Additive colour system

Additive colour mixing applies to the combination of light beams and is therefore the system employed in colour television and other display systems (see Chapter 3). 

An important feature of interference filters is that the blocked light is refleeted back into the beam path. Beeause the filter is placed in a collimated beam, the reflected light is perfeetly foeused back into the sample. This can cause notieeable afterpulses in the IRF of a TCSPC system. The remedy is often to use an additional coloured glass filter in front of the interference filter. If the filter has an additional absorptive layer on one side, this side should be oriented toward the light souree. 

When polymers or other water-soluble substances are present in the sample, it is advantageous to add a small amount of chloroform to the initial reaction mixture after the subsequent addition of water, a two-phase system results which may be titrated in the usual way to a starch end point or by observing the disappearance of the iodine colour in the chloroform layer. 

Somewhat better results have been obtained with octoates and benzoates but these still lead to some plate-out. The use of liquid cadmium-barium phenates has today largely resolved the problem of plate-out whilst the addition of a trace of a zinc salt helps to improve the colour. Greater clarity may often be obtained by the addition of a trace of stearic acid or stearyl alcohol. Thus a modem so-called cadmium-barium stabilising system may contain a large number of components. A typical packaged stabiliser could have the following composition ... 

In addition to one-shot processes, quasi-prepolymer systems are used commercially with rigid polyether foams. The quasi-prepolymer is commonly produced using excess TDI rather than diphenylmethane di-isocyanate. Sinee the former isocyanate is light in colour and the latter dark, quasi-prepolymer foams... 

Undercoats are invariably of high pigment content and low gloss. Their function is to provide a foundation that is uniform in both colour and texture for the finishing coats, thereby enhancing the final appearance of the completed system. On occasions, it is possible to achieve the same result by substituting an additional coat of finish for the undercoat, and this may improve the durability of the system. 

Spectrophotometric methods may often be applied directly to the solvent extract utilising the absorption of the extracted species in the ultraviolet or visible region. A typical example is the extraction and determination of nickel as dimethylglyoximate in chloroform by measuring the absorption of the complex at 366 nm. Direct measurement of absorbance may also be made with appropriate ion association complexes, e.g. the ferroin anionic detergent system, but improved results can sometimes be obtained by developing a chelate complex after extraction. An example is the extraction of uranyl nitrate from nitric acid into tributyl phosphate and the subsequent addition of dibenzoylmethane to the solvent to form a soluble coloured chelate. 

The variation of the colour of a system with change in concentration of some component forms the basis of what the chemist commonly terms colorimetric analysis. The colour is usually due to the formation of a coloured compound by the addition of an appropriate reagent, or it may be inherent in the desired constituent itself. The intensity of the colour may then be compared with that obtained by treating a known amount of the substance in the same manner. 

In the course of studying the bromination reactions of the bicyclic systems we noticed that the reaction temperature has a dramatic influence on the product distribution. Increasing of the temperature gives non-rearranged reaction products (refs. 1,2). For this reason, we submitted 1 to high temperature bromination. To a solution of 1 in decalin at 150 C was added a hot solution of bromine in decalin in one portion. The colour of bromine disappeared immediately. After silica gel chromatography followed by fractional crystallization we isolated four products 2-6 in yields 8, 35, 37, and 9 % respectively. The structure of these compounds has been elucidated on the basis of spectral data by iH NMR and NMR experiments and by comparison with those reported in the literature. Symmetrical endo-c/5-isomer 6 has been observed for the first time. Studies concerning the mechanism of syn-addition show that the syn-adduct can arise either from direct... 

It is certainly clear that a coulometric titration, like any other type of titration, needs an end-point detection system in principle any detection method that chemically fits in can be used, be it electrometric, colorimetric, photoabsorptionmetric, etc. for instance, in a few cases the colour change of the reagent generated (e.g., I2) may be observed visually, or after the addition of a redox, metal or pH indicator the titration end-point can be detected photoabsorptiometrically by means of a light source and photocell combination. Concerning the aforementioned coulometric titration of Fe(II), it is... 

Yolk colour plays a role in consumer acceptance, but the preferred colour varies in different countries. Yolk colour has no relation to nutrient content, flavour or freshness, but is often enhanced in conventional production systems by addition of synthetic pigments to the animal feed. In organic production, synthetic yolk pigments are prohibited and this normally results in paler yolks, but may also lead to greater variability in yolk colour intensity. In many European countries paler yolk colour is perceived by consumers as being associated with less natural production systems, an issue that clearly needs to be addressed by improved consumer information. 

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