Sparks colour

In enamels for chemical plant such as autoclaves it is not only the degree of acid resistance which is important but also the freedom of the finish from minute flaws detectable by high frequency spark testing or chemical methods. The chemical methods depend upon a colour change when the reagent such as ammonium thiocyanate reacts with the iron exposed at the bottom of the pinhole or flaw in the finish. Alternatively, an electric cell can be formed via the exposed iron in the flaw and detected chemically. 

Although it is known that the colour of black body radiation is only dependent upon temperature, sparks have colours that are also dependent upon the type of emitting material. However, the form of the radiance curves does not relate exactly with known molecular energy transitions. This suggests that the mechanism of emission in excess of black body radiation is not yet fully established. It is possible that some emission bands only become active when the metal oxide particle is molten, or that the energy is dissipated simply via collisions with other molecules rather than the emission of photons. 

Thus, although the colour of sparks is dependent upon flame temperature and may be similar to that of black body radiation, the overall colour effect can include contributions from atomic line emissions, from metals (seen in the UV and visible regions of the electromagnetic spectrum), from band emissions from excited oxide molecules (seen in the UV, visible and IR regions) and from continuum hot body radiation and other luminescence effects. So far as black body radiation is concerned, the colour is known to change from red (500 °C glowing cooker... 

A further factor that contributes to the overall appearance of a firework fountain is the brightness of the sparks. As with colour, the brightness is dependent upon the temperature and characteristics of the material used. The brightness of black body radiation varies with temperature as shown in Figure 5.5. 

WATERFALL A hrework assembly consisting of a row of fountains suspended in the inverted position or hred horizontally on a rope such that simultaneous ignition of the fountains produces a cascade of silver (or coloured) sparks. 

About 1775, J. Priestley 2 passed a series of electric sparks through atm, air confined in a suitable vessel over water coloured purple by a decoction of turnsole or archil. He found ... 

Colloidal Rhodium may be prepared by Bredig s method, which consists in sparking between rhodium electrodes submerged in ice-cooled water, a current of 2 amperes at 110 volts proving useful for the purpose.4 The solution has a reddish brown colour, and is very unstable. 

Platinum Hydrosol or Colloidal Platinum.—A solution of platinum hydrosol or colloidal platinum in water is easily prepared by sparking between platinum electrodes immersed in ice-cooled water,8 a current of about 10 amperes and 40 volts being employed. The electrodes consist of thick platinum wire, and, when placed from 1 to 2 mm. apart, sparking takes place, particles of the metal being tom off and suspended in the water. The liquid thus obtained is allowed to stand overnight, and decanted from any sediment. It has a dark colour, but the individual metallic particles cannot be distinguished even with the aid of a microscope. 

Dry Tests.—Iron salts, when moistened with hydrochloric acid and heated on a loop of platinum wire in a Bunsen flame, emit a shower of sparks. When heated on charcoal with sodium carbonate in the blowpipe flame, the compound is converted into a dark-coloured residue. If potassium cyanide is added to the sodium carbonate and iron compound, and the whole heated on charcoal in the inner flame of the blow-pipe, metallic iron is obtained as a grey, magnetic powder. 

Spectrum.—Compounds of chromium impart no distinctive colour to the non-luminous flame. The spectrum, however, is somewhat complicated, especially the spark spectrum. Careful and complete measurements have been made, for which the reader is referred to the literature. Exner and Haschek be. cit.) state that the most intense lines ( hauptlinien ) in the arc and spark spectra are as follows ... 

We have two kinds of colour producing light sources, the emitter (flames or sparks) and the reflector (smoke or parachute, flags, etc.). Here the former is described since it is the most important. 

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-Hanabiwhich 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 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. 

It is thought that fireworks began with the history of potassium nitrate. It has. been used for compositions which produce fire dust or sparks as well as a white smoke which has been called "Wabi (Japanese fire). It could not produce coloured flames, but before the appearance of potassium chlorate, fireworkers made various efforts to create colour with it as far as possible. 

Porphyrin complexes can be commonly produced in sparking mixtures. Thus, Hodgson and Baker showed that pyrrole and paraformaldehyde in the presence of copper(II), nickel(II) and vanadyl salts give rise to both free and metal complexes of porphyrins. Tlie most efiective ion for the template reaction is Ni", a result parallelling the observations outlined earlier on the preservation of porphyrin complexes in asphalts, sediments and rocks. It was pointed out that coloured species noticed in earlier experiments were also probably porphyrin coordination complexes. More recently it has been demonstrated that Ni(CN)/ increases the yield of porphyrins in such reactions, as does Fe(CN) . Since these ions were probably present in reasonable concentrations in the primitive oceans, their significance is obvious. 

These comprise, on the one hand, easily combustible substances such as charcoal, sulphur, antimony sulphide, resins, and tar and on the other hand, they include substances which readily give up oxygen and support combustion, such as saltpetre (potassium nitrate), and potassium chlorate or other chlorates. A third category includes those substances used for the various colour effects (barium strontium, copper, and other salts), and also finely divided metals, and coarse particles of charcoal to cause sparks and showers of fire ( golden rain and the like). Other substances are sometimes used to decrease the rate of burning and to increase brilliance (r.g. mercurous chloride and mercuric thiocyanate). 

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