46 CONSTRUCTION AND MANAGEMENT OF SMALL GASWORKS. 



apparatus between the hydraulic main and the gasholder is 

 simply a miscellaneous collection of cast-off stuff from 

 larger works, that is simply eating its head off, so far as 

 satisfactory working results are concerned ; and some of it 

 was possibly rejected and disposed of as much because of 

 its proved inefficiency as to make way for larger. 



It is true that the tar and liquor may be valueless, but 

 granting that such is the case, there is still a necessity that 

 the tar should be all taken out before the gas reaches the 

 dry purifiers, and that the ammonia should be extracted and 

 its purifying capabilities fully utilized. It is cheaper to 

 extract carbonic acid with ammonia than with lime. As a 

 matter of fact, an ample-sized foul main, condenser and 

 washer are as necessary in the small works as in the large, 

 and are equally a good investment. The foul main may be 

 carried round three sides of the retort house, and through 

 the purifier house, or coal shed, if these are adjoining, 

 before passing out to the condenser. And the fall should 

 be towards, and not away from, the flow of gas. The late 

 R. H. Patterson pointed out, many years ago, the advan- 

 tages incidental to drawing off the condensed liquids at 

 the hottest part. It is a known fact that lengthening an 

 ascension pipe has been found a cure for obstinate choking. 

 A foul main inclined towards the hydraulic, so that all the 

 condensed liquid flows back against the current of gas, 

 provides both advantages, and the practical result is 

 improved illuminating power, and that the hydraulic main, 

 seal trap, etc., are kept clear and free from pitch. I have 

 known the addition of a foul main on this principle to 

 improve the illuminating power to the extent of 2 candles, 

 enabling a cheap local coal to be used without the aid of 

 cannel or enriching material, and entirely obviating stop- 

 pages in the condenser or the clogging of the purifying 



