428 E X P E R I M E N T S o N 



affeits that the ah" over the ponds, v.-hich border on the 

 Mediterranean fea (the neighbourhood of which is equally 

 marlhy if not more fo than the neck termed by the junc- 

 tion of Schuylkill and the Delaware, as I convinced myfelf 

 during my refidence at Montpellier in the years 1795 and 

 I "796) was equally piu-e with that of Montpellier, tried 

 the fame day. When I affert that the atmofphere of marfh- 

 es is equally pure with that of other fituations, I mean that 

 it contains as large a proportion of oxygen gas as fuch 

 other atmofpheres do. I do not by any means intend to be 

 underflood that it is free from foreign mixtures. 



I have acknowledged that putrefadlion is going on 

 in marfhy places and likewife admit that this procefs de- 

 ftroys the purity of the atmofphere by abforbing its oxy- 

 gen ; therefore it may feem difficult to admit the abfolute 

 ■purity of the air being equal here to that of other places. 

 People being able to breathe with eafe over marfhy grounds, 

 is fufficient proof that the oxygen gas there is adequate to 

 fupport life. I fliall now attempt to account for the purity 

 of the air of marfhes as follows. Sennebier has proved by 

 numerous experiments, that living vegetables placed in an 

 atmofphere of carbonic acid gas or in water faturated with 

 this air, expofed to the adtion of the fun, thrive and grow 

 very rapidly : during the experiments the carbonic acid is 

 defi:royed and oxygen gas is difengaged. In addition to 

 thefe experiments, Ingenhoufz has taught us that the aqua- 

 tic plants, particularly luch as grow in the neighbourhood 

 of marfhes, poffefs the power above ftated to a furprifing 

 degree ; fee Experiences fur les Vegetaux, Tom. 2. p. 401. 

 Thefe fails when properly confidered and conned:ed with 

 the remarks I made when fpeaking of the effeds of mud on 

 the atmofphere, I think are fufficient to account for the 

 phenomenon, which at firft feemed at leaft doubtful. 



The above view of this difficult fubjedl will perhaps in 

 fome meafure alter our opinions refpeding the utility of 



marfhes. 



