ON THE CONSTRUCTION AND HEATING OF HOT-HOUSES, 
247 
and non-inflammable*, are liberated or formed ; and it is the mixing of the latter 
with carburetted hydrogen or coal-gas, which forms what is commonly called smoke, 
observed to rise so thick and dense from steam-engine and other furnace-chimneys ; 
and the difficulty of consuming this smoke, after it is once formed, will appear 
obvious, since it has been proved by Sir H. Davy and others, that one-sixth part 
of nitrogen, or one-eighth part of carbonic acid gas (both products of combustion), 
added to an explosive mixture, will prevent the inflammation of the whole. 
3 
In order to do away with smoke entirely, and to render combustion more com- 
* Non-inflammable, except at a great heat. 
