ECONOMIZER. An important adjunct to a steam-generating plant. Instead of being allowed to escape to the chimney direct from the furnaces, the waste gases are led through passages in which are placed sets of vertical tubes. Water passes through the tubes and the heat of the gases raises it to a useful temperature for various purposes, not merely to supply the feed for the boilers, but also for supply where a large quantity of hot water is required, as in laundries, hotels, breweries, dyeworks and so on. At the same time, strains on the boiler plates and parts through exposure to an inflow of cold water are prevented. Scale trouble in the boiler is also greatly reduced, because the scale forms instead inside the econo mizer tubes, and these are readily cleaned. Some 15% to 2o% of coal is saved on the installation of an economizer. Evidence of this is the fact that if the gases leave the boiler at 65o° F, the feed-water entering the economizer at 1 oo ° F will leave it at 2 7 2 ° F, reducing the temperature of the gases to 33o° F. The Green economizer consists of a number of vertical cast-iron tubes, 4-5in. external diameter, made up in sections, and connected with branch pipes at top and bottom. The outside of each tube is kept clean by encircling scrapers, which travel slowly up and down all the time, actuated by automatic mechanism at the top. The soot falls into a pit for convenient removal. There is also a horizontal type of economizer which is mounted above a water-tube boiler. In some designs of econo mizers tubes with gills are used, to obtain the maximum heat transference, and the soot is cleaned off by steam blowers.