137 
Iron o 
To correct these occasional imperfections in the quality 
of the air, and to devise methods to procure air always fit 
for proper combustion, ought to be an object of much con- 
sideration to the manufacturer of cast iron. Whether 
such a consideration has given rise to the different modes 
of receiving and discharging the air now in use, I cannot 
say ; I rather think not : a great quantity of air has hither- 
to been a greater object 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 most important object 
to unite both, however, would be an attainment of the 
greatest utility, and would rank the discoverer amongst 
the well-deserving of his country. How far the mechan- 
ism of our present machinery has been adapted to the ex- 
igencies of our atmosphere, will appear upon examining 
the nature and properties of the air, judged by its effects 
upon the blast-furnace. 
The air produced, by the blowing and receiving-cylin- 
der is less changed, and less subject to change, than that 
produced and lodged in contact with a vast body of air or 
water. If the blowing- cylinder is fixed in a dry cool spoy 
the only difference which the air undergoes is an increase 
! of temperature ; this is so very considerable, that upon 
entering the blowing- cylinder immediately after stopping 
the engine, I have found the thermometer rise fifteen to 
seventeen and a half degrees higher than the surrounding 
j air. That this heat is generated in the cylinder is urn 
! questionable ; but whether it is occasioned by the friction 
of the piston leather upon the sides of the cylinder, or ex- 
pressed from the air by its severe compression, I have not 
yet been able to decide. It very probably arises from 
both causes, although the latter is sufficient to produce a 
much greater degree of heat. What effect this increase 
of temperature has upon combustion we are unable to say, 
as the degree of heat accumulated will at all times bear a 
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