Colloidal solutions of these substances can, however, be prepared either by condensation or dispersion methods. The simplest dispersion method is mechanical grinding; another dispersion method is called peptisation (partial or incomplete dissolution) of coarse precipitates. In a condensation process the colloidal particles are built up from smaller units starting with a micromolecular solution. Thus a sulphur sol can, (after VON WEIMARN), be prepared as follows: a small amount of sulphur is first dissolved in absolute alcohol. This micromolecular solution is then poured into water. Since the solubility of sulphur in the resulting water-alcohol mixture is less than in alcohol, the excess sulphur precipitates in the form of tiny colloidal particles. The chemical methods of condensation by which colloidal particles of sparingly soluble substances are produced in chemical reactions have much wider applications. Examples are provided by the following preparations: arsenious sulphide from arsenious acid and hydrogen sulphide: gold or silver sols by reduction of the corresponding salts of gold or silver, silver chloride from very dilute solutions of silver nitrate and sodium chloride. In analytical procedures especially, colloids appear quite frequently and unintentionally, and since they can not be separated by the usual filtration procedure they are strongly disliked by analysts.
- 1 0 年前最佳解答
這些物質的膠質解答可能, 然而, 由結露或分散作用方法準備或。最簡單的分散作用方法是機械研; 其它分散作用方法叫做peptisation (部份或殘缺不全的溶解) 粗糙的沉澱物。在結露過程中膠質微粒被加強從更小的單位從一種micromolecular 解答開始。因而硫磺sol 裝於罐中, (在馮WEIMARN 以後), 準備如下: 小量的硫磺首先被溶化在absolute 酒精裡。這種micromolecular 解答然後傾吐入水。因為硫磺的可溶性在收效的水酒精混合物是較少比在酒精裡, 剩餘硫磺沉澱物以微小的膠質微粒的形式。稀少可溶解物質膠質微粒導致在化學反應結露的化工方法有更寬的應用。例子由以下準備提供: 亞砷硫化物從亞砷酸和氫化硫: 金或銀sols 由金子或銀, 銀色氯化物對應的鹽的減少從非常硝酸銀和氯化鈉的稀溶液。在分析規程特別是, 膠體相當頻繁地和有意無意地出現, 和因為他們無法由通常濾清做法分離他們由分析員強烈煩惡。