Dr. Playfair’s Lecture on the Great Exhibition of 1851. 35 
Coal-Gas.—The manufacture of coal-gas is an admirable ex- 
ample of the benefits conferred by Chemistry in all the three 
divisions of its uses; for it not only has economized human 
with its fuming smoke. It required a man of courage, as in- 
domitable as Winsor, its great advocate, to persuade the public 
P 
gas are sulphuretted hydrogen, which tarnished the metals, and 
with sulphuret of carbon produced sulphurous fumes; ammoni- 
acal compounds, which changed the colors of dyes and acted on 
leather ; tarry vapors, which caused the deposition of soot; and 
all these had to be removed. The ammonia and the tar were 
partially condensed in tubes kept cool, the sulphuretted hydrogen 
and carbonic acid were removed by lime, and the ammonia by 
washing the gas with water. This last operation was the least 
effective, and new substitutes had to be devised, one of which I 
may mention; superphosphate of lime, consisting of bones dis- 
solved in sulphuric acid, only required ammonia to make it a 
powerful and excellent manure; trays of this superphosphate 
Were therefore placed in a chamber through which the gas passed, 
and thus the ammonia was removed, while the phosphate became 
enriched, A new method is now extensively employed, a 
Shows the tendency to simplification resulting from discovery. 
