[ '5° ] 



Mr. Senebier have fhewn that the leaves of plants expofed to 

 the fun produce pure air ; now v^'ater has of late been proved 

 to contain about 87 per cwt. of pure air, the remainder being 

 inflammable air. Water is then decompofed by the afliftance of 

 light within the vegetable ; its inflammable part is employed in 

 the formation of oils, refins, gums, &c. ; its pure air is partly 

 applied to the produdion of vegetable acids, and partly expelled 

 as an excrement. 



Many indeed have aflerted that water is the fole food of 

 vegetables ; and among the experiments adduced to prove it, 

 that of Van Helmont, quoted by the illufl:rious Mr. Boyle *, 

 is by far the mofl fpecious. He planted a trunk of willow 

 weighing 5 lb. in an earthen veflTel filled with earth dried in 

 an oven, and then moiftened with rain water ; this veflTel it 

 appears he funk in the earth, and watered partly with rain 

 water and occafionally with difl;illed ; after five years he found 

 the tree to weigh 169 lb. and the earth in which it was planted, 

 being again dried, to have loft only 2 oz. of its former weight, 

 though the tree received an increafe amounting to 1 64 lb. 



Before I proceed to the explication of this experiment, I 

 muft remark fome circumflances attending it : Firft, that the 

 weight of the earth contained in the veflTel at the commence- 

 ment and at the end of five years could not be exadly com- 

 pared, 



* 2d Shaw's Boyle, 240. 



