38 Chemistry. [Lecture 25. 



however so strong an attraction for caloric in 

 this state, that they will not part with it in the 

 temperature of our atmosphere, or even at many 

 degrees below our ordinary temperature. 



Caloric combines readily with many of the 

 simple substances. With oxygen it forms oxy- 

 gen gas With hydrogen, hydrogen gas With 

 nitrogen, nitrogen or azotic gas With sulphur, 

 sulphureous gas. The metals and many of the 

 earths are reduced by it to a fluid state. 



It may then be laid down as a canon of che- 

 mistry? That all jluids, whether incompressible 

 or gaseous^ are combinations of caloric with some 

 other substance simple or compound. 



II. OXYGEN is a matter which is never found 

 in an uncombined state. It approaches nearest 

 to purity in the state of oxygen gas (or combined 

 only with caloric), which was formerly termed 

 pure, vital, or empyreal air, from its property 

 of sustaining animal life and combustion. 



Oxygen gas may be obtained by various easy 

 processes. It may be procured by means of heat 

 from all the oxides (or, as they were formerly 

 called, calces) of metals ; for it is the union of 

 oxygen with the metals that reduces them to 

 this calx, or cinder-like appearance. Thus red 

 lead is an oxide or calx of lead produced by 

 heating lead to a considerable degree in the open 

 air, by which it attracts a quantity of oxygen 

 from the atmosphere. The oxygen may again 

 be extracted from the lead in the form of gas. 



