488 TRANSACTIONS OF THE 



than 15 lbs. per foot of surface, and not less than 8 Ihs. per lb. of fuel ; 

 that costs not more than $1,50 per foot of surface ; and is accessible for 

 repairs ; and has few and simple joints. If it is light, so much the better; 

 but a heavy boiler tells in the fuel bills, and the bills for repairs of wheels 

 and roads, and is really of less expense than a complex and fragile boiler, 

 that costs more at first, and requires frequent repairs. Whoever can pro- 

 duce a new boiler, that in the highest degree combines these qualities, will 

 make a fortune by it if he manages it well. 



There may be considerable improvement ir. the present boilers ; they 

 may be made of steel, and much lightened ; the fire-boxes may be welded ; 

 and, perhaps, the outer shells may be welded ; which would make them 40 

 per cent, stronger, and more free from leakage. For very small upright 

 boilers, it is desirable that the fire-box should be free from the incum- 

 brance of riveted joints ; and if the weld is so good as not to leak, it will 

 be strong enough, supposing the fire-box to be stayed to the outer shell, as 

 it always should be. 



I will close this paper by expressing my conviction that high-pressure 

 boilers ought to be used in ships, in combination with both high and low- 

 pressure engines — the steam working first in the high pressure engine, and 

 being exhausted into an intermediate chamber ; from which, it should go 

 to the low-pressure engine. This would involve the necessity of fresh 

 water for the boilers ; but I believe this can now be supplied. 



After the reading of Mr. Fisher's paper, Mr, Tillman remarked, that to 

 produce perfect combustion, two-thirds of the air which supports the com- 

 bustion should be admitted below the fire grate, and one-third above ; and 

 that engines so constructed are now in use on the Hudson River railroad. 



Mr. Garvey considered that the employment of spirals in the tubes, by 

 European engineers, was only effective in delaying the warm gases, so that 

 they should part with a greater share of their heat, and consume more per- 

 fectly ; and that, if the fact stated by Mr. Fisher were exactly eon-ect, the 

 advantanfe of employing a quick current of smoke must be due to the de- 

 velopment of electricity, as friction ahvays produces some. 



Mr. Dibbin, in commenting on the production of steam, said that vapori- 

 zation is due to the heat from the fire ; and when steam, in the open air, 

 is produced rapidly, the lower stratum of water is at a less temperature than 

 212^^ when steam is being given off, and the upper stratum of water, or, at 

 least, the steam, is fully 212**, or more ; also, in the upright tubular boilers, 

 there is steam in contact with the tubes, not water, and to this the advant- 

 ao'c of such boilers is due, for the steam becomes super-heated whilst it is 

 beina generated. There is an interesting fact which he would like to hear 

 practical remarks upon, namely, " a marine boiler, above the water surface, 

 wears out in one-third the time that a fresh water boiler will last." 

 Prof. Hedriek thought it could not be a fact. 



Mr. Dibbin had seen a boiler so damaged in patches as to become use- 

 less, though to all appearance it was sound. 



