712 Traksactions of the American Institute. 



asunder, amounts to the enormous total of one million three hundred 

 and fifty thousand pounds, or if the boiler is cai'rying 100 pounds 

 per square inch, two million seven hnndred thousand pounds. Start- 

 ling as these figures may appear they are correct, and are far below 

 the actual facts in many cases, as, for instance, a boiler m a steam 

 flouring mill in New York city has a diameter of about seven feet^ 

 and hence circumference of about twenty-two feet or 264 inches, 

 and sixteen feet or 192 inches in length, or an area of shell of 

 50,688 square inches, which multiplied by ninety pounds, the 

 regular pressure, gives the total of four million ten hundred and 

 sixty-one thousand nine hundred and tw^enty pounds as the pressure 

 constantly sustained by the shell, not including the tubes or tube 

 sheets. This boiler is being overworked to a dangerous degree, so 

 much so that the sheet iron smoke pipe leading to the stack is often 

 red hot. 



It is surrounded by a very valuable property, and many lives are 

 hourly exposed to the terrible consequences that would result from 

 Its explosion. 



The tubes used in the safety boiler are four inches in diameter, 

 c»r say twelve inches circumference by ten feet or 120 inches long, 

 having an area of 1,440 square inches, hence at fifty pounds the 

 total bursting pressure is but 72,000 pounds instead of 900,000 

 pounds, which would be the pressure in a shell four feet in diame- 

 ter and ten feet long. 



Haswell says, in his Engineei'''s and Mechanic's Pochet Book: 

 •' The resistance to collapse of a flue or tube is much less than the 

 resistance to bursting.''^ Experiments show about one to two. This 

 is an important point, as our tubes are subject to bursting strain 

 only, and hence are stronger than in the ordinary boiler. The 

 tubes in the common forms of boilers are, however, many times 

 stronger than the shell. 



It is a well-known practical fact, that boiler tubes do not explode, 

 as is the case with the shells of boilers; but that excessive pres- 

 sure, many times greater than the shell will bear, merely causes a 

 rupture of greater or less extent, and thus relieves the pressure 

 without serious damage. 



Each of these tubes, containing but a small amount of water or 

 steam, might be ruptured without dangerous results, thus relieving 

 the boiler and preventing disaster. 



The first form of boilers, the plain cylinder, being very uneco- 

 nomical in fuel, and occupying the greatest space per horse power, 



