106 On Plaister of Paris, 



contains this gas^ the quantity of gas is very smali,^^ Practical 

 fanners know, that an overcharge of any manure is destruc- 

 tive. I have killed plants with dung water, too highly impreg- 

 nated ; but have forwarded their growth surprisingly, with 

 water moderately infused with dung. May not the water 

 mentioned by Dr. P. have been too highly impregnated with 

 the carbonic acid, when it destroyed the plants ? It is allow- 

 ed, that plants vegetated in such water, when " the quantity 

 of gas is very sjjialL^'' Nature has provided, that plants shall, 

 in ordinaiy operations, imbibe no more of their food than is 

 proper for them. In extraordinary instances, a plant may, 

 like an intemperate animal, be gorged with food, and, fall a 

 sacrifice to excess. It may be, too, that carbonic acid is only 

 a part of the food ; and requires to be corrected or aided 

 by some other ingredients, to produce salutary effects. Ingen- 

 hausz allows that " Plants die in pure carbonic acidJ''^ He 

 says, oxygene, or pure respirable air, and heat, are necessary 

 to vegetation. [Vide Ingenkausz on food of plants, pages 9, 

 10,11.] Plants absorb mephitic or phlogisticated air, and 

 emit vital air. Man, on the contrary, is kept alive by vital 

 air, and emits mephitic. Chaptal vol, 1 , page 117. But Ingen- 

 hausz [food of plants page 6.] pointedly asserts, that, "all airs, 

 which cannot be easily changed or decomposed into fixed air ^ 

 as possessing no oxygene, are true poisons to plants, such as 

 infammable air, putrid air, 7ix\6. azote, contrary to Dr. Priestly 

 and Mr. Scheele. He further says, that all " other airs poi- 

 sonous to vegetable life, are also destructive of animal life.'* 

 Such is even the carbonic acid, concentrated, or without a 

 great proportion of respirable air. 



When I began to extract the accounts of the latest writers 

 on chemistry, the food of plants, he, it was under the idea, 

 that the gypsum would be found to contain this food. Be 

 this as it may, the theories I have mentioned may possibly 

 afford amusement, if they are of no real use, to those who have 

 not access to the works of the writers, who entertain, on this 



