, and that it may be employed in explaining the formation of mixed colloids, is a further reason for making it. See Chapter VII on Peptoids. 

Electric Charge. — The amicrons of the hydrosol are charged negatively and migrate toward the anode in neutral, alkaline, or weakly acid solution. During, the electrolysis of neutral solutions silicic acid does not separate out at the anode as stannic acid and many other colloids do, but falls slowly to the bottom in striations much after the nature of sulfuric acid. 

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