24 Dr. Playfair’s Lecture on the Great Exhibition of 1851. 
chemical survey of these four divisions, and show you how every- 
where chemistry is affording her aid; but as this is impossible, I 
must content myself with isolated examples from the manufac- 
e mode of smelting iron consists in mixing the ore with 
lime.and coal, the former producing a slag or glass with the im- 
purities of the ore, while the coal reduces the oxyd of iron to its 
metallic state. Much heat is required in the process of smelting, 
but the cold air blown in, as the blast, lowers the temperature, 
and compels the addition of fuel, as a compensation for this re- 
duction. Science pointed to this loss, and now the air is heated 
before being introduced to the furnace. ‘The quantity of coal is 
_ Professor Biinsen, in an inquiry in which I was glad to afford 
him aid, has shown that she can. We examined the furnaces, 
in each portion of the burning mass, so as fully to expose the 
operations in every part of the blazing structure. This seem- 
means ; the furnaces are charged from the top, and the materials 
gradually descend to the bottom; with the upper charge a long 
graduated tube was allowed to descend, and the gases streaming 
according to the cl 
* Although the smelting of iron is not strietly within the division of manufactures, 
Hon SER co os one bat, eee mr 
Sei» ate Ur a a ge z J a} 
