34 THE BOOK OF THE LANTERN. 



who some years ago was killed by such an explosion of an 

 oxygen retort. 



Many old-fashioned operators use an iron mercury 

 bottle as a retort, and this, I believe, was the invariable 

 custom when oxygen was procured from manganese per- 

 oxide alone. The heat required was so great that a thick 

 and lasting receptacle was necessary. But now-a-days, 

 when chlorate is used so universally, the gas comes off at a 

 much-reduced temperature, and a thin retort will last, with 

 care, for about fifty charges. My lantern assistant prefers 

 to use a kitchen digester, which he has had fitted with 

 a pipe and safety cap, and which he regards as a triumph 

 of art, which will not only last his own life-time, but will 

 be handed down to his descendants as an heir-loom. One 

 more word on the subject of retorts. Do not buy a copper 

 one ; it is very expensive, and quickly wears out, and has 

 no advantages whatever. In case a retort should be 

 wanted in a hurry, and cannot be obtained, a common 

 cast-iron kettle is a capital substitute for one. Put the 

 chlorate mixture in the kettle, and fasten on the lid with 

 a luting of white lead or clay ; cut a piece of firewood 

 to the correct size, to fit tightly between the lid and 

 the inside of the handle of the kettle, so that no pressure 

 will force it open. Use the spout as a delivery tube of the 



The retort is charged with a mixture of chlorate of potash 

 and oxide of manganese, and the most usual proportions 

 are four parts by weight of the potash to one part of the 

 manganese. 



This is the mixture as given in the various chemical text- 



