On the Purification of Coal Gas. 139 
gested, that instead of superacetate of lead, an oxide of that me- 
tal be used, which, if any were present, would detect sulphuretted 
hydrogen with more precision. For this purpose we procured two 
large ale-glasses and nearly filled them with water; in one 
some finely-powdered litharge was placed; in the other, dry white 
lead (ceruss); and these substances were well mixed with the wa- 
ter: through each of these mixtures we passed for five minutes 
large streams of the purified gas; but without changing the 
original colour of the oxides in the most trifling degree. A brush - 
covered with white paint was then held under the gas tube; but. 
no alteration could be discovered on the paint. Lastly, the gas 
was passed tlwough lime-water, which was not in any degree 
clouded. These experiments prove to demonstration, that neither 
sulphuretted hydrogen nor carbonic acid gases were mixed with 
the carburetted hydrogen after having passed through this puri- 
fier, The peculiar excellence of Mr. Clegg’s lime-machine con- 
sists in the exposure of a large surface of lime and gas to the ac- 
tion of each other, which is assisted by moderate pressure ap- 
plied in the safest and most ingenious manner. 
The accompanying sketch (Plate I. fig. B) may serve to illus- 
trate its mode of action: a@a represents the vessel containing 
lime mixture; J an inner compartment into which the crude 
gas is conveyed by the pipe c; d the pipe which conveys the 
purified gas to the gasometer; e an opening through which 
cream of lime is supplied. When the outer vessel aa is first 
charged with lime mixture, the deved will be the same in 0 0, as 
will appear by the dotted line; but the moment gas enters by 
the pipe c, the mixture in the inner department is depressed, 
and a column about 14 inches raised and supported in aa, the 
gas at the same time not being able to escape until the lime 
mixture in JL is so far lowered as to expose the narrow divi- 
sions, which then present a means of escape; and bv having yet 
to pass through the column of fluid raised in.the outer vessel, the 
gas undergoes as complete a purification as can possibly be de- 
sired or effected. 
I have here merely endeavonred to describe the mode in which 
coal-gas is purified by the instrument in question. There are se- 
veral convenient appendages attached to it, which make it not 
only an important but a handsome piece of machinery, and 
which I am certain will be found a valuable acquisition to gas 
establishments in general. 
With much respect I am, sir, 
Your most obedient servant, 
Manchester, Jan, 21, 1819. Cu, Boiron. 
XXIII. No- 
