33^ Phenomeiia ohfeived in the Air-Vault 



?iverage, the produce was immediately incrcafed. It con- 

 tinued to be, on an average of nine months immediately 

 after this improvement, at the rate of 33 tons of iron per 

 week, of as good quahty as forvnerly; for during this period, 

 from the 2ifl of November 1795, to July 30, 1796, this one 

 furnace yielded 1x88 tons of iron. No more coals were con- 

 fumed in working the blall-engine, or other e.xpences about 

 the blowing machine incurred, and therefore no more power 

 was employed to produce this great cflcft. It is alfo of much 

 iDiportance to remark, that the confumption of materials, 

 from which this large produce was obtained, was by no means 

 fu great as formerly. The furnace required very confiderably 

 Ufs fuely lej's ironjlone, and lefs limejhne, than were em- 

 ployed to produce the fame quantity of iron by the former 

 ;nethod of blowing ; and according to the flatements made 

 out by the company's orders, as great a change was effecled 

 in the economical part of the bufinefs. 



From the fuccefs of this experiment, fo well authenticated, 

 and continued for fev^ral months, I am led to be of opinion, 

 that all blaft-furnaces, by a proper adjuftment of fuch ma- 

 chinery as they are provided with, miu;ht greatly and advan- 

 tageoufly increafe their produce, by alluming this as a prin- 

 ciple, viz. *' That with the given poiuer it is rather bj a 

 great quanlitj/ of air thrown into the furnace., ivith a mode- 

 rate velocity y than by a lefs quantity thrown in with a greater 

 '^elocify, that the greatefl benefit is derived, in the fvirlting of 

 irrjnfiones, in order to produce pig-iron." However, it is by 

 experiment alone, perhaps, that we can be enabled to find 

 out the exaft relations of power, velocity, and quantity of 

 air requifite to produce a maximum of effedl *. 



But 



* If Q^be the quantity of a fluid, iffuing in a given time through an 

 Merture of the diameter D, V it; velocity, and P the power Uv which it 

 is forced through the aperture; then the area (jf that apcrtuie being as 

 D*, the quantity of the fluid iffaing in the given time will be as VD', or 

 VD» = Q^ 



Again: this q\.antity multiplied into its velocity, will be as the mo- 

 nentum of the fluid expelled, or as the power by which it is expelled, 

 thatis, V*D^=P, or VD=v'P. . 



Jiere, therefore, if D is given, V is as y'P, as Mr. Roebuck affirm!;. 



Alio, 



