342 ECONOMY OF FUEL FOB, STEAM MACHINERY. 



either by hollow stay bolts, or by larger openings, which may be 

 opened or shut at pleasure. 



" If the gases in passing through the boiler are left to themselves, we 

 get without an effort the effect produced by Montgomery's third 

 claim, viz., the application of the heat to the upper half of the tubes, 

 by which circulation is established. And, however we wish to apply 

 the passing heat to the flues, complete control over the motion of the 

 gases may be had by a Venetian blind draught regulator at the smoke- 

 box end of the flues, made in two parts, the upper and lower parts 

 moving independently. Of course, by opeuing the lower and closing 

 the upper damper, we draw the gases downwards, and vice versa. 



" It might be objected that so much flat boiler surface would make a 

 form more liable to explosion, than the circular barrel. Experiments 

 lately made by Win. Eairbairn of England, induced by the bursting 

 of a locomotive fire-box at the flat sides, prove that the flat surfaces 

 are the strongest part of the boiler, or, to use his own words, ' are 

 conclusive as to the superior strength of flat surfaces, as compared with 

 the top, or even the cylindrical part of the boiler.' His experiments 

 show that two plates, 1-4 and 3-8 in., connected by screw stay bolts 

 at a distance of 4 inches from centre to centre, will resist over 1000 

 lbs., square inch, and where 5 inches from centre to centre over 500 

 lbs." 



By such a plan of engine we may always have any amount of heat- 

 ing surface with a moderate sized boiler and a low centre of gravity. 



Of course such a boiler would be impossible with inside connections, 

 but apart from the difficulty of keeping the flues tight and preventing 

 an accumulation of ashes and dirt on the lower flue sheet, there does 

 not appear to be any great practical difficulty in the way of construction 

 — though, with the insertion of ferrules in the upper end of the tubes 

 a serious obstacle would be offered to the disengagement of the steam 

 which might result in overheating the metal, and even to explosions. 



It has been surmised that the latent heat in water under pressure 

 could be more freely disengaged by the agency of electric currents, and 

 that in this way a great saving of fuel would be effected. We have 

 not until recently seen any definite proposal as to the mode of apply- 

 ing this agency. A Mr. Harshman of Dayton, Ohio, however, pro- 

 fesses to have made some important discovery in this direction, but 

 the details of his experiments are given in such a manner as not to 

 inspire much confidence in their value. Had the duration of the ex- 

 periments — the time required to raise the steam to the pressure indi- 

 cated — the temperature of the water at the commencement — the 



