The Romance of Modern Chemistry

PRODUCTION OF LIGHT AND HEAT seen that the lime water has become turbid, showing that the air left in the jar after the burning of the candle contained carbon dioxide. The production of water in the flame of a burning candle may be very readily demonstrated with domestic apparatus. A tumbler of cold water, the colder the better, is carefully wiped on the outside, so that it is perfectly dry, and is then held a little above the candle flame. The outside of the tumbler at once becomes cloudy owing to the condensation of tiny drops of water. The extent to which carbonaceous fuel is converted into carbon dioxide and water depends on the supply of the air which supports the combustion. If for any reason the supply of air is cut off, combustion ceases. Hence it comes that a candle cannot continue to bum in a closed space for more than a very short time. Not only does it exhaust the oxygen, but by its own combustion it pro- duces substances which are unfavourable to a continuance of the process. In an atmosphere of carbon dioxide and water vapour no combustion is possible. On the other hand, the more air or oxygen we supply to the burning fuel, the more complete is the combustion. The oldest method of supplying more air to burning fuel, and thereby securing more complete combustion, is the familiar one of making a draught. The difference between an oil-lamp flame with the chimney off, and the same flame with the chimney on, is due to the draught which the chimney makes ; this draught means an inrush of air at the bottom of the chimney and a better supply of oxygen to the flame of the burning oil. Perhaps the reader has tried sometimes to fan the flickering flame of a newly-lit fire by holding a newspaper in front of the upper part of the grate. The result of J 09