Colour Comparators

The colour of apricots can be determined by comparison with visual standard colour plates such as the Royal Horticultural colour charts. A disadvantage of colour plates is that they are two-dimensional and the eye sees colour in three dimensions, hue, value and chroma. 

Furthermore, the use of colour plates is limited due to errors by the observer and interpretation from one observer to another (Moore and Janick 1983). 

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A. Standard series method (Section 17.4). The test solution contained in a Nessler tube is diluted to a definite volume, thoroughly mixed, and its colour compared with a series of standards similarly prepared. The concentration of the unknown is then, of course, equal to that of the known solution whose colour it matches exactly. The accuracy of the method will depend upon the concentrations of the standard series the probable error is of the order of + 3 per cent, but may be as high as + 8 per cent. 

Theory Selenium is very toxic and its contamination is usually controlled by an absorptiometric method after destruction of the organic compound with fuming nitric acid. The latter converts selenium (Se) as selenous acid (H2Se03), which on subsequent treatment with 3,3 -diaminobenzidinc under controlled experimental parameters, results into the formation of a highly coloured compound known as 3,4-diaminophenylpiazselenol. The latter is consequently extracted with toluene after making the aqueous solution alkaline, and the colour compared with a standard prepared likewise from a known amount of selenium. The various reactions involved may be expressed as follows ... 

The colour is mainly determined by the minimum between the two visible main absorption bands. The energetic position of this minimum, however, is reflected by the position of the first main band (=d) in most cases, resulting in a direct relation between J and the colour, (compare Table 1 in (79)). A change in B35 is not necessarily indicated by a colour shift therefore. 

Put a piece of indicator paper (a universal indicator) on a watch glass and wet it with a sodium carbonate solution. Note the change in the indicator colour, compare it with a reference, and determine the pH of the sodium carbonate solution. Perform similar experiments with aluminium and sodium chlorides. Use the pH values obtained to calculate the hydrogen ion concentrations in the studied solutions. 

This area of analytical chemistry includes a great number of instruments that range from colour comparators and other visual comparison devices to automated spectrophotometers that can carry out multicomponent analysis. Liquid chromatography and capillary electrophoresis have accelerated the development of improved UV/Visible detectors, which are at the origin of the current mode of acquiring chromatograms, accompanied by the possibility of identification and quantification of compounds. 

Finally, with colours for oil painting, it is well to repeat the test by incorporating the necessary quantities of boiled linseed oil with the mixtures prepared from the colour under examination and from the standard colour, the paints thus obtained being spread on a sheet of glass and the colours compared when dry. 

Fastness against acids. The sample is soaked in 10% sulphuric acid or in 30% acetic acid and the colours compared with that of a sample soaked in water. The degrees of fastness are as follows I, alteration marked with mineral acids, weak with organic adds III, alteration marked with mineral adds, absent with organic adds V, no alteration with either mineral or organic acids. 

The Mount Vernon iex-Kronprinzessin Cecilie), seen postwar but still sporting deliberately contrasted funnel colours. Compare this with the picture on page 69. 

Anisotropic noble nanoparticle dispersions are very different in colour compared to dispersions of spherical particles. This is because the surface plasmon bands are more sensitive to particle shape than size [92]. All the metal nanorods have two absorbance maxima that correspond to the longitudinal and transverse plasmon bands. The longitudinal plasmon band strongly depends on the aspect ratio. For example, platelets have additional quadrupole bands [96]. Upon transition from nanorods to platelets, as the aspect ratio decreases, the longitudinal band is blue-shifted and the transverse band becomes broad due to overlap with the quadrupole band. In cubes, all three plasmon bands merge into a single band. In contrast, transition from nanorods to nanowires increases the aspect ratio, which produces a resultant red shift of the longitudinal band and a blue shift of transverse band [83]. 

Type 2 has a non-blue copper centre, with the copper coordinated to two or three nitrogen donors in addition to oxygen donor(s) in a square planar geometry, with the different donor set and shape together responsible for a markedly different colour compared with Type 1. 

For quality checks on colour or graphics, controlled lighting conditions are virtually obligatory. Eyeball colour comparison, by trained inspectors, is still a valid quality tool, although colour comparators or densitometers will provide recordable measurements. 

The reference cuvette is filled with the water sample to be analyzed without adding reagents. Both cuvettes are then placed in the comparator and adjusted until the colours are the same, with the aid of the colour comparator chart. The content of free available chlorine can then be read off. The values are normally read off in mg/1, taking into consideration the quantity of water involved. 

Colour comparators are frequently used in practice, the coloured sample... 

In polypropylene tape applications. HP-136 is very effective when used with a classic phenolic or in a ternary blend and. compared with a traditional binary blend, data indicate that there is potential for a 50% reduction in total stabilizer concentration, with comparable melt flow stability, improvement in colour, and an improvement in water carry-over, again providing a significant margin for optimization of formulation. In polypropylene fibre applications, a combination of HP-136 with a hindered amine and a phosphite shows melt flow and colour comparable with a traditional binary system, but superior gas-fade resistance and UV stability in phenol-free blends. This improvement is seen at 40% less concentration. 

The first successful selections from this programme were Vincent, bred in 1949 Ventura, bred in 1951 and Veeblanc, bred in 1953. Of these three, Vincent had superior stable colour compared with the traditional V. labruscana cultivars and a better flavour profile, Ventura had superior winter hardiness but was reminiscent of V. riparia flavours and Veeblanc had a neutral flavour and better cropping balance than most of the large clustered French hybrids. 

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