Carhov at cd Hydrogen Gas from Pit Coal. 21 ^ 



veys all the volatile products of the coal to the refrigeratory 

 of cast iron E f in which the tar, &c, extracted from the 

 coal is deposited, and from whence they can be pumped out 

 by means of the copper pipe F. G is the pipe which con- 

 veys the gas to the top of the cylindrical vessel or receiver 

 H ; this receiver is air tight at the top, and consequently 

 the gas displaces the water in the vessel H, to a level with 

 the small holes, where the gas is suffered to escape and rise 

 through the water of the well 2, into the large gazometer K. 

 The use of the vessel H is pointed out as follows, viz. If 

 the pipe G reached all through the wate-\ without passing 

 into the vessel H, the gas would not be rendered pure or 

 washed ; and if part of the pipe did not rise above the water, 

 the water would have free communication with the tar, be- 

 sides exposing the retort ^/toa very great pressure, so as to 

 endanger its bursting when red hot. This vessel or receiver 

 H, in a large apparatus, is about eighteen inches diameter, 

 and two feet long; the quantity of gas, therefore, which it 

 contains, is sufficient to fill the pipes and retort when cool, 

 and prevents the pipe G from acting as a syphon, and ex- 

 poses the gas to the water without endangering the retort. 



When the operation begins, the upper part of the cylin- 

 drical gazometer K, fig. 1, made of wrought iron plates, is 

 sunk down nearly to a level with the top of the circular 

 well 7, and is consequently nearly filled with water, but it 

 rises gradually as the gas enters it and displaces the water; 

 the two weights LL suspended over pulleys by chains keep 

 jt steady and prevent its turning round, otherwise the lower 

 stays M of the gazometer would come into contact with the 

 vessel H. There are two sets of these stays, one shown at 

 M, and the other at N. 



There is also an iron pipe made fast in the centre of 

 the gazometer by means of the stays, which slides over the 

 upright pipe P, by which contrivance the gazometer is kept 

 firm and steady , when out of the well ; it likewise prevents 

 the gas from getting into the cast iron pipe P, and the cop- 

 per pipe P. any where but through small holes made in the 

 pipe at S at the top of the gazometer, where the gas is 

 perfectly transparent and fit for use. 



The 



