92 On Plaister of Paris. 



assist and promote the growth of plants, fpj Perhaps 



(^p^Ingenhausz a celebrated advocate for the new chemis- 

 try, of which Mons. Lavoisier was the founder, has, this year, 

 (1796) pubUshed " an essay on the food of plants, and reno- 

 vation of soils." He imagines wonderiul effects may be pro- 

 duced by oil of vitriol (or any concentrated acid, much dilu- 

 ted with water, or mixed with earth) poured on the soil 

 immediately before sowing. The cost of this manure about 

 two shillings sterling per acre. He relates some experiments 

 on a small scale, confirmatory of this hypothesis, but ac- 

 knowledges it noTv to be mere theory. His opinion, and 

 that OT others cited by him, is, th.'&t fxed air ^ nov/ called, in the 

 new nomenclature, carbonic acid, Qrom. its being found plen- 

 tifully in chalk, it is also called cretacious acid J is, in a great 

 degree, the jood o:' plants. He asserts, in opposition to Dr. 

 Priestly and others, that plants thrive the best in oxygen 

 or vital air ; or at least cannot live without it. His theory, 

 which is among the most modern, is, that carbone (charcoal) 

 though of itseli no manure, is the foundation of the iood of 

 plants ; but must be mixed with oxygen or vital air. Plants, 

 according to this theory, decompose the air surrounding 

 them; and, by this process, assist in producing their own food. 

 That this process is performing at all times, by the roots 

 and flowers, but is carried on by the leaves and stalks in 

 the night, or shade, and inhaled by the latter in the cooler 

 parts of the day ; but constantly from tffe earth (where it 

 is chiefly deposited) by the roots. That plants accelerate 

 their growth in the dark, and advance the least in the 

 middle of the day. That they possess the power of shifting 

 carbonic acid from the air, by attracting its oxygen, and 

 furnishing it with carbon; and that they also possess a 

 wondenul faculty of changing water into oxygen or vital 

 air. That the oxygen is also acquired from the common 



