148 METALLOIDS. 



soon be exhausted, and vegetation cease upon the face 

 of the earth. 



348. OZONE. By passing an electrical 

 How is * ne current, continually, through oxygen gas, 

 for some time, it becomes mysteriously 

 changed in its proportions. In this changed condition 

 it is called ozone. It is, as it were, intensified in its affin- 

 ities by the current, so that like chlorine, it will attack 

 silver, and exhibit many other of the properties of the 

 latter gas. The electricity of the air has similar effects 

 on the oxygen which it contains, and, in consequence of 

 its varying electrical condition, the proportion of ozone 

 is, also, from time to time, extremely varied. There is 

 reason to believe that this substance has important influ- 

 ence upon health, and that either its deficiency or excess, 

 is injurious. In cholera seasons, it has been observed 

 to be present in comparatively small quantity, while, 

 during the prevalence of a species of influenza called 

 " grippe," it is said to be more abundant. These obser- 

 vations need confirmation, by further experiments, before 

 the facts can be regarded as fully established. The pres- 

 ence of ozone, is indicated by the discoloration, through 

 the influence of a current of air, of a test paper, de- 

 scribed in the section on chlorides. 

 Tir , 349. RELATIONS TO LIFE. Oxygen is 



What relation 



to life does ox- as essential to life, as it is to combustion. 



ygen sustain! The ^^ oxygen of the ^ ig better 



adapted to breathing, than pure air, but that which con- 

 tains much less than its due proportion, is no longer 

 fitted to support life. Respiration consumes oxygen, so 

 that the air of a close room is constantly being depri- 



