484 TRANSACTIONS OF THE 



be passed into the air chamber from below, the lower trap -door closed, and 

 the man or barrel passed to the surface through the upper trap-door, which 

 is intended to be always above water. 



Mr. Fisher being called upon, read his paper upon steam boilers. 



MR, FISHER ON STEAM BOILERS. 



In tilis paper I purpose to treat of locomotive boilers, and those which 

 are used for steam carriages, fire-engines, and other purposes which require 

 liohtness. 



The locomotives built before the multitubular boiler was invented, vapor- 

 ized more water per foot of surface than those of the present time. The 

 Killingswovth engines vaporized 24§ lbs. of water per foot of surface ; but 

 the best modern boilers vaporize but 15 lbs. ; and ordinary boilers not more 

 than 10 lbs. This difference is due to the greater proportion of fire-surface, 

 and the smaller proportion of flue-surface in the early boilers ; and not to 

 any great superiority, even on the score of lightness. The extended flue- 

 surface of modern boilers is lighter than an equal extent of surface in the 

 old boilers ; and it has the advantage of saving fuel. The old boilers 

 vaporized five or six pounds of water per pound of fuel ; the modern boilers 

 vaporize nine or ten pounds. 



Kecent practice has illustrated the merits of the two systems — that in 

 which fire-surface superabounds, and that in which flue-surface supera- 

 bounds ; and it appears that a medium proportion, in which there is more 

 surface exposed, to the radiant heat of the fire, and less to the contact of 

 smoke, gives a more economical result. There have been cases in which 

 flues have been reduced from eleven feet to four feet in length, the vacated 

 space being converted into a combustion chamber, and. yet the generation 

 of steam and the economy of fuel are increased ; and, in one of the South- 

 Western railway engines, the flues were reduced to twenty-two inches in 

 length, and with a good result. 



In the old engines, the grates were lar^ger than in the new, in proportion 

 to the total surface ; but not, therefore, larger in proportion to the vapor- 

 izing power. In recent coal-burning engines, the grates are larger, 

 approaching the early proportion, say one of grate to forty of surface ; one 

 to eighty-five being common in the multitubular systems, and one to 125 

 being sometimes adopted. 



The steam room is an important element in a boiler. If it is deficient 

 or ill disposed, the boiler will prime; and, intimately connected with this, 

 the area of water-level, which allows the steam to separate from the water, 

 is also important. One square foot of water area to thirty-flve of heating 

 surface, is not uncommon ; but one to tAventy-five is observed to work 

 better ; and one cubic foot of steam room to thirty square feet of surface 

 is frequent in practice. These proportions are for about 100 lbs. pressure — 

 if the pressure is much less, priming ensues ; if much greater the steam 

 room may be diminished. It seems that a certain volume of steam may be 

 delivered from a certain extent of water area and steam room ; and it makes 



