'12 REPOKT— 1878. 



3. On the Dublin Waterworks. By Parke Neville. 



4. The Design and Use of Boilers * By F. J. Rowan, M. Inst. M.E. 



The close relation between the engineer and the physical philosopher, though 

 obvious and often pointed out, has not been fully admitted. Yet the fact necessitates 

 the possession of accurate scientific knowledge in dealing with engineering problems, 

 and none demands it more strenuously than does that of the designing and working 

 steam boilers, and especially marine boilers, for various reasons. The proper genera- 

 tion of steam and circulation of heated water and gases are now attracting more 

 general attention than hitherto, and this is hopeful, because attention to principles 

 of thermo-dynamics has led to vast improvement in the steam-engine. On these 

 principles we must decide wh'at is the best pressure of steam to "work with, and 

 then we must study scientifically the characteiistics of a good boiler. 



Professor Osborne Reynolds's table of pressures of steam in relation to economy 

 and development of power is quoted, and also one compiled from Regnault and 

 other authorities to show the weight of water raised from 0° 0. to the state of 

 vapour at various temperatures by 1 lb. carbon. 



It being proved that high pressures of steam, say 150 to 200 lbs. per square inch, 

 are most economical, we need to find in a good boiler — 



1. The most economical and efficient means of generating steam of that pressure. 



2. Strength to carry it with safety under all the exigencies of practical working. 



3. Facility of construction and repair. 



1. Under the first head (a) combustion is first considered, and the theoretical 

 effect of the perfect combustion of 1 lb. carbon being known, we have a standard to 

 go by. 



But varying qualities of coal and unvarying defects in the mode of mixing the 

 coal and air produce bad results. 



Suction draught by jet blast is no real improvement. Mechanical stoking meets 

 imperfectly — more or less — only one evil ; and a combination of mechanical stoking 

 with forced combustion, or combustion under pressure, is needed for all the diffi- 

 culties of the case. 



A plan which the author proposes is illustrated and described. 



(b) Circulation of the heated gases necessarily comes in as an important ele- 

 ment under this head. The elements of quality of heating surface and time of 

 contact require to be taken into consideration, and show that the speed of travel of 

 the hot gases must be under control ; while surface is valuable in proportion as it 

 can deal with the heat brought to it by quickly transmitting it to a medium which 

 will convey it away. 



The plan of turning the gases downwards before they escape to the funnel prac- 

 tised by the author's late father, in conjunction with tbe plan of forcing in the pro- 

 ducts of combustion just proposed, allows the time of contact to be quite under 

 control, and only the heaviest, i e., the coolest, gases escape— not the hottest first, as 

 in up-draught arrangements. An interesting instance of saving in heat by giving 

 gases a downward current is quoted in a note. 



(c) Heating surface is then considered ; and the laws of thermal conductivity 

 are referred to. Formulae by Wiedmaun and Franz, and by Clerk Maxwell, express- 

 ing the quantity of heat which can be passed through the metal of boilers in a given 

 time, are quoted ; and also the results of Angstrom's investigations of the same 

 subject. These show that the relative values of different kinds of heating surface 

 must be determined by the facility of access which they afford to the heated gases 

 on the one hand and to fresh portions of the water on the other, and not by any 

 arbitrary rule as to their being in a horizontal or vertical position. 



(d) Circulation of water thus appears as one of the most important, though it is 

 one of the most generally neglected points in boiler design and working. 



The specific heat of water and that of steam being so different, it is necessary to 



* Published by E & F. N. Spon, London. 



