244 OXYGEN. 



of oxygen produced in the experiment, and the flask to contain 

 184 grains of mercury. Now 48 cubic inches of oxygen weigh 

 16 grains ; and a true analysis of the red precipitate has been 

 effected, of which the result is, that 200 grains of that sub- 

 stance consist of 



184 grains mercury. 

 16 oxygen, (48 cubic inches.) 



200 



But oxygen gas is more generally derived from two other 

 substances, oxide of manganese and chlorate of potash. 



2. When the gas is required in large quantity, and exact 

 purity is immaterial, the oxide of manganese is preferred from 

 its cheapness. This is a black, heavy mineral found in De- 

 vonshire and other parts of England, and of which upwards 

 of 40,000 tons are consumed annually in the manufactures of 

 the country. It is called an oxide of manganese, because it is 

 a compound of the metal manganese with oxygen. In expla- 

 nation of what takes place when this substance is heated, it is 

 necessary to state that manganese is capable of uniting with 

 oxygen in several proportions, namely one equivalent, or 3 46 

 parts of manganese, with 100, and with 200 parts of oxygen, 

 and two equivalents of manganese with 300 oxygen. These 

 compounds are : 



Protoxide of manganese . . Mn + O. 

 Deutoxide .... 2Mn+3O. 



Peroxide, or native black oxide . Mn + 2O. 



Now the peroxide however strongly heated, never loses more 

 than one third of its oxygen, being converted into a compound 

 of the first two oxides, that is, three equivalents of peroxide 

 (1638 parts) lose two equivalents of oxygen (200 parts), and 

 leave a compound of one of deutoxide and one of protoxide ; 

 a change which may be thus expressed : 



One of the malleable iron bottles in which mercury is imported, 

 is readily converted into a retort, in which the black oxide may 

 be heated, by removing its screwed iron stopper, and re- 



