994 Transa-ctions of the American Ixstituie. 



passes down in a circuitous direction, was tried, but it was found that 

 the bottom of the water was cold and the top hot. This was 

 due to the unequal expansion. The Perkins' boiler, spoken of by 

 Mr. Fisher, are the best that can be used. He had seen one of them 

 working where the steam blew right tlirough, and he also noticed the 

 gauge cock raise ten pounds in ten minutes. No other boiler could 

 be made to do this. The importance of a good circulation in boilers 

 to secure an equal temperature, and thus remove one of the principal 

 causes of explosion, is not sufficiently understood. 



Mr. C. E. Emery said the subject of circulation of water in 

 boilers is a very interesting one. Let us take the simplest form of 

 boiler, and see how inventors have undertaken to remedy its defects. 

 In practice, the currents go up on the sides and bubbles of steam, 

 would tend naturally to rise ; but the water is also tending to take 

 its place, and, unless the surfece is sufficiently extended, the circula- 

 tion will not be perfect. In the plain form of cylinder boiler the 

 currents go in two directions. In the tubular boiler the steam rises 

 up between the tubes and on the sides ; but the greatest heat is at 

 the crown sheet. The water rises up through the tubes, and higher 

 at the front end than tlierear, and in this mannei'it moves downward. 

 This is determined by water gauges, which prove that the water is 

 higher at the front than at the back of the boiler. The great diffi- 

 culty in this form of boiler is the want of circulation. In another 

 form of boiler the tubes are screwed into a larger one, lying hori- 

 zontally, the sealed ends of the smaller tubes being a little lower 

 than the ends opening into the larger tube. The water level i» 

 adjusted to half HU the larger tube, and completely fill the smaller 

 ones at their sealed ends. Tubes sealed at one CMd are often set 

 inclined, and entirely below the waiter level, with their open ends 

 connected to a front chamber. Alban, a German engineer, in \\\l> 

 work on the steam engine, says he made such a boiler many years 

 ago, and provided means to introduce the cooler water into the bot- 

 . tom of each tube, and take out the hot water into a separate channel 

 at the to]) of each ; but he had no way of producing positive circu- 

 lation in the tube itself. Sargent, in tliis country, uses a similar 

 arrangement of tubes, but places in each a diaphragm, extending 

 nearly the Avhole length, the water expected to pass down above it 

 jmd up beneath it. He has no means of separating the currents in 

 the front chamber. Mr. Miller, in one of his boilers, uses tubes simi- 

 larly arranged, but places a circulating tube inside each, which 



