Adjustment of the colour

The colour of beer is largely determined by the melanoidins and caramel present in the malt and adjuncts used but further caramelization occurs during wort boiling. Minor adjustments of the colour of beer can be made by the addition of caramel either to the copper or with primings. The chemistry of melanoidin and caramel formation is discussed in Chapter 14. 

Observe the combustion of a candle. Compare the colour of the flame with the colour of the Bunsen burner flame. Which adjustment of the burner makes the colours of the two flames most similar ... 

Add 1 drop of methyl violet indicator solution and introduce dilute HC1 or dilute NH3 solution (as necessary) dropwise and with constant stirring until the colour of the solution is yellow-green a blue-green colour is almost but not quite acid enough, yet it is acceptable for most analyses. (If the indicator paper is available, the thoroughly stirred solution should be spotted on fresh portions of the paper.) It is recommended that a comparison solution containing, say, 10 ml of 0-3m HC1 and 1 drop of indicator be freshly prepared this will facilitate the correct adjustment of the acidity. A more satisfactory standard is a buffer solution prepared by mixing 5 ml of m sodium acetate, 5 ml of 2m HC1, and 5 ml of water this has a pH of 0-5. 

Fig.33) Anyhow we can produce various colours of the fire dust or sparks except blue and green by adjusting the temperature and selecting substances which make up the component material in firework compositions according to the principle of the colour temperature. 

The molar absorptivity of the pseudo-solution of the magnesium compound with Titan Yellow is 3.6-10 at 545 (a = 1.5). The intensity and reproducibility of the colour obtained are affected by the method of pH adjustment, the excess of Titan Yellow, the protective colloid used, the temperature of the solution, and the time of standing. Immediately after the start of the colour reaction, an increase in absorbance is noticed, but after 10-30 min the colour of the solution remains almost constant. After this it weakens progressively. Hydroxylamine is reported to stabilize the colour [12]. 

The fire dust or sparks which are produced by iron or carbon create the colour which resembles that of the black body. The colour of the sparks of "Senko-Hanabi" which is caused not only by carbon but also other materials, also resembles the colour of the black body. We feel that the colour of the aluminium fire dust is a little different from the black body. The colour changes from red-orange to yellow, white yellow and silver as the temperature increases, and the locus may be written as the LH line (Fig.33). Anyhow we can produce various colours of the fire dust or sparks except blue and green by adjusting the temperature and selecting substances which make up the component material in firework compositions according to the principle of the colour temperature. 

Dubose s comparator. The observer adjusts the transmitted intensities, according to the two pathways. He can compare the quahty of the colours with great precision. The bottoms of the tubes are illuminated by a reflecting surface itself lit by an annexed light source. 

Clearly, control of rheological properties of coating colours is desirable, and this is achieved through polymeric additives. The aim is not only to favourably adjust the viscosity and other rheological parameters of the suspension per se, but also to improve the water retention properties of the colour. If the suspension dewaters too quickly before or on application, this can lead to severe runnability problems, such as the formation of streaks, dry stalagmites and uneven binder distribution. 

Caramel may be used either in the copper or in primings to make minor adjustments to the colour of beer but the fundamental colour of the beer will be determined by the choice of malt grist and the grade of adjuncts added to the copper. 

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. 

The principle of the automated UV titration is illustrated in Fig. 4-4. Suitable wavelengths are 450-470 nm for the I3 colour and about 660 nm for the colour of the starch indicator. Initially, the absorption of the 13 solution is beyond the validity of Beer-Lambert s law depending on the type and adjustment of the photometer. When the thiosuphate addition approaches the endpoint, the absorbance-thiosulphate addition relationship becomes linear. The piston increments of the burette are reduced (indicated by an expanded scale in Fig. 4-4) and data pairs of mL of thiosulphate added and relative absorbance are recorded. Regression lines are fitted (by computer) to the linear sections of the titration curve before and after the equivalence point. The equivalence thiosulphate addition is indicated by the calculated intersection of the regression lines. 

A spectrophotometer or a filter photometer at or close to 670 nm is used for the determination. Cuvettes with path lengths of 0.5,1,5 and 10 cm are used depending on the intensity of the colour development. Automatic piston pipettes adjusted to a volume of 0.5 mL are recommended for adding reagents. The absorbance readings should be recalculated according to the path length used for the calibration. 

Seemingly a copper-arsenic green (q.v.). Terry (1893) describes the process as involving the preparation of copper arsenite from copper sulfate and sodium arsenite ( arsenite of soda ). The precipitate is then treated widi acetic acid or, interestingly, formic acid the former would result in the usual copper acetate arsenite, the latter in copper formate arsenite. Terry comments The pigment thus produced is of good colour, but its superiority would not seem to justify the use of such an expensive article as pure formic acid, nor the minute adjustment of the proportions of die ingredients, in an operation to be conducted on a commercial scale. ... 

Prepare a double amount of the colour reference solution described in the previous paragraph in a beaker. Introduce half of it into each optical cell and check the optical density of the solution. With both cells in the compartments and the photometer adjusted for highest sensitivity bring the pointer at position 50 of the linear scale marked abs . Check whether the cells are matched by interchanging them. During the actual determination keep the right-hand cell in its place and titrate in the left-hand cell. 

Particular attention must be paid to the adjustment of the reagent and the end-point of the reaction. Standardise the 0-5N ethanolic potassium hydroxide by running it into a known volume of 0-5N acid until the full yellow colour of the indicator (a 0 2 per cent solution of methyl orange in 60 per cent ethanol) is obtained, i.e. that colour not changed by further addition of alkali. The necessity for the correction factor in this method is questionable in view of the limited degree of accuracy obtainable with the somewhat difficult assessment of the end-point. 

To 2.0 g of MnOj (preferably of y type) in a round bottom centrifuge tube, add 15 cm of 0.5 M solution of KCr(S04)2.12H20 whose pH is adjusted to 2.0 and heat in a water bath at 65°C for 60-80 minutes. When cold, centrifuge and filter the suspension. Put 10 cm of the filtrate into the column and allow the liquid out at the rate of 50 drops per minute. Collect the coloured fraction and run its absorption spectrum over the range of 300-600 nm. After the liquid level reaches the resin level, add 10 cm of dilute HCI and elute as above and run the spectrum of the coloured fraction in the range 350-650 nm. Comment on your results. 

---