68 0)1 the i'anrMsIL(fcL!s produced hy 



the quantity is reduced by a portion of the metal beirtg loft 

 in the fcoria*. 



To corrcft thefe occafional iinperfcftions in the quality of 

 the air, and to devile methods to procure air always fit for 

 proper combuftion, ought to be an obje6l of much confider- 

 ation to the manufacturer of caft iron. Whether fuch a 

 confideration has given rife to the different modes of receiv- 

 ing and discharging the air now in ufe, I cannot fay; I ra- 

 ther think not: a great quantity of air has hitherto been a 

 greater ohjcft than a certain and uniform quality ; and in 

 a country where there is more temperate and cold weather 

 than hot, it is by far the moft important objeft : to unite 

 both, however, would be an attainment of the grcateft uti- 

 lity, and would rank the difcovcrcr amoncfi; the well-deferv- 

 ing of his country. How far the mechanifm of our prefent 

 machinery has been adapted to the exigencies of our atmo- 

 fphere, will appear upon examining the nature and properties 

 of the air, judged by its effefts upon the blaft-furnace. 



The air produced by ihe blowing and receiving-cylinder 

 is lefs changed, and lefs fubjc6l to chance, than that produced 

 and lodged in contaft with a vafl body of air or water. If 

 tlic blowing-cylinder is fixed in a dry cool fpot, the only 

 difference which the air undergoes is an increafc of tempe- 

 rature ; this is fo very confidcrable, that upon entering the 

 blowing-cvlinder immediately after flopping the engine, I 

 have found the thermometer rife 15 to 17 ^ degrees higher 

 than the funounding air. That this heat is generated in the 

 cylinder is unqueftionable ; but whether it is occafioned by 

 the frlftion of the pifton leather upon the fides of the cylin- 

 der, or expreffed from the air by its fevere compreffion, I 

 have not yet been able to decide. It very probably arifes 

 from both caufes, although the latter is fufficient to prodnce 

 a much greater degree of heat. What effe<Sl this increafe 

 of temperature has upon combuftion we are unable to fay, 

 as the degree of heat accumulated will at all times bear a 

 reference to the temperature of the furrounding air, and as 



* May not the Cuperabundant azote of the fummer ntiv.ofpliere produce 

 part of thcfe cftccfls, by diflblving a poriion of die carbon, and forming 

 carbonated azotic gas, as has been proved by PvL L-.ivoiliLT ? 



tliere 



