PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 773 



with tubes ! As to complete circulation of the water, like the 

 ocean currents, it is seldom eflected. Most of our boilers can be 

 much improved by simply increasing the circulation of the water, 

 for the more rapidly steam made at the heated boiler plate, can 

 be mechanically carried to the surface, the more power we get 

 from a pound of coal, and so much less danger is there from 

 explosion. Premising that explosion is a violent action by which 

 the boiler is torn asunder, and all the steam and generally all the 

 water forced out, and not a simple rupture of the weakest part of 

 a boiler, letting out sufficient steam to reduce the pressure, I say 

 no boiler can explode that contains only steam and compact water, 

 if a proper safety valve is used. Here a word about the safety 

 valve; it is too frequently the case, that a number of boilers are 

 connected by one steam pipe, and that, for convenience, the safety 

 valve is placed in a position where it can, under no circumstances, 

 be more than a pressure gauge. It is a well known fact, that an 

 ordinary fifty norse-power steam boiler, with ample grate surface 

 and good draft, cannot make steam fast enough to maintain any 

 working pressure with a hole of 2 5-8 inches diameter in the shell 

 or other part of the boiler. Yet if this hole leads into pipe twelve 

 ftjet in length, having four elbows placed horizontally, the same 

 boiler Avill make steam enough to maintain forty pounds pressure, 

 while the steam is "blowing off" continually. It must therefore 

 be evident, that directly on the boiler and on each boiler, is the 

 proper place for the safety valve. 



It is laid down in every book on engineering, that a certain 

 number of square feet of heating surface of a boiler, with certain 

 proportion of grate surface, gives one nominal horse power, or at 

 least is equivalent to a certain amount of power. Such is not the 

 fact, and although the amount differs with each statement in such 

 books, yet not one of them is correct, even in respect to the same 

 kind of boiler. After the most careful experiments no such state- 

 ment can be verified, for surface has no relation to the steam 

 capacity of a boiler, at least not as now understood. 



In the well known "Hecker Brothers' flour mills" in this city, 

 where boilers, engines and attachments are of superior construc- 

 tion, and where no expense has been spared to jH'oduce the best 

 possible results, I placed within the boilers simple tubes like 

 those I exhibited here some evenings since, and reduced the con- 

 sumption of coal fully 30 per cent. Also, in a small boiler in this 

 city, by simply improving the circulation of the water, I have 



