Cobalt-blue glass

The compounds of the t/block elements show a wide range of interesting properties. Some are vital to life. Iron is an essential component of mammalian blood. Compounds of cobalt, molybdenum, and zinc are found in vitamins and essential enzymes. Other compounds simply make life more interesting and colorful. The beautiful color of cobalt blue glass, the brilliant greens and blues of kiln-baked pottery, and many pigments used by artists make use of d-block compounds. 

Figure 4.19 shows the p-PIXE X-ray spectra collected simultaneously from a fragment ( 1 mm in diameter) of an archaeological cobalt-blue glass (Uzonyi et al. 2001). This sample contains numerous minor and trace elements from carbon to lead, and the instrument employed both an ultra-thin window (UTW) detector as well as a Be-windowed detector. 

Figure 4.19. PIXE X-ray spectra collected by i-PIXE analysis in a new in-vacuum experimental set-up from a fragment of cobalt-blue glass. Upper spectra from a UTW detector and lower spectra from a Be-window detector. (Reproduced by permission of Uzonyi et al. 2001.)...

Dry test (flame colouration) Potassium compounds, preferably the chloride, colour the non-luminous Bunsen flame violet (lilac). The yellow flame produced by small quantities of sodium obscures the violet colour, but by viewing the flame through two thicknesses of cobalt blue glass, the yellow sodium rays are absorbed and the reddish-violet potassium flame becomes visible. A solution of chrome alum (310 g 1), 3 cm thick, also makes a good filter. 

Dry test (flame colouration) The non-luminous Bunsen flame is coloured an intense yellow by vapours of sodium salts. The colour is not visible when viewed through two thicknesses of cobalt blue glass. Minute quantities of sodium salts give this test, and it is only when the colour is intense and persistent that appreciable quantities of sodium are present. 

The sodium flame masks that of other elements, e.g, that of potassium. Mixtures can be readily detected with the direct vision spectroscope (see Fig. II.4). A less delicate method is to view the flame through two thicknesses of cobalt blue glass, whereby the yellow colour due to sodium is masked or absorbed, and the other colours are modified as listed in Table V.3. 

Violet (lilac) flame (crimson through cobalt-blue glass). K. 

The colour is often obliterated by trace impurites of sodium present (sodium gives an intense yellow colour). You can overcome this by viewing the colour through cobalt-blue glass which allows the lilac colouration from potassium to be seen. 

Viewing through cobalt-blue glass also allows calcium and strontium to be distinguished. In this case, calcium is light green in colour while strontium appears purple. 

The most common qualitative analytical test for the presence of potassium ions in an unknown sample is a flame test. If potassium is present, a wire that has been dipped in a solution will give a violet flame. Because sodium is likely also to be present, the yellow sodium flame will mask potassiums violet flame, since sodiums color is more intense. Therefore, the flame is viewed through a special glass called cobalt-blue glass that absorbs sodiums yellow color while transmitting potassium s violet color. 

Cations are simply identified by acidifying the water extract of the sample with hydrochloric acid and conducting a flame test with a platinum wire loop. The lavender color of potassium is best observed through cobalt blue glass, which filters out the yellow sodium emission. High levels of strontium will also be seen through the cobalt glass but, because of its... 

When sodium and potassium are both present in a sample, the yellow color of the sodium masks the violet color of the potassium. The violet color can be seen only when the combined sodium-potassium flame is viewed through a cobalt-blue glass. The glass blocks the yellow flame of sodium and makes it possible to see the violet flame of potassium. 

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