All About Engines

196 All About Engines gases then pass up through a tower filled with lumps of coke over which water is continually flowing. In this way they are freed from dust, which, if it entered the engine, would choke up the valves and lead to undesirable wear. As the coke in the lower portion of the scrubber comes first into contact with the gases it needs to be renewed more frequently than that in the upper portion. Each portion, therefore, rests on a separate tray, so that one can be renewed without interfering with the other. One great advantage of the suction gas producer, as compared with the earlier form, lies in the fact that the pressure inside is less than that of the atmo- sphere. Carbon monoxide is an extremely poison- ous gas, and is exceptionally dangerous because it has no smell. There is no simple chemical test by which its presence in the air can be detected, and it is a common plan to use a bird or a mouse as a sen- tinel. These little creatures are much more sensitive than human beings, and fall into a stupor long before a man would be affected. But with a suction gas producer there is practically no danger. The fuel employed may be anything that will burn. Good results are obtained with coke, but the best are given by anthracite. From this fuel at 30s. a ton, gas equal in heating value to the best town gas can be produced at nd. per thousand cubic feet. The stand-by losses are also small. When the engine is not working, just sufficient air is allowed to pass through to keep the fire in, and the coal consumed in a ioo-horse-power plant during an all-