40 THE BOOK OP THE LANTERN. 



by giving it a gentle pinch for half a second the sudden 

 ontrush of gas into the wash bottle will drive off any water 

 that has settled there. When the bag is half full there is 

 gene^a-Py a lull in the operation, and no bubbles are seen 

 he water in the wash bottle ; and this opportunity 

 may ^ssnoaken for turning on a little more gas, but not 

 much more, for presently the oxygen will run off with 

 redoubled vehemence, and if too much flame is applied to 

 the retort the pressure may become too great for the con- 

 nexions, or the cork of the safety valve may fly out. By 

 governing the amount of gas supplied to the stove, the 

 emission of oxygen can be very carefully regulated. (This 

 regulation becomes still easier if a certain amount of 

 common salt be added to the gas mixture in the retort. 

 This should be done just before the retort is charged. The 

 proportions are as follows : 



Chlorate of potash ... ... ... 8 parts 



Manganese ... ... ... ... 2 



Common salt ... .., ... ... 1J 



all by weight. When common salt is thus added to the 

 gas mixture, the chlorate should be powdered.) 



When the gas bag is full: and " as tight as a drum," the 

 various parts of the apparatus used in making the gas 

 must be disconnected, and here some caution is necessary. 

 The first thing to do is to pull the tube from the gas bag 

 and turn off the tap at the same instant. Next remove 

 the tube from the retort, and last of all turn off the gas 

 supply from the stove. Why I say that caution is necessary 

 here, is, because if the gas is turned off before the retort is 



