THE BOOK OF THE LANTERN. 



43 



in the same manner, they will be found to be square in out- 

 line, as in B. Should it be desired to use the manganese 

 over again, it must be freed from the chloride by repeated 



FIG. 19. 



changes of water. It will thus be dissolved out, while the 

 manganese remains behind in the form of black mud. 

 This latter must be dried before being again employed in 

 the retort. 



The operation of oxygen gas making is now with many 

 lanternists a thing of the past, for they prefer to buy it 

 ready made. For many years this gas has been supplied, 

 by one or two makers, compressed in iron or steel 

 cylinders. But the price, eightpence per foot, was too 

 high to induce consumers to relinquish the custom of 

 making it themselves. Of recent months, however, the 

 gas has been supplied at half that price, with the result that 

 many prefer to buy it rather than make it themselves. 

 The manufacture of oxygen gas therefore represents "A 

 curious new industry," and under that title I described it a 



