PURIFIERS. 1 1 1 



as it is attended with less nuisance, less pressure (which is also of importance) , 

 and the sulphur which has united with the lime may be sublimed from it by 

 putting the spent lime from the machine into burnt-out retorts kept at a heat 

 just red by daylight, with the refuse coke dust and cinders, for which there is 

 no sale. The sulphur thus produced is a marketable commodity. The larger 

 the surface of dry lime to which the gas is exposed the better ; for if it be 

 allowed to pass through the stratum with much velocity and in an undivided 

 stream, it will work a passage in such a way that a great bulk will not be 

 purified at all, for of course it will pass through that part where it meets with 

 the least resistance : from this not having been understood or attended to, 

 many superintendents have abandoned the use of dry-lime purifiers. The 

 quantity of lime required for purifying coal-gas by the above process will 

 depend upon the quality of both the lime and gas. One bushel of quicklime 

 will suffice in some places to purify 10,000 cubic feet of gas, while in others 

 twice that quantity will hardly serve. By being slacked and reduced to a 

 proper consistency for use, its bulk will be more than doubled ; two bushels of 

 this hydrate will spread over a surface of 25 square feet, 2^ inches deep, which 

 is about the thickness found in practice to be the best. 



In Plate XII. Figs. 1 and 2, are represented an elevation and plan in sec- 

 tion of one of a series of three " dry-lime" purifiers, through which the gas 

 passes successively ; in other words, they are " worked together," and, though 

 separate, may be considered as one machine. 



A is the inlet-pipe from the wash-vessel, entering at the bottom of the first 

 purifier. 



B is a plate of sheet-iron, about two feet square, placed over the mouth of 

 the inlet-pipe, to separate the stream of gas in some degree, as well as to 

 prevent any lime from falling into the pipe. 



C C C are the layers of hydrate of lime, spread upon screens formed of an 

 outside frame, and a number of round rods or wires about i^ths of an inch 

 in diameter, stretched across them in one direction, to afford greater facility 

 for clearing, with a small interstice between each. These screens are placed 

 one over another, in three tiers, from six to eight inches asunder ; each tier 

 may consist of four screens, for the convenience of lifting them out and 

 replacing them. 



D is the outlet-pipe leading to the second purifier. This arch-pipe is made 

 of thin plate-iron, sealed at each end by a water-joint ; because, when the lid 



