490 



SCIENCE. 



[N. S. Vol. XIX. No. 482. 



into gear, while in another are shown the 

 one chimney where the smoke preventer is 

 in use and the three where it is not, about 

 one minute after heavy firing. 



The writer has experimented somewhat 

 witli air jets maintained by a blower and 

 operated by a dash-pot, but the effect was 

 not so good as when steam-jets were used. 

 When the jets are used intermittently in 

 the manner indicated the waste of steam is 

 small, not over two or three per cent., while 

 the saving in coal is frequently fifteen per 

 cent. Any attempt to solve the problem 

 by admitting a constant additional supply 

 of air through the bridge or side walls has 

 been and will be a failure, since the air 

 supply must be varied as the demand 

 varies. 



Hand firing is at best a crude and un- 

 satisfactory method and is gradually being 

 superseded by mechanical means of feed- 

 ing the coal to the furnace. Mechanical 

 stokers, as they are now called, have two 

 great advantages over hand firing: (1) 

 The uniformity of coal feed which allows 

 a uniformity also in the air si;pply; and 

 (2) the fact that it is no longer necessary 

 to open the door. Add to these the saving 

 of hand labor and the possibility of hand- 

 ling the coal mechanically from car to fur- 

 nace, and you have a good argument for 

 the new way. 



All mechanical stokers, whether inclined 

 grate, underfeed or chain grate, are in- 

 tended to feed the coal steadily and uni- 

 formly at a speed proportionate to the de- 

 mand for steam, and by thus maintaining 

 a constant rate of combustion to simplify 

 the problem of air supply. There are at 

 the present time at least ten different makes 

 of stokers which are capable, when properly 

 cared for, of maintaining this uniform com- 

 bustion in such a way as to prevent smoke 

 and save fuel. Of course somewhat ex- 

 travagant claims have been made by manu- 

 facturers and agents with regard to the 



economy of these machines. Speaking in 

 a guarded and conservative way, it is safe 

 to say that any of the stokers above re- 

 ferred to can show a saving of from ten 

 to fifteen per cent, over the results of or- 

 dinary hand firing. 



Perhaps one of the most common causes 

 of smoke is the overcrowding of the boilers. 

 As the amount of work done in a factory 

 gradually increases, new machines are 

 added, more shafting and puUeys pur- 

 chased, perhaps under pressure from the 

 engineer a new engine is installed. The 

 boiler plant is usually the last to receive 

 attention, although all this time it has been 

 suffering from overload. A boiler gives 

 the best efficiency when worked up to or 

 slightly over its rating ; any further crowd- 

 ing will result in smoky fires and waste of 

 fuel. The writer recalls one instance of 

 this kind where an analysis of the ash 

 showed fifty per cent, of free carbon. 



Although mechanical stokers will some- 

 times increase the capacity of boilers, they 

 are liable to overcrowding as well as the 

 flat grate. This results in fires which are 

 too heavy to be successfully handled and 

 in a loss of economy. Overcrowding also 

 increases the repair bill on both furnace 

 and boiler and is on the whole an expensive 

 experiment. 



Cleaning fires is another common cause 

 of black smoke, in most cases without ex- 

 cuse. A careful and skilful fireman can 

 keep his fires clean and bright whether on 

 flat grates or mechanical stokers, without 

 any great disturbance of running condi- 

 tions. Many firemen do not, either because 

 they do not know or because they do not 

 care. The writer has seen a fireman so 

 completely uproot and tear in pieces his 

 fire in cleaning as to necessitate almost a 

 rebuilding. On the other hand, he has 

 seen a skilful man so clean fires on stokers 

 in an efficiency test where the boilers were 

 being crowded to their utmost, that there 



