398. Eaperiments on the. Gas: from Coal. 
decline in the value of the aériform products 
of coal, from the beginning to the end: of 
the distillation, similar to that which takes 
place on a small scale ;—at what stages of 
the process, those gases, which may.be con- 
sidered as impurities, are chiefly evolved; 
and whether they are essential or accidental — 
products ;—whether the method of removing 
the sulphuretted hydrogen, and carbonic 
acid gases by quicklime, which I suggested 
inthe second memoir, is adequate to the com- 
plete purification of coal gas ;—whether this 
purification is attended with any Joss of .that 
portion of the gas which, on account,of its 
superior. illuminating. power,, itis. desirable 
not to remove ;—and, if such a loss should,be 
found to ensue, whether it may not be avoided 
by.some modification of the purifying process. 
In determining these points, I was indebted 
for the necessary supplies of gas to Mr. Lee, 
at whose extensive manufactory, the princi- 
pal, facts were ascertained, that formed the 
basis of the first accurate calculations, . res- 
pecting the economy of gas from coal.*, 
~ * See Mr. Murdoch’s “ Account of the Application of 
the Gas from Coal to economical: Purposes.” Phil. Trans. 
1808,-page 124, hia? 
