Colour purity

In practice, both red and green star compositions are formulated to have a negative oxygen balance i.e. there is an oxygen deficiency) since the presence of a reducing atmosphere in the flame inhibits the oxidation of MCI to MO (where M is Sr or Ba), thus enhancing the colour purity of the flame. 

It is from the morphine that diamorphine is prepared. This is achieved by mixing the morphine with acetic anhydride and heating to approximately 85°C for about 5 h, or until all of the morphine has dissolved. Water is added to the mixture, followed by activated charcoal which absorbs any impurities. The mixture is repeatedly extracted with charcoal and filtered until the solution is clear. Sodium carbonate, dissolved in hot water, is slowly added to the mixture and the heroin base precipitates as a solid, which is then filtered and dried. The decolourizing and filtering process can be repeated a number of times until the desired colour/purity is achieved. From each kilogram of morphine, up to 700 g of diamorphine can be produced. 

Polymer LEDs with copolymers containing dibenzosiloles have been reported in the literature [39,42]. By varying the 3,6-dibenzosilole content in a fluorene-based polymer, superior colour purity and optimum external quantum and luminous efficiencies were obtained (Fig. 5) [39]. Compared to polyfluorene, these copolymers are also stable to thermal annealing. Similar results were reported for a 2,7-dibenzosilole-co-3,6-dibenzosilole polymer [42]. 

With a dielectric cover layer of ZnSe over the semitransparent Ca cathode, by a suitable choice of the layer thickness, both a high efficiency and good colour purity could be obtained. Here, the constructive interference of the directly emitted radi-... 

Figure 12.5 (a) Typical microcavity-based device structure for colour purity enhancement and (b) the resulting narrow spectral output... 

Said to be the first time glass pigments have been offered coated with titanium dioxide, giving a brilliant star-like glitter, with depth and multiple colours, another range by Engelhard, under the name Firemist, offers exceptional chroma, colour purity, brightness, transparency, and reflectivity. 

Although phenol gives these marked colour changes, the test is unsatisfactory with many other phenols, the precise tint obtained varying with the purity of the phenol, amount of reagents used, and temperature and time of heating. 

The stabilised nitrate may then be bleached with sodium hypochlorite, centrifuged to remove much of the water in which the polymer has been slurried and dehydrated by displacement with alcohol while under pressure in a press. It is interesting to note that in these processes approximately 35 000 gallons (160000 litres) of water are used for every ton of cellulose nitrate produced. Control of purity of the water is important in particular the iron content should be as low as 0.03 parts per million since iron can adversely affect both the colour and heat stability of the polymer. 

The elements are obtainable in a state of very high purity but some of their physical properties are nonetheless variable because of their dependence on mechanical history. Their colours (Cu reddish, Ag white and Au yellow) and sheen are so characteristic that the names of the metals are used to describe them. Gold can also be obtained in red, blue and violet colloidal forms by the addition of vtirious reducing agents to very dilute aqueous solutions of gold(III) chloride. A remarkably stable example is the Purple of Cassius , obtained by using SnCla as reductant, which not only provides a sensitive test for Au but is also used to colour glass and ceramics. Colloidal silver and copper are also obtainable but are less stable. 

Procedure. To determine the purity of a sample of boric acid, weigh accurately about 0.8 g of the acid, transfer quantitatively to a 250 mL graduated flask and make up to the mark. Pipette 25 mL of the solution into a 250 mL conical flask, add an equal volume of distilled water, 2.5-3 g of mannitol or sorbitol, and titrate with standard 0.1 M sodium hydroxide solution using phenolphthalein as indicator. It is advisable to check whether any blank correction must be made dissolve a similar weight of mannitol (sorbitol) in 50 mL of distilled water, add phenolphthalein, and ascertain how much sodium hydroxide solution must be added to produce the characteristic end point colour. 

To determine the purity of a sample of arsenic(III) oxide follow the general procedure outlined in Section 10.127 but when the 25 mL sample of solution is being prepared for titration, add 25 mL water, 15 mL of concentrated hydrochloric acid and then two drops of indicator solution (xylidine ponceau or naphthalene black 12B see Section 10.125). Titrate slowly with the standard 0.02M potassium bromate with constant swirling of the solution. As the end point approaches, add the bromate solution dropwise with intervals of 2-3 seconds between the drops until the solution is colourless or very pale yellow. If the colour of the indicator fades, add another drop of indicator solution. (The immediate discharge of the colour indicates that the equivalence point has been passed and the titration is of little value.)... 

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