220  Dr.  white’s  Experiments  on  Air , See. 
17.  Air  is  not  hurt  by  fuch  mud  when  perfectly  dry. 
18.  Air  is  alfo  infected  by  the  dirt  of  the  ftreets. 
19.  Pure  loamy  vegetable  earth  has  little  of  fuch 
effect. 
20.  Air  is  not  at  all  polluted  by  pure  clay  foils. 
2 1 . Nor  by  thofe  of  pure  fand. 
) . 
