C 84 ] 



precipitate per fe, and thefe be mixed, atmo- 

 fpheric or vital air will be formed. 



Oxygen gas conftitutes about one fourth of 

 the atmofphere, and is compofed of light, calo- 

 ric^, and oxygen. It is procured, by filling a 

 receiver with the green leaves of vegetables, and 

 inverting it in fpring water, and expofing it to the 

 dire 61 rays of the fun; the leaves yield a confi- 

 derable quantity of oxygen air, which afcends to 

 the upper part of the receiver, and may be eafily 

 removed from it for ufe. It is produced from 

 various other fubftances, and particularly from 

 nitre, or the metallic calces. One ounce of 

 nitre, expofed to a red, or rather white heat, in 

 an earthen retort for about four or five hours, 

 will give about 700 cubic inches of oxygen air; 

 as this gas contains a quantity of nitrous acid in 

 the form of vapour, it may be feparated from it 

 by agitating the air in lime water. 



But it is from manganefe that the greateft 

 quantity of this gas may be procured, and it is 

 now the fubftance generally ufed. One ounce of 

 good manganefe will, in a red heat, yield more 

 than two pints and a half, or about 80 cubic 

 inches of elaftic fluid, one tenth of which is car- 

 bonic acid, and the reft oxygen gas. 



(i) Caloric, latent heat, fixed heat, or principle of heat, is 

 only known by its efFecls ; invifible, imponderable, fubtile, per- 

 vading all bodies, infinuaiing itfelf between their particles. It 

 melts folid bodies, rarefies fluids, and renders them invifible. 

 There are but three fpecies of the undecompounded bodies, 

 which are known to be rendered into the ftate of gas by coloric; 

 namely, oxygen, hydrogen, and nitragen. 



AZOTIC 



