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SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE 



VOL. 27 



air holes in the jacket of the boiler, provided the boiler lie wrapped loosely 

 enough not to chill the flame below ignition. It is with reference to this effect 

 that the boilers, Fig. 11, were wound. A number of rifts aaa, Fig. 15, are then 

 lci't in the jacket through which air may enter in virtue of the burner flame act- 

 ing as a jet at the mouth of the boiler. 



" When so constructed the flame at first enters the inner coil only; but after 

 a little while it suddenly spreads out throughout the whole interior space and 

 envelops the coils. This sudden expansion is due, probably, to the assumption 

 of the spheroidal state by the water within the coils, the current now flaring on 

 an enveloping cushion of steam. The pump must work well, for deficient water 

 means a hot tube and deficient steam, or eventually a rupture of the tube. 



" Thus far the dependence for draft has been on the burner jet and the suc- 

 tion of the smoke-stack in virtue of the inertia of the moving gases. But even 

 with this ventilated boiler, this method is limited to certain dimensions of the 

 boiler. Thus a boiler 80 cm. long yielded about the same quantity of steam as a 

 boiler half as long and otherwise similar. Only the initial parts of the boiler 

 are, therefore, relatively efficient, and the reason of this seems to be that, apart 

 from shape, etc., the flame as a heat-producing agent is practically defunct, when 

 a certain amount of heat has been taken out of it : in other words, even with 



--Inside coil 

 ^Outside coil 

 Jacket 



fair ventilation the flame is eventually chilled off by the voluminous products of 

 combustion continually accumulating in the boiler. The same choking action ac- 

 companies the presence of unburnt gases. If, for instance, the flame be burnt 

 in the air, it is slender and much smaller in volume than in the boiler. The flame 

 is also of small volume and burns completely in a wide boiler, hut the steam is 

 always deficient, because of the distance between flame and coils (see above). 

 With the above apparatus about I lb. of dry steam per minute per square foot 

 of heating surface was attained. 



" This introduces the final condition for rapid steam generation. There 

 must be artificial suction at the smoke-stack. By passing the exhaust steam in 

 the form of a central jet through the smoke stack the yield of steam was increased 

 'JO to 30 per cent. In fact as the supply of gas from the burner is given, the 

 artificial suction in question means more air in the boiler for the same amount 

 of gas and it means also a more rapid removal of the exhaust gases. The ex- 

 periments with steam suction are yet to be completed, and with them the boiler 

 question is to be finally laid at rest. The chief points at issue are these: 



" 1. Seeing that the jet suction increases with the length of the smoke-stack, 

 up to a certain length at least, how long and how wide must the efficient smoke- 

 stack be made? Thus a smoke slack 10 cm. long is all but useless. Good re- 

 sults are obtained when the stack measures 30 cm. in length beyond the end of 

 the steam jet. 



