Images Dated 8th August 2003

Techncian welds with an oxyacetylene torch

Welding. Technician in protective clothing welds a section of an oil and gas pipeline with an oxyacetylene torch. Welding involves heating two pieces of metal so that they melt and fuse together. Oxyacetylene torches use a mixture of oxygen and acetylene to create the heat needed to melt the metal. The acetylene burns in oxygen to form carbon monoxide; this reaction provides most of the heat. The carbon monoxide then reacts with atmospheric oxygen to give the blue flame. The flame from an oxyacetylene torch is "neutral", meaning that it burns without leaving oxides in the cut region. Photographed during work on the Urengol-Ushgorod pipeline in Russia

© RIA NOVOSTI/SCIENCE PHOTO LIBRARY

Daniell cell battery

Daniell cell. Invented by the British chemist John Frederic Daniell (1790-1845), the Daniell cell (left) is made from two half-cells, the electrolytes of which are separated by a porous partition. The positive electrode is copper immersed in copper sulphate solution, the negative electrode is zinc immersed in dilute sulphuric acid. Zinc ions migrate across the porous partition, continuously forming zinc sulphate, while copper is plated out onto the copper electrode. It is the movement of ions which creates the electrical current of about 1.1 volts, which can be measured with a voltmeter (right)

© ANDREW LAMBERT PHOTOGRAPHY/SCIENCE PHOTO LIBRARY

Roll of 35mm photographic film

Photographic film. View of a roll of 35mm photographic film. When the film is exposed to light, silver halide crystals suspended in the film undergo chemical changes to form a latent image. Later the film is chemically processed to develop the latent image into a permanent image. In monochrome film there is only one layer of silver halide crystals. In colour film there are 3 separate layers of silver halide grains, which respond separately to blue, green & red light. During developing, the image recorded by each layer produces clouds of dye of the compl- imentary colour; yellow, magenta or cyan. Together the 3 layers can form any colour of the spectrum

© Tek Image/Science Photo Library