988 TEAysACTioxs of the American I institute. 



Influenced by these views, I have attempted to devise a remedy 

 for the notorious moisture of steam in tlie boilers of this period, 

 especially those wliich, for the sake of safety, are made up of small 

 tubes or spheres. . And I have settled down in the belief that the 

 true remedy is in conforming to the laws of nature which Wutt dis- 

 covered and taught, namely, that a certain amount of steam room 

 and of separating surface must be given to insure dry steam. If a 

 superabundance of water-level be given, less steam room will sufHce ; 

 and if a superabundance of steam room be given, less water-level will 

 suffice ; but how much of the one will atone for a given deflciency 

 of the other, is a question which I propose for discussion. If trials 

 show that a greater proportion of steam room is necessary to the 

 best effect, there are three means of getting it : First, the generating 

 tubes may be larger; second, the water may be carried lower; and 

 third, the pressure may be higher, so as to reduce the volume of 

 steam. In cylinders, the water-level and the heating surface increase 

 as the diameter, while the steam room increases as the square of the 

 diameter; hence the proportion of steam room increases as the diam- 

 eter. Therefore, if we wish to produce a greater volume of steam, 

 we must proportionally^ increase the diameter of the tubes in which 

 the steam is made. The tubes here shown are seven inches, and 

 the pressure is 140 pounds, and fifteen square feet of heating surface 

 is allowed to vaporize one cubic foot of water per hour. Suppose 

 that Ave have to increase the firing to do more work, we must increase 

 the pressure ; that is, we must keep the volume of steam constant, or 

 we shall have damp steam. If so high a pressure be disapproved, 

 and it be required that the usual pressure, seventy pounds, be 

 adopted, then the tubes must be fourteen inches to make steam equally 

 dry. I cId not here make allowance for the density of the steam, and 

 its effect in buoying and carrying particles of water, because I know 

 of no experiments to determine that part of the question, and because 

 it is not necessary in order to prove the superiority of the s^'stem I 

 am advocating. 



It is obvious that these rules favor a diminished volume, that is, a 

 higher pressure of steam; all modern boilers require a high pressure 

 to keep water in them ; and all will make dry steam if the pressure 

 be kept so high that not more than 300 feet per hour shall be made 

 for each foot of steam room. But the pressure requi-ied by this con- 

 dition could not be borne with safety by large-shelled boilers ; the 

 tubes licre shown will bear six times more pressure than the shells of 



