376 



SCIENTIFIC RECREATIONS. 



the fire. Before long the gas will issue from the stem of the pipe, and 

 may either be lighted or collected in a bladder. For the use of the 



" million," however, gas is prepared upon a 

 very large scale, and is divided into three 

 processes its " formation," " purification/' 

 and its " collection " for distribution to 

 consumers. The first process is carried on 

 by means of retorts shown in the illustration 

 (fig. 376). The first portion of the next figure 

 is a section of a furnace, the other part shows 

 two furnaces from the front. The following 

 is the mode employed. The coal is put 

 into retorts fitted to the furnace, so that they 

 are surrounded by the flames, and termi- 

 nating in a horizontal tube called the 

 hydraulic main, E, which is in its turn con- 

 nected with a pit or opening for the reception of the tar and ammoniacal 

 liquor, etc., which condenses from the gas. It then passes up and down 

 a series of tubes in water, called 

 a "condenser," and in this are 

 reservoirs or receptacles for any 

 tar and ammonia that remain. 

 But sulphur is still present, so 

 the gas is carried to the purify- 



ing apparatus (D in fig. 378), 



which consists of a large cylin- Fig . 377 ._ S ection. Front view. 



drical vessel air-tight, with an 



inverted funnel, nearly filled with a mixture of lime and water. The gas 



bubbles in, and the sulphur unites with the lime, while the gas rises to the 



Fig. 376. Retorts 



Fig. 378. Condenser. 



Purifier. 



Gasometer. 



Fig. 379. Gasometer.- 



top (trays of lime are used when the gas enters from the bottom). The 

 Gasometer, a large vessel closed at the top and open below, dips into a large 

 trough of circular shape. The gasometer is balanced by weights and chains, 



