Dyestuffs colloidal nature

Perhaps the most convincing evidence of the colloidal nature of dyestuffs is given by the ultramicroscopic observations of Raehlmann, Michaelis, Hober, and others. These investigators have demonstrated that solutions of dyestuffs are sometimes filled with ultramicrons even when the liquid becomes colorless because of the great dilution. In confirmation of this view are the experiments of Krafft J which show that many of these salts such as Methyl Violet raise the boiling point of water correspondingly less than that of alcohol. 

Sulphur dyes cannot be applied to protein fibres by normal methods on account of the strongly alkaline nature of the dye liquors. Wool is never dyed with these dyestuffs, but a reasonably fast black was obtained on wool and cotton unions by adding 5 per cent on the weight of the goods of a protective colloid such as glue or boiled starch. 

In the mid twenties several circumstances permitted a revised orientation of both content and style of areas of research at the Central Research Laboratory. In 1925 the Technical Committee (TEA) of I.G. Farben discussed the possibilities for producing artificial fibres. At this time, I.G. Farben was the second largest producer of artificial fibres in Germany. Therefore polymer chemistry became more important for the company at the same time as dyestuffs chemistry lost its former position. However, the science of synthetic, semi-synthetic and natural polymers was not yet established in the same way as structural chemistry was for organic dyestuffs, pharmaceuticals, and intermediates. Colloid chemists regarded substances such as cellulose, silk, and wool as... 

Solubility data were very confusing until it was found that traces of certain metal impurities and especially the presence of an amorphous or at least disturbed layer on the crystal surface caused variable results, especially at temperatures below 150 C. In 1952, Dempster and Ritchie (117) reported that siliceous dusts have a layer of high solubility that gradually blends into the solid core, which adsorbs basic dyestuffs (118). Alexanian (119) found by electron diffraction that quartz possesses a surface layer of amorphous silica about 100 A thick, which is removed by HF but is re-formed in ambient humidity. Waddams found that the quartz surface in water released mosaic silica, presumably as particles of colloidal size, since they scattered light (120). This was confirmed by Sakabe et al. (121), who found that in neutral or alkaline aqueous suspension, quartz released both soluble silica and colloidal particles of crystalline nature, 0.01-0.3 microns in size. Stober and Arnold (122) found that the amount of silica released was much more than a monomolecular layer, and that it decreased with successive changes of water. When quartz was intensively pulverized in water, the disturbed surface layer can amount to as high as 35%, with a specific surface area of 70 m g, and the solubility is increased from less than 10 to 70 ppm at 25 C (123). Paterson and Wheatley (124) made similar observations. 

Biltz found further that where acid and basic dyestuffs had opposite charges and were mutually precipitated, the formation of an insoluble chemical combination could be assumed. This corresponds to what is known of acid and basic dyestuffs in the state of crystalloids namely that they unite, and when the combination is insoluble a precipitate is of course formed. Doubtless such reactions occur in the case of many dyestuffs. The more colloidal the character of these dyestuffs the more nearly will the laws of colloidal reaction obtain. Moreover Biltz has pointed out that with colloids of the nature of gold such chemical reactions are not possible. Nevertheless colloidal gold is precipitated by positively charged dyestuffs. The cause is doubtless the neutralization of the charge on the particles. For further particulars attention is called to Chapter XI. 

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