various other useful Articles, from Pit-Coal. 335 
when the reservoir is full, and gas is making, and cannot 
be used, the cock may be turned, and prevent any gas from 
passing from the reservoir; and by opening the cock E on 
the top of the purifier, and firing it, all the gas which is 
made more than is wanted for use may be burnt away. If 
this was not done, the gas would continue to find its way 
into the reservoir K, which would overflow, and produce 
a disagreeable smell, which this simple way of burning it 
away as fast as it is made when not wanted, prevents. 
It may in some measure happen, that although the gas 
has passed through the purifier C, yet that a small portion 
of tar will pass along with it, and would cither clog the 
pipe S, or accumulate in the reservoir. To avoid this, there 
is placed at the bottom of the pipe S at G, before it rises 
into the reservoir, a jar into which a pipe made, as shown 
in the drawing, conducts the tar; this collects all that passes 
through the purifier; it is filled with water, over which the 
gas passes up into the reservoir, but the tar drains down this 
lead pipe and deposits itself in the jar of water. The longer 
this pipe Sis, the better, as it serves as a refrigeratory. H is 
a plain cask, made to apy proper size, and filled with water, 
with a cock to draw off the water when it becomes foul. 
The upper vessel K is made of sheet iron, riveted together 
in the manner engine-boilers are made. If it is only from 
five hundred to one thousand gallons in size, it will require 
only two cross iron bars at top, and four ribs dewn the 
sides to keep it in form, with a strong ring at top; and as 
’ there is no stress on this vessel, it will ascend and descend 
easily without any other support or framing, the plain sheet 
iron sides being riveted to the four ribs, and it is quite open. 
at the bottom. A strong rope runs over the pulleys LL, 
with a weight M to balance the vessel K, and assist it in 
rising and falling. The pipe J is that through which the 
gas passes from the reservoir or gazometer, and rising 
through the pipe T; is conveyed to all parts to be lighted. 
There is also another drain pipe at N, for after all the 
washing, &c. a very smal! portion of tar and. moisture 
may rise inte the pipes, and perhaps in time clog them; 
but by laying all the pipes in the first, second, and third 
stories on a small descent, if any tar or moisture should 
rise, it will drain down all the pipes from top to bottom, 
and be deposited in the earthen jar at N: by that means 
the pipes will not clog up in half acentury. These jars 
must be sometimes remoyed and emptied, fresh water put 
In, as also the water in the vessel H must be changed, to 
*keep it clean and sweet; and the water in the purifier C 
should: 
