COLD AND HOT BLAST VS. COMBUSTION.
There are four kinds of blast. The first is called " cold blast," the second ''warm blast," the third " hot blast," and the fourth " superheated blast." Cold blast is generally employed by founders in remelting metals in a cupola, air, or crucible furnace; also by charcoal blast furnace operators. Warm, hot, and superheated blasts are generally used for smelting ores to produce iron or other metals. Warm blast is air heated from 250 to 400 degrees F. Blast heated above 1,100 degrees F. is generally termed superheated blast, and if the temperature ranges from 700 to 1,100 degrees F. it is generally known as hot blast. There are two properties in the blast, the first being physical and the second chemical. With a temperature of 60 degrees F. and the barometer at 30 inches, air weighs about one-eight-hundred-fifteenth part as much as water.* The weight of blast passing through a furnace in smelting ore to produce iron is greater than the combined weight of the fuels, ore, and flux charged. Blast or air contains chiefly a mixture of two gases, nitrogen and oxygen, which is recorded by volume and weight in the following Table 14:
* Table 131, page 591, at the close of this work, gives the difference in value of degrees between Fahrenheit and Centigrade methods.per R is quickly thrust into the hole, which at once chills the slag around it, and stops the leakage of blast. The stopper R is a wrought iron bar with a cast iron cone cast on the rod which forms the plug as shown. The difference between this method of tapping a flushing-hole and the old plan used is simply in the convenience, and the use of clay is avoided. The iron and slag-holes of a furnace are sometimes lowered or raised from their original positions by reason of a furnace filling up with chilled iron, but if this can be avoided by tapping the