THE BOOK OF THE LANTERN. 39 



pose that this has been done, and that everything is ready 

 for making the gas. 



The stove should be lighted and turned down almost to 

 its lowest point, for it is as well to begin with a small 

 amount of heat, although I believe that it is the practice 

 of some workers to begin with a full heat, and to turn the 

 supply down when gas commences to come off. The tube 

 is joined to the retort and to the wash bottle ; but the 

 tube joined to the delivery end of the bottle is for the 

 present left free at its other end. After an interval of 

 about five or six minutes, the water in the wash bottle 

 should show by its bubbling that the gas is being generated, 

 but those bubbles are not as yet pure gas, but are partly 

 air which has been contained in the retort, and which is 

 expanded and driven out by the heat. We must wait 

 some time longer, until these bubbles are given off 

 with regularity, before attempting to fasten the open 

 tube to the gas bag ; and before doing so it is as well 

 to apply the test of the blown-out match to the free end of 

 the rubber tube. If the spark on the match bursts into 

 flame directly it is applied to the tube, we may be sure that 

 gas is coming off in earnest, and we can by a dexterous 

 movement fasten the tube on the tap of the gas bag, at the 

 same time turning on that tap. 



Everything should now go on with regularity and with- 

 out attention, until the bag is nearly half full. During 

 this time it may be noticed that the tube leading from the 

 retort will emit a kind of bubbling noise. This is due to 

 water lodging there which comes from the crystals of 

 potash in the retort. By simply lifting this tube up, and 



