60 Water, its Properties and Uses. U^h', 



be perceived at once that water is capable of affording two highly 

 essentive elements of the vegetable s}"stem. We find in fact more 

 than one-half the weight of all vegetables, when freshly gather- 

 ed, is attributable to this fluid. Whether it is all actually exist- 

 ing in the plant as simple water may be questioned, but the two 

 gases are there and in precisely the proper proportions to form it. 

 Thus starch, gum, woody fibre, sugar, &c., all proximate princi- 

 ples of vegetable matter, may be regarded as compounds of car- 

 bon and water, for they consist of carbon united to ox}'gen and 

 hydrogen in just the atomic proportions to form water. 



During combustion of vegetable matter, a certain variable por- 

 tion of the bulk escapes as water. This may be seen by holding 

 a glass vessel as a tumbler, perfectly dr)', over a fire or burning 

 lamp or candle. The fluid will immediately be seen collecting 

 upon the inside of the vessel. 



Now it is admitted that the water in these instances may be 

 generated by the process of combustion, by the direct union of 

 the erases. The hydroo:en was there, and beinsr burned in the at- 

 mosphere which contains oxygen would be converted into water, 

 even if none of this latter gas were existing in the plant. But it 

 must not be forgotten that there was a quantity of ox}'gen 

 just suflficient, with the hydrogen, to form the same amount of 

 water, and we are only able to account, rationally, for the dispo- 

 sal of this, by supposing it to be united with the hydrogen, and 

 being already in the form of water in the plant before it is 

 burned. 



A trifling experiment will seem to demonstrate this to be the 

 fact. If a small stick of wood is subjected to the action of sul- 

 phuric acid, the water is separated, by its action, from the woody 

 fibre, and charcoal is the residue. This result is owing to the 

 powerful affinit}' existing between this acid and water. 



It is not then certain that the water, which growing plants ab- 

 sorb and appropriate, is changed in any respect, in entering into 

 the composition of the body of the vegetable, but may be still the 

 same, though having but its former sensible properties and its 

 fluid form by union with a third body — carbon — and we may 



