Colouring soap

In makiug coloured soaps by the cold process, it is recommended to add the colouring matter to the fatty materials before the ley is poured in, by which it becomes ore thoroughly mixed. 

Marling Soaps.— Mr. Dunn suggested marking soaps, coloured soap, or other similar material in this way ... 

A demand still exists for brightly coloured soaps, and this is nsn-ally met by the use of coal-tar dyes. The quantity required is of course extremely small, so that no harm or disagreeable result cotxld possibly arise from their use. 

Vanillin, a white crystalline solid, melting at 80°-82° C. and prepared by the oxidation of isoeugenol. It has a strong characteristic odour, and occurs, associated with traces of benzoic acid and hiehotropin, in the vanilla bean. It can only be used in small quantity in light-coloured soaps, as it quickly tends to darken the colour of the soap. 

Non-soap greases using finely divided solids as thickeners are useful as lubricants at elevated temperatures. Materials used include organO Clays such as dimethyldioctyl-decyl-ammonium bentonite (Bentone greases) or selected dyestuffs which produce brightly coloured greases. 

Check for leaks with soap solution, aqueous ammonia or colour indicator tubes. 

Personal care products Leave-on rinse-off cosmetics toiletries Colour cosmetics, hair care, baby infant care Skin creams / lotions, wet-wipes, sun-care Bath shower gels, hand body wash, soaps... 

Figure 15.11 Cross section of a sample from a painting from the Hudson River School presenting a round protruding mass, (a) SEM image and EDX images of (b) lead, (c) lead soaps, (d) azelaic acid and (e) stearic acid. Reprinted from Boon et ah, Microscopy and Microanalysis, 11, Supplement 2, pp. 444 445, 2005, by permission of Cambridge University Press (see colour Plate 6)...

Zinc oxides can be prepared from chemical industry by-product sources and from zinc soaps from a variety of industrial processes. These grades are generally off-coloured and consequently considered of lower grade and offered at lower cost and are confined to use in black compounds. These grades can also vary in consistency, batch to batch, causing cure variation in compounds containing them. 

To purify the soap 20-30 g. are dissolved in boiling water, salted out from the hot solution, and again allowed to solidify. In this way the small amount of alkali in the crude product is removed. The soap, however, remains alkaline to litmus and turmeric papers. The hydrolysis of the quite pure soap is, however, not sufficiently extensive, the concentration of OH-ions not sufficiently large, for phenolphthalein to be coloured. 

Toilet soaps are prepared by using better grades of fats and oils and care is taken to remove excess alkali. Colour and perfumes are added to make these more attractive. 

We have noted that the adhesion of the polar groups to water and to one another is much greater than the weak adhesion of hydrocarbon chains either to water or to one another. It is thus reasonable to assume, an anticipation verified by Perrin Ann. Rhys. X. 160, 1918), that soap films may be made up of composite surfaces each of which consists of two layers of orientated molecules of soap the outer surface of each side consisting of hydrocarbon chains and the polar groups held together with water as a sandwich between the orientated hydrocarbon chains. These elementary leaflets which will possess but little adhesion for one another may be built up to form thick films similar in structure to the crystalline fatty acids examined by Shearer (see p. 73). The leaflets may slip over one another with great ease, thus providing the play of interference colours noticed in soap films. The elementary leaflet has in fact been shown by Perrin and others to be two molecules in thickness. 

The equilibrium thickness of a (meta-)stable soap film will depend on the strength and range of the repulsive forces in the film. Electrostatic forces are long-range in water and hence give rise to thick (0.2 micron) films, which are highly coloured due to the interference of visible light... 

In this situation, the equilibrium thickness at any given height h is determined by the balance between the hydrostatic pressure in the liquid (hpg) and the repulsive pressure in the film, that is n = hpg. Cyril Isenberg gives many beautiful pictures of soap films of different geometries in his book The Science of Soap Films and Soap Bubbles (1992). Sir Isaac Newton published his observations of the colours of soap bubbles in Opticks (1730). This experimental set-up has been used to measure the interaction force between surfactant surfaces, as a function of separation distance or film thickness. These forces are important in stabilizing surfactant lamellar phases and in cell-cell interactions, as well as in colloidal interactions generally. 

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