The Chemistry of Colloids Volume 1-2 (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1917 Excerpt: ...J obtained a molecular weight of 49,000 by this method. Bruni and Pappada could not observe any lowering of the freezing point with their preparations. The more sensitive direct measurement of the osmotic pressure shows that the colloid exhibits such against its filtrate. The pressure becomes smaller as coagulation proceeds. 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. Precipitation with Electrolytes.--As already pointed out silicic acid is not immediately precipitated by all electrolytes. Hydrochloric acid, chlorides of the alkali, and alkaline earth metals give no precipitate but may cause gelatinization after standing for hours, days, or perhaps weeks. It is precipitated immediately by barium hydroxide, concentrated solutions of ammonium sulfatc, dilute solutions of egg albumin, glue, and many basic dyestuffs such as Methylene Blue. Regarding the effect of the salts of the alkali metals on the precipitation, Pappada found that the anions played little part but that the influence of the cathions increased with the molecular weight, caesium having the greatest and lithium the least. t R. Zsigmondy und R. Heyer: Zeit. f. anorg. Chemie, 68, 169-187 (1910). I A. Sabanejeff: Journ. d. russ. phys.-chem. Ges., 21, 515-525 (1889); Ber., 23, R., 87 (1890). G. Bruni e N. Pappada: Atti della R. Accad. dei Lincei Roma (5), 9, 354-358 (1900); Gazzetta chimica ital., 31, 1, 244-252 (1901). Protective Influence of Silicic Acid.--Silicic ac...