NITEATES FROM ATMOSPHERE SCOTT. 381 



A slight change in the kind of coal, and the whole of. the gas appa- 

 ratus has to be readjusted, and in the meantime the gas engines may 

 have dropped to half power. On the other hand, with a steam boiler 

 a change in the quality of the coal makes very little difference. The 

 steam coming away is always of the same quality, however much the 

 fuel may ^'ary. 



The Johannesburg liasco is still fresh in our minds, but before that 

 there had been similar troubles in large gas-power installations in 

 Spain and elsewhere. As compared with the steam boiler, the large 

 gas producer is still a faulty piece of apparatus, although it is being 

 improved. On the other hand, the present type of boiler is not 

 above criticism, for in size it has not kept pace with the steam-tur- 

 bine prime mover. For example, at the Lot's Road power house 

 there are eight boilers for each of the 6,000-kilowatt steam-turbo gen- 

 erators, and the cubic space occupied by the boilers is about five times 

 that occupied by the steam-turbine set. 



In the near future, steam-turbo generators will be of 20,000 

 kilowatts and over — one of larger size than that is now under 

 construction by Parsons & Co. — and as the size of the prime mover 

 increases, this space difficulty of the boilers also increases. It is 

 absurd that one turbo generator should require a dozen or so boilers 

 to supply it with steam. 



A solution of the problem is the manufacture of the coal into gas 

 Avith the recovery of sulphate of ammonia, tar, and oils. Then the 

 gas must be burned in much more efficient boilers than those at pres- 

 ent in use. 



Hitherto gas-fired boilers have been of very low efficiency, say, 

 somewhere about 50 per cent, but with the new method of Prof. 

 Bone and Mr. C D. McCourt an efficiency of over 90 per cent is 

 attainable. The experimental plants at Leeds and at the Skininy- 

 grove Iron Works have demonstrated this beyond a doubt. 



The method depends primarily on mixing gas and ah' together 

 in the exact proportions for complete combustion, then forcing the 

 mixture imder pressure through tubes which are packed with pieces 

 of refractory material. The mixture is fired at the outlet end of the 

 tubes and strikes back to the entrance end. The flame quickly raises 

 the refractory material to an intense heat, and complete combustion 

 of the mixture takes place in about the first 6 inches from point of 

 entry. The combustion having been completed, the remainder of the 

 material acts as a baffle toward the burned gases as they traverse the 

 tubes at high velocity, causing them to impinge repeatedly on the 

 walls of the tubes. The evaporation is sO rapid that the scaling 

 troubles met with in other types of multitubular boilers are com- 

 pletely obviated, the scale being automatically shed in thin films 

 about one-thii^tieth inch thick as rapidlj" as it is formed. 



The core of the material is maintained at a high temperature, but 

 when it comes in contact witli the walls of the tube it is so rapidly 



