^^^o Phenoniena obferved i7i the Air-Vault 



This contrivance was confidered as of much ufe, and was 

 afterwards always quoted in the company's journal books, to 

 {how the aftual (late of the blowing machine, in comparing 

 the daily produce of the furnaces. 



I hope you will not think me tedious, when I explain to 

 you another experiment, which appears to me to be of con- 

 iiderable importance to all manufafturers of caft iron. 



I had reafon to conje£lure, from my own obfervations on 

 the efFefts of blowing machinery on blaft-furnaces, as well 

 as from the knowledge I had acquired from my father. Dr. 

 Roebuck, and from my communications with other expe- 

 rienced iron mafters, that a great part of the power of fuch 

 machinery was mifapplied in general practice by throwing 

 air into furnaces with much greater velocity than neceflary ; 

 and that, if this velocity was^ to a certain degree, diminifhed, 

 the fame power, by properly adjufting the blowing machinery, 

 of whatever nature, would be capable of throwing into the 

 furnace a proportionally greater quantity of air. For, " Since 

 the quantities ojanyjiuid, i(fuing through the fame aperture^ 

 are as the fquare roots of the frejfure'" it follows, that it 

 would require four times the preffure, or power, to expel 

 double tlie quantity of air, through the fame aperture, in the 

 f^me time : but if the area of the aperture was doubled, then 

 the quantity of air expelled by the fame power, and in the 

 fame time, would be increafed in the ratio of the fquare root 

 of % to I, though its velocity would be diminifhed exadlly in 

 the fame proportion. Again : I confidered that the quantity 

 and intenfity of heat produced in blaft-farnaces, and confe- 

 quently its effefts in increafing the produce, might be only 

 in proportion to the quantity of air decompofed in the proceft 

 of combuftion, without regard to its greater velocity ; that is 

 ta fay, whether or not the fame quantity of air was forced, 

 in the fame time, into the furnace through a fmall pipe, or, 

 through one of larger dimenlions ; for, in attending to the 

 proccis of a ccmmon air-furnace for remelting of iron, where 

 there is a very large quantity of air admitted through the large 

 areas between the bars, it is well known that a much greater 

 inteufity of heat is produced than takes place in a blaft-fur- 



nac^ 



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