Sodium-containing lamp

In recent years, concentrated phosphoric acids, which may contain as much as 70% to 75% P2O5 content, have become of great importance to agriculture and farm production. World-wide demand for fertilizers has caused record phosphate production. Phosphates are used in the production of special glasses, such as those used for sodium lamps. 

The first high-intensity sodium lamp was introduced in Europe in 1931. Figure 9.26 shows a schematic view of a sodium lamp it comprises a glass shell containing sodium vapour at low pressure, metal electrodes to generate a current, and neon gas. The pressure inside the tube is at a relatively low pressure of 30 Pa, so some of the sodium evaporates to become a vapour. The inner side of the lamp is coated with the remainder of the metallic sodium as a thin film. 

The lamp above is more properly called a low-pressure sodium lamp. Such lamps are ideal for street and road illumination, but the monochromatic nature of the emission makes seeing in colour impossible. An adaptation which emits a range of colours is the high-pressure sodium-vapour lamp, which is similar to that described above but contains a mixture of mercury and sodium. Such lamps emit a whiter light and are useful for extra-bright lighting in places such as road intersections, car parks and sports stadia. 

Strip lighting in a classroom, hospital, business hall or kitchen is often called fluorescent lighting, although in fact it is a phosphorescent process, as above. Each bulb consists of a thin, hollow glass tube that is sealed at both ends. It contains gas such as helium, argon or krypton, and a drop of liquid mercury (about 0.5 mg of mercury per kilogram of lamp, or 0.5 parts per million). Like the neon and sodium lamps above, the pressure inside the tube is about 30 Pa, so the mercury evaporates to become a vapour. It is the mercury that yields the light, albeit indirectly. 

This means that the D line of a sodium lamp (Z = 599.6 nm) was used for light, that a temperature of 25 °C was maintained and that a sample containing 1.00 g/mL of the optically active morphine, in a 1 dm tube, produced a rotation of 132° in an anti-clockwise direction. 

As a second essential, lamps containing free metallic sodium (e.g. low pressure sodium vapour lamps) are not permitted. This does not confine the use of high pressure sodium vapour lamps. 

Table I. Types of Commercial Discharge Lamps Containing Sodium...

Low-Pressure Sodium Lamp - A type of lamp that produces light from sodium gas contained in a bulb operating at a partial pressure of 0.13 to 1.3 Pascal. The yellow light and large size make them applicable to lighting streets and parking lots. 

The observed rotation for 100 mL of an aqueous solution containing 1 g of sucrose (ordinary sugar), placed in a 2-decimeter sample tube, is +1.33° at 25°C (using a sodium lamp). Calculate and express the specific rotation of sucrose. 

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